The automatic computation of pressure-derived maximal shortening velocity (Vmax) of the unloaded contractile element in the intact canine heart left ventricle

Myocardial Contractility: Historical and Contemporary Considerations

The term myocardial contractility is thought to have originated more than 125 years ago and has remained and enigma ever since. Although the term is frequently used in textbooks, editorials and contemporary manuscripts its definition remains illusive often being conflated with cardiac performance or inotropy. The absence of a universally accepted definition has led to confusion, disagreement and misconceptions among physiologists, cardiologists and safety pharmacologists regarding its definition particularly in light of new discoveries regarding the load dependent kinetics of cardiac contraction and their translation to cardiac force-velocity and ventricular pressure-volume measurements. Importantly, the Starling interpretation of force development is length-dependent while contractility is length independent. Most historical definitions employ an operational approach and define cardiac contractility in terms of the hearts mechanical properties independent of loading conditions. Literally defined the term contract infers that something has become smaller, shrunk or shortened. The addition of the suffix “ility” implies the quality of this process. The discovery and clinical investigation of small molecules that bind to sarcomeric proteins independently altering force or velocity requires that a modern definition of the term myocardial contractility be developed if the term is to persist. This review reconsiders the historical and contemporary interpretations of the terms cardiac performance and inotropy and recommends a modern definition of myocardial contractility as the preload, afterload and length-independent intrinsic kinetically controlled, chemo-mechanical processes responsible for the development of force and velocity.

Systolic time intervals in canine experimental acute hemorrhagic pancreatitis

The effect of experimental acute hemorrhagic pancreatitis on hemodynamics and systolic time intervals were studied simultaneously by catheterization in dogs. Following the initial hemodynamic measurements pancreatitis was induced by a mixture of trypsin and sodium taurocholate infused into the pancreatic duct (PG, n = 7). After 60 min of surveillance the hemodynamic measurements were repeated and the results were compared to those obtained from the sham-operated group (CG, n = 7) paced at a similar contraction frequency to the PG after the follow-up time. Left ventricular ejection time (LVET) and the ratio of PEP/LVET (PEP, preejection period) increased more in the PG than in the CG (P less than 0.05 and P less than 0.001, respectively). This was related to a lower left ventricular end-diastolic volume and pressure in the PG in comparison to the CG (P less than 0.05). PEP remained unaltered in both groups during the interventions. No significant differences between the groups were observed in the responses of the maximum value of the left ventricular systolic pressure rise (dP/dtmax). The ejection fraction decreased more in the PG than in the CG (P less than 0.05), which was related to the decreased end-diastolic volume in the PG (P less than 0.001). Mean aortic pressure decreased significantly in the PG (P less than 0.01). The results indicate that experimental acute hemorrhagic pancreatitis leads to altered loading conditions of the heart and causes marked alterations in the systolic phases of the contraction cycle. This model of experimental pancreatitis does not depress the myocardial contractility on the basis of these results.

Impaired venous return causes circulatory failure in experimental pancreatitic shock in dogs

The haemodynamic effects in the early phase of canine acute experimental pancreatitis (AP) were studied using a cardiac catheterization technique. AP was induced in anaesthetized dogs with an infusion of trypsin-sodium-taurocholate into the pancreatic duct. The initial haemodynamic measurements were performed after the preparation of the animal and 5 min after the induction of AP. Thereafter, pressure and volume parameters were measured at 10 min intervals. AP induced significant increases in heart rate, dP/dtmax and mean arterial pressure, but a decrease in Vmax 5 min after the induction of AP. After the initial phase, the heart rate remained significantly increased, while constant and significant decreases of stroke volume, cardiac output, end-diastolic volume and end-diastolic pressure developed. The parameters of the contractility of the left ventricle were not affected to the same extent. It is suggested that the circulatory failure observed in AP, characterised by a prompt reduction of cardiac output, was primarily due to a heavy reduction in preload. This supports the theory that cardiac output is primarily affected by impaired venous return with consequently decreased preload rather than by a loss of ventricular contractility. Hence, the existence of a myocardial depressant factor in the early phase of experimental AP does not gain support from the present results.

Myocardial contractility, blood flow, and oxygen consumption in healthy dogs during anesthesia with isoflurane or enflurane

Left ventricular contractility (Vmax), myocardial blood flow (MBF), and oxygen consumption (O2C) were determined together with systemic hemodynamic parameters in a total of 21 mongrel dogs. Baseline recordings were obtained under basal anesthetic conditions with a narcotic (piritramid, IV). In the control group (n = 7), recordings were obtained during a three-hour observation period with infusion of piritramid. In experimental groups measurements were repeated with equi-anesthetic concentrations of isoflurane (0.7 and 1.4 vol%; n = 8) and enflurane (1.1 and 2.2 vol%; n = 6). Dose-dependent reductions of arterial pressure, cardiac output (CO) and peripheral vascular resistance were observed with isoflurane and enflurane. CO at the higher anesthetic level was depressed significantly more with enflurane. This difference was obviously due to a more severe depression of myocardial contractility with enflurane; Vmax was decreased by 18% and 26% with enflurane, but only by 10% and 17% with isoflurane (P less than 0.01). MBF and the fraction of CO received by the heart were increased above their baseline values with both concentrations of isoflurane. In contrast, the fraction of CO remained constant with enflurane while MBF decreased. O2C was reduced due to decreases of afterload and left ventricular contractility. The reduction was greater with enflurane than with isoflurane. All parameters remained unchanged in the control group. The results of this study indicate that the most striking difference in the actions of isoflurane and enflurane on cardiac parameters is on myocardial vascular resistance; MBF is increased with isoflurane, but is decreased with enflurane although myocardial perfusion pressure is reduced by almost identical amounts.(ABSTRACT TRUNCATED AT 250 WORDS)

Anabolic steroids alter the haemodynamic effects of endurance training on the canine left ventricle

The effects of six week, high-dose anabolic steroid treatment (methandienone, 1.5 mg/kg/day) on the changes in left ventricular function induced in dogs by endurance training were studied by a catheterization technique under anaesthesia. Pacing, isoproterenol and dextran infusions were used as loading tests (respectively). Dogs were randomized into an exercise group (EG, n = 7) and an exercise-steroid group (ESG, n = 7), the latter receiving anabolic steroids as well as participating in the training program. In a standardized submaximal exercise test, the heart rate of unanesthetized dogs was lower both in the EG (p less than 0.001) and in the ESG (p less than 0.01) after the training period than before it. In the EG the resting systemic vascular resistance (SVR) before haemodynamic interventions was lower (p less than 0.05) and left ventricular stroke work (SW) was higher (p less than 0.05) after the training period than before. In the ESG, left ventricular ejection fraction (EF) decreased with training and anabolic steroid treatment (p less than 0.05). After the training period isoproterenol increased the maximum velocity of the cardiac contractile element significantly more (p less than 0.05) in the EG than in the ESG. Also SW increased in the EG (29%, p less than 0.001), but not in the ESG (-11%, NS). Endurance training increased the left ventricular end-diastolic and stroke volumes during isoproterenol infusion, but this training effect was attenuated by simultaneous anabolic steroid treatment (p less than 0.05 between the groups in both cases). During the isoproterenol test SVR decreased less in ESG than in EG (p less than 0.05 between).(ABSTRACT TRUNCATED AT 250 WORDS)

Anabolic steroids alter the haemodynamic responses of the canine left ventricle

The effect of an anabolic steroid on canine left ventricular function was studied by catheterization exposing control (n = 7) and methandienone-treated (n = 6) dogs to pacing, volume and isoproterenol tests at the beginning of the experiment and 6 weeks later. The physical performance of the animals was evaluated by submaximal exercise test (SMT), in which the steroid-treated dogs had lower heart rate than the sedentary controls (P less than 0.001). Heart weight was greater in the steroid than in the control group (P less than 0.05). Isoproterenol infusion increased the maximum value of the left ventricular pressure curve (dP/dtmax) less in the steroid-treated than in the control animals (P less than 0.05). Also heart rate was lower in the steroid than in the control group after inotropic load, while end-diastolic, end-systolic and stroke volumes decreased significantly more in the control group (P less than 0.05). Systemic vascular resistance decreased in the steroid treated animals, but remained unchanged in the control group (P less than 0.05 between the groups). During volume overload dP/dtmax increased in the control group but decreased slightly in the steroid group (P less than 0.05 between the groups). The pressure-volume diagram showed that the left ventricle of the steroid-treated animals worked on higher ventricular volumes than in the control group. In conclusion, long-term methandienone treatment results in cardiac hypertrophy in dogs, reduces its response to an inotropic loads and leads to working on larger ventricular volumes.