BACKGROUND

The dynamic decrease in inspiratory capacity (IC) during exercise with restriction of tidal volume (VT) is known as dynamic hyperinflation (DH) and is described mostly in patients with COPD differentiating between a "hyperinflator" and a "non-hyperinflator". Recent studies have revealed DH in patients with idiopathic pulmonary arterial hypertension (iPAH), but the influence of the DH on the reduced exercise capacity with exertional dyspnoae is still being debated.

METHODS

We analysed flow-volume curves during cardiopulmonary exercise testing (CPET) in idiopathic PAH (n = 19), in COPD (n = 17), in idiopathic pulmonary fibrosis (IPF) (n = 19) and a control group (n = 30). We measured IC at rest and during maximal exercise and furthermore ventilation, VT and oxygen uptake (VO2 peak). In iPAH a right heart catheter test and a 6-minute walk test (6MWT) were performed, also the B-type naturetic peptide (BNP) and the NYHA/WHO functional class were determined.

RESULTS

The IC decreased significantly in 11 PAH "hyperinflators" (PAH-H) (Δ IC: - 0.34 ± 0.14 L, p < 0.001) compared to 8 PAH "non-hyperinflators" (PAH-NH) (Δ IC: 0.08 ± 0.2 L). COPD patients exhibited a characteristic hyperinflation pattern with a decrease in IC throughout exercise (Δ IC: - 0.61 ± 0.3 L, p < 0.001), while patients with IPF (Δ IC: 0.03 ± 0.15 L) and the control group responsed to exercise with a non-hyperinflator pattern (Δ IC: 0.1 ± 0.2 L). Both PAH collectives showed a reduced IC/TLC, while VT/IC was elevated with a decreased peak VO2 and max. performance compared to the control group. Correlations of the IC rest/max (L) were shown in PAH-H and PAH-NH with the VO2 peak, max. performance and VT.

CONCLUSION

The analysis of flow-volume curves during CPET can indentify DH in a subgroup of patients with iPAH. The DH contributes significantly but slightly to the development of exertional limitations and dyspnoe in a subgroup of iPAH. Further studies with a larger sample size will be required to definitively measure the impact of the DH seen in these patients.