Hypercapnic ventilatory response in patients with and without obstructive sleep apnea: do age, gender, obesity, and daytime PaCO(2) matter?

Study Objective: To evaluate the relationship between obstructive sleep apnea (OSA) and ventilatory responsiveness to carbon dioxide in both men and women.

Design: An analysis of 219 patients referred to an university-based sleep center between 1989 to 1994 was conducted (104 with OSA and 115 without OSA; 43 women and 176 men). These patients had spirometry and a daytime hypercapnic ventilatory response (HCVR) test that was corrected to the patient's ability to attain maximal ventilation. Comparisons between OSA and no-OSA groups, as well as between men and women, were made using multivariate modeling techniques.

Results: There was no significant difference in the slope of correlated HCVR (cHCVR) between those with and without OSA (1.57 +/- 0.57 vs 1.63 +/- 0.66; p = 0.48). In men, an inverse correlation between daytime PCO(2) and cHCVR was observed in both crude and multivariate analyses (crude beta-coefficient = - 0.04 +/- 0.02, p = 0.02; adjusted beta-coefficient = 0.07 +/- 0.02, p < 0.01). Although age and cHCVR did not share a significant relationship in the crude analysis (crude beta-coefficient = - 0.01 +/- 0.01, p = 0.10), with adjustments for confounding variables, a significant inverse relationship between age and cHCVR was observed (beta-coefficient = - 0.02 +/- 0.01, p = 0.04). On the other hand, in women, only body mass index (BMI) was positively correlated with cHCVR (crude beta-coefficient = 0.03 +/- 0.01, p = 0.01; adjusted beta-coefficient = 0.04 +/- 0.01, p < 0.01).

Conclusion: OSA disorder is not associated with a blunted ventilatory chemoresponsiveness to carbon dioxide. Elevated PaCO(2) and older age are significant correlates for a low cHCVR in men. For women only, BMI was associated with cHCVR. These findings suggest that men and women may have different ventilatory control mechanisms.