DLCO, a potential indicator of pulmonary microvasculopathy, and its association with exercise capacity, oxygenation, and hemodynamics in patients with chronic thromboembolic pulmonary hypertension aft

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Abstract Background Balloon pulmonary angioplasty (BPA) improves prognosis and hemodynamic parameters in patients with chronic thromboembolic pulmonary hypertension (CTEPH). However, exercise-induced hypoxemia and reduced exercise tolerance persist in some patients even after BPA, potentially due to pulmonary microvasculopathy. Diffusing capacity of the lung for carbon monoxide (DLCO) reflects the efficiency of gas exchange from the alveoli to red blood cells and is influenced by the condition of the capillary membrane and the volume of blood in the alveoli, making it a potential indicator of pulmonary microvasculopathy. However, DLCO, its pathophysiological determinants, and its clinical implications remain poorly understood in patients with CTEPH. Objective To examine the prevalence of reduced DLCO, suggestive of pulmonary microvasculopathy, and to investigate the relationship between DLCO and hemodynamic and oxygenation parameters at rest and during exercise, as well as exercise capacity in CTEPH patients after BPA. Methods An invasive cardiopulmonary exercise test (CPX) with right heart catheterization (RHC) and pulmonary function tests were performed in 87 CTEPH patients who had undergone BPA (median age: 66 years; 70% female; mean pulmonary artery pressure: 19 ± 4 mmHg). Correlations between DLCO% and CPX with RHC parameters were analyzed. Results The mean DLCO% was 68 ± 17%, with 67 patients (77%) exhibiting DLCO% < 80%. DLCO% significantly correlated with hemoglobin (r = 0.38), arterial oxygen saturation (SaO₂) (at rest: r = 0.44, at peak exercise: r = 0.44), cardiac output (CO) (at rest: r = 0.36, at peak exercise: r = 0.56), oxygen consumption (VO₂) (at rest: r = 0.35, at peak exercise: r = 0.53), pulmonary vascular resistance (at rest: r = -0.33, at peak exercise: r = -0.35), alveolar-arterial oxygen gradient (P(A-a)O₂) (at rest: r = -0.31, at peak exercise: r = -0.31), and dead space ventilation ratio (VD/VT) (at rest: r = -0.096, at peak exercise: r = -0.36). Notably, stronger correlations with CO, VO₂, and VD/VT were observed during exercise compared to a rest. Conclusion In patients with CTEPH after BPA, lower DLCO was common, and associated with exercise-induced hypoxia and reduced exercise capacity, along with decreased CO and worsened ventilatory efficiency, especially during exercise.

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