Differences in the Acute Pulmonary Vascular Effects of Oxygen with Nitric Oxide and Diltiazem: Implications for the Long-term Treatment of Pulmonary Arterial Hypertension

Objective. Right heart catheterization is performed in patients with pulmonary arterial hypertension to determine the severity of disease and their pulmonary vascular reactivity. This study sought to determine whether the acute pulmonary vasodilatory effects of diltiazem and oxygen with nitric oxide are similar enough to support the practice of using nitric oxide as a surrogate agent to identify patients to treat with an oral calcium channel blocker alone. Design. Retrospective descriptive study. Setting. A tertiary medical center for children. Patients. Twenty-four individuals (7 months to 17 years of age) with pulmonary arterial hypertension who met criteria for a favorable acute pulmonary vasodilatory response to oxygen with nitric oxide, and were also evaluated with intravenous diltiazem. Interventions. Right heart catheterization and an evaluation of pulmonary vascular reactivity. Outcome Measures. The pulmonary vasodilatory effects of oxygen, oxygen with nitric oxide, and intravenous diltiazem; and the need for medications other than amlodipine to decrease long-term pulmonary arterial pressure. Results. Oxygen, oxygen with nitric oxide, and diltiazem acutely decreased pulmonary arterial pressure. Diltiazem also decreased systemic arterial pressure. A lower mean pulmonary arterial pressure was achieved with oxygen and nitric oxide than with diltiazem (30 +/- 2mm Hg vs. 39 +/- 3mm Hg, P<.05). Half of the patients who were treated long term with amlodipine alone failed to develop a long-term 20% decrease in pulmonary arterial pressure and were treated with additional medications. Conclusions. The combination of oxygen and nitric oxide decreased pulmonary arterial pressure more than a dose of intravenous diltiazem that was large enough to decrease systemic arterial pressure. Oxygen and nitric oxide may identify patients who can be treated safely with a calcium channel blocker; however, they should not be used as surrogates to identify patients to treat with a calcium channel blocker alone.