Ventilatory afterdischarge is not different between healthy young men and women: [P164] in [Abstracts for the Annual Scientific Meeting of the Thoracic Society of Australia and New Zealand, 26 February – 3 March 1999, Canberra, Australia]

The gradual decay in ventilation following removal of a ventilatory stimulus (ventilatory afterdischarge (VAD)) has been proposed to protect against cyclic breathing disorders such as obstructive sleep apnea (OSA). The male predominance of OSA, and the increased incidence of OSA in women after menopause, indicates that the respiratory stimulating effect of progesterone may provide protection against OSA by altering VAD. It was therefore hypothesised that VAD is longer in women than in men, and is longer in the luteal menstrual phase compared to the follicular phase. Methods: The half time (T) of VAD was measured in 12 men, and in 11 women at both their luteal and follicular phases, following cessation of isocapnic hypoxia, hypercapnia and two isocapnic voluntary hyperventilation tasks (one free and one fixed breathing frequency). The T was compared between genders, and between menstrual phases by students t-tests. Results: The was different between the hyperventilation stimuli (mean (SEM) all subjects: hypoxia, 4.9 (0.8); hypercapnia, 20.2 (2.5); free voluntary, 1.9 (0.6); fixed voluntary, 1.4 (0.4)s, p<0.05), however, there were no significant gender or menstrual phase differences in the τ following any method of hyperventilation. Conclusions: This suggests the higher occurrence of OSA in men does not reflect an underlying gender difference in VAD, and the increased prevalence of OSA in women after menopause is not representative of an effect of progesterone on VAD.