Phasic menstrual cycle effects on the control of breathing in healthy women

This study examined the effects of menstrual cycle phase on ventilatory control. Fourteen eumenorrheic women were studied in the early follicular (FP; 1–6 days) and mid-luteal (LP; 20–24 days) phase of the menstrual cycle. Blood for the determination of arterial PCO2(PaCO2)PCO2(PaCO2), plasma strong ion difference ([SID]), progesterone ([P4]), and 17β-estradiol ([E2]) concentrations were obtained at rest. Subjects performed a CO2 rebreathing procedure that included prior hyperventilation and maintenance of iso-oxia to evaluate central and peripheral chemoreflex, and nonchemoreflex drives to breathe. Resting PaCO2PaCO2 and [SID] were lower; minute ventilation (V˙E), [P4] and [E2] were higher in the LP versus FP. Within the LP, significant correlations were observed for PaCO2PaCO2 with [P4], [E2] and [SID]. Menstrual cycle phase had no effect on the threshold or sensitivity of the central and/or peripheral ventilatory chemoreflex response to CO2. Both (V˙E) and the ventilatory response to hypocapnia (representing nonchemoreflex drives to breathe) were ∼1 L/min greater in the LP versus FP accounting for the reduction in PaCO2PaCO2. These data support the hypothesis that phasic menstrual cycle changes in PaCO2PaCO2 may be due, at least in part, to the stimulatory effects of [P4], [E2] and [SID] on ventilatory drive.