Barium contracture: a model for systole.

Studies of cardiac mechanics, metabolism, and coronary hemodynamics have traditionally been carried out in rhythmically beating hearts. We have developed an isolated rabbit heart preparation that is free from contractions and allows a stable graded ventricular pressure to be established. Rabbit hearts were rapidly excised and perfused at constant pressure with heated (39 degrees C) Tyrode solution bubbled with 98% O2-2% CO2. A latex balloon was inserted into the left ventricle (lv) to adjust lv volume and measure pressure. Nine hearts were depleted of calcium by reducig the calcium concentration in the Tyrode's from 5 to 0.078 mM. When barium (Ba2+) was added to the perfusate, the hearts spontaneously developed pressure that was free of an overriding beat (contracture). The intensity of the contracture increased in a sigmoid fashion as the barium concentration was increased. During contracture balloon pressure ranged between 33.8 +/- 5.0% (SE) (Ba2+ 0.5 mM) and 79.0 +/- 4.5% (Ba2+ 1.5 mM) of control systolic developed pressure Ventricular pressure-volume curves were linear (r > 0.98) and indicated increased ventricular stiffness as barium concentration increased. We believe that barium-induced contracture is a good model of systolic cardiac muscle interactions.