Transition from obstructive sleep apnea (OSA) to obesity hypoventilation syndrome (OHS)

Abstract

Background: Some obese patients with OSA also develop OHS at some point, which is thought to be a gradual process. The aim of this study is to characterize a spectrum of OSA patients to further elucidate the transition from pure OSA to OHS. Methods: We present data from a prospective observational study. Patients with (suspected) SRBD and BMI >30 kg/m² got arterial blood gas analyses (ABG) before, during and after initial polysomnography (PSG). Following measurements comprised bodyplethysmography, cardiopulmonary exercise testing (CPET), lung compliance and hypercapnic ventilatory response (HCVR). Results: Until now, 18 patients were examined (4 f, 55.4±13.5 y, BMI 40±6 kg/m², ESS Score 7±5). Mean PaCO2 before/during/after PSG was normal (39±3/42±5/39±6mmHg). Mean AHI was 50±31/h, oxygen desaturation index 45±34/h with minimal saturation of 70±19%. Lung function was normal except for reduced expiratory reserve volume (45±23%). Mean lung compliance was normal with large interindividual variation (Cstat 3.8±5.4, Cdyn 2.4±3.3). Mean HCVR was 2.0±1.4 L/min/mmHg. CPET (n=17) showed reduced maximal performance (75±37%pred.), good O2 uptake (VO2max 112±20%pred, VO2 at AT 1527±425 ml/min), no pulmonary limitations (AaDo2 35±8, BR 17±23, VT/IC 0.7±0.2). Heart rate reserve was not reached (HRR 36±12). 2/17 patients were hypercapnic (PaCO2 47 & 54 mmHg) and thus showed signs of OHS onset. Conclusion: These preliminary data do not yet allow for comprehensive characterization of different stages in the development from OSA to OHS. However, a small fraction of patients showed indication of being in a transitory state. An increasing number of study subjects will allow doing a more detailed analysis in the future.