Peter Rolfe | Harbin Institute Of Technology (original) (raw)

Papers by Peter Rolfe

Research paper thumbnail of Optics in cell and tissue engineering (Invited Paper)

SPIE Proceedings, 2005

ABSTRACT

Research paper thumbnail of Sleep staging from the EEG signal using multi-domain feature extraction

Biomedical Signal Processing and Control, 2016

The analysis of the electroencephalogram (EEG) can yield much useful information about brain func... more The analysis of the electroencephalogram (EEG) can yield much useful information about brain function, including indications of sleep stage. During the process of EEG analysis, feature extraction is one of the most critical technical aspect. Traditional EEG feature extraction methods are mainly based on single domain analysis. However, due to the highly non-stationary and nonlinear characteristics of the EEG, it is difficult to extract comprehensive information only from single domain analysis. In the present study, a novel feature extraction method was proposed based on the multi-domain analysis of the EEG. Fifteen characteristic parameters were extracted based on the multifractal detrended fluctuation analysis (MF-DFA), visibility graph algorithm (VGA), frequency analysis and nonlinear analysis. Ten optimal parameters of the fifteen parameters were selected by the genetic algorithm (GA). Then the Least Squares-Support Vector Machines (LS-SVM) were used to classify the sleep states. The cross validation results demonstrated that multi-domain feature extraction method can obtain more useful information in the EEG signal. Compared to the frequency domain parameters, nonlinear parameters and time domain parameters, the predictive accuracy of sleep staging classification with optimal multi-domain parameters improved 11.08%, 10.76% and 6.40% respectively.

Research paper thumbnail of EEMD and bidimensional RLS to suppress physiological interference for heterogeneous distribution in fNIRS study

Journal of Innovative Optical Health Sciences, 2018

Near-infrared spectroscopy (NIRS) can provide the hemodynamics information based on the hemoglobi... more Near-infrared spectroscopy (NIRS) can provide the hemodynamics information based on the hemoglobin concentration representing the blood oxygen metabolism of the cerebral cortical, which can be deployed for the cerebral function study. However, NIRS-based cerebral function detection accuracy can be significantly influenced by the physiological activities such as cardic cycle, respiration, spontaneous low-frequency oscillation and ultra-low frequency oscillation. The distribution difference of the capillary, artery and vein leads to the heterogeneity feature of the cerebral tissues. In the case that the heterogeneity is not serious, good detection accuracy and stable performance can be achieved through the regression analysis as the reference signal can well represent the interference in the measurement signal when conducting the multi-distance measurement approach. The direct use of the reference signal to estimate the interference is not able to achieve good performance in the case ...

Research paper thumbnail of Flexible approach to amperometric oxygen determination

Journal of Biomedical Engineering, 1988

In vitro and in vivo results obtainedfiom a noveljlexible amperometric oxygen sensor are reported... more In vitro and in vivo results obtainedfiom a noveljlexible amperometric oxygen sensor are reported. The sensor is fabricated using thin film deposition techniques and is operated by the application of a pulsed waveform. Deveiopment of the sensor was undertaken in order to produce a device that is capable of being sited at the interface of a wound and an overlying wound dressing. Oxygen determinations in such an environment would aid in gaining an undertanding of the role of oxygen in wound healing and the type of wound dressing that would provide an environment condwive towards wound healing. In vitro data indicate that linearity of response is good although other performance characteristics are irreproducible. In vivo response to oxygen has been observed 50 h after insertion into a porcine sham wound. Expected trends were followed when changes to the oxygen regime of the wound space were effected, but absolute values of oxygen tension are d$ficult to state with certainty. This may be due to poor calibration stability and inadequate sealing of the sensor from the surrounding enoironnent.

Research paper thumbnail of Current developments in non-invasive measurement of arterial blood pressure

Journal of Biomedical Engineering, 1988

Two new types of non-invasive method for measuring arterial blood pressure recently developed by ... more Two new types of non-invasive method for measuring arterial blood pressure recently developed by us are reviewed. Both oj the methoo?s are based on the characteristics of the pressure-volume relationship in the artery. One is the volume-oscillometn'c method; and the other is the volume-compensation method, based on the vascular unloading principle. Both methods employ photoelectric plethysmography for detection of artenal volume changes in the biological segment. The volume-oscillometric method can measure systolic and mean arterial pressure, and is applicable to long-term ambulatory monitoring. The volumecompensation method allows the beat-by-beat measurement of systolic and diastolic pressure and the recording of the pressure waveform continuously and non-invasively. This paper discusses the measurement principle and evaluates the accuracy of each method as compared with direct measurements. Preliminary descriptions of newly designed instruments based on these two methoo!s, and a few examples of the indirect pressure recordings, are also &scribed. The results obtained show that the noninvasive methoak for measuring arterial pressure presented here appear promising for use not onb in physiological studies, but also in clinical practice and research laboratories.

Research paper thumbnail of Near infra-red spectroscopy: a new technique for the non-invasive monitoring of tissue and blood oxygenation in vivo

Biochemical Society Transactions, 1988

Research paper thumbnail of Application of near-infrared spectroscopy for the assessment of the oxygenation level of myoglobin and haemoglobin in cardiac muscle in vivo

Biochemical Society Transactions, 1990

Research paper thumbnail of Insularity and professional protectionism or matrixing and professional security in the provision of perfusion services

Perfusion, 1995

Address for correspondence: G Wright, WE Dunn Unit of Cardiology, Department of Biological Scienc... more Address for correspondence: G Wright, WE Dunn Unit of Cardiology, Department of Biological Sciences, Keele University, Staffordshire ST5 5BG, UK. The role of medical technicians, engineers and scientists in the multidisciplinary teams responsible for patient care may often be underestimated. Compared with their clinical colleagues, these groups have relatively limited career expectations, employment is less secure, levels of remuneration are lower and incidental opportunities for salary enhancement are less frequent. Perfusionists are affected by these constraints as much as any other group and often feel too insular. Working in departments that are remote from their administrative and professional base, they may feel unprotected and unsupported by the departmental structure. Their career structure and prospects may be of little concern to their clinical colleagues. Although this insularity has often been the cause of some despondency, the increasing demand for technical specialist services has at least helped to make perfusionists feel wanted and the prospect of employment redundancy has not become a major concern. Nevertheless, warning signs are around that are ignored only at great risk. One of these is the likelihood of a significant decrease in coronary heart disease (CHD) in future years. Since CHD contributes over 60%

Research paper thumbnail of The development and use of a hand held transducer for intermittent fetal scalp blood measurements

Research paper thumbnail of A two dimensional three layer model of a transcutaneous blood-gas probe for use with a mass spectrometer

Research paper thumbnail of Non-Invasive Physiological Measurements Vol 2

Research paper thumbnail of Near infrared specroscopy in fetal monitoring

British journal of hospital medicine

ABSTRACT

Research paper thumbnail of A catheter-tip oxygen electrode: experience in newborn infants with respiratory distress

Archives of Disease in Childhood

Research paper thumbnail of High frequency variability of transcephalic electrical impedance — A new parameter for monitoring of neonatal cerebral circulation?

Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 1992

ABSTRACT

Research paper thumbnail of Fetale Laserspektroskopie während mütterlicher O2-Atmung - Fetal Laser Spectroscopy During Administration of Oxygen to the Mother

Geburtshilfe und Frauenheilkunde, 2000

Die Minderversorgung mit Sauerstoff nach Einsetzen der Wehentätigkeit ist eine der gröûten Gefahr... more Die Minderversorgung mit Sauerstoff nach Einsetzen der Wehentätigkeit ist eine der gröûten Gefahren für den Feten am Ende der Schwangerschaft. In Bezug auf die Behandlung dieser fetalen Hypoxie wurde die Sauerstoffgabe an die Mutter untersucht und kontrovers diskutiert. Mit der NIR-Laserspektroskopie steht ein Verfahren zur Verfügung, das aufgrund der direkten Erfassung der Gewebsoxygenierung zur Verifizierung der Wirksamkeit von Sauerstoffgabe an die Mutter beitragen kann. Methode: Zur Klärung dieser Frage wurden bei 24 Patientinnen in Terminnähe NIR-laserspektroskopische Messungen während Wehentätigkeit und Sauerstoffgabe an die Mutter durchgeführt. Ergebnisse: Die statistische Analyse erbrachte den signifikanten Nachweis, dass die Oxygenierung im fetalen Blut ansteigt. Auch das Cytochrom aa 3 welches in der oxydierten Form als direktes Maû für die Gewebsoxygenierung im fetalen Gehirn gilt, stieg in den Wehenpausen bei Sauerstoffgabe an. Schlussfolgerung: Die hier gefundene Zunahme der Oxygenierung bei Sauerstoffgabe an die Mutter zeigt, dass diese Maûnahme die fetale Sauerstoffversorgung bei eutrophen Kindern verbessern kann, wenn eine kindliche Notfallsituation auftritt.

Research paper thumbnail of Electrochemical aspects of intravascular oxygen transducers

Journal of Biomedical Engineering, 1984

ABSTRACT

Research paper thumbnail of iPhysioMeter: a smartphone photoplethysmograph for measuring various physiological indices

Methods in molecular biology (Clifton, N.J.), 2015

iPhysioMeter is a new smartphone application ("App") for the Apple iPhone and iPod touc... more iPhysioMeter is a new smartphone application ("App") for the Apple iPhone and iPod touch that allows photoplethysmography (PPG) to be implemented without the need for any additional devices. The resulting signal, the photoplethysmogram, allows the calculation of basic but valuable and frequently used physiological indices such as heart rate (HR) and pulse volume (PV). The design of iPhysioMeter has very much been influenced by a consideration of usability, as is immediately evident from ones first experience with it. However, its apparent simplicity in use should not disguise the need for correct operation, which otherwise might lead to collection of invalid or inaccurate data. There are several unexpected pitfalls that might not only produce inaccurate values, but, under some circumstances, could also damage the device or present a hazard to the user or subject. We therefore describe here, firstly, the core technology that makes it possible to perform PPG and to calculate...

Research paper thumbnail of Cardiovascular hemodynamic effects of Red Bull® Energy Drink during prolonged, simulated, monotonous driving

SpringerPlus, 2013

The purpose of this study was to investigate the cardiovascular hemodynamic effects of Red Bull® ... more The purpose of this study was to investigate the cardiovascular hemodynamic effects of Red Bull® Energy Drink during prolonged, simulated, monotonous driving. This was a double-blind, within-subjects-design, crossover study. Twelve healthy volunteers (21.7 ± 0.8 years old) experienced each of three conditions at various times: 1) consumption of Red Bull® Energy Drink; 2) consumption of placebo-controlled drink; and 3) no test drink. All subjects undertook 90-min periods of simulated monotonous driving, during which physiological measurements were made. The variables recorded were cardiovascular indices, i.e., mean blood pressure (MBP), cardiac output (CO), electrocardiogram RR interval (RR), total peripheral-vascular resistance (TPR: = MBP/CO), and normalized pulse volume (NPV). Additional parameters were the standard deviation of lateral position, i.e., the weaving of the car, and subjective rating of sleepiness. CO, RR, and TPR during the monotonous task were significantly differe...

Research paper thumbnail of Near infrared spectroscopy used to observe changes in fetal cerebral haemodynamics during labour

Journal of perinatal medicine, 1994

Near Infrared Spectroscopy (NIRS) has been used in the neonate to observe changes in the cerebral... more Near Infrared Spectroscopy (NIRS) has been used in the neonate to observe changes in the cerebral haemodynamics and concentration of oxygenated haemoglobin. Specific changes have been demonstrated in response to spontaneous bradycardias and alterations in the inspired oxygen concentration. We report here changes in fetal cerebral haemodynamics using NIRS in response to rapid spontaneous delivery and the "topping up" of a maternal epidural with bupivacaine. NIRS offers a new way of observing changes in cerebral haemodynamics in the fetus during labour.

Research paper thumbnail of Skin surface PO2 measurement and the effect of externally applied pressure

Archives of physical medicine and rehabilitation, 1981

The effect of externally applied load on the partial pressure of oxygen in tissue, measured at th... more The effect of externally applied load on the partial pressure of oxygen in tissue, measured at the skin surface (PSO2) was examined by applying a load to a transcutaneous O2 monitor mounted on the skin of healthy subjects. The load was increased every 4 minutes, and the PSO2 was recorded at the end of the 4-minute period. Three sites were investigated: the sacrum, the greater trochanteric area, and the lateral aspect of the thigh. Mean initial values for the 3 sites were found to be 10.1, 11.1, and 10.1 kPa, respectively. On increasing the applied load, values were found to reduce gradually at first and then at an increasing rate to zero at the "cut-off" load. The mean cut-off pressure for the 3 areas was 15.2, 18.8, and 18.1 kPa.

Research paper thumbnail of Optics in cell and tissue engineering (Invited Paper)

SPIE Proceedings, 2005

ABSTRACT

Research paper thumbnail of Sleep staging from the EEG signal using multi-domain feature extraction

Biomedical Signal Processing and Control, 2016

The analysis of the electroencephalogram (EEG) can yield much useful information about brain func... more The analysis of the electroencephalogram (EEG) can yield much useful information about brain function, including indications of sleep stage. During the process of EEG analysis, feature extraction is one of the most critical technical aspect. Traditional EEG feature extraction methods are mainly based on single domain analysis. However, due to the highly non-stationary and nonlinear characteristics of the EEG, it is difficult to extract comprehensive information only from single domain analysis. In the present study, a novel feature extraction method was proposed based on the multi-domain analysis of the EEG. Fifteen characteristic parameters were extracted based on the multifractal detrended fluctuation analysis (MF-DFA), visibility graph algorithm (VGA), frequency analysis and nonlinear analysis. Ten optimal parameters of the fifteen parameters were selected by the genetic algorithm (GA). Then the Least Squares-Support Vector Machines (LS-SVM) were used to classify the sleep states. The cross validation results demonstrated that multi-domain feature extraction method can obtain more useful information in the EEG signal. Compared to the frequency domain parameters, nonlinear parameters and time domain parameters, the predictive accuracy of sleep staging classification with optimal multi-domain parameters improved 11.08%, 10.76% and 6.40% respectively.

Research paper thumbnail of EEMD and bidimensional RLS to suppress physiological interference for heterogeneous distribution in fNIRS study

Journal of Innovative Optical Health Sciences, 2018

Near-infrared spectroscopy (NIRS) can provide the hemodynamics information based on the hemoglobi... more Near-infrared spectroscopy (NIRS) can provide the hemodynamics information based on the hemoglobin concentration representing the blood oxygen metabolism of the cerebral cortical, which can be deployed for the cerebral function study. However, NIRS-based cerebral function detection accuracy can be significantly influenced by the physiological activities such as cardic cycle, respiration, spontaneous low-frequency oscillation and ultra-low frequency oscillation. The distribution difference of the capillary, artery and vein leads to the heterogeneity feature of the cerebral tissues. In the case that the heterogeneity is not serious, good detection accuracy and stable performance can be achieved through the regression analysis as the reference signal can well represent the interference in the measurement signal when conducting the multi-distance measurement approach. The direct use of the reference signal to estimate the interference is not able to achieve good performance in the case ...

Research paper thumbnail of Flexible approach to amperometric oxygen determination

Journal of Biomedical Engineering, 1988

In vitro and in vivo results obtainedfiom a noveljlexible amperometric oxygen sensor are reported... more In vitro and in vivo results obtainedfiom a noveljlexible amperometric oxygen sensor are reported. The sensor is fabricated using thin film deposition techniques and is operated by the application of a pulsed waveform. Deveiopment of the sensor was undertaken in order to produce a device that is capable of being sited at the interface of a wound and an overlying wound dressing. Oxygen determinations in such an environment would aid in gaining an undertanding of the role of oxygen in wound healing and the type of wound dressing that would provide an environment condwive towards wound healing. In vitro data indicate that linearity of response is good although other performance characteristics are irreproducible. In vivo response to oxygen has been observed 50 h after insertion into a porcine sham wound. Expected trends were followed when changes to the oxygen regime of the wound space were effected, but absolute values of oxygen tension are d$ficult to state with certainty. This may be due to poor calibration stability and inadequate sealing of the sensor from the surrounding enoironnent.

Research paper thumbnail of Current developments in non-invasive measurement of arterial blood pressure

Journal of Biomedical Engineering, 1988

Two new types of non-invasive method for measuring arterial blood pressure recently developed by ... more Two new types of non-invasive method for measuring arterial blood pressure recently developed by us are reviewed. Both oj the methoo?s are based on the characteristics of the pressure-volume relationship in the artery. One is the volume-oscillometn'c method; and the other is the volume-compensation method, based on the vascular unloading principle. Both methods employ photoelectric plethysmography for detection of artenal volume changes in the biological segment. The volume-oscillometric method can measure systolic and mean arterial pressure, and is applicable to long-term ambulatory monitoring. The volumecompensation method allows the beat-by-beat measurement of systolic and diastolic pressure and the recording of the pressure waveform continuously and non-invasively. This paper discusses the measurement principle and evaluates the accuracy of each method as compared with direct measurements. Preliminary descriptions of newly designed instruments based on these two methoo!s, and a few examples of the indirect pressure recordings, are also &scribed. The results obtained show that the noninvasive methoak for measuring arterial pressure presented here appear promising for use not onb in physiological studies, but also in clinical practice and research laboratories.

Research paper thumbnail of Near infra-red spectroscopy: a new technique for the non-invasive monitoring of tissue and blood oxygenation in vivo

Biochemical Society Transactions, 1988

Research paper thumbnail of Application of near-infrared spectroscopy for the assessment of the oxygenation level of myoglobin and haemoglobin in cardiac muscle in vivo

Biochemical Society Transactions, 1990

Research paper thumbnail of Insularity and professional protectionism or matrixing and professional security in the provision of perfusion services

Perfusion, 1995

Address for correspondence: G Wright, WE Dunn Unit of Cardiology, Department of Biological Scienc... more Address for correspondence: G Wright, WE Dunn Unit of Cardiology, Department of Biological Sciences, Keele University, Staffordshire ST5 5BG, UK. The role of medical technicians, engineers and scientists in the multidisciplinary teams responsible for patient care may often be underestimated. Compared with their clinical colleagues, these groups have relatively limited career expectations, employment is less secure, levels of remuneration are lower and incidental opportunities for salary enhancement are less frequent. Perfusionists are affected by these constraints as much as any other group and often feel too insular. Working in departments that are remote from their administrative and professional base, they may feel unprotected and unsupported by the departmental structure. Their career structure and prospects may be of little concern to their clinical colleagues. Although this insularity has often been the cause of some despondency, the increasing demand for technical specialist services has at least helped to make perfusionists feel wanted and the prospect of employment redundancy has not become a major concern. Nevertheless, warning signs are around that are ignored only at great risk. One of these is the likelihood of a significant decrease in coronary heart disease (CHD) in future years. Since CHD contributes over 60%

Research paper thumbnail of The development and use of a hand held transducer for intermittent fetal scalp blood measurements

Research paper thumbnail of A two dimensional three layer model of a transcutaneous blood-gas probe for use with a mass spectrometer

Research paper thumbnail of Non-Invasive Physiological Measurements Vol 2

Research paper thumbnail of Near infrared specroscopy in fetal monitoring

British journal of hospital medicine

ABSTRACT

Research paper thumbnail of A catheter-tip oxygen electrode: experience in newborn infants with respiratory distress

Archives of Disease in Childhood

Research paper thumbnail of High frequency variability of transcephalic electrical impedance — A new parameter for monitoring of neonatal cerebral circulation?

Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 1992

ABSTRACT

Research paper thumbnail of Fetale Laserspektroskopie während mütterlicher O2-Atmung - Fetal Laser Spectroscopy During Administration of Oxygen to the Mother

Geburtshilfe und Frauenheilkunde, 2000

Die Minderversorgung mit Sauerstoff nach Einsetzen der Wehentätigkeit ist eine der gröûten Gefahr... more Die Minderversorgung mit Sauerstoff nach Einsetzen der Wehentätigkeit ist eine der gröûten Gefahren für den Feten am Ende der Schwangerschaft. In Bezug auf die Behandlung dieser fetalen Hypoxie wurde die Sauerstoffgabe an die Mutter untersucht und kontrovers diskutiert. Mit der NIR-Laserspektroskopie steht ein Verfahren zur Verfügung, das aufgrund der direkten Erfassung der Gewebsoxygenierung zur Verifizierung der Wirksamkeit von Sauerstoffgabe an die Mutter beitragen kann. Methode: Zur Klärung dieser Frage wurden bei 24 Patientinnen in Terminnähe NIR-laserspektroskopische Messungen während Wehentätigkeit und Sauerstoffgabe an die Mutter durchgeführt. Ergebnisse: Die statistische Analyse erbrachte den signifikanten Nachweis, dass die Oxygenierung im fetalen Blut ansteigt. Auch das Cytochrom aa 3 welches in der oxydierten Form als direktes Maû für die Gewebsoxygenierung im fetalen Gehirn gilt, stieg in den Wehenpausen bei Sauerstoffgabe an. Schlussfolgerung: Die hier gefundene Zunahme der Oxygenierung bei Sauerstoffgabe an die Mutter zeigt, dass diese Maûnahme die fetale Sauerstoffversorgung bei eutrophen Kindern verbessern kann, wenn eine kindliche Notfallsituation auftritt.

Research paper thumbnail of Electrochemical aspects of intravascular oxygen transducers

Journal of Biomedical Engineering, 1984

ABSTRACT

Research paper thumbnail of iPhysioMeter: a smartphone photoplethysmograph for measuring various physiological indices

Methods in molecular biology (Clifton, N.J.), 2015

iPhysioMeter is a new smartphone application ("App") for the Apple iPhone and iPod touc... more iPhysioMeter is a new smartphone application ("App") for the Apple iPhone and iPod touch that allows photoplethysmography (PPG) to be implemented without the need for any additional devices. The resulting signal, the photoplethysmogram, allows the calculation of basic but valuable and frequently used physiological indices such as heart rate (HR) and pulse volume (PV). The design of iPhysioMeter has very much been influenced by a consideration of usability, as is immediately evident from ones first experience with it. However, its apparent simplicity in use should not disguise the need for correct operation, which otherwise might lead to collection of invalid or inaccurate data. There are several unexpected pitfalls that might not only produce inaccurate values, but, under some circumstances, could also damage the device or present a hazard to the user or subject. We therefore describe here, firstly, the core technology that makes it possible to perform PPG and to calculate...

Research paper thumbnail of Cardiovascular hemodynamic effects of Red Bull® Energy Drink during prolonged, simulated, monotonous driving

SpringerPlus, 2013

The purpose of this study was to investigate the cardiovascular hemodynamic effects of Red Bull® ... more The purpose of this study was to investigate the cardiovascular hemodynamic effects of Red Bull® Energy Drink during prolonged, simulated, monotonous driving. This was a double-blind, within-subjects-design, crossover study. Twelve healthy volunteers (21.7 ± 0.8 years old) experienced each of three conditions at various times: 1) consumption of Red Bull® Energy Drink; 2) consumption of placebo-controlled drink; and 3) no test drink. All subjects undertook 90-min periods of simulated monotonous driving, during which physiological measurements were made. The variables recorded were cardiovascular indices, i.e., mean blood pressure (MBP), cardiac output (CO), electrocardiogram RR interval (RR), total peripheral-vascular resistance (TPR: = MBP/CO), and normalized pulse volume (NPV). Additional parameters were the standard deviation of lateral position, i.e., the weaving of the car, and subjective rating of sleepiness. CO, RR, and TPR during the monotonous task were significantly differe...

Research paper thumbnail of Near infrared spectroscopy used to observe changes in fetal cerebral haemodynamics during labour

Journal of perinatal medicine, 1994

Near Infrared Spectroscopy (NIRS) has been used in the neonate to observe changes in the cerebral... more Near Infrared Spectroscopy (NIRS) has been used in the neonate to observe changes in the cerebral haemodynamics and concentration of oxygenated haemoglobin. Specific changes have been demonstrated in response to spontaneous bradycardias and alterations in the inspired oxygen concentration. We report here changes in fetal cerebral haemodynamics using NIRS in response to rapid spontaneous delivery and the "topping up" of a maternal epidural with bupivacaine. NIRS offers a new way of observing changes in cerebral haemodynamics in the fetus during labour.

Research paper thumbnail of Skin surface PO2 measurement and the effect of externally applied pressure

Archives of physical medicine and rehabilitation, 1981

The effect of externally applied load on the partial pressure of oxygen in tissue, measured at th... more The effect of externally applied load on the partial pressure of oxygen in tissue, measured at the skin surface (PSO2) was examined by applying a load to a transcutaneous O2 monitor mounted on the skin of healthy subjects. The load was increased every 4 minutes, and the PSO2 was recorded at the end of the 4-minute period. Three sites were investigated: the sacrum, the greater trochanteric area, and the lateral aspect of the thigh. Mean initial values for the 3 sites were found to be 10.1, 11.1, and 10.1 kPa, respectively. On increasing the applied load, values were found to reduce gradually at first and then at an increasing rate to zero at the "cut-off" load. The mean cut-off pressure for the 3 areas was 15.2, 18.8, and 18.1 kPa.