Pulmonary arterial compliance: a physiological variable still searching for clinical relevance?

• Published in: Heart (British Cardiac Society) Vol. 109; no. 14; pp. 1052 - 1053
• Main Authors: Kearney, Katherine, Lau, Edmund M
• Format: Journal Article
• Language: English
• Published: England BMJ Publishing Group Ltd and British Cardiovascular Society 01.07.2023; BMJ Publishing Group LTD
• Subjects: Clinical Relevance; Compliance; Editorial; Heart rate; Hemodynamics; Humans; Hypertension, Pulmonary; Medical prognosis; Mortality; Physiology; Pulmonary Arterial Hypertension; Pulmonary arteries; Pulmonary Artery; Pulmonary hypertension; Risk assessment; Thromboembolism; Variables; Veins & arteries; Pulmonary Arterial Hypertension
• ISSN: 1355-6037; 1468-201X
• DOI: 10.1136/heartjnl-2022-322222

At the systemic level, higher aortic stiffness or its inverse (compliance) is associated with an increased risk of cardiovascular events independent of traditional risk factors. An early small single-centre study of 104 patients with idiopathic PAH demonstrated that PAC was a powerful predictor of mortality.2 However, subsequent studies including a large registry study of nearly 1000 patients with idiopathic PAH found that PAC, after multivariable analysis, was no longer a predictor of prognosis at both diagnosis and first follow-up.3 Pulmonary hypertension specialists will all be familiar with the current ‘PAH risk assessment’ which encompass a multidimensional approach to stratify patients into low, intermediate and high risk as a way to guide the therapeutic decision. More recent research have clarified this to not be strictly accurate, with studies showing that RC time is shortened with higher left atrial filling pressure,6 in chronic thromboembolic pulmonary hypertension7 and RC time also changes with heart rate and body surface area.8 McCormick et al9 used data from the Pulmonary Hypertension Association (PHAR) registry to further investigate differences in PAC and RC time among different subtypes of PAH, and whether PAC was an independent predictor of survival in a large, real-world dataset, beyond the predictive value of a validated risk score. Consistent with these findings, isobaric PAC (ie, PAC adjusted for mean pulmonary artery pressure) was highest for drug/toxin-induced PAH, followed by idiopathic PAH and lowest in CTD-PAH. Since compliance is intrinsically influenced by the distending pressure due to non-linear stress–strain behaviour of arteries, PAC adjusted for mean pulmonary artery pressure suggests that the CTD-PAH group have pulmonary arteries with the greatest remodelling in the mechanical properties of the arterial wall.