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  • 1.
    Ahlström, Christer
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Rask, Peter
    University Hospital, Örebro, Sweden .
    Karlsson, Jan-Erik
    County Hospital Ryhov, Jönköping, Sweden.
    Nylander, Eva
    Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärtcentrum, Fysiologiska kliniken.
    Dahlström, Ulf
    Linköpings universitet, Institutionen för medicin och vård, Kardiologi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärtcentrum, Kardiologiska kliniken.
    Hult, Peter
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Assessment of Suspected Aortic Stenosis by Auto Mutual Information Analysis of Murmurs2007Inngår i: Engineering in Medicine and Biology Society, 2007. EMBS 2007, 2007, s. 1945-1948Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Mild sclerotic thickening of the aortic valve affects 25% of the population, and the condition causes aortic valve stenosis (AS) in 2% of adults above 65 years. Echocardiography is today the clinical standard for assessing AS. However, a cost effective and uncomplicated technique that can be used for decision support in the primary health care would be of great value. In this study, recorded phonocardiographic signals were analyzed using the first local minimum of the auto mutual information (AMI) function. The AMI method measures the complexity in the sound signal, which is related to the amount of turbulence in the blood flow and thus to the severity of the stenosis. Two previously developed phonocardiographic methods for assessing AS severity were used for comparison, the murmur energy ratio and the sound spectral averaging technique. Twenty-nine patients with suspected AS were examined with Doppler echocardiography. The aortic jet velocity was used as a reference of AS severity, and it was found to correlate with the AMI method, the murmur energy ratio and the sound spectral averaging technique with the correlation coefficient R = 0.82, R = 0.73 and R = 0.76, respectively.

  • 2.
    Ahlström, Christer
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Hult, Peter
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Filosofiska fakulteten.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Detection of the 3(rd) heart sound using recurrence time statistics2006Inngår i: 2006 IEEE International Conference on Acoustics, Speech and Signal Processing, Vols 1-13, 2006, Vol. 1-13, s. 2288-2291Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The 3(rd) heart sound (S3) is normally heard during auscultation of younger individuals, but it is also common in many patients with heart failure. Compared to the 1(st) and 2(nd) heart sounds, S3 has low amplitude and low frequency content, making it hard to detect (both manually for the physician and automatically by a detection algorithm). We present an algorithm based on a recurrence time statistic which is sensitive to changes in a reconstructed state space, particularly for detection of transitions with very low energy. Heart sound signals from ten children were used in this study. Most S3 occurrences were detected (98%), but the amount of false extra detections was rather high (7% of the heart cycles). In conclusion, the method seems capable of detecting S3 with high accuracy and robustness.

  • 3.
    Ahlström, Christer
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Hult, Peter
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Detection of the 3rd Heart Sound using Recurrence Time Statistics2006Inngår i: Proc. 31st IEEE Int. Conf. on Acoustics, Speech and Signal Processing, Toulouse, France, 2006, 2006, s. 1040-1043Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The 3rd heart sound (S3) is normally heard during auscultation of younger individuals, but it is also common in many patients with heart failure. Compared to the 1st and 2nd heart sounds, S3 has low amplitude and low frequency content, making it hard to detect (both manually for the physician and automatically by a detection algorithm). We present an algorithm based on a recurrence time statistic which is sensitive to changes in a reconstructed state space, particularly for detection of transitions with very low energy. Heart sound signals from ten children were used in this study. Most S3 occurrences were detected (98 %), but the amount of false extra detections was rather high (7% of the heart cycles). In conclusion, the method seems capable of detecting S3 with high accuracy and robustness.

  • 4.
    Ahlström, Christer
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Hult, Peter
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Thresholding distance plots using true recurrence points2006Inngår i: Acoustics, Speech and Signal Processing, 2006. ICASSP 2006, IEEE , 2006, s. 688-691Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Recurrence plots (RP) visualize multi-dimensional state spaces and represent the recurrence of states of a system. Recurrence points can be divided into true recurrence points and false recurrence points (also called sojourn points). We introduce the true recurrence point recurrence plot, TRP, a variant of the traditional RP excluding the sojourn points. This is a cleaned up RP free from recurrence points originating from tangential motion, and hence a more robust representation of unstable periodic orbits. The method is demonstrated with three simple systems, a periodic sine wave, a quasi-periodic torus and the x-component of the chaotic Lorenz system

  • 5.
    Ahlström, Christer
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Hult, Peter
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Ask, Per
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Wheeze analysis and detection with non-linear phase-space embedding2005Inngår i: Nordic Baltic Conference Biomedical Engineering and Medical Physics,2005, Umeå: IFMBE , 2005, s. 305-Konferansepaper (Fagfellevurdert)
  • 6.
    Ahlström, Christer
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Hult, Peter
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Rask, P
    Karlsson, J-E
    Nylander, Eva
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Östergötlands Läns Landsting, Hjärtcentrum, Fysiologiska kliniken.
    Dahlström, Ulf
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Kardiologi. Östergötlands Läns Landsting, Hjärtcentrum, Kardiologiska kliniken.
    Ask, Per
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Using the intelligent stethoscope for extraction of features for systolic heart murmur classification2006Inngår i: World Congress on Medical Physics and Biomedical Engineering WC2006,2006, 2006Konferansepaper (Annet vitenskapelig)
  • 7.
    Ahlström, Christer
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Hult, Peter
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Rask, Peter
    Örebro university.
    Karlsson, Jan-Erik
    Nylander, Eva
    Linköpings universitet, Institutionen för medicin och hälsa, Klinisk fysiologi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärtcentrum, Fysiologiska kliniken.
    Dahlström, Ulf
    Linköpings universitet, Institutionen för medicin och hälsa, Kardiologi. Linköpings universitet, Hälsouniversitetet.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Feature Extraction for Systolic Heart Murmur Classification2006Inngår i: Annals of Biomedical Engineering, ISSN 0090-6964, E-ISSN 1573-9686, Vol. 34, nr 11, s. 1666-1677Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Heart murmurs are often the first signs of pathological changes of the heart valves, and they are usually found during auscultation in the primary health care. Distinguishing a pathological murmur from a physiological murmur is however difficult, why an “intelligent stethoscope” with decision support abilities would be of great value. Phonocardiographic signals were acquired from 36 patients with aortic valve stenosis, mitral insufficiency or physiological murmurs, and the data were analyzed with the aim to find a suitable feature subset for automatic classification of heart murmurs. Techniques such as Shannon energy, wavelets, fractal dimensions and recurrence quantification analysis were used to extract 207 features. 157 of these features have not previously been used in heart murmur classification. A multi-domain subset consisting of 14, both old and new, features was derived using Pudil’s sequential floating forward selection (SFFS) method. This subset was compared with several single domain feature sets. Using neural network classification, the selected multi-domain subset gave the best results; 86% correct classifications compared to 68% for the first runner-up. In conclusion, the derived feature set was superior to the comparative sets, and seems rather robust to noisy data.

  • 8.
    Ahlström, Christer
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Hult, Peter
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Schmekel, Birgitta
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Östergötlands Läns Landsting, Hjärtcentrum, Fysiologiska kliniken.
    Ask, Per
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Automatisk detektering av ronki med icke-linjära metoder2004Inngår i: Svenska Läkaresällskapets riksstämma,2004, 2004, s. 66-66Konferansepaper (Annet vitenskapelig)
  • 9.
    Ahlström, Christer
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Hult, Peter
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Schmekel, Birgitta
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Östergötlands Läns Landsting, Hjärtcentrum, Fysiologiska kliniken.
    Ask, Per
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Wheeze detection with nonlinear statespace embedding2004Inngår i: International Lung Sound Association,2004, 2004, s. 38-39Konferansepaper (Annet vitenskapelig)
  • 10.
    Ahlström, Christer
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Hälsouniversitetet.
    Höglund, Katja
    Hult, Peter
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Hälsouniversitetet.
    Häggström, Jens
    Kvart, Clarence
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Hälsouniversitetet.
    Assessing Aortic Stenosis using Sample Entropy of the Phonocardiographic Signal in Dogs2008Inngår i: IEEE Transactions on Biomedical Engineering, ISSN 0018-9294, E-ISSN 1558-2531, Vol. 55, nr 8, s. 2107-2109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In aortic valve stenosis (AS), heart murmurs arise as an effect of turbulent blood flow distal to the obstructed valves. With increasing AS severity, the flow becomes more unstable, and the ensuing murmur becomes more complex. We hypothesize that these hemodynamic flow changes can be quantified based on the complexity of the phonocardiographic (PCG) signal. In this study, sample entropy (SampEn) was investigated as a measure of complexity using a dog model. Twenty-seven boxer dogs with various degrees of AS were examined with Doppler echocardiography, and the peak aortic flow velocity (Vmax) was used as a reference of AS severity. SampEn correlated to Vmax with R = 0.70 using logarithmic regression. In a separate analysis, significant differences were found between physiologic murmurs and murmurs caused by AS (p < 0.05), and the area under a receiver operating characteristic curve was calculated to 0.96. Comparison with previously presented PCG measures for AS assessment showed improved performance when using SampEn, especially for differentiation between physiological murmurs and murmurs caused by mild AS. Studies in patients will be needed to properly assess the technique in humans.

  • 11.
    Ahlström, Christer
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Höglund, Katja
    Dept. of Anatomy and Physiology, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Hult, Peter
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Häggström, Jens
    Dept. of Clinical Sciences, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Kvart, Clarence
    Dept. of Anatomy and Physiology, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Distinguishing Innocent Murmurs from Murmurs caused by Aortic Stenosis by Recurrence Quantification Analysis2006Inngår i: ROCEEDINGS OF WORLD ACADEMY OF SCIENCE, ENGINEERING AND TECHNOLOGY, VOL 18, Canakkale, Turkey: World Academy of Science, Engineering and Technology (W A S E T) , 2006, s. 40-45Konferansepaper (Fagfellevurdert)
    Abstract [en]

    It is sometimes difficult to differentiate between innocent murmurs and pathological murmurs during auscultation. In these difficult cases, an intelligent stethoscope with decision support abilities would be of great value. In this study, using a dog model, phonocardiographic recordings were obtained from 27 boxer dogs with various degrees of aortic stenosis (AS) severity. As a reference for severity assessment, continuous wave Doppler was used. The data were analyzed with recurrence quantification analysis (RQA) with the aim to find features able to distinguish innocent murmurs from murmurs caused by AS. Four out of eight investigated RQA features showed significant differences between innocent murmurs and pathological murmurs. Using a plain linear discriminant analysis classifier, the best pair of features (recurrence rate and entropy) resulted in a sensitivity of 90% and a specificity of 88%. In conclusion, RQA provide valid features which can be used for differentiation between innocent murmurs and murmurs caused by AS.

  • 12.
    Ahlström, Christer
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Johansson, Anders
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Hult, Peter
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Ask, Per
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Chaotic dynamics of respiratory sounds2006Inngår i: Chaos, Solitons & Fractals, ISSN 0960-0779, E-ISSN 1873-2887, Vol. 29, nr 5, s. 1054-1062Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There is a growing interest in nonlinear analysis of respiratory sounds (RS), but little has been done to justify the use of nonlinear tools on such data. The aim of this paper is to investigate the stationarity, linearity and chaotic dynamics of recorded RS. Two independent data sets from 8 + 8 healthy subjects were recorded and investigated. The first set consisted of lung sounds (LS) recorded with an electronic stethoscope and the other of tracheal sounds (TS) recorded with a contact accelerometer. Recurrence plot analysis revealed that both LS and TS are quasistationary, with the parts corresponding to inspiratory and expiratory flow plateaus being stationary. Surrogate data tests could not provide statistically sufficient evidence regarding the nonlinearity of the data. The null hypothesis could not be rejected in 4 out of 32 LS cases and in 15 out of 32 TS cases. However, the Lyapunov spectra, the correlation dimension (D2) and the Kaplan-Yorke dimension (DKY) all indicate chaotic behavior. The Lyapunov analysis showed that the sum of the exponents was negative in all cases and that the largest exponent was found to be positive. The results are partly ambiguous, but provide some evidence of chaotic dynamics of RS, both concerning LS and TS. The results motivate continuous use of nonlinear tools for analysing RS data. © 2005 Elsevier Ltd. All rights reserved.

  • 13.
    Ahlström, Christer
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Johansson, Anders
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Länne, Toste
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Östergötlands Läns Landsting, Hjärtcentrum, Thorax-kärlkliniken.
    Ask, Per
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    A respiration monitor based on electrocardiographic and photoplethysmographic sensor fusion2004Inngår i: IEEE Engineering in Medical and Biological Society,2004, Piscataway, N.J. USA: IEEEEMBS , 2004, s. 2311-Konferansepaper (Fagfellevurdert)
  • 14.
    Ahlström, Christer
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Johansson, Anders
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Länne, Toste
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Fysiologi. Östergötlands Läns Landsting, Hjärtcentrum, Thorax-kärlkliniken.
    Ask, Per
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Monitorering av andning and blodtrycksförändringar baserat på EKG och hjärtljud2007Inngår i: Medicinteknik dagarna,2007, 2007Konferansepaper (Annet vitenskapelig)
  • 15.
    Ahlström, Christer
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Johansson, Anders
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Uhlin, Fredrik
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Njurmedicin.
    Länne, Toste
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Östergötlands Läns Landsting, Hjärtcentrum, Thorax-kärlkliniken.
    Ask, Per
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Noninvasive investigation of blood pressure changes using the pulse wave transit time: A novel approach in the monitoring of hemodialysis patients2005Inngår i: Journal of Artificial Organs, ISSN 1434-7229, E-ISSN 1619-0904, Vol. 8, nr 3, s. 192-197Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Severe blood pressure changes are well known in hemodialysis. Detection and prediction of these are important for the well-being of the patient and for optimizing treatment. New noninvasive methods for this purpose are required. The pulse wave transit time technique is an indirect estimation of blood pressure, and our intention is to investigate whether this technique is applicable for hemodialysis treatment. A measurement setup utilizing lower body negative pressure and isometric contraction was used to simulate dialysis-related blood pressure changes in normal test subjects. Systolic blood pressure levels were compared to different pulse wave transit times, including and excluding the cardiac preejection period. Based on the results of these investigations, a pulse wave transit time technique adapted for dialysis treatment was developed and tried out on patients. To determine systolic blood pressure in the normal group, the total pulse wave transit time was found most suitable (including the cardiac preejection period). Correlation coefficients were r = 0.80 ± 0.06 (mean ± SD) overall and r = 0.81 ± 0.16 and r = 0.09 ± 0.62 for the hypotension and hypertension phases, respectively. When applying the adapted technique in dialysis patients, large blood pressure variations could easily be detected when present. Pulse wave transit time is correlated to systolic blood pressure within the acceptable range for a trend-indicating system. The method's applicability for dialysis treatment requires further studies. The results indicate that large sudden pressure drops, like those seen in sudden hypovolemia, can be detected. © The Japanese Society for Artificial Organs 2005.

  • 16.
    Ahlström, Christer
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik.
    Liljefeldt, Olle
    Hult, Peter
    Linköpings universitet, Institutionen för medicinsk teknik.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik.
    Heart sound cancellation from lung sound recordings using recurrence time statistics and nonlinear prediction.2005Inngår i: Medicinteknikdagarna, 2005, Vol. 12, s. 812-815Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Heart sounds (HS) obscure the interpretation of lung sounds (LS). This letter presents a new method to detect and remove this undesired disturbance. The HS detection algorithm is based on a recurrence time statistic that is sensitive to changes in a reconstructed state space. Signal segments that are found to contain HS are removed, and the arising missing parts are replaced with predicted LS using a nonlinear prediction scheme. The prediction operates in the reconstructed state space and uses an iterated integrated nearest trajectory algorithm. The HS detection algorithm detects HS with an error rate of 4% false positives and 8% false negatives. The spectral difference between the reconstructed LS signal and an LS signal with removed HS was 0 34 0 25, 0 50 0 33, 0 46 0 35, and 0 94 0 64 dB/Hz in the frequency bands 20–40, 40–70, 70–150, and 150–300 Hz, respectively. The cross-correlation index was found to be 99.7%, indicating excellent similarity between actual LS and predicted LS. Listening tests performed by a skilled physician showed high-quality auditory results.

  • 17.
    Ahlström, Christer
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Liljefeldt, Olle
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Hult, Peter
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Heart sound cancellation from lung sound recordings using recurrence time statistics and nonlinear prediction2005Inngår i: IEEE Signal Processing Letters, ISSN 1070-9908, E-ISSN 1558-2361, Vol. 12, nr 12, s. 812-815Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Heart sounds (HS) obscure the interpretation of lung sounds (LS). This letter presents a new method to detect and remove this undesired disturbance. The HS detection algorithm is based on a recurrence time statistic that is sensitive to changes in a reconstructed state space. Signal segments that are found to contain HS are removed, and the arising missing parts are replaced with predicted LS using a nonlinear prediction scheme. The prediction operates in the reconstructed state space and uses an iterated integrated nearest trajectory algorithm. The HS detection algorithm detects HS with an error rate of 4% false positives and 8% false negatives. The spectral difference between the reconstructed LS signal and an LS signal with removed HS was 0.34/spl plusmn/0.25, 0.50/spl plusmn/0.33, 0.46/spl plusmn/0.35, and 0.94/spl plusmn/0.64 dB/Hz in the frequency bands 20-40, 40-70, 70-150, and 150-300 Hz, respectively. The cross-correlation index was found to be 99.7%, indicating excellent similarity between actual LS and predicted LS. Listening tests performed by a skilled physician showed high-quality auditory results.

  • 18.
    Ahlström, Christer
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Hälsouniversitetet.
    Länne, Toste
    Linköpings universitet, Institutionen för medicin och hälsa, Fysiologi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärtcentrum, Thorax-kärlkliniken.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Hälsouniversitetet.
    Johansson, Anders
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Hälsouniversitetet.
    A method for accurate localization of the first heart sound and possible applications2008Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 29, nr 3, s. 417-428Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have previously developed a method for localization of the first heart sound (S1) using wavelet denoising and ECG-gated peak-picking. In this study, an additional enhancement step based on cross-correlation and ECG-gated ensemble averaging (EA) is presented. The main objective of the improved method was to localize S1 with very high temporal accuracy in (pseudo-) real time. The performance of S1 detection and localization, with and without EA enhancement, was evaluated on simulated as well as experimental data. The simulation study showed that EA enhancement reduced the localization error considerably and that S1 could be accurately localized at much lower signal-to-noise ratios. The experimental data were taken from ten healthy subjects at rest and during invoked hyper- and hypotension. For this material, the number of correct S1 detections increased from 91% to 98% when using EA enhancement. Improved performance was also demonstrated when EA enhancement was used for continuous tracking of blood pressure changes and for respiration monitoring via the electromechanical activation time. These are two typical applications where accurate localization of S1 is essential for the results.

  • 19. Andersson, R
    et al.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Force to restore the shape of an asymmetric extracorporeal tube as the basis for non-invasive pressure measurements.2002Inngår i: International Journal of Artificial Organs, ISSN 0391-3988, E-ISSN 1724-6040, Vol. 25, nr 4, s. 281-289Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A zero-balance principle is described where intraluminal pressure is estimated from the counter force needed to restore the tube shape of an elastic extra corporeal tube. The aim was to optimise cross-sectional tube geometry for tube expansion due to pressure and to reduce the sensitivity to variation in mechanical tube characteristics using an experimental statistical and factorial design. The main application is pressure monitoring in blood and dialysate tubes during hemodialysis. Improving the monitoring of the dialysis process will reduce complications, such as sudden decreases in systemic blood pressure or occlusion at the artero-venous fistula. The factorial design indicated strong influence from the geometrical characteristics of the tube as well from the geometrical design parameters of the pressure transducer. We found a consistent relationship between the intraluminal pressure and the applied force needed to restore the tube shape. The modified cross-sectional tube geometry enhances measurement sensitivity and facilitates the desired behavior of tubes during pressure applications.

  • 20. Andersson, R
    et al.
    Loyd, Dan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska högskolan.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Pressure sensed non-invasively directly on the extra corporeal bloodline tube2001Inngår i: PROCEEDINGS OF THE 23RD ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY, VOLS 1-4: BUILDING NEW BRIDGES AT THE FRONTIERS OF ENGINEERING AND MEDICINE, 2001, Vol. 23, s. 3179-3181Konferansepaper (Fagfellevurdert)
    Abstract [en]

    To clinically measure blood pressure at extra corporeal bloodlines involves a hazard due to the infection risk and a risk for thrombosis formation. The aim was to design a non-invasive pressure sensor, measuring directly on a tube section. A modified tube cross-section was used to improve sensitivity. Using the developed sensing principle, a consistent relation (r=0.999) was obtained between pressure and output signal. The output was stable and an acceptable drift within the temperature-range. The method shows great promise for applications in monitoring of the dialysis process.

  • 21.
    Andersson, Roger
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    An asymmetric dialysis tube as an integrated part of a pressure-monitoring sensor2001Inngår i: Technology and Health Care, ISSN 0928-7329, E-ISSN 1878-7401, Vol. 9, nr 5, s. 417-425Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A sensor has been designed consisting of a tube holder with a force transducer and a tube with a modified cross-section. The holder has a lid that encloses the tube. By having a stiff holder and a compliant tube, the idea is that the intraluminal pressure in the tube can be obtained from the measured force. The method is intended for non-invasive pressure measurements in blood or dialysate tubes.

    We have used a tube cross-sectional geometry where the outer surface is elliptic and the inner surface is circular with a relation of 2:1 between the thinnest and thickest tube sides. The pressure transducer system shows a linear relationship between the applied pressure and the sensor output (r = 0.999). Within the temperature range, 32°–36°C, which corresponds to the blood and dialysate temperatures, the sensor accuracy is within ±0.8 kPa (±6 mm Hg). This indicates that the sensor should be clinically useful during dialysis and similar applications.

  • 22.
    Andersson, Roger
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Force to restore the shape of an asymmetric extracorporeal tube as the basis for non-invasive pressure measurements2002Inngår i: International Journal of Artificial Organs, ISSN 0391-3988, E-ISSN 1724-6040, Vol. 25, nr 4, s. 281-289Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A zero-balance principle is described where intraluminal pressure is estimated from the counter force needed to restore the tube shape of an elastic extra corporeal tube. The aim was to optimise cross-sectional tube geometry for tube expansion due to pressure and to reduce the sensitivity to variation in mechanical tube characteristics using an experimental statistical and factorial design. The main application is pressure monitoring in blood and dialysate tubes during hemodialysis. Improving the monitoring of the dialysis process will reduce complications, such as sudden decreases in systemic blood pressure or occlusion at the artero-venous fistula. The factorial design indicated strong influence from the geometrical characteristics of the tube as well from the geometrical design parameters of the pressure transducer. We found a consistent relationship between the intraluminal pressure and the applied force needed to restore the tube shape. The modified cross-sectional tube geometry enhances measurement sensitivity and facilitates the desired behavior of tubes during pressure applications.

  • 23.
    Andersson, Roger
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Ask, Per
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Pressure sensed non-invasively directly on the extracorporeal dialysis tube2001Inngår i: ESAO Congress,2001, 2001Konferansepaper (Annet vitenskapelig)
  • 24.
    Andersson, Roger
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Fridolin, Ivo
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Magnusson, Martin
    Linköpings universitet, Institutionen för medicin och vård, Njurmedicin. Linköpings universitet, Hälsouniversitetet.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Lindberg, Lars-Göran
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Analysis of the relationship between UV-absorbance of solute contents during a dialysis sessionManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    In this paper, the influence from patient anamnesis and haemodialysis session specifications onto the relationship between obtained ultra violet (UV) absorbance and urea concentration in the spent dialysate were discussed. A characterisation of the relationship was done by an intercept value and a slope. Recently, a new a dialysate monitoring device, using UV- absorbance, been developed by our group which has found a relationship between the UV- absorbance and waste products in the dialysate but this relationship vary between patients. In the present investigation, 13 patients performing totally 84 sessions were characterised using 31 possible affecting parameters. Using a multi-regression analysis 11 parameters were found significant as affecting parameters. In a novel mathematical model approach the obtained UV- absorbance and incorporating possible affecting parameters we could predict urea concentration from the UV-absorption in the spent dialysate in the total material of patients and dialysis sessions. For all the 84 sessions R2 between 0.938 and 0.996 were obtained. A performed analysis of variance rejects the assumption of equal conditions for the relationship between diabetics and non-diabetics patients in the material (F=5.2 for intercept and F=14.4 for slope). The urea concentration could be estimated with an accuracy of 11% (one standard deviation) which is normally clinically sufficient. The non-invasive UV -absorption method therefore seems to have great potential for monitoring and control haemodialysis sessions.

  • 25.
    Andersson, Roger
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Loyd, Dan
    Linköpings universitet, Institutionen för konstruktions- och produktionsteknik. Linköpings universitet, Tekniska högskolan.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Cross-sectional changes in an asymmetric tube with bearing on non-invasive pressure measurements2003Inngår i: Technology and Health Care, ISSN 0928-7329, E-ISSN 1878-7401, Vol. 11, nr 1, s. 11-20Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study aims at investigating the radial dimensional changes, as a result of an applied intraluminal pressure for an elastic tube with non-uniform cross section. The study is related to a method for non-invasive pressure measurement using the extracorporeal tube as part of the sensor. The intended application is for monitoring of pressure in the blood and dialysate tubes during haemodialysis. The intention is to find a tube cross-section geometry that results in an expansion of the tube so that it is suitable to use as a component in a pressure sensor. The tube should have high radial compliance and expand in a well-defined manner to be able to transfer the intraluminal pressure to a transducer element sensing the radial force. Radial expansion was studied experimentally for tubes with different cross-section geometries. For small tube expansions the resolution in the experimental measurements was not sufficient to study the radial expansion. In this case, numerical simulation was performed. We conclude that a tube with essentially elliptic outer surface and circular inner surface, with a relation of 1:2 between the size of the thin and thick wall, results in a radial expansion upon application of pressure indicating that this tube is suitable for use as part of a sensor.

  • 26.
    Andersson, Roger
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Loyd, Dan
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Mekanisk värmeteori och strömningslära.
    Ask, Per
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Pressure sensed non-invasively directly on the extra corporeal blood line tubes2001Inngår i: Int Conference of the IEEE Engineering in Medicine and Biology Society,2001, 2001Konferansepaper (Fagfellevurdert)
  • 27.
    Ask, P.
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Carlsson, P.Öberg, P.Å.Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.Pettersson, H.Tibbling, L.Törngren, P.
    An integrating transducer for oesophageal manometry.: The IV Nordic Meeting on Medical and Biological Engineering, Lyngby/Copenhagen, June 29 - July 2 1977.1977Konferanseproceedings (Annet vitenskapelig)
  • 28.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    EKG-elektroder: en svag länk vid övervakning1974Inngår i: Medicinsk Teknik, ISSN 0346-542X, nr 4, s. 12-15Artikkel i tidsskrift (Annet vitenskapelig)
  • 29.
    Ask, Per
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    How to assess heart valve function with echocardiography1997Inngår i: European Conference on Engineering and Medicine,1997, 1997Konferansepaper (Fagfellevurdert)
  • 30.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Low-compliance perfusion pump for oesophageal manometry.1978Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 16, nr 6, s. 732-738Artikkel i tidsskrift (Fagfellevurdert)
  • 31.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Measurement techniques for urodynamic investigations.1989Inngår i: Critical reviews in biomedical engineering, ISSN 0278-940X, E-ISSN 1943-619X, Vol. 17, nr 5, s. 413-449Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Important measurement techniques for investigating lower urinary tract function are flow and pressure measurements. The demands on urinary flowmeters and the measurement principles of balance type, rotating disc, dipstick, and air-displacement type are described. Urological pressure measurements are performed in the bladder, in the urethra, and in the abdominal cavity. Various fluid-filled and microtransducer systems are reviewed and demands for performance given. Differences in measuring a mechanical pressure, like in the urethra, and a fluid pressure in the bladder are discussed. Electromyography (EMG) technique is used to investigate various neurological disturbances in the lower urinary tract. The electrode technique is also described. Furthermore, techniques for incontinence detection are reviewed.

  • 32.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Oesophageal manometry: design and evaluation of measurement systems1978Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The aim of this study was to investigate the technical characteristics of oesophageal manometry systems and to improve the performance of these systems.

    The investigation of the characteristics of oesophageal manometry systems with non-perfused catheters or catheters perfused with a flow generated by a syringe pump did not show properties which fullfilled the requirements for accurate pressure measurements. The bandwidth of the pressure mesurement system was limited by the high compliance of the syringe perfusion pump. The characteristics of perfused systems were improved by the design of a low-compliance perfusion pump. The frequency characteristics of a pressure measurement system utilizing the low-compliance perfusion pump seemed to be determined by the properties of the cathetermanometer system. The frequency content of oesophageal peristaltic pressure was studied by use of a measurement system including the low-compliance perfusion pump. This investigation showed that a bandwidth of about 8 Hz or more is necessary for accurate measurements, which bandwidth can only be obtained with a low-compliance system. In a clinical study a non-perfused system and a system perfused with a syringe pump were compared simultaneously to a system with the low-compliance perfusion pump. The non-perfused system and the system perfused with the syringe pump gave lower peristaltic and sphincter pressure amplitudes than the system with the low-compliance perfusion pump. Since the oesophageal sphincter pressure varies in different radial directions, a pressure transducer has been devised, the mechanical design of which gives an integration of a radial pressure profile. The transducer has a linear static and dynamic transfer function.

  • 33.
    Ask, Per
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Brandberg, Joakim
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Janerot-Sjöberg, Birgitta
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Östergötlands Läns Landsting, Hjärtcentrum, Fysiologiska kliniken.
    Karlsson, Matts
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk modellering och simulering.
    Loyd, Dan
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Mekanisk värmeteori och strömningslära.
    Wranne, Bengt
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Östergötlands Läns Landsting, Hjärtcentrum, Fysiologiska kliniken.
    Assessment of heart valve function with echocardiography1997Inngår i: World Congress on Medical Physics and Biomedical Engineering,1997, 1997, s. 394-394Konferansepaper (Fagfellevurdert)
  • 34.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Carlsson, P
    Öberg, Åke
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Pettersson, H
    Törngren, P
    Tibbling, Lita
    Feedback system for control of abdominal compression in oesophageal investigations.1981Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 19, nr 4, s. 501-503Artikkel i tidsskrift (Fagfellevurdert)
  • 35.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Edwall, G
    Johansson, K E
    Accuracy and choice of procedures in 24-hour oesophageal pH monitoring with monocrystalline antimony electrodes.1986Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 24, nr 6, s. 602-608Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In 24 h pH monitoring, the evaluation is dependent on the absolute accuracy of the pH measurements. Several sources of error exist, such as the chemical composition of calibration buffers and reference electrode gel and the effect of temperature on both the pH and the reference electrodes. We investigated the magnitude of these errors for the monocrystalline antimony electrode. Similar analysis applies to other types of pH electrodes. The errors we found are important when choosing a calibration procedure. We recommend a calibration procedure in which the pH and reference electrodes are both put in a beaker with the calibration buffers prior to and after the 24 h measurements. The calibration buffers and the electrode gel should have a specially selected ion composition where, for example, the Cl-ion concentration is critical. Corrections for differences in temperature between the calibration and the in situ measurements must be added. The pH measurements can be checked by performing in situ calibration.

  • 36.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Edwall, G
    Johansson, K E
    Tibbling, Lita
    On the use of monocrystalline antimony pH electrodes in gastro-oesophageal functional disorders.1982Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 20, nr 3, s. 383-389Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Monocrystalline antimony electrodes have been shown to be suitable for thein vivo determination of pH in blood, tissue and in the upper gastro-intestinal canal. Thanks to their small dimensions it has been possible to mount them into conventional manometry catheters for oesophageal investigation. The monocrystalline antimony pH electrode has several advantages over the conventional pH glass electrode; better accuracy, shorter rise time, smaller dimensions. The monocrystalline antimony electrode has been used for long-term registration of gastro-oesophageal reflux, for the oesophageal acid clearing test and for identification of the pH gradient zone between the gastric and oesophageal mucosa. Its use in combination with pressure sensors has added a new dimension to the diagnosis of functional disorders in the gastro-oesophageal region.

  • 37.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Edwall, G
    Tibbling, Lita
    Combined pH and pressure measurement device for oesophageal investigations.1981Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 19, nr 4, s. 443-446Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A combined pH- and pressure-measurement device for oesophageal investigations has been designed using monocrystalline antimony pH electrodes and perfused polyvinyl catheters. The combined device facilitates pressure measurements simultaneously with pH recording, both distal and proximal to the pH electrode. The device is easier to pass through the nose to the oesophagus than the conventional glass pH electrode. pH and pressure measurements in the oesophagus are therefore simplified and valuable information about the function of the region of the lower oesophageal sphincter is added owing to the simultaneous recording of the two parameters.

  • 38.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    EDWALL, G
    Tibbling, Lita
    ESOPHAGEAL PH MEASUREMENTS USING AN ANTIMONY ELECTRODE1980Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 18, nr 1Artikkel i tidsskrift (Fagfellevurdert)
  • 39.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Ekstrand, Kristina
    Katrineholm City, Sweden.
    Hult, Peter
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Lindén, Maria
    Mälardalen University, Västerås, Sweden.
    Pettersson, Nils-Erik
    Örebro County Council, Sweden.
    NovaMedTech - a regional program for supporting new medical technologies in personalized health care2012Inngår i: Studies in Health Technology and Informatics, ISSN 0926-9630, E-ISSN 1879-8365, Vol. 177, s. 71-5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    NovaMedTech is an initiative funded from EU structural funds for supporting new medical technologies for personalized health care. It aims at bringing these technologies into clinical use and to the health care market. The program has participants from health care, industry and academia in East middle Sweden. The first three year period of the program was successful in terms of product concepts tried clinically, and number of products brought to a commercialization phase. Further, the program has led to a large number of scientific publications. Among projects supported, we can mention: Intelligent sensor networks; A digital pen to collect medical information about health status from patients; A web-based intelligent stethoscope; Methodologies to measure local blood flow and nutrition using optical techniques; Blood flow assessment from ankle pressure measurements; Technologies for pressure ulcer prevention; An IR thermometer for improved accuracy; A technique that identifies individuals prone to commit suicide among depressed patients; Detection of infectious disease using an electronic nose; Identification of the lactate threshold from breath; Obesity measurements using special software and MR camera; and An optical probe guided tumor resection. During the present three years period emphasis will be on entrepreneurial activities supporting the commercialization and bringing products to the market.

  • 40.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Enberg, Anders
    Öberg, Åke
    Spånberg, Anders
    A SHORT-TIME-DELAY URINARY FLOWMETER1985Inngår i: Neurourology and Urodynamics, ISSN 0733-2467, E-ISSN 1520-6777, Vol. 4, nr 3, s. 247-256Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A urinary flowmeter has been designed, using a quickly rotating disc and a balance principle. The flowmeter has a fast and accurate response to changing flows. The time delay of the flowmeter is less than about 0.25 s. The improved accuracy in recording urinary flow using the presented flowmeter should make it possible to extract more information from the detrusor pressure and urinary flow relations, relevant for assessing lower urinary tract function.

  • 41.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    ENGVALL, J
    Loyd, Dan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska högskolan.
    Wranne, Bengt
    Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärt- och Medicincentrum, Fysiologiska kliniken US.
    THEORETICAL AND EXPERIMENTAL-ANALYSIS OF AORTIC COARCTATION1989Inngår i: IMAGES OF THE TWENTY-FIRST CENTURY, PTS 1-6, 1989, Vol. 11, s. 103-103Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Aortic coarctation, which could severely influence the haemodynamic conditions of the body, is discussed. A theory has been developed which relates the pressure drop over the coarctation to the flow. This theory indicates that the pressure drop across the actual coarctation is related to the flow squared. For the collateral flow the expected pressure drop is either linearly or quadratically related to the flow. Model experiments and patient data support the present theoretical model

  • 42.
    Ask, Per
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Flaschemkampf, F
    Hasenkam, M
    Non-invasive approach to hemodynamic assessment of heart valves (INVADYNE)1997Inngår i: World congress on Medical Physics and Biomedical Engineering,1997, 1997, s. 1186-Konferansepaper (Fagfellevurdert)
  • 43.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Hult, Peter
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Filosofiska fakulteten.
    Fjallbrant, T
    Wranne, Bengt
    Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärt- och Medicincentrum, Fysiologiska kliniken US.
    Bioacoustic techniques is applicable to primary health care2001Inngår i: PROCEEDINGS OF THE 23RD ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY, VOLS 1-4: BUILDING NEW BRIDGES AT THE FRONTIERS OF ENGINEERING AND MEDICINE, 2001, Vol. 23, s. 1911-1914Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The stethoscope has been used diagnostically for nearly two hundred years to assess the heart function. We can envision the intelligent stethoscope which combines the advantages of the traditional instrument with advanced functionality for analysis of the signal and other information support. The bioacoustic technique is basically simple and robust and fits therefore into a scenario where investigations are performed in a distributed health care system as in primary health care or even home health care. We have focused on detection of respiratory sounds and third heart sounds. The later is performed with a new wavelet technique which makes it possible to automatically detect and identify the sounds and possibly relate them to myocardial insufficiency.

  • 44.
    Ask, Per
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Hägglund, Sture
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för datavetenskap, ASLAB - Application Systems Laboratory.
    Olsson, J.
    Pettersson, N-E
    Sjöqvist, Bengt Arne
    Åhlfeldt, Hans
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik.
    3G-satsning och 'pensionärsdatorer' kan lösa hälso- och sjukvårdens problem2003Inngår i: Läkartidningen, ISSN 0023-7205, E-ISSN 1652-7518, Vol. 100, s. 1257-1258Artikkel i tidsskrift (Annet vitenskapelig)
  • 45.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Hägglund, Sture
    Linköpings universitet, Institutionen för datavetenskap, Interaktiva och kognitiva system. Linköpings universitet, Tekniska högskolan.
    Olsson, Jan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling. Linköpings universitet, Filosofiska fakulteten.
    Pettersson, Nils-Erik
    Sjöqvist, Bengt-Arne
    Åhlfeldt, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    36-nätet och "pensionärsdatorer" kan bidra till att lösa sjukvårdens problem2003Inngår i: Läkartidningen, ISSN 0023-7205, E-ISSN 1652-7518, Vol. 100, nr 14, s. 1257-1258Artikkel i tidsskrift (Fagfellevurdert)
  • 46.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Hök, B
    Loyd, Dan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska högskolan.
    Teriö, H
    Bio-acoustic signals from stenotic tube flow: state of the art and perspectives for future methodological development.1995Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 33, nr 5, s. 669-675Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To study the degree of stenosis from the acoustic signal generated by the turbulent flow in a stenotic vessel, so-called phonoangiography was first suggested over 20 years ago. A reason for the limited use of the technique today may be that, in the early work, the theory of how to relate the spectrum of the acoustic signal to the degree of the stenosis was not clear. However, during the last decade, the theoretical basis for this and other biological tube flow applications has been clarified. Now there is also easy access to computers for frequency analysis. A further explanation for the limited diagnostic use of bio-acoustic techniques for tube flow is the strong competition from ultrasound Doppler techniques. In the future, however, applications may be expected in biological tube flow where the non-invasive, simple and inexpensive bio-acoustic techniques will have a definite role as a diagnostic method.

  • 47.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Hök, Bertil
    PRESSURE MEASUREMENT TECHNIQUES IN URODYNAMIC INVESTIGATIONS1990Inngår i: Neurourology and Urodynamics, ISSN 0733-2467, E-ISSN 1520-6777, Vol. 9, nr 1, s. 1-15Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is apparent that the use of accurate pressure measurement techniques is essential for the outcome of urodynamic investigations. The aim of this paper is to estimate the demands on urodynamic pressure measurements and to review the properties of various techniques used. For the infused catheter technique, the dynamic properties are very much dependent on the complicance of the infusion system. With optimal infusion, the bandwidth and the pressure rise rate seem to be sufficient for most applications. Intraluminal microtransducers have a high bandwidth, but a certain fiber optic transducer cannot accurately measure mechanical pressure in the collapsed urethra. The principal differences in measuring hydrostatic pressure between the infused catheter technique and microtransducers should be observed. Flexion artefacts are a problem when measuring urethral pressure profiles. Newly developed transducers may offer a solution to this problem.

  • 48.
    Ask, Per
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Hök, Bertil
    Loyd, Dan
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Mekanisk värmeteori och strömningslära.
    Teriö, Heikki
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Bioacoustic signals from stenotic tube flow1995Inngår i: Medical & Biological Engineering & Computing, ISSN 0140-0118, Vol. 33, s. 669-675Artikkel i tidsskrift (Fagfellevurdert)
  • 49.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Levitan, H
    Robinson, P J
    Rapoport, S I
    Peripheral nerve as an osmometer: role of the perineurium in frog sciatic nerve.1983Inngår i: American Journal of Physiology, ISSN 0002-9513, E-ISSN 2163-5773, Vol. 244, nr 1, s. C75-81Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Measurements of volume and hydrostatic pressure in the frog sciatic nerve in vitro demonstrate that the nerve acts as an osmometer, in large part because the perineurium is a semipermeable membrane for water flow. Endoneurial hydrostatic pressure in nerves in isotonic Ringer exceeds bath pressure by about 7 mmHg. In Ringer made hypertonic by addition of sucrose, nerve volume and endoneurial pressure fall linearly in relation to 1/osmolality. The slope of the plot of pressure against volume provides a value for nerve compliance equal to 0.006 mm2/mmHg. Calculations based on the model of the nerve as an osmometer indicate that the nerve has an osmotically "inactive" volume equal to 0.19 mm3/mm, which is about 75% of the total volume of a nerve segment of unit length in normal Ringer. Perineurial hydraulic conductivity (Lp) equals 7.5 x 10(-13) cm3.s-1.dyn-1, a value characteristic of nonleaky epithelia. The perineurium is an elastic tissue with a constant modulus of elasticity equal to 3 x 10(6) dyn/cm2 when not markedly stretched and may limit nerve swelling under pathological conditions of nerve edema.

  • 50.
    Ask, Per
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Loyd, Dan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska högskolan.
    Wranne, Bengt
    Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärt- och Medicincentrum, Fysiologiska kliniken US.
    Regurgitant flow through heart valves: a hydraulic model applicable to ultrasound Doppler measurements.1986Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 24, nr 6, s. 643-646Artikkel i tidsskrift (Fagfellevurdert)
12345 1 - 50 of 208
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