Relating exercise-induced desaturation and gas-exchange in pulmonary artery hypertension

We measured pulmonary gas exchange during six minute walk test (6MWT) in patients with idiopathic (IPAH) and congenital heart disease-related pulmonary hypertension (CHDPH), and determined the relationship between the degree of desaturation and changes in minute ventilation to carbon dioxide production V˙_EV˙CO₂ and end-tidal partial pressure for carbon dioxide (P_etCO₂) in both groups. Fifty-two patients (IPAH, n = 28; CHDPH, n = 24) completed 6MWT with simultaneous pulmonary gas exchange. Whilst no significant difference in six minute walk distance was observed between groups (IPAH: 529 ± 89; CHDPH: 476 ± 119 m, p = 0.10), oxygen uptake, carbon dioxide production, and minute ventilation were higher in IPAH than CHDPH (p < 0.01). In addition, CHDPH desaturated to a greater extent than IPAH with a lower post-6MWT S_PO₂ (IPAH: 92.3 ± 7.9; CHDPH: 73.3 ± 14.9%, p < 0.01). The change in S_pO₂ correlated to the change in V˙_E/V˙CO₂ (r=-0.44, p = 0.02) and P_etCO₂ (r = 0.49, p < 0.01) for CHDPH, but not IPAH. The exercise-induced hypoxic stimulus during 6MWT in CHDPH may be associated with an enhanced ventilatory response.