The effects of oxygenation on acute vasodilator challenge in pulmonary arterial hypertension

Background Identification of long-term calcium channel blocker (CCB) responders with acute vasodilator challenge is critical in the evaluation of patients with pulmonary arterial hypertension. Currently there is no standardized approach for use of supplemental oxygen during acute vasodilator challenge. Methods Retrospective analysis of patients identified as acute vasoresponders, treated with CCBs. All patients had hemodynamic measurements in three phases: 1) at baseline; 2) with 100% fractional inspired oxygen; and 3) with 100% fractional inspired oxygen plus inhaled nitric oxide (iNO). Patients were divided into two cohorts. Those meeting the definition of acute vasoresponsiveness from phase 2 to phase 3 were labeled “iNO Responders.” Those who did not reach the threshold of acute vasoresponsiveness from phase 2 to phase 3 but did meet the definition from phase 1 to phase 3 were labeled “Oxygen Responders.” Survival, hospitalization for decompensated right heart failure, duration of CCB monotherapy, and functional data were collected. Results iNO Responders, when compared to Oxygen Responders, had superior survival (100% vs 50.1% 5-year survival, respectively), fewer hospitalizations for acute decompensated right heart failure (0% vs 30.4% at 1 year, respectively), longer duration of CCB monotherapy (80% versus 52% at 1 year, respectively), and superior six-minute walk distance. Conclusion Current guidelines for acute vasodilator testing do not standardize oxygen coadministration with iNO. This study demonstrates that adjusting for the effects of supplemental oxygen before assessing for acute vasoresponsiveness identifies a cohort with superior functional status, tolerance of CCB monotherapy, and survival while on long-term CCB therapy.