Long-term Effects of Treatment with Nasal Continuous Positive Airway Pressure on Daytime Lung Function and Pulmonary Hemodynamics in Patients with Obstructive Sleep Apnea

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Abstract
Fifty-four patients with obstructive sleep apnea (OSA) syndrome received long-term treatment with nasal continuous positive airway pressure (CPAP). The effects on daytime lung function and pulmonary hemodynamics were prospectively evaluated by repeating pulmonary function tests, including right heart catheterization after a follow-up period of at least 1 yr (554 .+-. 28 days, mean .+-. SEM). PaO2 increased in the patient group as a whole from 69.9 .+-. 1.4 to 72.8 .+-. 1.4 mm Hg (p < 0.02). The increase in PaO2 was greater (from 60.4 .+-. 1.0 to 66.4 .+-. 2.1, p < 0.01) in those patients who were hypoxemic prior to treatment. PaCO2 decreased significantly only in the subgroup of patients with significant hypercapnia prior to treatment (n = 7), from 48.5 .+-. 1.3 to 44.5 .+-. 1.5 mm Hg (p < 0.01). The improvement in daytime blood gases seemed to be related to an increase in the alveolar ventilation, from 5.2 .+-. 0.2 to 5.9 .+-. 0.3 L/min without a change in the alveolar-arterial PO2 difference, as caculated in 25 patients. Both the red blood cell count and the hematocrit decreased significantly, from 5,347 .+-. 90 to 5,024 .+-. 61 103/mm3 and from 49.4 .+-. 0.9 to 47.1 .+-. 0.6%, p < 0.001 and p < 0.02, respectively. No change was observed in the resting pulmonary arterial pressure. We conclude that nasal CPAP is effective in improving daytime blood gases in patients with OSA.