SEX MODULATES THE VENTILATORY RESPONSE TO PASSIVE LIMB-INDUCED MUSCLE MECHANORECEPTOR ACTIVATION DURING HYPOXIA IN HUMANS.

Abstract

Sex appears to modulate interactions between neural mechanisms involved in regulating pulmonary ventilation during mild hypoxic exercise. Therefore, we compared pulmonary ventilation responses elicited by isolated and combined stimulation of the carotid chemoreflex and muscle mechanoreflex between males and females. Twenty-eight healthy adults (14 females) underwent four experimental manipulations: 1) normoxic rest (no stimulation), 2) hypoxic rest (carotid chemoreflex stimulation), 3) normoxic passive movement (muscle mechanoreflex stimulation), and 4) hypoxic passive movement (reflexes costimulation). Isocapnia was maintained using a rebreathing system, and hypoxia was induced by breathing 12% oxygen. Passive movement involved 30-second bouts of unilateral knee manipulation at 300º/s, with surface electromyography confirming absence of voluntary muscle contractions. In males, the pulmonary ventilation response to passive limb movement (last 10 seconds change versus rest) was greater under hypoxia than normoxia (mean ± SD: hypoxia = 3.6 ± 2.0 vs. normoxia = 1.6 ± 2.4 L/min; P = 0.003), whereas no difference was observed in females (hypoxia = 1.9 ± 2.4 vs. normoxia = 2.2 ± 1.5 L/min; P = 1.000). Moreover, pulmonary ventilation remained elevated in males (hypoxia = 2.7 ± 2.4 vs. normoxia = -0.1 ± 2.2; P < 0.001) but not in females (hypoxia = 0.4 ± 3.3 vs. normoxia = 0.5 ± 1.5; P = 1.000), 30 seconds following passive limb movement under hypoxia. These findings support a synergistic carotid chemoreflex-muscle mechanoreflex interaction in males but not in females. The persistent ventilatory elevation post-stimulation indicates that short-term potentiation contributes to this synergistic interaction in males.