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.