The usefulness of submaximal exercise gas exchange to define pulmonary arterial hypertension

The 6-minute walk test is widely used to characterize activity tolerance and response to therapy in pulmonary arterial hypertension (PAH) but provides little information about cardiopulmonary pathophysiology. The aim of the present study was to determine whether measures of pulmonary gas exchange during relatively light exercise could differentiate between PAH patients and healthy individuals and also stratify disease severity.

The study comprised 40 PAH patients and 25 matched controls. Each completed a sub-maximal exercise test, consisting of 2 minutes of rest, 3 minutes of exercise, and 1 minute of recovery. Ventilation, pulmonary gas exchange, arterial oxygen saturation (Sao(2)), and heart rate were measured throughout using a simplified gas analysis system.

A number of gas exchange variables differentiated PAH patients and controls. End-tidal CO(2) (P(ET)co(2)) and Sao(2) were lower in PAH vs controls (31 ± 7 vs 39 ± 3 mm Hg and 89% ± 5% vs 95% ± 2%, respectively, p < 0.05). Breathing efficiency (V(E)/Vco(2) ratio) was poorer in PAH vs controls (42 ± 10 vs 33 ± 5, p < 0.05). In addition, P(ET)co(2) and V(E)/Vco(2) discriminated between different severities of PAH.

Gas exchange variables obtained during light sub-maximal exercise differentiated PAH patients from healthy controls and also between different severities of PAH. Sub-maximal exercise gas exchange may be a useful end point measure in a PAH population.