Use of nitric oxide inhalation in chronic obstructive pulmonary disease

Background-Inhalation of nitric oxide with oxygen could be a promising treatment in patients with chronic obstructive pulmonary disease (COPD) and pulmonary hypertension. However, the current methods of delivery of NO are cumbersome and unsuitable for long term use. The present study was undertaken to investigate the safety and efficacy of a mixture of nitric oxide (NO) and oxygen administered via a nasal cannula for 24 hours in patients with oxygen dependent COPD. Methods-Twenty five parts per million (ppm) of NO was administered by inhalation combined with supplemental oxygen at a flow rate of 2 l/min via a nasal cannula for 24 hours to 11 ambulatory men with stable, oxygen dependent COPD. Room air with supplemental oxygen at 2 l/min was administered in an identical manner for another 24 hours as control therapy in a randomised, double blind, crossover fashion to all patients. Pulmonary function tests, exercise tolerance, dyspnoea grade, and lung volumes were measured at baseline, 24, and 48 hours. Pulmonary artery pressure (PAP), cardiac output (CO), pulmonary vascular resistance (PVR), arterial blood gas tensions, and minute ventilation were measured at baseline, after 30 minutes and 24 hours of breathing NO and oxygen. Venous admixture ratio (Qs/Qt) and dead space ratio (Vd/Vt) were also calculated. Concentrations of nitrogen dioxide (NO2) and NO in the inhaled and ambient air were monitored continuously. Differences in pulmonary function, arterial blood gas tensions, pulmonary haemodynamics, exercise tolerance, and dyspnoea between oxygen and NO breathing periods were analysed for significance using paired t tests. Results-A significant (p<0.05) fall was observed in PVR (183.1 (116.05) and 137.2 (108.4) dynes.s.cm(-3) before and after breathing NO for 24 hours, respectively) with NO administration without significant changes in symptoms, pulmonary function, arterial oxygen tension, or exercise tolerance. Conclusions-NO at a concentration of 25 ppm blended with oxygen can be safely administered by nasal cannula for 24 hours without significant adverse effects and lowers PVR in stable patients with COPD receiving long term oxygen therapy.