Measures of Gas Exchange During Six Minute Walk Test Predict Changes in Disease Severity in Pulmonary Artery Hypertension

Purpose: The six minute walk distance (6MWD) is a validated measure of functional capacity and is related to mortality and morbidity in pulmonary arterial hypertension (PAH). We have demonstrated that gas exchange measures (end exercise VE/VCO2 and PETCO2) during a six minute walk test (6MWT) correlate with disease severity in PAH. It is unknown if changes in gas exchange measures are sensitive to changes in disease status. Aim: To determine relationship between changes in disease severity as measured by right ventricular systolic pressure (RVSP) and indices of gas exchange measured during a 6MWT in idiopathic PAH (IPAH). Methods: Prospectively, 16 idiopathic PAH (IPAH) patients (11F, 44.6 ± 13.5 yr, NYHA 2.2 ± 0.4) from a tertiary Pulmonary Hypertension Centre, completed two 6MWT mean 551± 203 days apart. Gas exchange was measured using a portable metabolic cart. End exercise measurements of oxygen uptake (VO2), VE/VCO2 and PETCO2 were determined from 60s averages. All patients underwent echocardiography and standard measurements of right ventricular function on the same day. Results: There was no statistical change in the 6MWD (pre: 532 ± 85; post: 547 ± 121 m p > 0.5), however there was a small but non-significant reduction in RVSP (pre: 72 ± 23; post: 67 ± 19 mmHg, p= 0.74). Changes in RVSP correlated significantly with end exercise VE/VCO2 (r= 0.78, p< 0.05) and PETCO2(r= -0.75, p< 0.05) and 6MWD (r= 0.61, p< 0.05). There was no correlation with the change in VO2 from baseline to follow up. Conclusion: This study demonstrates that changes in gas exchange measures from a 6MWT relate to changes in disease severity in a small sample of patients with IPAH. Further research needs to determine if applicable in a larger sample of IPAH patients.