Cardiovascular and respiratory reflex control systems in the regulation of pulmonary blood flow and ventilation during exercise

The regulation of pulmonary blood flow and ventilation during exercise is mediated by numerous factors, yet the role of certain cardiovascular and pulmonary reflex control systems is unknown. Therefore this thesis investigated the pulmonary vascular response to the activation of the muscle metaboreflex alone, and combined with activation of the muscle mechanoreflex. The ventilatory responses to the activation of the muscle metaboreflex were also studied under a background of activated ventilatory chemoreceptors. Finally the effect of increased metabolism on the ventilatory sensitivity to carbon dioxide was investigated in healthy humans. We found that activation of the muscle metaboreflex induced pulmonary vasoconstriction that was alleviated by muscle mechanoreflex activation. Furthermore a respiratory response to the activation of the muscle metaboreflex was observed in hypercapnia but not when breathing room air. Finally we found that increases in metabolic rate induced elevations in the ventilatory sensitivity to carbon dioxide. Overall these data suggest that the interplay between cardiovascular and respiratory control systems contribute to the regulation of pulmonary haemodynamics and breathing during exercise. Our findings could be implicated in the reduced exercise tolerance seen in chronic heart failure patients