RESUMEN
Three indices of regional coronary flow were tested to determine if a good correlation between calculated driving pressure and flow could be found. Four different myocardial depths were examined. All three indexes were based on subtraction of a backpressure to flow. The first assumed backpressure to be equal to ventricular pressure; the second assumed backpressure to be twice ventricular pressure; and the third index assumed backpressure to be zero and thus was simply coronary pressure. Only the index that used left ventricular pressure as the backpressure to flow exhibited proportionality for the subendocardial samples. Similarly, only coronary pressure yielded a good fit for the subepicardial samples. Although subendocardial flow was always in proportion to the index, the index was poor at predicting the absolute value of that flow. The usefulness of such a directional predictor of subendocardial perfusion was illustrated by examining the phase shift resulting from partial occlusion of a coronary artery. The index predicted that subendocardial flow would be lower when coronary pressure was reduced by partially occluding the coronary vessel than when it was presented with an equivalent steady pressure. Microsphere measurements confirmed this prediction. We conclude that an index that assumes ventricular pressure to be the backpressure to flow is an accurate predictor of relative changes in subendocardial perfusion.
Asunto(s)
Presión Sanguínea , Circulación Coronaria , Perros/fisiología , Flujo Sanguíneo Regional , Animales , Radioisótopos de Cesio , Radioisótopos de Cromo , Endocardio/fisiología , Femenino , Masculino , Microesferas , Valores de Referencia , EstroncioRESUMEN
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.
Asunto(s)
Bario/farmacología , Tono Muscular/efectos de los fármacos , Contracción Miocárdica/efectos de los fármacos , Sístole/efectos de los fármacos , Animales , Presión Sanguínea , Circulación Coronaria , Conejos , Flujo Sanguíneo RegionalRESUMEN
Following a case of mannitol-induced respiratory and circulatory collapse, the effects of hyperosmolar injections on pulmonary arterial pressure, systemic blood pressure, and cardiac output were studied in dogs. The injection of 20 ml of 10% NaCl into the pulmonary artery increased pulmonary arterial pressure and decreased systemic blood pressure by approximately 50% of control values. Injections of solutions of equal hyperosmolar strength, 50 ml of 25% mannitol or 50 ml of 4% NaCl into the pulmonary artery produced no significant elevation of pulmonary arterial pressure, but were associated with comparable decreases in systemic blood pressure. When allowed to vary, cardiac output increased with injections of all three hyperosmolar solutions, yet was still accompanied by falls in systemic blood pressure as large as when cardiac output was held constant. Vagotomy did not prevent these changes in systemic and pulmonary arterial pressure, nor the increase in cardiac output. After five to 10 injections, the decreases in system blood pressure with any of the solutions and the increases in pulmonary arterial pressure with 10% NaCl disappeared and further injections were without effect. It is concluded that adminstration of mannitol probably does not cause pulmonary edema due to fluid overload, nor does it cause heart failure as evidenced by increases in pulmonary arterial pressure. However, rapid injection may cause a fall in blood pressure and may on occasion be accompanied by bronchospasm, especially in sensitive subjects.