An assessment of blood vessel vasoactivity using photoplethysmography.

The vasoactivity of the vessels of the earlobe, nailbed, finger pad, and nasal septum was investigated in 11 human subjects to determine the suitability of these sites for use in indirect oximetry. The subjects were healthy, nonsmoking volunteers in an age range of 20-32 years. Each site was illuminated with infrared radiation at 880 nm, and the reflected pulsatile signals from the tissue beds were displayed on a multichannel analog recorder. The decrease in pulse amplitude detected at each site in response to a cold-pressor test was used as the measure of vasoactivity. Among the sites investigated, the earlobe was the least vasoactive. The nasal septum, nailbed, and finger pad were similar in degrees of vessel reactivity.