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 PCO(2) (PaCO(2)) , plasma strong ion difference ([SID]), progesterone ([P(4)]), and 17beta-estradiol ([E(2)]) concentrations were obtained at rest. Subjects performed a CO(2) rebreathing procedure that included prior hyperventilation and maintenance of iso-oxia to evaluate central and peripheral chemoreflex, and nonchemoreflex drives to breathe. Resting PaCO(2) and [SID] were lower; minute ventilation (V (E)), [P(4)] and [E(2)] were higher in the LP versus FP. Within the LP, significant correlations were observed for PaCO(2) with [P(4)], [E(2)] and [SID]. Menstrual cycle phase had no effect on the threshold or sensitivity of the central and/or peripheral ventilatory chemoreflex response to CO(2). Both (V (E)) and the ventilatory response to hypocapnia (representing nonchemoreflex drives to breathe) were approximately 1L/min greater in the LP versus FP accounting for the reduction in PaCO(2) . These data support the hypothesis that phasic menstrual cycle changes in PaCO(2) may be due, at least in part, to the stimulatory effects of [P(4)], [E(2)] and [SID] on ventilatory drive.