Reduced perception of pain via baroreceptor unloading in patients with chronic back pain

Abstract

Nociceptive transmission at the spinal cord is modulated by descending pain inhibitory systems originating in the brainstem that interact with neural cardiovascular pathways, such as baroreceptor input. However, data regarding antinociceptive properties of cardiopulmonary baroreceptors are largely mixed, and no studies have examined cardiopulmonary baroreceptor modulation of pain perception in patients with chronic pain. Therefore, we tested the hypothesis that cardiopulmonary baroreceptor unloading would reduce pain perception in chronic back pain (CBP) patients and healthy participants. Mechanical pressure pain threshold (algometer on the upper trapezius) and pain perception of a repetitive heat stimulus (thermode on the anterior forearm) was tested in 12 CBP patients and 8 healthy controls during supine lower body negative pressure (LBNP) of ‐10 mmHg and 0 mmHg (control condition). Pressure pain threshold during LBNP was significantly increased compared with the control condition in CBP patients (270 ± 31 vs. 240 ± 27 kPa, P=0.04) and healthy controls (293 ± 59 vs. 259 ± 50 kPa, P=0.02), indicating reduced pain perception. Similarly, the average pain rating (scale 0‐100) of the repetitive heat stimulus was significantly reduced during LBNP compared with the control condition in CBP patients (42 ± 6 vs. 48 ± 6, P<0.01). However, no significant change was observed in average pain rating of the repetitive heat stimulus during LBNP in healthy controls (38 ± 5 vs. 37 ± 7, P=0.89). Together, these preliminary findings suggest reduced pain perception during cardiopulmonary baroreceptor unloading with a potentially greater effect in patients with CBP compared with healthy individuals.