Exercise Capacity and Ventilatory Efficiency in Patients With Pulmonary Arterial Hypertension

Area of Science:

• Cardiology
• Pulmonology
• Exercise Physiology

Background:

• Pulmonary arterial hypertension (PAH) significantly impairs exercise capacity, primarily presenting as dyspnea on exertion.
• Even after successful medical treatment leading to normalized hemodynamics, patients with PAH often experience persistent exercise intolerance.
• The specific contributions of central and peripheral factors to this residual exercise limitation in PAH remain incompletely understood.

Purpose of the Study:

• To investigate the key factors influencing exercise capacity in patients with hemodynamically normalized PAH.
• To identify determinants of ventilatory efficiency in PAH patients post-treatment.
• To explore the relationship between central hemodynamic parameters, peripheral factors like muscle strength, and exercise performance.

Main Methods:

• Cardiopulmonary exercise testing (CPET) combined with right heart catheterization was performed on 82 PAH patients with normalized mean pulmonary arterial pressure (mPAP ≤ 30 mmHg).
• Exercise capacity was assessed using the 6-minute walk distance (6MWD) and peak oxygen consumption (pVO2).
• Ventilatory efficiency was evaluated by the minute ventilation/carbon dioxide output (VE/VCO2) slope, and quadriceps muscle strength was measured.

Main Results:

• Peak arterial mixed venous oxygen content difference was the strongest predictor of 6MWD (β=0.46, P<0.001).
• Peak oxygen consumption was predicted by peak cardiac output (β=0.72, P<0.001), peak arterial mixed venous oxygen content difference (β=0.56, P<0.001), and resting mPAP (β=-0.25, P=0.026).
• Resting mPAP was the primary predictor of VE/VCO2 slope (β=0.35, P=0.041), and quadriceps strength moderately correlated with exercise capacity (ρ=0.57 for 6MWD, P<0.001).

Conclusions:

• Both central hemodynamic factors (e.g., cardiac output, oxygen content difference) and peripheral factors (e.g., muscle strength) are significantly associated with impaired exercise tolerance in PAH patients even after hemodynamic normalization.
• Residual pulmonary hypertension, indicated by resting mPAP, impacts ventilatory efficiency.
• Addressing both central and peripheral limitations may be crucial for improving exercise capacity in treated PAH patients.