Change in time course of posthyperventilation hyperpnea during menstrual cycle.

Area of Science:

• Cardiorespiratory Physiology
• Human Physiology
• Reproductive Physiology

Background:

• The ventilatory response to hyperventilation (HV) and its recovery dynamics are crucial physiological parameters.
• Menstrual cycle phases influence various physiological functions, including respiratory control.
• Progesterone is known to have potential effects on ventilation.

Purpose of the Study:

• To investigate the time constant (tau) of post-hyperventilation (post-HV) hyperpnea recovery.
• To compare the post-HV ventilatory response between the follicular (F) and luteal (L) phases of the menstrual cycle.
• To explore the influence of progesterone on the ventilatory afterdischarge mechanism.

Main Methods:

• Voluntary hyperventilation (HV) for 1 minute in 10 healthy women.
• Maintenance of end-tidal PCO2 (PETCO2) between resting levels and 60 Torr during and after HV.
• Calculation of the time constant (tau) for the decay of post-HV hyperpnea and comparison between F and L phases.

Main Results:

• Post-HV hyperpnea occurred in most runs, with hypopnea in a few instances.
• An inverse correlation was found between tau and PETCO2 during the test, consistent in both F and L phases.
• During the L phase compared to the F phase, tau increased (17.7 to 23.7 s), resting PETCO2 decreased (40.8 to 37.7 Torr), and minute ventilation (VE) increased by 10%.

Conclusions:

• The prolonged post-HV recovery time constant in the luteal phase is attributed to decreased resting PETCO2, not increased resting VE.
• Progesterone's influence on ventilatory control may not directly involve the brain stem's afterdischarge mechanism.
• These findings contribute to understanding respiratory regulation during the menstrual cycle and hormonal influences on ventilation.