It is Lawrence Medical Systems' hypothesis that noninvasive determination of cardiac output will identify the pathophysiologic basis of a patient's hypertension. That is, whether the hypertension is due to elevated cardiac output, increased systemic vascular resistance, or both. This knowledge will be useful in selecting the best antihypertensive regimen for individual patients, resulting in better blood pressure control, fewer medications, fewer adverse side effects, and better prescription compliance.In order to develop market potential, innovation is required in two areas:(1) The ease of use of noninvasive cardiac output measurement must be enhanced to match the expected operator skill levels found in the outpatient treatment setting.(2) Hypertension treatment practices must be changed from the accepted "stepped care" drug therapy protocols to one that selects the best drug treatment regimen based on each patient's hemodynamic pattern.In Phase I, Lawrence's current continuous cardiac output measurement system will be modified and its accuracy will be verified for use in the physician's o ce. Phase II will be a multi-center study of the benefits of hemodynamic-based, controlled drug therapy for hypertension.National Heart, Lung, and Blood Institute (NHLBI)