Chronic CO2 drive in patients with obstructive sleep apnea and effect of CPAP.

Obstructive sleep apnea (OSA) can be associated with depressed hypercapnic ventilatory response (HCVR) (White D.P., N.J. Douglas, C.K. Pickett, C.W. Willich and J.V. Weil, Am. Rev. Respir. Dis 128:984-986, 1983), which might be responsible for aggravating the sleep-related breathing disorder (SRBD). The present study evaluated whether in patients with various types of sleep apnea a significant decrease in the HCVR could be found (COMPARATIVE STUDY). In a second part of the study chronic CPAP therapy (Continuous Positive Airway Pressure) was evaluated in relation to control of breathing (CPAP STUDY). In the comparative study a significant increase of the slope in the normocapnic OSA and overlap group could be seen. A depressed HCVR could only be observed in chronic hypercapnic OSA. In the CPAP-study it was shown that changes in the AHI after CPAP do not parallel the HCVR. We conclude that in eucapnic OSA patients CPAP therapy does not change CO2 drive. We believe that increased chemical CO2 drive can contribute to its pathogenesis.