Chemoreflex control of breathing during wakefulness in healthy men and women

1 School of Physical and Health Education, Departments of 2 Physiology and 3 Obstetrics and Gynaecology, and 4 Division of Respirology and Critical Care, Department of Medicine, Queen's University, Kingston, Ontario, Canada Submitted 11 November 2003 ; accepted in final form 15 November 2004 This study used a modified CO 2 rebreathing procedure to examine the effect of gender on the chemoreflex control of breathing during wakefulness in healthy men ( n = 14) and women ( n = 14). Women were tested in the follicular phase of the menstrual cycle. During rebreathing trials, subjects hyperventilated to reduce the partial pressure of end-tidal CO 2 (P ET CO 2 ) below 25 Torr and were then switched to a rebreathing bag containing a normocapnic hypoxic or hyperoxic gas mixture. During the trial, P ET CO 2 increased, while O 2 was maintained at a constant level. The point at which ventilation began to rise as P ET CO 2 increased was identified as the ventilatory recruitment threshold (VRT). Ventilation below the VRT was measured, and the slope of the ventilatory response above the VRT was determined. Gender had no effect on the hyperoxic or hypoxic VRT for CO 2 . Central chemoreflex sensitivity was significantly greater in men than women but not after correction for forced vital capacity. Measures of peripheral chemoreflex sensitivity were similar between genders. However, the slope of the tidal volume (V T ) response to hyperoxic and hypoxic CO 2 rebreathing (corrected and uncorrected) was greater in men than women, respectively. We conclude that central chemoreflex sensitivity is greater in men compared with women as reflected by differences in ventilatory (uncorrected) and V T (corrected and uncorrected) responses to CO 2 . However, gender has no significant effect on the central chemoreflex VRT for CO 2 . The peripheral chemoreflex control of breathing during wakefulness is similar between men and women. hypoxia; chemoreflex sensitivity; ventilatory recruitment threshold; sleep-disordered breathing Address for reprint requests and other correspondence: L. A. Wolfe, School of Physical and Health Education, Queen's Univ., Kingston, Ontario, Canada K7L 3N6 (E-mail: wolfel{at}post.queensu.ca )