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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 31 (1993), S. 135-141 
    ISSN: 1741-0444
    Keywords: Haematocrit ; Haemolysis ; In vitro model ; Oxygen saturation ; Pulse oximetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract In situations in which it may be impossible and/or unethical to evaluate pulse oximetry in humans, an in vitro model with circulating blood may be a necessity. The main objective was to develop such an in vitro model and, in this model, validate the pulse oximetry technique at various haematocrit levels. The pulsating character of arterial blood flow in a tubing system was simulated by using a specially constructed pressure-regulated roller pump. The tubing system was designed to minimise damage to red blood cells. The pulse oximeter readings (SpO2) were compared with oxygen saturation analyses by a haemoximeter (SaO2). The pulse oximetry readings were recorded at various haematocrit levels and during haemolysis in the SaO2 range 60–100 per cent. At a haematocrit level of 41–44 per cent, there was no correlation between SaO2 and SpO2 readings. After diluting the blood with normal saline to a haematocrit of 10–11 per cent, a good correlation between SaO2 and SpO2 was found. Following haemolysis, the agreement between SaO2 and SpO2 was further improved. Using the developed in vitro model, the results indicate that the accuracy of a pulse oximeter may be dependent on the haematocrit level.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 29 (1991), S. 48-54 
    ISSN: 1741-0444
    Keywords: Local temperature provocation ; Photoplethysmography ; Pulsatile signal ; Skin blood perfusion ; Slowly fluctuating signal ; Wavelength
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract When the microvascular blood perfusion in human skin is measured by photoplethysmography (PPG), infra-red light (800–960 nm) is normally used as the light source. The PPG signal, which consists of a pulsatile (AC) and a slowly fluctuating (DC) component, was studied at different optical wavelengths utilising optical fibres for guiding the light to and from the skin surface. Finger and forearm skin was examined and high and low skin blood perfusion was brought about by local water-induced temperature provocation. The analysis of the measurement results provided evidence that the use of shorter wavelengths in PPG (AC) for monitoring skin perfusion changes could be applicable. The use of different optical wavelengths also raises the possibility of recording perfusing changes at different depths in the superficial tissue. The sweat water content in stratum corneum of human skin will probably determine the total amount of reflected and backscattered radiation reaching the photodetector. This is important when the skin perfusion is changed by alterations in the environmental temperature conditions activating the sweat glands in tissue. Temperature-dependent optical characteristics of blood-free skin tissue may explain the limited ability of the DC component of PPG to monitor skin perfusion changes.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 29 (1991), S. 40-47 
    ISSN: 1741-0444
    Keywords: Laser Doppler flowmetry ; Local temperature provocation ; Photoplethysmography ; Probe geometry ; Skin blood perfusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Photoplethysmography (PPG) and laser Doppler flowmetry (LDF) were compared and evaluated. The comparison was accomplished considering differences in physical principles and geometrical and optical conditions. Changes in human skin perfusion were induced by cold and hot water provocation on limited areas of the finger and the forearm. The results showed that LDF and PPG, using red light at 630–660 nm and a commercial PPG probe, were in general equally sensitive in detecting a blood perfusion increase following a skin temperature elevation. However, we also found that PPG occasionally showed an inverse response to a skin temperature elevation, especially in finger skin. Furthermore, the study indicated that laser light is unsuitable as a light source in PPG using optical fibres of small diameter and with no fibre separation. It was also found that the physical dimensions of the probe (including the light source and photodetector) play an important role in determining the measuring volume and the quality of the signal.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 30 (1992), S. 533-537 
    ISSN: 1741-0444
    Keywords: Fibre-optic probe ; Heart rate ; Photoplethysmography ; Respiratory rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract A new method, which uses a fibre-optic probe to monitor respiratory and heart rates simultaneously has been developed and evaluated. The results provide evidence that it is possible to monitor respiratory and heart rates using the reflection mode of photoplethysmography (PPG). The fibre-optic probe makes it possible to monitor from different sites on the patient, and the method is convenient to use. In addition, the probe is X-ray transparent, insensitive to electromagnetic interference (e.g. during MRI investigation) and may be made very light and small. Therefore the method is suitable for the observation of both adults and neonates, in hospitals as well as in other environments.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 30 (1992), S. 568-568 
    ISSN: 1741-0444
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
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  • 6
    Publication Date: 2000-11-21
    Print ISSN: 0031-9155
    Electronic ISSN: 1361-6560
    Topics: Biology , Medicine , Physics
    Published by Institute of Physics
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  • 7
    Publication Date: 2000-11-21
    Print ISSN: 0031-9155
    Electronic ISSN: 1361-6560
    Topics: Biology , Medicine , Physics
    Published by Institute of Physics
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