Background Haemodynamic measurements may be superior to the 6-min walk distance (6MWD) as outcome measures in pulmonary hypertension (PH) as they are directly linked to the mechanisms of disease and are not subject to a ceiling effect. The aim of this study was to determine if treatment response in precapillary PH could be detected by pulmonary blood flow (PBF) and stroke volume (SV) measured non-invasively by the inert gas rebreathing (IGR) method at rest and during submaximal constant-load cycle exercise.

Methods Twenty-four patients with precapillary PH receiving de novo or modified disease-targeted therapy were studied. Isotime metabolic variables, PBF and SV were measured at rest and during constant-load cycle exercise at 40% maximal work rate alongside conventional outcome variables, at baseline and after 3 months of new therapy.

Results At follow-up there was a significant increase in PBF (supine rest: mean 0.7±SD 0.9 l/min, erect rest: 0.7±0.8 l/min, exercise: 0.8±1.0 l/min, p<0.005) and SV (supine rest: 7±10 ml, erect rest: 10±11 ml, exercise: median 6 (IQR 3–11) ml, p<0.005). There was a trend for 6MWD to increase by 17±42 or 29 (13–47) m (p=0.061), whereas WHO functional class, N-terminal pro-brain natriuretic peptide or Cambridge Pulmonary Hypertension Outcome Review score were unchanged. In patients with higher baseline 6MWD, IGR measurements were more sensitive than 6MWD in detecting treatment response.

Conclusions Non-invasive IGR haemodynamic measurements could be used to detect treatment response in patients with precapillary PH and may be more responsive to change than 6MWD in fitter patients.