Pulmonary vascular response patterns during exercise in interstitial lung disease

When overt pulmonary hypertension arises in interstitial lung disease (ILD), it contributes to exercise intolerance. We sought to determine the functional significance of abnormal pulmonary arterial pressure (PAP) responses to exercise in ILD. 27 ILD patients and 11 age-matched controls underwent invasive cardiopulmonary exercise testing (iCPET). Mean PAP (mPAP) was indexed to cardiac output (Q'T) during exercise, with a mPAP-Q'T slope >= 3 mmHg.min.L-1 defined as an abnormal pulmonary vascular response. All control subjects had mPAP-Q'T slopes <3 mmHg.min.L-1 (mean +/- SEM 1.5 +/- 0.1 mmHg.min.L-1). 15 ILD patients had mPAP-Q'T slopes >= 3 mmHg.min.L-1 (4.1 +/- 0.2 mmHg.min.L-1) and were labelled as having ILD plus pulmonary vascular dysfunction (PVD). Subjects without pulmonary hypertension and with mPAP-Q'T slopes <3 mmHg.min.L-1 (1.9 +/- 0.2 mmHg.min.L-1) were labelled as ILD minus PVD (n=12). ILD+PVD and ILD-PVD patients did not differ in terms of age, sex, body mass index, pulmonary function testing or degree of exercise oxygen desaturation. Peak oxygen consumption was lower in ILD+PVD than in ILD-PVD (13.0 +/- 0.9 versus 17 +/- 1.1 mL.kg(-1).min(-1), p=0.012) and controls (19.8 +/- 1.7 mL.kg(-1).min(-1), p=0.003). ILD+PVD patients had increased dead space volume (V-D)/tidal volume (V-T) and minute ventilation/carbon dioxide production at the anaerobic threshold. In ILD, mPAP-Q'T slope >= 3 mmHg.min.L-1 is associated with lower peak oxygen consumption, increased V-D/V-T and inefficient ventilation. While noninvasive parameters were unable to predict those with abnormal pulmonary vascular responses to exercise, iCPET-derived mPAP-Q'T slope may aid in identifying physiologically significant, early pulmonary vascular disease in ILD.