B68-04 Pulmonary Vascular Distensibility in Systemic Sclerosis-associated and Idiopathic Pulmonary Arterial Hypertension

Abstract Rationale Systemic sclerosis-associated pulmonary arterial hypertension (SSc-PAH) has a worse prognosis than idiopathic pulmonary arterial hypertension (IPAH). The mechanisms underlying this difference remain incompletely characterized. Prior work from our group has not shown differences in right ventricular afterload or resistance-compliance relationships in the pulmonary vasculature between SSc-PAH and IPAH. However, these measurements may not fully capture the dynamic interaction between the pulmonary circulation and right ventricle. Pulmonary vascular distensibility (alpha-distensibility) describes the ability of the pulmonary vessels to accommodate increasing flow and may be an early and more sensitive indicator of pulmonary vascular disease. Given the fibrotic vasculopathy and microangiopathy that typify SSc, we hypothesized that SSc-PAH patients may have reduced pulmonary vascular distensibility compared to IPAH patients which may contribute to impaired right ventricular function. Methods We performed a retrospective observational study of patients who underwent supine bicycle exercise right heart catheterization. Participants included individuals with SSc without PH (SSc-no PH), SSc-PAH, and IPAH, defined as a mean PAP ≥25 mmHg and PVR 3 WU. Demographic, clinical, and physiologic data were collected. Hemodynamic data obtained at rest and with a standardized exercise protocol were used to estimate alpha-distensibility according to the Linehan model and compared among groups using the Kruskal-Wallis test with post-hoc pairwise group comparisons via Dunn’s test with adjustment for multiple comparisons. Results Seventy-three patients were analyzed: 16 SSc-no PH, 34 SSc-PAH, and 23 IPAH. Subjects were mostly women (N = 59, 80.8%), aged 56 ± 14 years, and predominantly white (N = 53, 72.6%). Most had WHO FC 2 symptoms with mild impairment in functional capacity by 6MWD (417 ± 112 m). Hemodynamic measurements obtained at rest and exercise showed expected differences in hemodynamic impairment between SSc-no PH and PAH subjects and similar impairment in SSc-PAH and IPAH. No differences in resting, peak, or delta pulmonary artery compliance were found. Median alpha-distensibility was 0.0035 0.0014-0.0074 %/mmHg in SSc-PAH and 0.0031 0.0020-0.0056 %/mmHg in IPAH (p = 0.62). SSc-no PH patients demonstrated higher alpha-distensibility (0.012 0.008-0.020 %/mmHg) than those with either form of PAH (p 0.005). Conclusion While pulmonary vascular distensibility was higher in SSc patients without PH compared to PAH patients, there were no differences in alpha-distensibility between patients with SSc-PAH and those with IPAH. This finding extends prior observations noting no differences in larger pulmonary vessel compliance between SSc-PAH and IPAH and may further implicate intrinsic right ventricular dysfunction as the primary driver of worse outcomes in SSc-PAH. This abstract is funded by: None