Acute effect of nasal continuous positive air pressure on the ventilatory control of patients with obstructive sleep apnea

Background: Sleep fragmentation can decrease the awake ventilatory control. Since patients with obstructive sleep apnea (OSA) patients exhibit sleep f ragmentation linked to respiratory events, their ventilatory control could be impaired. However, most of these patients are also obese, which could co nversely increase the ventilatory control. The effect of nasal continuous p ositive airway pressure (CPAP) on the awake ventilatory control in normocap nic OSA patients is unclear. Objectives: To study the acute effect of nasal CPAP on the awake ventilatory control in normocapnic OSA patients. Methods : 12 normocapnic OSA patients, with an apnea/hypopnea index (AHI) >15 with moderate obesity (body mass index: 33.5 kg/m(2)) and normal pulmonary funct ion tests were submitted to two polysomnography studies (diagnostic and for CPAP titration). Before and after 3 consecutive nights of nasal CPAP we an alyzed the hypersomnia score and the ventilatory and the mouth occlusion pr essure (P.(1)) responses at rest (breathing room air and a mixture of 8% CO 2 + 40% O-2) Results: The respiratory drive of OSA patients as evaluated by P.(1) was in the range of the controls of our laboratory. After nasal CPAP , a significant decrease in AHI (mean: 51.9-9.4/h) and arousal (mean: 88.7- 43/h) occurred, as well as improve ment in nocturnal oxyhemoglobin. There w as a marginal increase in DeltaV(E)/DeltaP(ET)CO(2) (mean: 1.41-1.87 liters /min/mm Hg, p = 0.09) and a significant rise in P .(1)/DeltaP(ET)CO(2) (mea n: 0.29-0.43 cm H2O/mm Hg), a better indicator of ventilatory drive. Conclu sions: Normocapnic OSA patients increased their awake ventilatory drive res ponse to a hypercapnic and hyperoxic mixture with the use of 3 consecutive nights of nasal CPAP. Copyright (C) 2001 S. Karger AG, Basel.