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

Group 1 of PAH patients encompasses patients with a diverse underlying etiological condition, having histological modifications that can affect gas exchange across the alveolar-capillary membrane, as reflected by decreased DLCO. Values of DLCO did not identify the exact reason for their decrease, but they can provide insights into the underlying pathobiology and prognosis of PAH patients. Our aim was to explore whether PAH patients with low DLCO constitute a different subpopulation and describe their characteristics and response to treatment. A total of 69 PAH patients were studied retrospectively and divided into two groups: <i>group 1</i>: DLCO ≥ 45% and <i>group 2</i>: DLCO < 45%. IPAH and PAH-CTD mainly constituted our population. The proportion of IPAH to PAH-CTD was almost the same between the two groups. Patients in <i>group 2</i> were older (66.83 ± 11.61 vs. 59.27 ± 111.90, <i>p</i> = 0.035), mostly male (47.5% vs. 11.5% <i>p</i> = 0.008), and ever smokers (59% vs. 22%, <i>p</i> = 0.049). They mainly had WHO-FC III (68% vs. 32%) and had received more advanced therapy (40% on triple combination therapy vs. 16%). The two groups had similar mean PAP (<i>group 1</i> = 32 (22.00-38.00) vs. <i>group 2</i> = 35 (28.50-48.50) mmHg), while PVR was higher in <i>group 2</i> (6.49 (4.10-9.52) vs. 3.61 (2.95-5.22) WU). In <i>group 2</i>, neither IPAH nor PAH-CTD patients improved WHO-FC, 6MWD, or NT-proBNP after treatment. In our center, PAH patients with low DLCO had some distinct clinical characteristics, such as poor prognosis and poor treatment response to vasodilatory therapy. Understanding the role of DLCO in both phenotyping PAH patients and in treatment response would be useful in guiding therapeutic approaches, especially now that new therapeutic targets are involved in PAH treatment.