On the hemodynamic consequence of the chemoreflex and muscle mechanoreflex interaction in women and men: two tales, one story

• Published in: The Journal of physiology 2022-07, Vol.600 (16), p.3671-3688
• Main Authors: Wan, Hsuan-Yu, Weavil, Joshua C., Thurston, Taylor S., Georgescu, Vincent P., Morrissey, Candice K., Amann, Markus
• Format: Article
• Language: English
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/JP283051

The cardiovascular response resulting from the individual activation of the muscle mechanoreflex (MMR), or the chemoreflex (CR), is different between men and women. Whether the hemodynamic consequence resulting from the interaction of these sympathoexcitatory reflexes is also sex-dependent remains unknown. MMR and CR were activated by passive leg movement (LM) and exposure to hypoxia (O 2 -CR), or hypercapnia (CO 2 -CR), respectively. Twelve young men and 12 young women completed two experimental protocols: 1) resting in normoxia (P ET O 2 : ~83mmHg, P ET CO 2 : ~34mmHg), normocapnic hypoxia (P ET O 2 : ~48mmHg, P ET CO 2 : ~34mmHg), and hyperoxic hypercapnia (P ET O 2 : ~524mmHg, P ET CO 2 : ~44mmHg); 2) LM under the same gas conditions. During the MMR:O 2 -CR coactivation, in men, the observed blood pressure (MAP) and cardiac output (CO) were not different (additive effect), while the observed leg blood flow (LBF) and vascular conductance (LVC) were significantly lower (hypo-additive), compared with the sum of the responses elicited by each reflex alone. In women, the observed MAP was not different (additive) while the observed CO, LBF, and LVC were significantly greater (hyper-additive), compared with the summated responses. During the MMR:CO 2 -CR coactivation, in men, the observed MAP, CO, and LBF were not different (additive), while the observed LVC was significantly lower (hypo-additive), compared with the summated responses. In women, the observed MAP was significantly higher (hyper-additive), while the observed CO, LBF, and LVC were not different (additive), compared with the summated responses. The interaction of the MMR and CR has a pronounced influence on the autonomic cardiovascular control, with the hemodynamic consequences differing between men and women. The chemoreflex and the muscle mechanoreflex are sympathoexcitatory mechanisms which, via neural feedback to the cardiovascular centre in the medulla, mediate neurocirculatory responses during physical activity. The interaction of the peripheral chemoreflex and muscle mechanoreflex potentiates vasoconstriction in men, but potentiates vasodilatation in women (left panel). The interaction of the central chemoreflex and muscle mechanoreflex also potentiates vasoconstriction in men, whereas the reflex interaction is simply additive for the vasomotor tone in women (right panel).