Optical methods for monitoring physiological and biochemical variables

The use of optical methods for performing non-invasive physiological and biochemical monitoring has been investigated, with particular emphasis on the application of near-infrared spectrophotocetry for following changes in the redox state of cytochrome oxidase. Initial studies of the gross optical properties of in vivo tissue were made using an image intensifier. These demonstrated that some light is transmitted through biological tissues and that such material is very highly scattering.In order to investigate the feasibiity of non-invasively monitoring changes in the redox state of cytochrome oxidase in vivo. spectrophotometric and oxygen measurements were made on solutions containing the pure enzyme and yeast cell suspensions. These demonstrated the high affinity that the enzyme has for oxygen in such preparations, in contrast to the much lower apparent affinities in vivo that have been reported. These results were then modelled mathematically, and a possible-explanation for this anomaly suggested. Potential problems with applying this method are also presented. The interest in cytochrome oxidase is due to its importance in oxidative metabolism. However in performing this role it also assists in the prevention of oxidative damage, whose contribution to various disease states in paediatrics is briefly considered.Two instruments were also constructed, and used, firstly to measure the spectral characteristics of transmitted and reflected light in vivo. ana secondly to study the cardiac synchronous pulsatile component of this light (commonly referred to as the photoplethysmogram).