Relationship between compliance and pulmonary vascular resistance in pulmonary arterial hypertension

Background: Pulmonary arterial compliance (PAC) was previously shown to be an important prognostic factor in pulmonary arterial hypertension (PAH), in addition to the conventional pulmonary vascular resistance (PVR). The product of PAC and PVR, the arterial time (RC) constant, expresses the logarithmic relationship between the hemodynamic parameters. The objective of the study was to test RC constant stability in PAH patients followed beyond 12 months after diagnosis, and to report possible RC variations in different etiologies. Methods: Fourteen PAH patients followed between 2008 and 2019 were included. Type 1 PAH was defined as a mean pulmonary artery pressure (PAP) >= 25 mmHg at rest and PVR >= 3 Wood units (WU). All patients who fulfilled WHO group I PAH criteria and had undergone two right heart catheterization at least 1 year apart were included. The recorded hemodynamic data for each patient were used to compute PVR and PAC. Results: PAH etiologies included scleroderma (n=2), liver cirrhosis (n=1), hereditary hemorrhagic telangiectasia (HUT) (n=1), mixed connective tissue disease (MCTD) (n=3), and idiopathic (n=7). The RC constant remained stable for all 14 patients over a follow-up period of 3.9 +/- 2 years. Patients with MCTD displayed more favorable hemodynamics, evidenced by higher RC (12.54 vs. 10.01, P<0.01) and PAC values (2.59 vs. 1.62, P=0.02), when compared with non-MCTD PAH patients. For the entire cohort the mean PAP measured 51 +/- 14 mmHg at baseline, and 46 +/- 13 mmHg at follow-up, respectively. Conclusions: The relationship between PAC and PVR remains stable in follow-up periods averaging 4 years, making compliance an important disease marker past the early stages. Patients with MCTD displayed more advantageous hemodynamic profiles when compared with patients with other PAH etiologies.