The pathophysiology of exercise limitation in patients with pulmonary arterial hypertension (PAH) remains unclear. In addition, whether the peripheral airway obstruction observed at rest contributes to exercise limitations is also unknown. We hypothesized that exercise induced expiratory airflow limitation occurs in PAH patients contributing to their ventilatory constraint and dyspnea with exercise.
We examined the degree of airflow limitation in PAH patients (n=12; age=27±13 yrs; PAPm=64±18 mmHg) and healthy volunteers (n=6; age=32±4yrs) by plotting the tidal flow-volume responses to graded exercise in relation to the maximal flow-volume loops (MFVL) obtained at rest. Inspiratory Capacity (IC) maneuvers were performed to follow changes in end-expiratory lung volume (EELV) during exercise; the degree of airflow limitation was assessed as percentage of the tidal volume (VT) that met or exceeded the expiratory boundary of the MFVL; tidal FV loops were measured at rest and at 40%, 60%, and 80% of peak workload during cardiopulmonary exercise testing. EELVs are one of the reserves that contribute to the VT increases during exercise.
EELV progressively decreased in controls as exercise intensity increased. In contrast, in PAH patients, although the EELV initially decreased with light exercise, it increased to ≥ baseline as minute ventilation and expiratory airflow limitation increased with greater workloads. Significant airflow limitation occurred at as low as 40% of the patients’ peak workload; at 80% peak workload it was 46±23% of the VT in PAH patients versus 5% of the VT in controls(p<0.05).
We conclude that moderate to severe exercise induced airflow limitation occurs with dynamic hyperinflation during exercise resulting in ventilatory constraint that may contribute to the exercise intolerance in PAH patients.
Bronchodilators, by decreasing airflow limitation, may improve patients’ dyspnea on exertion.Rest40%60%80%Airflow Limitation (%)PAH045 ± 17*52 ±12*46 ± 23*Controls0005EELV (L)PAH2.8 ± 0.32.7 ± 0.22.8 ± 0.22.9 ± 0.2Controls3.1 ± 0.23.1 ± 0.33.0 ± 0.32.8 ± 0.2Inspiratory Flow/Capacity (%)PAH44 ± 749 ± 857 ± 768 ± 7Controls39 ± 743 ± 750 ± 765 ± 18*
p<0.05 vs controls
Alpana Chandra, None.