DC PHOTOPLETHYSMOGRAPHY IN THE EVALUATION OF SYMPATHETIC VASOMOTOR RESPONSES

The d.c. component of the photoplethsmographic signal was used to dete rmine the response of the finger vasculature to three standard tests o f vasomotor function: (1) an inspiratory gasp (IG), (2) immersion of t he contralateral hand in ice water (IW), and (3) the Valsalva maneouvr e. The vasconstrictor response to the first two of these stimuli could be measured in all of 25 normal subjects. The response to the Valsalv a maneouvre could not be detected consistently. Seven patients with kn own sympathetic autonomic dysfunction showed no response to either IG or IW. In 30 patients with diabetes mellitus of over 10 years duration , 46.7% had no response to IG, and 20% had no response to IW. Absent r esponses correlated with abnormal autonomic cardiovascular reflexes, w ith absent sympathetic skin responses and with the severity of periphe ral somatic neuropathy. The d.c. photoplethysmographic determination o f the vasoconstrictor response in the finger after a deep inspiratory gasp and after ice water immersion offers an additional measure of the function of small (2mu-6mu) peripheral nerve fibres. Because of varia bility in the amplitude of the responses in normals, only an absent re sponse should be accepted as abnormal.