The Usefulness of Submaximal Exercise Gas Exchange in Pulmonary Arterial Hypertension: A Case Series

INTRODUCTION: Submaximal exercise gas exchange may be a useful tool to track responses to therapy in pulmonary arterial hypertension (PAH) patients. METHODS: Three patients diagnosed with idiopathic PAH, on differing therapies, were included. Standard clinical tests (echocardiography; 6 minute walk) were performed pre and 3-5 months after treatment. Gas exchange was measured during 3 minutes of step exercise at both time points. RESULTS: Gas exchange variables, end tidal CO(2) (P(ET)CO(2)) and the ratio of ventilation to CO(2) production (V(E)/VCO(2)), during submaximal exercise were able to track patient responses to therapy over a 3-5 month period. Two patients demonstrated positive improvements, with an increased P(ET)CO(2) and decreased V(E)/VCO(2) during light exercise, in response to an altered therapeutic regime. The third patient had a worsening of gas exchange (decreased P(ET)CO(2) and increased V(E)/VCO(2)) following no changes in the medical regime from the baseline visit. CONCLUSION: Gas exchange variables measured during light submaximal exercise, such as P(ET)CO(2) and V(E)/VCO(2), may be able to better detect small changes in functional status following treatment and could, therefore, be a useful tool to track disease severity in PAH patients. Further study is required to determine the clinical usefulness of these gas exchange variables.