Oxygen Pathway Limitations in Patients with Chronic Thromboembolic Pulmonary Hypertension

Background: Exertional intolerance is a limiting and often crippling symptom in patients with chronic thromboembolic pulmonary hypertension (CTEPH). Traditionally the etiology has been attributed to central factors, including ventilation-perfusion mismatch, increased pulmonary vascular resistance and right heart dysfunction and uncoupling. Pulmonary endarterectomy and, balloon pulmonary angioplasty provide substantial improvement of functional status and hemodynamics. However, despite normalization of pulmonary hemodynamics, exercise capacity often does not return to age-predicted. By systematically evaluating the oxygen (O2) pathway we aimed to elucidate the cause/s of functional limitations in CTEPH patients before and after pulmonary vascular intervention. Methods: Using exercise cardiac magnetic resonance (CMR) imaging with simultaneous invasive hemodynamic monitoring, we sought to quantify the steps of the O2 transport cascade from the mouth to the mitochondria in patients with CTEPH (n=20) as compared to healthy subjects (n=10). Furthermore we evaluated the effect of pulmonary vascular intervention (pulmonary endarterectomy or balloon angioplasty) on the individual components of the cascade (n=10). Results: Peak VO2 was significantly reduced in CTEPH patients relative to controls (56±17 vs 112±20% of predicted, p