Oxygen status determined by the photo-electric method - a circular finger-probe constructed for detection of blood oxygen content, blood flow and vascular density

Abstract

Three factors are the major determinants of tissue oxygenation: blood oxygen content, blood flow and vascular density. Blood oxygen content can be measured in vitro by haemoximetry or in vivo by oximetry. The blood flow and the vascular density may be estimated by a further development of pulse oximetry, based on the photo-electric method separating the signal into an AC and DC-part.

A circular finger-probe was constructed to analyse the propagation of light through blood perfused tissue by the photo-electric method. The AC and DC-signals were compared at different positions around the finger. The detectors were placed at -45°, 45°, 90°, 180° and 215° in relation to the light source. The preliminary results have shown that it is possible to record AC and DC-signals from the different angles. The size and configuration of the AC-signals are very similar but the levels of the DC-signals decrease with the distance between source and detector. It is our suggestion that blood flow can be estimated from the area of the AC-signal and the vascular density from the relationship between the DC-levels at different positions.

Key Words:

• Hemoximetry
• oximetry
• photo-electric plethysmography
• pulse oximetry