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  • 1.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute (VTI), Linköping, Sweden.
    Nystrom, Marcus
    Lund University, Sweden .
    Holmqvist, Kenneth
    Lund University, Sweden .
    Fors, Carina
    Swedish National Road and Transport Research Institute (VTI), Linköping, Sweden.
    Sandberg, David
    Swedish National Road and Transport Research Institute (VTI), Linköping, Sweden.
    Anund, Anna
    Swedish National Road and Transport Research Institute (VTI), Linköping, Sweden.
    Kecklund, Goran
    Stockholm University, Sweden .
    Akerstedt, Torbjorn
    Stockholm University, Sweden .
    Fit-for-duty test for estimation of drivers sleepiness level: Eye movements improve the sleep/wake predictor2013In: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X, E-ISSN 1879-2359, Vol. 26, p. 20-32Article in journal (Refereed)
    Abstract [en]

    Driver sleepiness contributes to a considerable proportion of road accidents, and a fit-for-duty test able to measure a drivers sleepiness level might improve traffic safety. The aim of this study was to develop a fit-for-duty test based on eye movement measurements and on the sleep/wake predictor model (SWP, which predicts the sleepiness level) and evaluate the ability to predict severe sleepiness during real road driving. Twenty-four drivers participated in an experimental study which took place partly in the laboratory, where the fit-for-duty data were acquired, and partly on the road, where the drivers sleepiness was assessed. A series of four measurements were conducted over a 24-h period during different stages of sleepiness. Two separate analyses were performed; a variance analysis and a feature selection followed by classification analysis. In the first analysis it was found that the SWP and several eye movement features involving anti-saccades, pro-saccades, smooth pursuit, pupillometry and fixation stability varied significantly with different stages of sleep deprivation. In the second analysis, a feature set was determined based on floating forward selection. The correlation coefficient between a linear combination of the acquired features and subjective sleepiness (Karolinska sleepiness scale, KSS) was found to be R = 0.73 and the correct classification rate of drivers who reached high levels of sleepiness (KSS andgt;= 8) in the subsequent driving session was 82.4% (sensitivity = 80.0%, specificity = 84.2% and AUC = 0.86). Future improvements of a fit-for-duty test should focus on how to account for individual differences and situational/contextual factors in the test, and whether it is possible to maintain high sensitive/specificity with a shorter test that can be used in a real-life environment, e.g. on professional drivers.

  • 2.
    Fors, Carina
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Evaluation of a Laser Doppler System for Myocardial Perfusion Monitoring2007Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Coronary artery bypass graft (CABG) surgery is a common treatment for patients with coronary artery disease. A potential complication of CABG is myocardial ischemia or infarction. In this thesis, a method - based on laser Doppler flowmetry (LDF) - for detection of intra- and postoperative ischemia by myocardial perfusion monitoring is evaluated.

    LDF is sensitive to motion artifacts. In previous studies, a method for reduction of motion artifacts when measuring on the beating heart has been developed. By using the ECG as a reference, the perfusion signal is measured in intervals during the cardiac cycle where the cardiac motion is at a minimum, thus minimizing the artifacts in the perfusion signal.

    The aim of this thesis was to investigate the possibilities to use the ECG-triggered laser Doppler system for continuous monitoring of myocardial perfusion in humans during and after CABG surgery. Two studies were performed. In the first study, changes in myocardial perfusion during CABG surgery were investigated (n = 13), while the second study focused on postoperative measurements (n = 13). In addition, an ECG-triggering method was implemented and evaluated.

    It was found that the large variations in myocardial perfusion during CABG surgery could be monitored with the ECG-triggered laser Doppler system. Furthermore, a perfusion signal of good quality could be registered postoperatively from the closed chest in ten out of thirteen patients. In eight out of ten patients, a proper signal was obtained also the following morning, i.e., about 20 hours after probe insertion. The results show that respiration and blood pressure can have an influence on the perfusion signal.

    In conclusion, the results indicate that the method is able to detect fluctuations in myocardial perfusion under favourable circumstances. However, high heart rate, abnormal cardiac motion, improper probe attachment and limitations in the ECG-triggering method may result in variations in the perfusion signal that are not related to tissue perfusion.

    List of papers
    1. Myocardial perfusion monitoring during coronary artery bypass using an electrocardiogram-triggered laser Doppler technique
    Open this publication in new window or tab >>Myocardial perfusion monitoring during coronary artery bypass using an electrocardiogram-triggered laser Doppler technique
    2005 (English)In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 43, no 5, p. 582-588Article in journal (Refereed) Published
    Abstract [en]

    Electrocardiogram (ECG)—triggered laser Doppler perfusion monitoring (LDPM) was used to assess myocardial perfusion, with minimum myocardial tissue motion influence, during coronary artery bypass grafting (CABG). Thirteen subjects were investigated at six phases: pre- and post-CABG; post aorta cross-clamping; pre and post left internal mammary artery (LIMA) graft declamping; and post aorta declamping. The perfusion signal was calculated in late systole and late diastole, with expected minimum tissue motion, and compared with arrested heart measurements. Patient conditions or artifacts caused by surgical activity made it impossible to perform and analyse data in all six phases for some patients. No significant (n=5) difference between perfusion signals pre- and post-CABG was found. Diastolic perfusion signal levels were significantly (p<0.02) lower compared with systolic levels. After aorta cross-clamping, the signal level was almost zero. A distinct perfusion signal increase after LIMA and aorta declamping, compared with pre-LIMA declamping, was found in ten cases out of 13. A significantly (p<0.04) lower perfusion signal in the arrested heart compared with in the beating heart was registered. Influence from mechanical ventilation was observed in 14 measurements out of 17. In conclusion, ECG-triggered LDPM can be used to assess myocardial perfusion during CABG. Perfusion signals were lower in the arrested heart compared with in the beating heart and in late diastole compared with late systole. No significant difference between pre- and post-CABG was found.

    Place, publisher, year, edition, pages
    Springer, 2005
    Keywords
    Laser Doppler perfusion monitoring, Coronary artery bypass grafting, Beating heart, Myocardial microcirculation, Movement artifacts, Electrocardiography
    National Category
    Medical Laboratory and Measurements Technologies
    Identifiers
    urn:nbn:se:liu:diva-14612 (URN)10.1007/BF02351031 (DOI)000234262300007 ()2-s2.0-29244438810 (Scopus ID)
    Available from: 2007-08-27 Created: 2007-08-27 Last updated: 2017-12-13Bibliographically approved
    2. Analysis of breathing-related variations in ECG-triggered laser Doppler perfusion signals measured on the beating heart during surgery
    Open this publication in new window or tab >>Analysis of breathing-related variations in ECG-triggered laser Doppler perfusion signals measured on the beating heart during surgery
    2006 (English)In: Computers in cardiology, ISSN 0276-6574, Vol. 33, p. 181-184Article in journal (Refereed) Published
    Abstract [en]

    Laser Doppler perfusion monitoring (LDPM) is a

    method to assess microvascular perfusion. A modified,

    ECG-triggered LDPM system has been developed to

    measure myocardial perfusion with minimum influence

    from heart motion. With this method, one systolic (PLS)

    and one diastolic (PLD) perfusion value is obtained.

    The aim of this study was to analyse breathing-related

    variations in PLS and PLD measured during open-heart

    surgery. The phase delays between PLS, PLD, mean

    arterial blood pressure (MAP), heart rate and, indirectly,

    the respiration were determined.

    MAP tended to be in phase with or precede the

    variations in PLD, i.e., PLD was at a maximum at the end

    of inspiration or at the beginning of expiration. No clear

    relation between PLS and any of the other signals could

    be found.

    National Category
    Medical Laboratory and Measurements Technologies
    Identifiers
    urn:nbn:se:liu:diva-14613 (URN)2-s2.0-50149103402 (Scopus ID)
    Available from: 2007-08-27 Created: 2007-08-27 Last updated: 2017-12-13Bibliographically approved
    3. Determination of appropriate times during the cardiac cycle for online laser Doppler measurements of myocardial perfusion
    Open this publication in new window or tab >>Determination of appropriate times during the cardiac cycle for online laser Doppler measurements of myocardial perfusion
    2007 (English)Article in journal (Refereed) Submitted
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14614 (URN)
    Available from: 2007-08-27 Created: 2007-08-27 Last updated: 2017-02-16Bibliographically approved
  • 3.
    Fors, Carina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Ahn, Henrik Casimir
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Thoracic Surgery. Östergötlands Läns Landsting, Heart Centre, Department of Thoracic and Vascular Surgery.
    Wårdell, Karin
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Analysis of Breathing-related Variations in ECG-triggered Laser Doppler Perfusion Signals Measured on the Beating Heart during Surgery2006In: IEEE 2006,2006, 2006, p. 181-184Conference paper (Refereed)
    Abstract [en]

        

  • 4.
    Fors, Carina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Ahn, Henrik Casimir
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medical and Health Sciences, Thoracic Surgery. Östergötlands Läns Landsting, Heart Centre, Department of Thoracic and Vascular Surgery.
    Wårdell, Karin
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Online Laser Doppler Measurements of Myocardial Perfusion2008In: IFMBE Proceedings 22,2008, Springer Berlin Heidelberg , 2008, p. 1718-1721Conference paper (Refereed)
    Abstract [en]

    Laser Doppler perfusion monitoring is a suitable method for microvascular blood perfusion measurements. When used on a moving tissue or organ, the Doppler signal arising from the moving blood cells may be distorted. ECG triggering of the laser Doppler signal can be used for reducing the influence from movements during measurements on the beating heart. The aim of this study was to determine the most appropriate triggering intervals during the cardiac cycle for online measurements. Recordings from thirteen coronary artery bypass graft (CABG) patients were included in the study. During surgery, the fibre-optic probe was passed through the chest wall and sutured to the left anterior ventricular wall with the probe tip inserted 3–5 mm into the myocardium. After the patient arrived at the intensive care unit a second measurement was initiated and lasted for about two hours. Before the probe was removed a third measurement was performed for about 5 minutes the following morning. A total of 97 data sequences were analysed and the intervals of low and stable perfusion signal were compared to the positions of the T and P peaks in the ECG.

    It was found that the most appropriate time intervals were in late systole at the T peak [−3, 9] ms and just before the P peak [−28, -10] ms in late diastole. However, the position of these intervals may vary between individuals, because of e.g., abnormal cardiac motion. With the use of the appropriate interval online measurement of the myocardial perfusion on a beating heart appears possible.

  • 5.
    Fors, Carina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Ahn, Henrik Casimir
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Thoracic Surgery. Östergötlands Läns Landsting, Heart Centre, Department of Thoracic and Vascular Surgery.
    Wårdell, Karin
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Postoperativa mätningar av myokardperfusion med EKG-triggad laser Doppler2006In: Medicinteknikdagarna 2006,2006, 2006Conference paper (Other academic)
  • 6.
    Fors, Carina
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Casimir Ahn, Henrik
    Linköping University, Department of Medical and Health Sciences, Thoracic Surgery. Linköping University, Faculty of Health Sciences.
    Wårdell, Karin
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Analysis of breathing-related variations in ECG-triggered laser Doppler perfusion signals measured on the beating heart during surgery2006In: Computers in cardiology, ISSN 0276-6574, Vol. 33, p. 181-184Article in journal (Refereed)
    Abstract [en]

    Laser Doppler perfusion monitoring (LDPM) is a

    method to assess microvascular perfusion. A modified,

    ECG-triggered LDPM system has been developed to

    measure myocardial perfusion with minimum influence

    from heart motion. With this method, one systolic (PLS)

    and one diastolic (PLD) perfusion value is obtained.

    The aim of this study was to analyse breathing-related

    variations in PLS and PLD measured during open-heart

    surgery. The phase delays between PLS, PLD, mean

    arterial blood pressure (MAP), heart rate and, indirectly,

    the respiration were determined.

    MAP tended to be in phase with or precede the

    variations in PLD, i.e., PLD was at a maximum at the end

    of inspiration or at the beginning of expiration. No clear

    relation between PLS and any of the other signals could

    be found.

  • 7.
    Fors, Carina
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Casimir Ahn, Henrik
    Linköping University, Department of Medical and Health Sciences, Thoracic Surgery. Linköping University, Faculty of Health Sciences.
    Wårdell, Karin
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Determination of appropriate times during the cardiac cycle for online laser Doppler measurements of myocardial perfusion2007Article in journal (Refereed)
  • 8.
    Fors, Carina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Karlsson, Daniel M G
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Ahn, Henrik Casimir
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Thoracic Surgery. Östergötlands Läns Landsting, Heart Centre, Department of Thoracic and Vascular Surgery.
    Wårdell, Karin
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Myocardial perfusion assessment using an ECG triggered laser doppler technique2005In: 13th Nordic Baltic Conference Biomedical Engineering and Medical Physics,2005, Umeå: IFMBE , 2005, p. 83-84Conference paper (Refereed)
  • 9.
    Fors, Carina
    et al.
    Linköping University, Department of Biomedical Engineering.
    Karlsson, M G Daniel
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Ahn, Henrik Casimir
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Thoracic Surgery. Östergötlands Läns Landsting, Heart Centre, Department of Thoracic and Vascular Surgery.
    Wårdell, Karin
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    A system for on-line laser Doppler monitoring of ECG-traced myocardial perfusion2004In: IEEE EMBS,2004, Piscataway, NJ, USA: IEEE , 2004, p. 3796-Conference paper (Refereed)
  • 10.
    Hallvig, David
    et al.
    The Swedish Road and Transport Research Institute (VTI), Linköping, Sweden.
    Anund, Anna
    The Swedish Road and Transport Research Institute (VTI), Linköping, Sweden.
    Fors, Carina
    The Swedish Road and Transport Research Institute (VTI), Linköping, Sweden.
    Kecklund, Goran
    Stockholm University, Sweden .
    Karlsson, Johan G.
    Autoliv Dev AB, Sweden .
    Wande, Mattias
    Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden.
    Akerstedt, Torbjorn
    Stockholm University, Sweden .
    Sleepy driving on the real road and in the simulator-A comparison2013In: Accident Analysis and Prevention, ISSN 0001-4575, E-ISSN 1879-2057, Vol. 50, p. 44-50Article in journal (Refereed)
    Abstract [en]

    Sleepiness has been identified as one of the most important factors contributing to road crashes. However, almost all work on the detailed changes in behavior and physiology leading up to sleep related crashes has been carried out in driving simulators. It is not clear, however, to what extent simulator results can be generalized to real driving. This study compared real driving with driving in a high fidelity, moving base, driving simulator with respect to driving performance, sleep related physiology (using electroencephalography and electrooculography) and subjective sleepiness during night and day driving for 10 participants. The real road was emulated in the simulator. The results show that the simulator was associated with higher levels of subjective and physiological sleepiness than real driving. However, both for real and simulated driving, the response to night driving appears to be rather similar for subjective sleepiness and sleep physiology. Lateral variability was more responsive to night driving in the simulator, while real driving at night involved a movement to the left in the lane and a reduction of speed, both of which effects were absent in the simulator. It was concluded that the relative validity of simulators is acceptable for many variables, but that in absolute terms simulators cause higher sleepiness levels than real driving. Thus, generalizations from simulators to real driving must be made with great caution.

  • 11.
    Karlsson, Daniel M. G.
    et al.
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    Fors, Carina
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    Wårdell, Karin
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    Casimir-Ahn, Henrik
    Östergötlands Läns Landsting, Heart Centre.
    Myocardial perfusion monitoring during coronary artery bypass using an electrocardiogram-triggered laser Doppler technique2005In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 43, no 5, p. 582-588Article in journal (Refereed)
    Abstract [en]

    Electrocardiogram (ECG)—triggered laser Doppler perfusion monitoring (LDPM) was used to assess myocardial perfusion, with minimum myocardial tissue motion influence, during coronary artery bypass grafting (CABG). Thirteen subjects were investigated at six phases: pre- and post-CABG; post aorta cross-clamping; pre and post left internal mammary artery (LIMA) graft declamping; and post aorta declamping. The perfusion signal was calculated in late systole and late diastole, with expected minimum tissue motion, and compared with arrested heart measurements. Patient conditions or artifacts caused by surgical activity made it impossible to perform and analyse data in all six phases for some patients. No significant (n=5) difference between perfusion signals pre- and post-CABG was found. Diastolic perfusion signal levels were significantly (p<0.02) lower compared with systolic levels. After aorta cross-clamping, the signal level was almost zero. A distinct perfusion signal increase after LIMA and aorta declamping, compared with pre-LIMA declamping, was found in ten cases out of 13. A significantly (p<0.04) lower perfusion signal in the arrested heart compared with in the beating heart was registered. Influence from mechanical ventilation was observed in 14 measurements out of 17. In conclusion, ECG-triggered LDPM can be used to assess myocardial perfusion during CABG. Perfusion signals were lower in the arrested heart compared with in the beating heart and in late diastole compared with late systole. No significant difference between pre- and post-CABG was found.

  • 12.
    Wårdell, Karin
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Fors, Carina
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Antonsson, Johan
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Eriksson, Ola
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    A laser Doppler system for intracerebral measurements during stereotactic neurosurgery2007In: Engineering in Medicine and Biology Society, 2007. EMBS 2007, IEEE , 2007, p. 4083-4086Conference paper (Refereed)
    Abstract [en]

    A laser Doppler system for intracerebral measurements during stereotactic and functional neurosurgery is presented. The system comprises a laser Doppler perfusion monitor, an optical probe adapted for the Leksellreg stereotactic system and a personal computer with software for acquisition, data analysis and presentation. The software makes it possible to present both the perfusion and the total backscattered light intensity (TLI) in real-time. During intracerebral measurements, the perfusion signal records the tissue's microcirculation whereas the TLI signal may be used to distinguish between grey and white matter. Evaluation of the system has been done during stereotactic neurosurgery in relation to implantation of deep brain stimulation electrodes. Measurements were made along trajectories towards targets in the deep brain structure as well as in pre-calculated target areas. The measurements show that the system has a potential to be used for intracerebral guidance but further evaluation of the technique is needed.

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