Objectives: This study was designed to examine respiratory control in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS), with or without CO(2) 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 PaCO(2). Five patients were hypercapnic (PaCO(2), > or = 45 mm Hg), and five patients were eucapnic. Hypoxic responses (the ratio of the change in minute ventilation [DeltaV(E)] to the change in arterial oxygen saturation [DeltaSaO(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 DeltaSaO(2)) and hypercapnic responses (DeltaV(E)/DeltaPCO(2) ratio and DeltaP(0.1)/DeltaPCO(2) 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) DeltaV(E)/DeltaSaO(2) ratio than eucapnic patients (-0.17 +/- 0.04 vs -0.34 +/- 0.04 L /min/%SaO(2), respectively), lower mean DeltaP(0.1)/DeltaSaO(2) ratio (-0.04 +/- 0.02 vs -0.14 +/- 0.03 cm H(2)O/%SaO(2), respectively), and lower DeltaP(0.1)/DeltaPCO(2) ratio (0.23 +/- 0.1 vs 0.49 +/- 0.1 cm H(2)O/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 PaCO(2) 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 CO(2) retention in some OSAHS patients, and it may be a response to sleep-disordered breathing.