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  • 1.
    Ahlström, Christer
    et al.
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, Faculty of Health Sciences.
    Länne, Toste
    Linköping University, Department of Medicine and Health Sciences, Physiology . Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Thoracic and Vascular Surgery.
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, Faculty of Health Sciences.
    Johansson, Anders
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, Faculty of Health Sciences.
    A method for accurate localization of the first heart sound and possible applications2008In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 29, no 3, p. 417-428Article in journal (Refereed)
    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.

  • 2.
    Haddaway, Michael J.
    et al.
    Robert Jones and Agnes Hunt Orthopaed Hospital NHS Fdn, England .
    Davie, Michael W. J.
    Robert Jones and Agnes Hunt Orthopaed Hospital NHS Fdn, England .
    Davies, Helen L.
    Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences. Robert Jones and Agnes Hunt Orthopaed Hospital NHS Fdn, England .
    Sharp, Christopher A.
    Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences. Robert Jones and Agnes Hunt Orthopaed Hosp NHS Fdn, England Linkoping Univ, Dept Clin and Expt Med, Div Clin Chem, Linkoping, Sweden .
    Application of sub-regional analysis to bone mineral density of the lower limb from whole body DXA scans2013In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 34, no 7, p. 757-768Article in journal (Refereed)
    Abstract [en]

    Bone mineral density at spine and hip is widely used to diagnose osteoporosis. Certain conditions cause changes in bone density at other sites, particularly in the lower limb, with fractures occurring in non-classical locations. Bone density changes at these sites would be of interest for diagnosis and treatment. We describe an application, based on an existing software option for Hologic scanners, which allows reproducible measurement of bone density at six lower limb sites (upper femur, mid-femur, lower femur; upper leg, mid-leg, lower leg). In 30 unselected subjects, referred for bone density, precision (CV%) measured on 2 occasions, separated by repositioning, ranged from 1.7% (mid-femur) to 4.5% at the lowest leg site. Intra-operator precision, measured by three operators on ten subjects on three occasions, was between 1.0% and 2.9%, whilst inter-operator precision was between 1.0% and 3.6%, according to region. These values compare well with those at the spine and upper femur, and in the literature. There was no evidence that this operator agreement improved between occasions 1 and 3. This technique promises to be useful for assessing bone changes at vulnerable sites in the lower limb, in diverse pathological states and in assessing response to treatment.

  • 3.
    Hagblad, Jimmie
    et al.
    Malardalen University, Sweden .
    Folke, Mia
    Malardalen University, Sweden .
    Lindberg, Lars-Göran
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Linden, Maria
    Malardalen University, Sweden .
    Technical issues related to the long-term monitoring of blood flow at different depths using LDF and PPG2012In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 33, no 6, p. 985-996Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to evaluate an integrated probe using LDF and multiple PPG, for the long-term aspects of skin temperature and blood flow variations at different tissue depths, and especially to investigate whether the presence of the probe affects the temperature. Measurements of temperature and blood flow were performed over 60 min on the lower back of ten subjects, lying on a mattress. The surface temperature of the skin was also measured before and after the 60 min period, and repeated with three probe configurations with the probe switched on, turned off and in the absence of a probe. A general increase in the blood flow was found to occur during the 60 min interval at all depths reached by this probe, but with variations over time. No difference was found in temperatures recorded for the different probe configurations. According to our measurements, the presence of the probe does not affect the skin surface temperature at 60 min. Our investigation shows that skin temperature can be expected to increase and approach the body core temperature by just lying in supine position on the mattress. The increase in temperature and blood flow that is known to occur, possibly attributable to pressure-induced vasodilatation, must be taken into consideration when performing these kinds of measurements.

  • 4.
    JAFFARI, SA
    et al.
    ; .
    TURNER, APF
    Cranfield University, UK.
    RECENT ADVANCES IN AMPEROMETRIC GLUCOSE BIOSENSORS FOR IN-VIVO MONITORING1995In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 16, no 1Article, review/survey (Refereed)
    Abstract [en]

    Electrochemical biosensors for glucose, based on the specific glucose oxidizing enzyme glucose oxidase, have generated considerable interest. Several commercial devices based on this principle have been developed and are widely used for in vitro monitoring of glucose e.g. in hospitals, doctors surgeries and for home monitoring by patients themselves. A significant advance in the application of biosensor technology would be the development of portable, implantable sensors which could continuously indicate the blood glucose concentration, enabling swift corrective action to be taken by the patient. This review highlights recent developments in amperometric glucose biosensors for in vivo monitoring and also considers the remaining barriers which need to be overcome to enable successful introduction of an implantable sensor.

  • 5.
    Nilsson, Lena
    et al.
    Linköping University, Department of Medical and Health Sciences, Anesthesiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Anaesthetics, Operations and Specialty Surgery Center, Department of Anaesthesiology and Intensive Care in Linköping. Östergötlands Läns Landsting, Anaesthesiology and Surgical Centre.
    Goscinski, Tomas
    Linköping University, Department of Medical and Health Sciences, Pharmacology. Linköping University, Faculty of Health Sciences.
    Lindenberger, Marcus
    Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Faculty of Health Sciences.
    Länne, Toste
    Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Thoracic and Vascular Surgery.
    Johansson, Anders
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Respiratory variations in the photoplethysmographic waveform: acute hypovolaemia during spontaneous breathing is not detected2010In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 31, no 7, p. 953-962Article in journal (Refereed)
    Abstract [en]

    Recent studies using photoplethysmographic (PPG) signals from pulse oximeters have shown potential to assess hypovolaemia during spontaneous breathing. This signal is heavily filtered and reports are based on respiratory variations in the small pulse synchronous variation of PPG. There are stronger respiratory variations such as respiratory synchronous variation (PPGr) in the baseline of the unfiltered PPG signal. We hypothesized that PPGr would increase during hypovolaemia during spontaneous breathing. Hemodynamic and respiratory data were recorded together with PPG infrared signals from the finger, ear and forearm from 12 healthy male volunteers, at rest and during hypovolaemia created by the application of a lower body negative pressure (LBNP) of 15, 30 and 60 cmH(2)O. Hemodynamic and respiratory values changed significantly. From rest to the LBNP of 60 cmH(2)O systolic blood pressure fell from median (IQR) 116 (16) to 101 (23) mmHg, the heart rate increased from 58 (16) to 73 (16) beats min(-1), and the respiratory rate increased from 9.5 (2.0) to 11.5 (4.0) breaths min(-1). The amplitude of PPGr did not change significantly at any measurement site. The strongest effect was seen at the ear, where the LBNP of 60 cmH(2)O gave an amplitude increase from 1.0 (0.0) to 1.31 (2.24) AU. PPG baseline respiratory variations cannot be used for detecting hypovolaemia in spontaneously breathing subjects.

  • 6.
    Nilsson, Lena
    et al.
    Linköping University, Department of Medical and Health Sciences, Anesthesiology. Linköping University, Faculty of Health Sciences.
    Johansson, Anders
    Linköping University, Department of Biomedicine and Surgery. Linköping University, Faculty of Health Sciences.
    Kalman, Sigga
    Linköping University, Department of Medical and Health Sciences, Anesthesiology. Linköping University, Faculty of Health Sciences.
    Macrocirculation is not the sole determinant of respiratory induced variations in the reflection mode photoplethysmographic signal2003In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 24, no 4, p. 925-937Article in journal (Refereed)
    Abstract [en]

    Photoplethysmography (PPG) is a non-invasive optical technique sensitive to variations in blood volume and perfusion in the tissue. Reflection mode PPG may have clinical advantages over transmission mode PPG. To improve clinical usefulness and further development of the reflection mode PPG, studies on factors that modify the signal are warranted. We studied the coherence between the respiratory induced intensity variations (RIIV) of the PPG signal and respiratory synchronous pressure variations in central venous pressure (CVP), peripheral venous pressure (PVP) and arterial blood pressure (ABP) during positive pressure ventilation on 12 patients under anaesthesia and on 12 patients with spontaneous breathing. During positive pressure ventilation the coherence between all signals was high. Inspiration was followed first by an increase in CVP, then by increases in ABP and PVP and lastly by RIIV indicating less back-scattered light. In spontaneously breathing patients the coherence was high, but the phases between the signals were changed. During inspiration, ABP decreased slightly before CVP, followed by a decrease in RIIV and PVP. The phase relation between RIIV and respiratory induced variation in macrocirculation changed with ventilatory mode, but not in a uniform way, indicating the influence of mechanisms other than macrocirculation involved in generating the RIIV signal.

  • 7.
    Toma-Daşu, Iuliana
    et al.
    Umeå University.
    Waites, Anthony
    Umeå University.
    Daşu, Alexandru
    Umeå University.
    Denekamp, Juliana
    Umeå University.
    Theoretical simulation of oxygen tension measurement in tissues using a microelectrode: I. The response function of the electrode2001In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 22, no 4, p. 713-725Article in journal (Refereed)
    Abstract [en]

    The aim of this article is to determine the correlation between the actual oxygen distribution in tissues and the distribution of oxygen measured by microelectrodes. This correlation is determined by the response function of the electrode, which depends on the oxygen consumed by the electrode. In tissue it is necessary to consider the gradients resulting from cellular respiration. A computer program has been used to simulate the vascular structure of various tissues and also the measurements of oxygen tension using a polarographic electrode. The electrode absorption process is described using a theoretical model. The gradient of oxygen in tissue is described by a mathematical model that takes into consideration both diffusion and cellular consumption of oxygen. We have compared the results obtained using the response function of the electrode and some simplifications of it. The results of these comparisons show that there are some differences in the 'observed' distributions of the oxygen tension in tissues predicted using different formulae for the electrode response function. Also, there are considerable differences between the input oxygen distribution and the measured values in all cases. All the results of the simulations of the oxygen tension 'observed' by a 12 microm polarographic electrode, using different response functions of the electrode, show that the electrode averages the values from many cells. Care should be taken in using a simplification for the response function of the electrode, especially if the results are going to be used as input values in modelling the tumour response to new treatments and/or as a basis of selecting patients for treatments. A computer simulation of measurement of oxygen tensions in regions of steep pO2 gradients shows that extremely high and extremely low pO2 values will not be detected.

  • 8.
    Zdolsek, Hans Joachim
    et al.
    Linköping University, Department of Medicine and Care, Anaesthesiology. Linköping University, Faculty of Health Sciences.
    Lindahl, Olof Anton
    Department of Applied Physics and Electronics, Umeå University and Biomedical Engineering and Informatics, University Hospital of Northern Sweden, Umeå, Sweden .
    Sjöberg, Folke
    Linköping University, Department of Clinical and Experimental Medicine, Burn Center. Linköping University, Department of Biomedicine and Surgery, Plastic Surgery, Hand Surgery and Burns. Linköping University, Faculty of Health Sciences.
    Non-invasive assessment of fluid volume status in the interstitium after haemodialysis2000In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 21, no 2, p. 211-220Article in journal (Refereed)
    Abstract [en]

    During dialysis excess fluid is removed from uraemic patients. The excess fluid is mainly located in the skin and subcutaneous tissues. In this study we wished, with two non-invasive techniques, the IM (impression method) and BIA (bioimpedance analysis), to study what mechanical (IM) and electrical cellular membrane (BIA) effects the fluid withdrawal has on these tissues. The IM measures the resistive force of the tissues when mechanically compressed. From the force curve two parameters are calculated, the F(0), indicative of interstitial tissue pressure and the FT corresponding to the translocation of tissue fluid (interstitial movable water).

    The BIA phase angle shift (), i.e. geometrical angular transformation of the ratio between reactance and resistance, which has been associated with cellular membrane function, was used as a measurement of electrical cellular membrane effects.

    Twenty patients were studied before and after haemodialysis measuring the F(0), FT and . The results showed that the patients lost a median of 3.7 kg during the haemodialysis. F(0) increased until after dialysis, but did not reach significant values, whereas FT increased significantly after dialysis, p < 0.001, as compared with before. After a peak at one hour postdialysis the FT value returned to predialysis values at four hours after termination of dialysis. Also increased from before to after dialysis, p < 0.001, but already after one hour it returned to predialysis values.

    It is common knowledge that dialysis alters the dynamics of fluid in the interstitium of the skin and subcutis. We conclude that the impression method is sensitive enough to detect and chronicle these changes. Furthermore, with the BIA, (phase angle) signs of changes in the electrical properties of the tissues, possibly reflecting cellular membrane function, could be detected.

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