Effect of nasal CPAP on ventilatory drive in normocapnic and hypercapnic patients with obstructive sleep apnoea syndrome.

The purpose of this study was to evaluate the effect of nasal continuous positive airway pressure (CPAP) on the abnormal ventilatory drive in hypercapnic patients with the obstructive sleep apnoea syndrome (OSAS). Six patients with hypercapnic OSAS (Group I) and 24 patients with eucapnic OSAS (Group II) were studied. All patients had arterial blood gas analysis, overnight sleep studies, and an assessment of ventilatory drive (progressive hyperoxic hypercapnic response and progressive isocapnic hypoxic ventilatory response) prior to and during nasal CPAP therapy (at 2 weeks and 1 month of treatment). Nasal CPAP effectively improved the hypopnoea/apnoea index in both groups (Group I: 87 +/- 14 vs 8 +/- 4; Group II: 63 +/- 17 vs 6 +/- 3). Both hypercapnic and hypoxic ventilatory drive before treatment were significantly impaired in Group I as compared to Group II. Both the slope and baseline level of the ventilatory response and the mouth occlusion pressure (P0.1) improved significantly after 2 weeks of nasal CPAP therapy in Group I, with normalization of arterial carbon dioxide tension (PaCO2) (6.3 +/- 0.2 to 5.2 +/- 0.4 kPa). We conclude that it is possible to completely correct the abnormal ventilatory drive in hypercapnic OSAS patients within 14 days of initiating nasal CPAP therapy.