Effects of arterial and cardiopulmonary baroreceptor activation on the upper limb nociceptive flexion reflex and electrocutaneous pain in humans

Attenuation of the lower limb nociceptive flexion reflex (NFR) during the cardiac cycle has been attributed to inhibition of sensorimotor function by arterial baroreceptor activation. It has been proposed that cardiopulmonary baroreceptors might have similar inhibitory effects. This study examined the effects of arterial and cardiopulmonary baroreceptor stimulation on nociceptive responding in the upper limb by delivering electrocutaneous stimuli to the ulnar nerve at 0, 150, 300, 450, or 600 ms after the R-wave of the electrocardiogram while participants lay supine with their legs raised or lowered. Nociceptive responding varied in a quadratic manner with phase of the cardiac cycle; responses were lowest at R+450 ms. Nociceptive responding and pain ratings did not differ between postures suggesting no cardiopulmonary effects. This phasic modulation of the upper limb withdrawal response provides further support for arterial baroreceptor-mediated inhibition of nociceptive transmission.