Non-invasive positive pressure ventilation improves lung volumes in the obesity hypoventilation syndrome

Background: Our objective was to study the Long-term effects of non-invasive positive pressure ventilation (NPPV) on lung function and gas exchange in patients with the obesity hypoventilation syndrome (OHS). Design: Prospective observational study in OHS patients performing NPPV over a period of 24 months. Results: We studied 35 clinically stable OHS patients with a mean body mass index (BMI) 45.9 +/- 8.8 kg/m(2) and daytime PaCO2 at room air of 6.92 +/- 0.48 kPa at baseline. Nocturnal NPPV was initiated with pressure-cycted devices on IPAP 24 +/- 3cm H2O, EPAP 6 +/- 2 cm H2O and respiratory frequency of 18.8 +/- 3.7/min. After 12 and 24 months of NPPV hypercapnia was persistently normalized and hypoxemia was markedly improved white no changes in calculated alveolar-arterial oxygen difference occurred. Augmented ventilation was followed by a significant reduction in hemoglobin and hematocrit (P < 0.001 each). Daily duration of ventilator use significantly correlated with the decrease in PaCO2 after 12 months (r = 0.37; P < 0.05) and 24 months (r = 0.47; P < 0.05). Vital capacity (VC) and expiratory reserve volume (ERV) significantly increased after 12 and 24 months NPPV compared to the baseline values, though BMI was only slightly reduced. The 2-year survival rate was 91% with three patients (9%) discontinuing NPPV during the study period. Conclusion: Long-term domiciliary NPPV normalizes hypercapnia and markedly improves hypoxemia as well as polycythemia in OHS patients. In addition, NPPV Leads to a significant reduction in restrictive ventilatory disturbance, predominantly by increasing ERV.