Steady and Pulsatile Energy Losses in the Systemic Circulation under Normal Conditions and in Simulated Arterial Disease

External left ventricular work was calculated from records of pressure and flow in the ascending aorta of 1 unanaesthetized and 21 anaesthetized dogs. Work was divided into pulsatile and steady components, the former representing energy lost in vascular pulsations and the latter, energy lost in maintaining steady flow. The ratio of pulsatile to total (steady + pulsatile) external work averaged 10% under control conditions but increased markedly when heart rate slowed, when cardiac output rose, or when arterial distensibility was impaired.