title: Decreased time constant of the pulmonary circulation in chronic thromboembolic pulmonary hypertension.
abstract: This study analyzed the relationship between pulmonary vascular resistance (PVR) and pulmonary arterial compliance (Ca) in patients with idiopathic pulmonary arterial hypertension (IPAH) and proximal chronic thromboembolic pulmonary hypertension (CTEPH). It has recently been shown that the time constant of the pulmonary circulation (RC time constant), or PVR × Ca, remains unaltered in various forms and severities of pulmonary hypertension, with the exception of left heart failure. We reasoned that increased wave reflection in proximal CTEPH would be another cause of the decreased RC time constant. We conducted a retrospective analysis of invasive pulmonary hemodynamic measurements in IPAH (n = 78), proximal CTEPH (n = 91) before (pre) and after (post) pulmonary endarterectomy (PEA), and distal CTEPH (n = 53). Proximal CTEPH was defined by a postoperative mean pulmonary artery pressure (PAP) of ≤25 mmHg. Outcome measures were the RC time constant, PVR, Ca, and relationship between systolic and mean PAPs. The RC time constant for pre-PEA CTEPH was 0.49 ± 0.11 s compared with post-PEA-CTEPH (0.37 ± 0.11 s, P < 0.0001), IPAH (0.63 ± 0.14 s, P < 0.001), and distal CTEPH (0.55 ± 0.12 s, P < 0.05). A shorter RC time constant was associated with a disproportionate decrease in systolic PAP with respect to mean PAP. We concluded that the pulmonary RC time constant is decreased in proximal CTEPH compared with IPAH, pre- and post-PEA, which may be explained by increased wave reflection but also, importantly, by persistent structural changes after the removal of proximal obstructions. A reduced RC time constant in CTEPH is in accord with a wider pulse pressure and hence greater right ventricular work for a given mean PAP.
authors.affiliation: Pulmonary Vascular Disease Unit, Papworth Hospital, Cambridge, UK.
authors.forename: Robert V
authors.initials: RV
authors.lastname: MacKenzie Ross
authors.forename: Mark R
authors.initials: MR
authors.lastname: Toshner
authors.forename: Elaine
authors.initials: E
authors.lastname: Soon
authors.forename: Robert
authors.initials: R
authors.lastname: Naeije
authors.forename: Joanna
authors.initials: J
authors.lastname: Pepke-Zaba
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D062186:Arterial Pressure; D006328:Cardiac Catheterization; D002908:Chronic Disease; D003187:Compliance; D016894:Endarterectomy, Carotid; D065627:Familial Primary Pulmonary Hypertension; D005260:Female; D006439:Hemodynamics; D006801:Humans; D006976:Hypertension, Pulmonary / Q000209:etiology* / Q000503:physiopathology / Q000601:surgery; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011651:Pulmonary Artery / Q000503:physiopathology* / Q000601:surgery; D011652:Pulmonary Circulation; D011655:Pulmonary Embolism / Q000150:complications* / Q000503:physiopathology / Q000601:surgery; D012189:Retrospective Studies; D012720:Severity of Illness Index; D013997:Time Factors; D016896:Treatment Outcome; D014655:Vascular Resistance; D018497:Ventricular Dysfunction, Right / Q000209:etiology / Q000503:physiopathology; D016278:Ventricular Function, Right
keywords: chronic thromboembolic pulmonary hypertension; hypertension; pulmonary; pulmonary arterial hypertension; pulmonary circulation; pulmonary endarterectomy