Non-invasive studies of peripheral vascular compliance using a non-occluding photoplethysmographic method

A non-invasive technique is implemented to measure a peripheral vascular co mpliance index C-index, using an infrared photoplethysmographic waveform as an indicator of intravascular volume change and a continuous blood pressur e monitor to measure the blood pressure during each heart-beat. The non-lin ear behaviour of C-index with pressure and the effect of age on C-index are studied in 62 males (15-73 years). Repeatability tests and the effect of i ce-water exposure of a portion of a limb are studied in 10 and 14 subjects, respectively. For each individual, C-index measurements are taken at discr ete values of local mean arterial pressure (P-mean), and a C-index against P-mean plot is obtained. There is a statistically significant difference (p <0.05) in C-index for the lower values of P-mean (60-100 mmHg) between two age groups formed (15-52 and 58-73 years). The cold-presser test (CPT) show s a 66% median decrease in C-index, with an inter-quartile range of 60-77%, in a matter of seconds. The results suggest that C-index may be a useful n oninvasive indicator of peripheral vascular compliance in humans.