Effect of pain on autonomic nervous system indices derived from photoplethysmography in healthy volunteers

Background. Photoplethysmographic pulse wave amplitude (PPGA) and heart rate (HR) can be used to measure cold, nociception-induced autonomic responses, or both. The aim of our study was to correlate the intensity of experimental pain to changes in physiological variables reflecting the autonomic nervous system response to pain. Methods. PPGA, HR, and subjective measurements of pain intensity were measured in 29 healthy male volunteers during two heat stimuli (438C and 488C) and the cold pressor test (CPT). Surgical pleth index (SPI), autonomic nervous system state (ANSS), and ANSS index (ANSSi) were calculated using PPGA and HR. Results. Pain intensity scores increased on the average by 1.6, 3.5, and 8.1 for the 438C, 488C, and CPT stimuli, respectively. The pain intensity scores for all three stimuli groups were significantly different from each other (P,0.001). All three stimuli changed HR, PPGA, SPI, ANSS, and ANSSi values significantly from their respective baseline values (P,0.001 for all). Heat stimuli-induced pain intensity did not correlate with the magnitude of the respective changes in HR, PPGA, SPI, ANSS, and ANSSi. CPT-induced pain intensity correlated with the magnitude of the respective changes in HR, PPGA, SPI, ANSS, and ANSSi. PPGA, ANSSi, ANSS, and SPI differentiated between heat and cold stimuli-induced pain.