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In patients with a Mustard operation and failing right ventricle, pulmonary artery banding (PAB) is often performed to condition the left ventricle (LV) for a systemic afterload preparation for an arterial switch operation. It is assumed that once a systemic peak pressure is achieved pressure is achieved with PAB, the workload presented to the LV is equivalent to the systemic arterial afterload. In the cardiovascular system, work is comprised of both steady work (energy utilized to maintain volume flow) and oscillatory work (energy lost due to pulsations). The purpose of this study is to illustrate that the workload of a proximal obstruction is different from the workload of high peripheral resistance. Methods: This study was performed using a 3 element Windkessel in vitro flow model of three afterload conditions: (1) systemic, (2) pulmonary, and (3) banded pulmonary arterial afterload. The flow rate was 4.2 l/min and the pulse rate was 60 bpm for each condition. Simultaneous pressure (P) and flow (Q) waveforms from the ascending aorta of the model were recorded and resolved into ten harmonies using Fourier series analysis. Static work was calculated as Pmean·Qmean. Pulsatile work was calculated as 1/2 Σ PiQi cosΘ, where Pi and Qi are the magnitudes of the ith pressure and flow harmonics, respectively. Θ represents the phase angle between P and Q. Results: For systemic arterial flow, proximal arterial pressure was 120/75 mmHg, peripheral resistance 23 Wood units. Pulmonary arterial pressure was 27/14, resistance 4.5. When this was banded, the pressure proximal to the band increased to 119/16. For these conditions, the workload data are: (Table)Conclusions: The usual workload for the cardiovascular is less than 10% pulsatile, as illustrated in our flow model. When a proximal obstruction is placed on the pulmonary system, the total work approximates that of the systemic afterload, but a much larger portion of this is pulsatile work. Proximal pulmonary artery banding may not provide the physiologic stimulus for hypertrophy, and may explain in part why some patients do not respond to this load with expected increase in LV mass.
Tacy, T., Iyengar, A. & Teitel, D. Proximal Pulmonary Artery Banding Does Not Simulate a Systemic Afterload for Conditioning a Left Ventricle in Mustard Patients.
Pediatr Res45, 31 (1999). https://doi.org/10.1203/00006450-199904020-00193
