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BACKGROUND: Pulmonary vascular resistance (PVR) and compliance are comparable in proximal and distal chronic thromboembolic pulmonary hypertension (CTEPH). However, proximal CTEPH is associated with inferior right ventricular (RV) adaptation. Early wave reflection in proximal CTEPH may be responsible for altered RV function. The aims of the study are 1) investigate whether reflected pressure returns sooner in proximal than in distal CTEPH, and 2) elucidate whether timing of reflected pressure is related to RV dimensions, ejection fraction (RVEF), hypertrophy and wall stress.METHODS: Right heart catheterization and cardiac MRI were performed in 17 patients with proximal and 17 patients with distal CTEPH. In addition to determination of PVR, compliance and characteristic impedance, wave separation analysis was performed to determine the magnitude and timing of the peak reflected pressure (as % of systole). Findings were related to RV dimensions and time-resolved RV wall stress.RESULTS: Proximal CTEPH was characterized by higher RV volumes, mass and wall stress, and lower RVEF. While PVR, compliance and characteristic impedance were similar, proximal CTEPH was related to an earlier return of reflected pressure than distal CTEPH (proximal 53±8% vs. distal 63±15%, PCONCLUSIONS: Poor RV function in patients with proximal CTEPH is related to an early return of reflected pressure wave. PVR, compliance and characteristic impedance do not explain differences in RV function between proximal and distal CTEPH.

Right ventricular (RV) afterload is commonly defined as pulmonary vascular resistance, but this does not reflect the afterload to pulsatile flow. The purpose of this study was to quantify RV afterload more completely in patients with and without pulmonary hypertension (PH) using a three-element windkessel model. The model consists of peripheral resistance ( R), pulmonary arterial compliance ( C), and characteristic impedance ( Z). Using pulmonary artery pressure from right-heart catheterization and pulmonary artery flow from MRI velocity quantification, we estimated the windkessel parameters in patients with chronic thromboembolic PH (CTEPH; n = 10) and idiopathic pulmonary arterial hypertension (IPAH; n = 9). Patients suspected of PH but in whom PH was not found served as controls (NONPH; n = 10). R and Z were significantly lower and C significantly higher in the NONPH group than in both the CTEPH and IPAH groups ( P < 0.001). R and Z were significantly lower in the CTEPH group than in the IPAH group ( P < 0.05). The parameters R and C of all patients obeyed the relationship C = 0.75/ R ( R2 = 0.77), equivalent to a similar RC time in all patients. Mean pulmonary artery pressure P and C fitted well to C = 69.7/P (i.e., similar pressure dependence in all patients). Our results show that differences in RV afterload among groups with different forms of PH can be quantified with a windkessel model. Furthermore, the data suggest that the RC time and the elastic properties of the large pulmonary arteries remain unchanged in PH.