Low DLCO Can Provide Insights into Treatment Response in PAH Patients Irrespectively of the Reason of Its Decrease

Group of PAH patients encompasses patients with a diverse underlying aetiological condition, having histological modifications that can affect gas exchange across the alveolar-capillary membrane as it is reflected by decreased DLCO. DLCO values did not identify the exact reason of its decrease, but can provide insights into the underlying pathobiology and prognosis of PAH patients. Our aim was to explore if PAH patients with low DLCO constitute a different subpopulation and describe their characteristics and response to treatment. 69 PAH patients were studied retrospectively and divided into group1: DLCO≥45% and group2: DLCO< 45%. IPAH and PAH-CTD constituted mainly our population. The proportion of IPAH and PAH-CTD was almost the same. Patients in group 2 were older (66.83± 11.61 vs 59.27±111.90, p=0.035), more often male (47.5% vs 11.5% p=0.008) and ever smokers (59% vs 22%, p=0.049). They had mainly WHO-FC III ((68%) vs 32%) and have received more advanced therapy (40% on triple combination therapy vs 16%). The two groups had the same mean PAP (group1=32 (22.00-38.00) vs group2=35 (28.50-48.50) mmHg) and PVR was higher in group 2 (6.49(4.10-9.52) vs 3.61 (2.95-5.22) WU). In group 2 neither IPAH nor PAH-CTD patients did improve WHO-FC, 6MWD, or NT-proBNP after treatment. In our centre PAH patients with low DLCO have some distinct clinical characteristics. poor prognosis and treatment response in vasodilatory therapy. Understanding the role of DLCO in phenotyping PAH patient and in treatment response would be useful in guide therapeutic approaches, especially now that new therapeutic targets are involved in the PAH treatment.