Sexual and postural differences in cardioventilatory responses during and after breath holding at rest.

Twelve subjects (six men, six women) were studied in resting conditions for simple breath holding (BH) in either the supine or upright position. Ventilation (VT, V, fr) heart rate (fc) and arterial blood pressure (ABP) were recorded or measured in steady state and then transiently during BH and its recovery. Each subject performed seven HB in the supine position and two in the upright position. Several criteria were used for fc data analysis. During BH, in either the supine or upright position, no change in heart rate was observed, but subjects taken individually may exhibit some significant cardiac responses (tachycardia or bradycardia) for all the tests. In contrast, an increase in mean ABP is always observed, with different patterns in males and females. The upright position allows the responses to be greater, more rapid and significant. As a general rule, males have larger and slower responses than females. After BH, there is a ventilatory cost of apnea which is more important in males. However the delay in repayment of the ventilatory deficit observed during BH is very short (about 40 s): ventilatory and cardiac recovery are complete within 120 s. The results support the ideas that, (1) cardiac responses during BH are dependent on pulmonary physical conditions and metabolic levels before BH, (2) cardiac changes during recovery are, at least in great part, due to the concomitant hyperventilation.