BACKGROUND: In patients with proximal pulmonary artery (PA) thromboembolism, an increased PA resistance contributes to abnormal right ventricular (RV) afterload. However, the effects of proximal thromboembolism on the dynamic properties of RV afterload, which is determined by PA impedance, have not been analyzed quantitatively. The present study aimed to identify changes in PA impedance after the pulmonary perfusion volume was greatly reduced by unilateral proximal PA occlusion. METHODS AND RESULTS: Ten male Sprague-Dawley rats were used. PA flow and pressure waveforms were recorded during irregular pacing, before and 10 min after left PA occlusion. PA impedance was parameterized by using a three-element Windkessel model consisting of peripheral resistance (RP), arterial compliance (CP) and characteristic impedance (ZC). After proximal PA occlusion, PA impedance modulus increased over a frequency range of interest.ZCincreased significantly (after PA occlusion vs. baseline: 0.128±0.016 vs. 0.074±0.010 mmHg·min/ml, P<0.001), whereasCPandRPdid not change significantly. CONCLUSIONS: Proximal PA occlusion increasedZCwith the attenuation ofRPincrease andCPdecrease predicted from the decreased pulmonary perfusion volume. The insignificant changes inRPandCPindicate that a recruitment phenomenon may result in this attenuation. The existence of compensation by a recruitment mechanism suggests the relative importance of increasedZCin defining abnormal RV afterload in patients with proximal PA thromboembolism. (Circ J 2016; 80: 2010-2018).
BACKGROUND: In patients with proximal pulmonary artery (PA) thromboembolism, an increased PA resistance contributes to abnormal right ventricular (RV) afterload. However, the effects of proximal thromboembolism on the dynamic properties of RV afterload, which is determined by PA impedance, have not been analyzed quantitatively. The present study aimed to identify changes in PA impedance after the pulmonary perfusion volume was greatly reduced by unilateral proximal PA occlusion. METHODS AND RESULTS: Ten male Sprague-Dawley rats were used. PA flow and pressure waveforms were recorded during irregular pacing, before and 10 min after left PA occlusion. PA impedance was parameterized by using a three-element Windkessel model consisting of peripheral resistance (RP), arterial compliance (CP) and characteristic impedance (ZC). After proximal PA occlusion, PA impedance modulus increased over a frequency range of interest.ZCincreased significantly (after PA occlusion vs. baseline: 0.128±0.016 vs. 0.074±0.010 mmHg·min/ml, P<0.001), whereasCPandRPdid not change significantly. CONCLUSIONS: Proximal PA occlusion increasedZCwith the attenuation ofRPincrease andCPdecrease predicted from the decreased pulmonary perfusion volume. The insignificant changes inRPandCPindicate that a recruitment phenomenon may result in this attenuation. The existence of compensation by a recruitment mechanism suggests the relative importance of increasedZCin defining abnormal RV afterload in patients with proximal PA thromboembolism. (Circ J 2016; 80: 2010-2018).