The Efficiency of Pulmonary Blood Transport Following Single Lung Transplantation

Perioperative right ventricular (RV) dysfunction remains a significant problem following single lung transplantation (SLT), especially in patients with pulmonary hypertension. Total RV power ( W t), a determinant of RV function, is the sum of the mean component ( W m) which contributes to actual blood flow and the oscillatory component ( W o) which is the energy expended on arterial pulsation. Calculation of W o is possible only through harmonic analysis of pulmonary arterial (PA) pressure and flow waveforms, and as much as 33% of RV power is attributed to it. The purpose of this study was to precisely quantify changes in RV power output using Fourier analysis of PA pressure and flow waveforms after SLT. Fourteen dogs (donors) were instrumented with a PA ultrasonic flow probe, PA and left atrial (LA) micromanometers, and LA epicardial pacing leads. Control (Pre-Tx) pressure-flow data were acquired during transient occlusion of the right PA at a heart rate of 140. The PA was cannulated, the lungs were flushed with 1 liter of modified Euro-Collins solution at 4°C, and the left lung was harvested and transplanted to 14 recipienT dogs in a standard manner. After 1 hr of reperfusion. PA (Post-Tx) pressure-flow data were acquired as above. All recipient animals survived SLT with a mean ischemic time of 183 ± 3 min. Following SLT, both the mean, W m, (69 ± 9 to 161 ± 23 mW) and oscillatory, W o, (23 ± 3 to 46 ± 10 mW) components of RV power output increased significantly after SLT ( P < 0.05). Transpulmonary vascular efficiency was derived by analyzing these data in terms of PA flow per milliwatt expended by the RV. Calculation of this index clearly shows that pulmonary blood transport is much less efficient immediately following SLT (Pre-Tx: 16.1 ± 1.2 vs Post-Tx: 10.3 ± 0.7 ml/min/mW, P < 0.002). This model may be applied to assess therapeutic interventions which improve the efficiency of pulmonary blood transport after SLT.