Exercise hyperpnea and hypercapnic ventilatory responses in women

SummaryWe studied the relationship between exercise hyperpnea (i.e., ventilatory dynamics) at the onset of exercise and hypercapnic ventilatory response (HCVR), and their differences between the follicular (FP) and luteal (LP) phases of the menstrual cycle in six healthy females. HCVR was tested under three O2 conditions: hyperoxia (FiO2=1.0), normoxia (0.21), and hypoxia (0.12). HCVR was defined as the relationship between the end-tidal PCO2PCO2 and minute ventilation (V˙E) using the regression line of the CO2 slope and a mimetically apneic threshold of CO2. HCVR provocation and measurements were conducted using an inspired CO2 concentration of up to approximately 8 mmHg higher than the end-tidal PCO2PCO2 level of basal isocapnic the end-tidal PCO2PCO2 at each menstrual both the slope and threshold in HCVR showed no statistically significant difference between LP and FP under any inspired FiO2 conditions. In the case of exercise hyperpnea during the onset of submaximal exercise, the mean response time (MRT) in V˙E dynamics showed no significant difference between LP and FP. Consequently, MRT in V˙E response was not related to the slope in HCVR. During steady-state exercise, even though the V˙E/V˙CO2 showed no significance between LP and FP, V˙E/V˙CO2 was significantly related to the slope in HCVR (r=0.59r=0.59, P<0.05P<0.05). Exercise ventilation (i.e., V˙E/V˙CO2) would partly be adjusted by the enhancement of the chemoreflex drive to CO2 only during the steady-state exercise.