Sex differences in cardiac responses to successive apnea periods.

Cardiac response to breath-holding is generally described as a bradycardia, which is explained by a two-fold mechanism involving the pulmonary mechanoreceptors and the arterial chemoreceptors. This study was conducted to determine the cardiac effects of five successive apnea periods separated by 1 min of free ventilation (FV). Heart rate (HR) and ventilation (V, VT, f) were measured during this protocol in 12 young subjects (6 men, 6 women). Ventilatory responses during FV periods were similar in both sexes, but HR responses were different during the apnea periods. The mean exhibited a bradycardia and the women a tachycardia. Although the statistical significance of the results was weak, they showed a clear tendency which was interpreted as differences in central cardioventilatory interactions. Sex difference in the cardiac consequences of static work from respiratory muscle is also evoked.