Addition of Nitric Oxide to Oxygen Improves Cardiopulmonary Function in Patients With Severe COPD: Discussion
Several trials of domiciliary LTOT have demonstrated a considerable improvement in exercise tolerance and neuropsychological function, as well as a reduction in the requirement for hospitalization. Although no significant change of MPAP was observed in the Medical Research Council study in patients receiving LTOT for 15 h/d, a regimen delivering oxygen for 18 h/d over a period of 6 months caused a significant decrease in PVRI. canadian neighbor pharmacy
There is evidence that impaired endogenous synthesis of NO by the pulmonary endothelium as a sult of chronic hypoxia may contribute to the development of chronic pulmonary hypertension. Inhaled NO causes striking local (ie, pulmonary) vasodilation, but it is rapidly inactivated on contact with hemoglobin, which limits its access to the systemic circulation. It is effective for the treatment of pulmonary hypertension in ARDS, persistent pulmonary hypertension of the newborn, congenital heart disease, acute pneumonia, and COPD. In addition, inhaled NO is carried to lung units with the best ventilation, where it enhances perfusion. V/Q mismatch due to local hypoventilation within the inflamed small bronchi is substantially reduced, with improved oxygenation in ARDS patients.
Previous studies on the use of inhaled NO in patients with severe COPD have yielded conflicting results. Although pulmonary vascular resistance is consistently decreased, the effects of oxygenation are variable and even detrimental. It has been suggested that some patients preserve V/Q matching of poorly perfused lung zones by hypoxic pulmonary vasoconstriction, and that by reversing this, NO may worsen Pa02.
Adnot et al compared the effect of infused acetylcholine and inhaled NO (5 to 40 ppm) on hemodynamics and gas exchange in patients with COPD. Three of the 13 patients studied were maintained on a regimen of oxygen therapy, while the remainder were receiving room air. They concluded that whereas acetylcholine produces both pulmonary and systemic vasodilation but impairs oxygenation, inhaled NO induces selective pulmonary vasodilation and improves gas exchange.