Treatment effects on carbon dioxide retention in patients with obstructive sleep apnea-hypopnea syndrome

Objectives: This study was designed to examine respiratory control in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS), with or without CO2 retention. Methods: We recruited 10 body mass index-matched, apnea-hypopnea index-matched, age-matched, and lung function-matched OSAHS patients, according to their awake PaCO2. Five patients were hypercapnic (PaCO2, greater than or equal to 45 mm Hg), and five patients were eucapnic. Hypoxic responses (the ratio of the change in minute ventilation [Delta (V) over dot E] to the change in arterial oxygen saturation [Delta Sao(2)] and the ratio of the change in mouth occlusion pressure over the first 100 ms of inspiration against an occluded airway [DeltaP(0.1)] to Delta Sao(2)) and hypercapnic responses (Delta (V) over dotE/Delta PCO2 ratio and Delta P0.1/Delta PCO2 ratio) were tested during wakefulness before treatment in all 10 patients, and before and during treatment (at 2, 4, and 6 weeks) with pressure support in the hypercapnic group. Results: Hypercapnic patients had lower mean (+/- SD) Delta (V) over dotE/Delta SaO(2) ratio than eucapnic patients (-0.17 +/- 0.04 vs -0.34 +/- 0.04 L/min/%SaO(2), respectively), lower mean DeltaP(0.1)/Delta SaO(2) ratio (-0.04 +/- 0.02 vs -0.14 +/- 0.03 cm H2O/%SaO(2), respectively), and lower DeltaP(0.1)/Delta PCO2, ratio (0.23 +/- 0.1 vs 0.49 +/- 0.1 cm H2O/mm Hg, respectively) [p < 0.05]. After receiving noninvasive ventilation treatment, the hypercapnic and hypoxic responses of the hypercapnic patients increased. At 4 to 6 weeks, values for both responses had increased to within the normal range and PaCO2 had fallen to < 45 mm Hg, while weight was unchanged. Conclusions: Depressed chemoresponsiveness plays a role that is independent of obesity in the development of CO2 retention in some OSAHS patients, and it may be a response to sleep-disordered breathing.