Computation of haemodynamic power and input impedance in the ascending aorta of patients undergoing open heart surgery.

Ascending aortic blood pressure and flow were successfully measured shortly after sternotomy in 16 patients undergoing coronary artery bypass graft surgery. Total haemodynamic power in the aorta was 953.9(444.7) mJ.s-1 (mean (SD], of which 11.65% was pulsatile. Quadrature components accounted for 50.8% of the pulsatile power. The mean (SD) term of the input impedance spectrum was 149.3(51.1) X 10(6) kg.m-4.s-1 and the characteristic impedance was 81.6(3.88) X 10(6) kg.m-4.s-1. Arterial pulsations are thought to be important for adequate tissue perfusion and the movement of tissue fluids and lymph. It is suggested that atheroma may increase the workload of the heart by diminishing the capacitative coupling between the aorta and the peripheral resistance vessels as well as pathological changes in other organs by impeding the lateral transmission of energy into the tissues.