Oscar H.L. Bing

Pericardial modulation of right and left ventricular diastolic interaction.

We studied the effects of the right ventricle (RV) and pericardium on left ventricular (LV) diastolic pressure-volume (P-V) relations in the normothermic isolated blood-perfused dog heart. Studies were performed at a constant heart rate (atrial pacing at 120 beats/min) with a coronary perfusion pressure of 100 mm Hg. LV volume was directly controlled by an intraventricular balloon, whereas RV filling pressure was increased stepwise from zero to 20 mm Hg. During progressive increases in RV filling pressure, with the pericardium intact, the LV diastolic P-V relations were shifted up and to the left; this leftward shift of the LV diastolic P-V relation was associated with an increase in the modulus of LV chamber stiffness. Closing the small pericardial incisions with sutures significantly increased this effect. In the absence of the pericardium, progressive filling of the RV resulted in minor changes in LV diastolic P-V relations. Only when the RV filling pressure was markedly elevated (20 mm Hg) was there a significant effect on LV diastolic pressure. The pericardium has a small but significant effect on LV diastolic P-V relations at physiological RV filling pressures, and this effect becomes considerable at high RV filling pressures. The RV influence on LV diastolic P-V relations is significantly modulated by the presence of tightness of the pericardium. Circ Res 48: 233-238, 1981

Loading Conditions and Left Ventricular Relaxation

Relaxation refers to the process by which the myocardium returns to its initial or resting length and tension; in the intact heart the term refers to the process by which the left ventricle returns to its presystolic or end diastolic pressure and volume. Relaxation is controlled by a complex interaction between deactivation (the time-dependent decay of active-force-generation capacity) and loading conditions (forces affecting myocardial length and tension). These forces may be subdivided into loads that are applied early in the cardiac cycle (contraction loads) and those that are abruptly applied late in the cycle (relaxation loads) (Table 14-1). Our rationale for separating early and late loads rests in the experimental observation that the application of an early or contraction load results in a more prolonged relaxation, whereas the application of a late or relaxation load results in a premature and more rapid relaxation; this latter phenomenon has been called “load dependent relaxation” [1].

Postextrasystolic compliance of the left ventricle.

The effects of a single premature contraction (PC) on left ventricular diastolic distensibility was studied in man, in the conscious chronically instrumented dog, and in the isolated (isovolumic) blood perfused dog heart. In the isolated dog heart at a constant volume, there was no difference in end-diastolic pressure when control diastolic pressure was compared to that following a PC. In man and conscious dogs, there was no difference between the overall pressure-volume or pressure-length plots when control diastolic data were compared to data from the diastole immediately following a PC (no change in the modulus of chamber stiffness). In the intact circulation of man and dog, increased filling during the post PC pause causes the ventricle to operate higher on the steep (stiffer) portion of its pressure-volume or pressure-length curve (decrease in preloaddependent compliance). Thus, although a PC does not alter the modulus of chamber stiffness, a preload-dependent change in compliance may occur during post PC diastole.

Isolated cardiac muscle performance during fluorocarbon immersion and effects of metabolic blockade.

Summary The mechanical performance of isolated trabecular muscle preparations from the left ventricle of rats was evaluated while immersed in Krebs-Henseleit and fluorocar-bon solution under oxygenated conditions and during hypoxia and total metabolic blockade with combined hypoxia and iodoa-cetic acid 10-4 M. Under oxygenated conditions, mechanical performance was relatively stable in both Krebs-Henseleit and fluorocar-bon solutions for 60 minutes. With glycolytic blockade, performance in both groups was relatively stable, although it was significantly increased in fluorocarbon solution in comparison to Krebs-Henseleit solution at 60 min (P < 0.01). With total metabolic blockade, mechanical performance fell to zero within 10 min in both Krebs-Henseleit and fluorocarbon solution. With hypoxia alone, mechanical performance declined more promptly and remained at lower levels in fluorocarbon solution than in Krebs-Henseleit solution (P < 0.001).

Myocardial protection by coronary washout during global ischemic cardiac arrest

The effect of intermittent coronary washout (WO) during global ischemic cardiac arrest (ICA) was evaluated in isolated blood perfused dog hearts undergoing 90 min normothermic ICA and 90 min reperfusion. WO consisted of infusion of 100 ml normothermic dog plasma at 100 mm Hg every 10 min during ICA. Systolic and diastolic pressures were measured at constant volume with a left ventricular balloon. Coronary blood flow (CBF) was measured, and transmyocardial oxygen, lactate, and glucose differences were calculated. Adenosine triphosphate (ATP), creatine phosphate (CP), calcium (Ca2+), glycogen, and water content were measured from left ventricular biopsies. During 90 min of WO, hearts extracted glucose (15 ± 4 mg/g dry wt LV) and lost lactate (90 ± 5 μmole/g dry wt LV). ATP and CP were significantly depressed at arrest in both groups although WO resulted in significantly higher levels of ATP and CP. CP returned to control levels at 90 min reperfusion in the WO group but remained depressed in the ICA group. Calcium accumulation was greater in hearts with ICA. With reperfusion, both ICA and WO groups demonstrated early hyperemia and rapid lactate washout. There were no differences in total CBF, AVO2, MOV2, and myocardial glycogen or water content. Systolic performance was equally depressed in both groups at 90 min of reperfusion. Diastolic compliance, while still impaired, was better preserved in WO when measured in the arrested heart at 90 min ICA (P < 0.01) and in the contracting heart after 90 min reperfusion (P < 0.02). Normothermic coronary washout during 90 min of normothermic ischemic arrest without cardioplegic agents produces improved ventricular compliance and energy metabolism, and reduces myocardial calcium accumulation.

Effect of temperature change on the tolerance of isolated contracting cardiac muscle to hypoxia

Abstract The effects of graded temperature changes on tolerance to hypoxia are evaluated in isometrically contracting isolated muscle preparations from the rat. After equilibration at 28 °C, the temperature was changed to either 21 ° or 35 °C. Mechanical performance was measured after temperature change, during 60 min of hypoxia at a given temperature and a subsequent 30 min-period of reoxygenation at 28 °C. Performance as measured by (1) developed tension, (2) contracture tension, and (3) recovery on reoxygenation was diminished by raising temperature to 35 °C during hypoxia while no change in tolerance was demonstrated by lowering temperature from 28 ° to 21 °C.

A STOIC-based application language for muscle mechanics research

An application language for the control and analysis of isolated cardiac muscle experiments is described. It is defined using an extensible language, STOIC (derived from FORTH), which consists of a set of basic operations called words. The basic words are readily combined to form higher level words which perform more complex operations. A suitable set of higher level words forms an application language. The resulting language takes full advantage of system hardware capabilities, is easily used by those with little programming experience, and provides flexibility in a research environment where experimental protocols frequently change.

Myocardial relaxation. I. Effect of nitroprusside on the tension prolongation phenomenon

The effects of nitroprusside and cyanide on myocardial relaxation were studied during hypoxia and reoxygenation of isolated rat papillary muscle, and during segmental ischemia and reperfusion in the intact dog heart. Nitroprusside did not affect isolated muscle performance before or during hypoxia. During reoxygenation of hypoxic muscles, the tension prolongation phenomenon (which characterizes abnormal or prolonged relaxation) was only slightly attenuated by the addition of nitroprusside to the muscle bath; in contrast, cyanide (at concentrations that did not prevent the return of tension) abolished tension prolongation during reoxygenation. During reperfusion of ischemic segments in intact hearts, the prolongation of segment tension was not affected by systemic administration of nitroprusside, but was abolished by intracoronary cyanide. Attenuation of the tension prolongation phenomenon by nitroprusside in the isolated muscle may be due to the liberation of cyanide. Inasmuch as nitroprusside did not affect the tension prolongation phenomenon in the intact heart, it is unlikely that the influence of this drug on left ventricular diastolic compliance is mediated through an alteration in the tension prolongation phenomenon.