Effect of 6-min Walk Test on pro-BNP Levels in Patients with Pulmonary Arterial Hypertension.

Abstract

Plasma pro-BNP (brain natriuretic peptide) levels are often elevated in response to right ventricular (RV) volume and pressure overload, parameters potentially affected by exercise. Plasma pro-BNP levels change in association with long-term changes in pulmonary hemodynamics, thereby serving as a potential biomarker in pulmonary arterial hypertension (PAH). The 6-min Walk Test (6MWT) and pro-BNP level are often checked in a single office visit. There is no universal standard for measuring Pro-BNP levels relative to the timing of the 6MWT. Based on the studies in normal subjects indicating that pro-BNP levels changes after exercise, we hypothesized that the pro-BNP might rise after the 6MWT in PAH patients, potentially impacting clinical decisions. Patients at our center with WHO Group 1 PAH on active therapy at a stable dose for 30days or more were enrolled. After resting the patient for 30min, blood was drawn for baseline pro-BNP and a 6MWT was performed. Pro-BNP levels were drawn immediately after the 6MWT and 1 and 2h later. Pro-BNP was measured using a commercially available ELISA kit. The levels before exercise and after exercise were compared using student's paired t tests. There were 17 females and 3 male subjects. The mean age was 53±11years. Seven patients had systemic lupus erythematosus-related PAH, six had idiopathic PAH, three had scleroderma, three had portopulmonary hypertension, and one had HIV-related PAH. The mean PA pressure was 50±15mmHg with a mean pulmonary vascular resistance of 10±4Wood units. The majority of the patients were on multimodality PAH therapy, including parenteral prostacyclins. Mean 6MWT distance was 377±140m. In 14/20 patients, the pro-BNP level increased immediately after the 6MWT; in 12/20 patients, the pro-BNP level was elevated at 1h post exercise. In the majority of the patients, the pro-BNP fell to baseline 2h post 6MWT. There appears to be a trend of pro-BNP level increasing immediately after exercise and continuing to be elevated at 1h. Pro-BNP levels then return to baseline at 2h post 6MWT.