Reduced hemoglobin-corrected diffusing capacity in pulmonary arterial hypertension with preserved pulmonary function...

The diffusing capacity and the transfer coefficient of the lung for carbon monoxide (D_LCO and K_CO, respectively) are reduced in pulmonary arterial hypertension; however, the effect of pulmonary arterial hypertension alone on these parameters and their clinical impact remain unclear. We aimed to elucidate the exclusive impact of pulmonary arterial hypertension on these two parameters and examine their association with other parameters.

We retrospectively selected patients with pulmonary arterial hypertension with normal pulmonary function upon pulmonary function testing and with normal lung parenchyma upon chest computed tomography. We calculated the hemoglobin-corrected D_LCO (D_LCO-Hbc) and K_CO (K_CO-Hbc) and examined their association with established pulmonary hypertension-related parameters. An exploratory analysis of pulmonary vasculopathy was performed in an autopsy case.

We included 50 patients with pulmonary arterial hypertension for analysis. Their median %D_LCO-Hbc and %K_CO-Hbc were 62 % and 70 %, respectively. The D_LCO-Hbc was associated with functional class, 6-min walk distance, alveolar-arterial oxygen tension difference, cardiac output, and pulmonary arterial hypertension-related death. The D_LCO-Hbc and K_CO-Hbc were also correlated with the lowest minute ventilation/carbon dioxide production ratio (ρ = -0.84 and -0.49, respectively), an index that represents ventilation-perfusion mismatch. The autopsy revealed pulmonary arterial hypertension-specific arteriopathy that was heterogeneously distributed in the lungs.

The D_LCO-Hbc and K_CO-Hbc were reduced to 60 %-70 % in patients with pulmonary arterial hypertension even when their pulmonary function and morphology were preserved. The decreases were associated with pulmonary hypertension-related clinical parameters and survival and may be caused by heterogeneous vasculopathy and subsequent ventilation-perfusion mismatch.