Chest
Volume 117, Issue 2, February 2000, Pages 454-459
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Clinical Investigations
Hypercapnic Ventilatory Response in Patients With and Without Obstructive Sleep Apnea: Do Age, Gender, Obesity, and Daytime Paco2 Matter?

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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 Pco2 and cHCVR was observed in both crude and multivariate analyses (crude β-coefficient = − 0.04 ± 0.02, p = 0.02; adjusted β-coefficient = 0.07 ± 0.02, p < 0.01). Although age and cHCVR did not share a significant relationship in the crude analysis (crude β-coefficient = − 0.01 ± 0.01, p = 0.10), with adjustments for confounding variables, a significant inverse relationship between age and cHCVR was observed (β-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 β-coefficient = 0.03 ± 0.01, p = 0.01; adjusted β-coefficient = 0.04 ± 0.01, p < 0.01).

Conclusion

OSA disorder is not associated with a blunted ventilatory chemoresponsiveness to carbon dioxide. Elevated Paco2 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.

Section snippets

Materials and Methods

We reviewed the files of 249 consecutive patients (seen by G.C.M.) who underwent nocturnal polysomnography for suspicion of OSA at the University of Alberta Sleep Center between 1989 and 1994. As part of their workup, all of these patients underwent a daytime HCVR test. In view of the possible interactions between hypnotics and major tranquilizers on ventilatory responsiveness, we excluded 24 patients who were actively taking these medications at the time of their assessment in our clinic. We

Results

Baseline features of subjects with and without OSA are presented in Table 1. OSA was associated with higher BMIs and a higher prevalence of female subjects. Extreme obesity (BMI > 40), however, was uncommon in either group; but among those who had BMI > 40, 7 of the 20 (35%) had OSA by our a priori criteria. Correlates for cHCVR were determined using a linear regression modeling technique, and the results are shown in Table 2. Paco2 was inversely associated with cHCVR, such that a 1-mm Hg

Discussion

We have found that OSA is not independently associated with cHCVR or daytime Paco2. Our results appear to conflict with other studies that have shown an inverse relationship between AHI and HCVR.2, 17, 18 Since many factors influence HCVR, confounding by other variables is an important threat to the validity of results. Airways obstruction, for instance, has been shown to be an independent correlate of daytime hypercapnia among OSA patients.19 Since obstructive airways disease is common20 in

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    Dr. Sin is supported by a fellowship from the Alberta Heritage Foundation for Medical Research.

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