The purpose of this proposal is to evaluate the determinants of right ventricular (RV) function under variable loading conditions using high fidelity pressure monitoring and a cast-validated biplane cineangiographic method in patients with normal, pressure, and volume overloaded right ventricles. In addition, M-mode echocardiography and high fidelity pressure monitoring of the left ventricle (LV) will record concomitant LV dimensions and pressures. After a control study is performed, loading conditions will be altered by saline infusion to test the following hypotheses: 1) the RV is dependent upon the active length-tension relationship to a greater extent than the LV during volume loading; 2) exquisite afterload sensitivity will limit the augmentation of RV performance produced by volume loading; 3) septal shifting produced by RV dilatation during volume loading compromises LV filling and shifts the LV pressure-dimension relation upward and to the left. In order to evaluate RV contractile function independent of loading conditions maximum time varying elastance (Emax) will be derived by determining isochronal pressure-volume and stress-volume relations during altered loading. Intravenous nitroglycerin will be infused to decrease RV filling pressure and pulmonary artery systolic pressure below control values. Right ventricular high fidelity pressures and cineventriculography will be recorded thereby completing an evaluation of RV function at three loading conditions during control, after volume load, and during nitroglycerin infusion. The relation between RV Emax and end-systole or end-ejection will be compared using pressure (stress)-volume relations at the following points: 1) the maximum relation of RV pressure (stress) to volume, 2) minimum RV volume, and 3) zero pulmonary artery flow. Right ventricular wall stress will be calculated using M-mode echocardiography to measure RV free wall thickness and a method to calculate local myocardial wall stress which has been validated by Janz for the left ventricle. This investigation will provide new insights into the determinants of RV performance and the ability to apply concepts regarding peak systolic elastance to this chamber in patients with normal, pressure, and volume overloaded right ventricles.
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