Influence of Acute Pain Induced by Activation of Cutaneous Nociceptors on Ventilatory Control

Background: Although many studies show that pain increases breathing, they give little information on the mechanism by which pain interacts with ventilatory control. The authors quantified the effect of experimentally induced acute pain from activation of cutaneous nociceptors on the ventilatory control system.

Methods: In eight volunteers, the influence of pain on various stimuli was assessed: room air breathing, normoxia (end-tidal pressure of carbon dioxide (PETCO2) clamped, normoxic and hyperoxic hypercapnia, acute hypoxia, and sustained hypoxia (duration, 15-18 min; end-tidal pressure of oxygen, approximately 53 mmHg). Noxious stimulation was administered in the form of a 1-Hz electric current applied to the skin over the tibial bone.

Results: While volunteers breathed room air, pain increased ventilation (V with dotI) from 10.9 +/- 1.7 to 12.9 +/- 2.5 l/min sup -1 (P < 0.05) and reduced PETCO2 from 38.3 +/- 2.3 to 36.0 +/- 2.3 mmHg (P < 0.05). The increase in V with dotI due to pain did not differ among the different stimuli. This resulted in a parallel leftward-shift of the V with dotI -carbon dioxide response curve in normoxia and hyperoxia, and in a parallel shift to higher V with dotI levels in acute and sustained hypoxia.