Mechanisms of contraction of the normal and failing heart

New perspectives in the echocardiographic hemodynamics multiparametric assessment of patients with heart failure

International Guidelines consider left ventricular ejection fraction (LVEF) as an important parameter to categorize patients with heart failure (HF) and to define recommended treatments in clinical practice. However, LVEF has some technical and clinical limitations, being derived from geometric assumptions and is unable to evaluate intrinsic myocardial function and LV filling pressure (LVFP). Moreover, it has been shown to fail to predict clinical outcome in patients with end-stage HF. The analysis of LV antegrade flow derived from pulsed-wave Doppler (stroke volume index, stroke distance, cardiac output, and cardiac index) and non-invasive evaluation of LVFP have demonstrated some advantages and prognostic implications in HF patients. Speckle tracking echocardiography (STE) is able to unmask intrinsic myocardial systolic dysfunction in HF patients, particularly in those with LV preserved EF, hence allowing analysis of LV, right ventricular and left atrial (LA) intrinsic myocardial function (global peak atrial LS, (PALS)). Global PALS has been proven a reliable index of LVFP which could fill the gaps "gray zone" in the previous Guidelines algorithm for the assessment of LV diastolic dysfunction and LVFP, being added to the latest European Association of Cardiovascular Imaging Consensus document for the use of multimodality imaging in evaluating HFpEF. The aim of this review is to highlight the importance of the hemodynamics multiparametric approach of assessing myocardial function (from LVFP to stroke volume) in patients with HF, thus overcoming the limitations of LVEF.

One step closer to myocardial physiology: From PV loop analysis to state-of-the-art myocardial imaging

Recent advances in cardiac imaging have revitalized the assessment of fundamental physiological concepts. In the field of cardiac physiology, invasive measurements with pressure-volume (PV) loops have served as the gold standard methodology for the characterization of left ventricular (LV) function. From PV loop data, fundamental aspects of LV chamber function are derived such as work, efficiency, stiffness and contractility. However, the parametrization of these aspects is limited because of the need for invasive procedures. Through the utilization of recent advances in echocardiography, magnetic resonance imaging and positron emission tomography, it has become increasingly feasible to quantify these fundamental aspects of LV function non-invasively. Importantly, state-of-the-art imaging technology enables direct assessment of myocardial performance, thereby extending functional assessment from the net function of the LV chamber, as is done with PV loops, to the myocardium itself. With a strong coupling to underlying myocardial physiology, imaging measurements of myocardial work, efficiency, stiffness and contractility could represent the next generation of functional parameters. The purpose of this review is to discuss how the new imaging parameters of myocardial work, efficiency, stiffness and contractility can bring cardiac physiologists, researchers and clinicians alike one step closer to underlying myocardial physiology.

Secreted Frizzled-Related Protein 5 Protects Against Cardiac Rupture and Improves Cardiac Function Through Inhibiting Mitochondrial Dysfunction

Background: Secreted frizzled-related protein 5 (Sfrp5) has been suggested to be a protective regulatory protein in coronary heart disease. However, the role of Sfrp5 in regulating ischemic injury and its consequences is not known. The aim of our study was to explore the effects of Sfrp5 on hearts after myocardial infarction (MI) and to investigate the underlying mechanisms.

Methods and Results: We found that Sfrp5 was downregulated over time in the heart tissue of MI mice. To further elucidate the role of Sfrp5 during MI, we established a cardiac overexpression of an Sfrp5 mouse model using the cardiotropic adeno-associated virus serotype 9 (AAV9). Overexpression of Sfrp5 significantly reduced infarct size as demonstrated by a decrease in mortality owing to cardiac rupture. Moreover, cardiac overexpression of Sfrp5 increased left ventricular function and mitochondrial biogenesis, decreased cardiomyocyte apoptosis, suppressed inflammation reaction, inhibited oxidative stress, and ameliorated cardiac remodeling as demonstrated by left ventricular ejection fraction, mitochondrial morphology, heart weight, NADH oxidase activity levels, and myocardial fibrosis at 2 weeks post-MI. At the molecular level, overexpression of Sfrp5 significantly increased the expression of p-AMPK^Thr172 protein with higher expression of mitochondrial fusion protein (MFN1 and MFN2) and lower expression of mitochondrial fission protein (p-Drp1^Ser616/Mid49/MFF/Fis-1). In isolated neonatal rat cardiac myocytes, Sfrp5 treatment attenuated hypoxia-induced mitochondrial dysfunction. Inhibition of AMPK activity with compound C abrogated this benefit.

Conclusions: Sfrp5 overexpression inhibits ischemic injury, reduces risk of cardiac rupture, ameliorates post-MI remodeling, and decreases the progression to heart failure via disrupting mitochondrial dysfunction and partly through normalizing the AMPK activity.

Perioperative fluid management in kidney transplantation: a black box

The incidence of delayed graft function in patients undergoing kidney transplantation remains significant. Optimal fluid therapy has been shown to decrease delayed graft function after renal transplantation. Traditionally, the perioperative volume infusion regimen in this patient population has been guided by central venous pressure as an estimation of the patient’s volume status and mean arterial pressure, but this is based on sparse evidence from mostly retrospective observational studies. Excessive volume infusion to the point of no further fluid responsiveness can damage the endothelial glycocalyx and is no longer considered to be the best approach. However, achievement of adequate flow to maintain sufficient tissue perfusion without maximization of cardiac filling remains a challenge. Novel minimally invasive technologies seem to reliably assess volume responsiveness, heart function and perfusion adequacy. Prospective comparative clinical studies are required to better understand the use of dynamic analyses of flow parameters for adequate fluid management in kidney transplant recipients. We review perioperative fluid assessment techniques and discuss conventional and novel monitoring strategies in the kidney transplant recipient.

Periodontitis and bone metabolism in patients with advanced heart failure and after heart transplantation

AIMS

Heart failure (HF) is a multi-organ, pro-inflammatory syndrome that impairs bone metabolism. Pro-inflammatory cytokines and bone catabolism enhance periodontal disease, a local inflammatory, bacteria-induced disease that causes bone loss and periodontal soft tissue destruction.

METHODS AND RESULTS

Medical and dental examinations were performed on patients with HF (n = 39), following heart transplantation (post-HTx, n = 38) and controls (n = 32). Blood, saliva, and gingival crevicular fluid were analysed for bone metabolism and inflammation markers. HF average New York Heart Association classification was III. Average time since HTx was 1414 days. Pro-inflammatory tumour necrosis factor-alpha was higher in HF and HTx as compared with controls (P < 0.05). Both HF and HTx participants had higher levels of bone resorption marker C-terminal telopeptide and parathyroid hormone with subjects in the HF group having the highest serum levels of all groups (P ≤ 0.05). In contrast, 25-hydroxyvitamin D was lowest in HF. HF patients had greater clinical attachment loss, cumulative pockets depth (greater than 3 mm) and probing depth (P < 0.05) as compared with controls. Cumulative pockets depth correlated significantly with measures of the inflammatory burden, β-glucuronidase in saliva (r = 0.4863, P < 0.01), interleukin-1b in saliva (r = 0.5149, P < 0.01), and gingival crevicular fluid (r = 0.6056, P < 0.001) in HF. However, adjustment of periodontal results for measures of oral hygiene (plaque, bleeding on probing), systemic 25-hydroxyvitamin D, and race attenuated significant differences between groups.

CONCLUSIONS

Patients with HF exhibit more severe periodontal disease associated with increased bone turnover markers when compared with control patients. However, local and systemic factors may account for this association and should be evaluated in future studies.

"Freeze, Don't Move": How to Arrest a Suspect in Heart Failure - A Review on Available GRK2 Inhibitors

Cardiovascular disease and heart failure (HF) still collect the largest toll of death in western societies and all over the world. A growing number of molecular mechanisms represent possible targets for new therapeutic strategies, which can counteract the metabolic and structural changes observed in the failing heart. G protein-coupled receptor kinase 2 (GRK2) is one of such targets for which experimental and clinical evidence are established. Indeed, several strategies have been carried out in place to interface with the known GRK2 mechanisms of action in the failing heart. This review deals with results from basic and preclinical studies. It shows different strategies to inhibit GRK2 in HF in vivo (βARK-ct gene therapy, treatment with gallein, and treatment with paroxetine) and in vitro (RNA aptamer, RKIP, and peptide-based inhibitors). These strategies are based either on the inhibition of the catalytic activity of the kinase (“Freeze!”) or the prevention of its shuttling within the cell (“Don’t Move!”). Here, we review the peculiarity of each strategy with regard to the ability to interact with the multiple tasks of GRK2 and the perspective development of eventual clinical use.

Left Ventricle-Arterial System Interaction in Heart Failure

Ejection fraction (EF) has been viewed as an important index in assessing the contractile state of the left ventricle (LV). However, it is frequently inadequate for the diagnosis and management of heart failure (HF), as a significant subset of HF patients have been found to have reduced EF (HFrEF) whereas others have preserved EF (HFpEF). It should be noted that the function of the LV is dependent on both preload and afterload, as well as its intrinsic contractile state. Furthermore, stroke volume (SV) is dependent on the properties of the arterial system (AS). Thus, the LV-arterial system interaction plays an important role in those patients with HF. This aspect is investigated through the analysis of the specific parameters involved in the coupling of the LV and AS. This includes contractility and the systolic/diastolic indices of the LV. Furthermore, AS afterload parameters such as vascular stiffness and arterial compliance, and their derived coupling coefficient, are also investigated. We conclude that those parameters, which relate to LV structural changes, are most appropriate in quantifying the LV-AS interaction.

Heart failure

Despite major improvements in the treatment of virtually all cardiac disorders, heart failure (HF) is an exception, in that its prevalence is rising, and only small prolongations in survival are occurring. An increasing fraction, especially older women with diabetes, obesity, and atrial fibrillation exhibit HF with preserved systolic function. Several pathogenetic mechanisms appear to be operative in HF. These include increased hemodynamic overload, ischemia-related dysfunction, ventricular remodeling, excessive neurohumoral stimulation, abnormal myocyte calcium cycling, excessive or inadequate proliferation of the extracellular matrix, accelerated apoptosis, and genetic mutations. Biomarkers released as a consequence of myocardial stretch, imbalance between formation and breakdown of extracellular matrix, inflammation, and renal failure are useful in the identification of the pathogenetic mechanism and, when used in combination, may become helpful in estimating prognosis and selecting appropriate therapy. Promising new therapies that are now undergoing intensive investigation include an angiotensin receptor neprilysin inhibitor, a naturally-occurring vasodilator peptide, a myofilament sensitizer and several drugs that enhance Ca++ uptake by the sarcoplasmic reticulum. Cell therapy, using autologous bone marrow and cardiac progenitor cells, appears to be promising, as does gene therapy. Chronic left ventricular assistance with continuous flow pumps is being applied more frequently and successfully as destination therapy, as a bridge to transplantation, and even as a bridge to recovery and explantation. While many of these therapies will improve the care of patients with HF, significant reductions in prevalence will require vigorous, multifaceted, preventive approaches.

Role of cardiac stem cells in cardiac pathophysiology: a paradigm shift in human myocardial biology

For nearly a century, the human heart has been viewed as a terminally differentiated postmitotic organ in which the number of cardiomyocytes is established at birth, and these cells persist throughout the lifespan of the organ and organism. However, the discovery that cardiac stem cells live in the heart and differentiate into the various cardiac cell lineages has changed profoundly our understanding of myocardial biology. Cardiac stem cells regulate myocyte turnover and condition myocardial recovery after injury. This novel information imposes a reconsideration of the mechanisms involved in myocardial aging and the progression of cardiac hypertrophy to heart failure. Similarly, the processes implicated in the adaptation of the infarcted heart have to be dissected in terms of the critical role that cardiac stem cells and myocyte regeneration play in the restoration of myocardial mass and ventricular function. Several categories of cardiac progenitors have been described but, thus far, the c-kit-positive cell is the only class of resident cells with the biological and functional properties of tissue specific adult stem cells.

Cardiac efficiency

Efficiency is defined as the ratio of the energy delivered by a system to the energy supplied to it. Depending on the particular question being addressed, there exist a plethora of definitions of efficiency in medical texts, thus hampering their comparison. If only the ventricular work seen by the arterial system is under investigation, pressure-volume work will serve as a useful numerator. If, on the other hand, external and internal work together, i.e. the total mechanical work, is of interest, the pressure-volume area might be employed. Total myocardial oxygen consumption (MVO2) will be a useful denominator in the case of aerobic energy production. The MVO2 for the unloaded contraction must be assessed if, as in other energy transfer systems, net efficiency is to be addressed. If even smaller steps in the chain of energy transfer are to be investigated MVO2 for the arrested heart must be assessed. With an appropriate therapy, hemodynamic determinants can be varied, to improve cardiac efficiency. Nonetheless, measurement of all variables necessary for the calculation of efficiency remains a challenge, in particular in the clinical setting. Separation of the direct effects of drugs on efficiency is even more difficult, since hemodynamic conditions can hardly be controlled throughout the observation period, and changes in efficiency might be secondary to changes in hemodynamics. Whether the heart by itself employs mechanisms to improve its efficiency is still a matter of discussion: there is evidence that when oxygen supply decreases, the heart can switch from one substrate to a less costly one, or possibly can improve efficiency through better use of oxygen. Moreover, the heart seems to "sense" an even more decreased oxygen supply and reduce function in response. Myocardial stunning could be regarded as a protective mechanism as well, with function remaining depressed and the oxygen supply being normal or close to normal. One may conclude from the decreased efficiency that the excess oxygen consumption is used up for repair processes. The improved efficiency found in hypertrophied hearts represents another adaptive process. The underlying mechanism is unclear: a shift towards isomyosin V3 or some undefined shift in metabolic pathway is discussed. It is also still a moot question towards which objective the efficiency of the heart is adjusted. It has been described that under physiologic conditions, the efficiency of both the left and the right ventricle ought to be maximized.(ABSTRACT TRUNCATED AT 400 WORDS)

Myocardial magnesium: relation to laboratory and clinical variables in patients undergoing cardiac surgery

Magnesium concentration was measured in the right atrial appendage of 100 patients undergoing cardiac surgery and associations with serum and mononuclear blood cell magnesium, other laboratory values and patient clinical variables were studied. In addition, magnesium was measured in the right atrial appendage and left ventricular free wall in 23 autopsy subjects to determine whether there was a proportional relation between right atrial appendage and left ventricular free wall magnesium. The mean left ventricular free wall/right atrial appendage magnesium ratio was 2.13 +/- 0.39 (r = 0.67, p = 0.0009). In the group with cardiac surgery, the right atrial appendage magnesium concentration correlated inversely with age (r = -0.54, p = 0.001). The mean right atrial appendage magnesium concentration (micrograms/g wet weight tissue) was lower in patients with postoperative cardiac arrhythmia than in those without arrhythmia (103 +/- 13 versus 111 +/- 10, p = 0.009) and in diabetic than in nondiabetic patients (103 +/- 13 versus 109 +/- 12, p = 0.02). The right atrial appendage magnesium concentration also tended to be lower in patients receiving potassium/magnesium-losing diuretics, although this difference did not achieve statistical significance (105 +/- 14 versus 109 +/- 11, p = 0.16). Right atrial appendage magnesium concentration correlated positively with serum creatinine concentration (r = 0.31, p = 0.002) and negatively with serum calcium concentration (r = -0.29, p = 0.013). Serum magnesium did not correlate with right atrial appendage or mononuclear blood cell magnesium concentration or clinical variables. There was a statistically significant correlation between mononuclear blood cell and right atrial appendage magnesium concentrations in some subgroups of patients.

Fascinating rhythm: a primer on chaos theory and its application to cardiology

Nonlinear dynamics is an exciting new way of looking at peculiarities that in the past have been ignored or explained away. We have attempted to give a general introduction to the basics of the mathematics, applications to cardiology, and a brief review of the new tools needed to use the concepts of nonlinear mathematics. The careful mathematical approach to problems in cardiac electrical dynamics and blood flow is opening a window on behaviors and mechanisms previously inaccessible.

The fundamental law of electrostimulation and its application to defibrillation

Around the turn of the last century, there was an intensive discussion among physiologists as to whether there is a law describing the phenomena of electrostimulation and which formula may best approximate it mathematically. J.L. Hoorweg found in 1892 that the voltage at which a capacitor must be charged to elicit an excitation, was a function of the capacitance in an inverse correlation. G. Weiss reported in 1901 that according to his investigations a linear relationship existed between the duration of a pulse and the corresponding quantity of electricity applied and called it "formule fondamentale." We are now able to give the "fundamental formula" a physical interpretation that yields, as result, the electric field produced by the electrode acting on the excitable membrane. The electric field in the extracellular space is transformed by the cell geometry ratio: cell length to membrane thickness yielding a high transmembrane field capable of reducing the inherent electric field to its threshold level. The consequences drawn from this hypothesis are remarkable and (should) have an influence on all applications of electrostimulation including the discussions on defibrillation. The application of the stimulation theory to defibrillation yields as results: (1) The basic engineering principle of defibrillation is to produce an electric field within the ventricles of 400 V/m or more. An orthogonal pulse application may reduce the energy requirements, as more fibers are longitudinally reached by the electric field; (2) The shape of the defibrillation pulse and its polarity plays no role. Consequently it follows that biphasic pulses must be less efficient than monophasic pulses, if they are close to the chronaxie; and (3) The most serious disadvantage in today's defibrillation practice is its dose characterization in "energy"; but this physical quantity cannot be justified in the light of the fundamental law of electrostimulation.

Intravenous use of amrinone for the treatment of the failing heart

Amrinone, a new nonadrenergic, nonglycosidic agent with combined positive inotropic and vasodilating properties, was approved recently for parenteral use in the treatment of left ventricular failure. Its mechanism of action is mediated primarily by selective phosphodiesterase fraction III inhibition, although at high doses alterations of calcium transport may occur. Acute hemodynamic changes produced by amrinone include augmentation of cardiac output and decreases in pulmonary capillary wedge pressure, right atrial pressure and systemic vascular resistance. Heart rate and blood pressure remain unaltered. Myocardial oxygen consumption declines concomitantly with the decrease in systolic wall tension. The efficacy of amrinone is comparable to that of dobutamine and dopamine. Synergistic interactions with catecholamines and vasodilators are described. Adverse effects are minimal, with dosage limited predominantly by decreases in filling pressures.

Ischemic cardiomyopathy

The term "ischemic cardiomyopathy" was used initially to describe a clinical syndrome that was indistinguishable from primary congestive cardiomyopathy but due to severe, diffuse coronary artery disease. The term has been expanded to include the larger category of myocardial disease secondary to coronary artery disease. Using this expanded definition, we have discussed the varied clinical presentations of congestive ischemic cardiomyopathy and restrictive ischemic cardiomyopathy (stiff heart syndrome and right ventricular infarction), and how the effects of ischemia on left ventricular systolic and diastolic performance may cause these varied presentations. The prognosis of any ischemic cardiomyopathy is related primarily to the degree of ventricular dysfunction and the extent of coronary artery disease. Therapy is aimed at preventing or ameliorating myocardial ischemia and halting the progression of, or even reversing, the deterioration in myocardial function.

A new method for clinical assessment of the negative inotropic action of anaesthetics--with special reference to isoflurane and its effect on myocardial oxygenation

A new method for maintaining the peripheral determinants of myocardial oxygen demand constant is described. Intravenously administered phenylephrine and nitroglycerin were used to control afterload and preload. Heart rate was kept constant with atrial pacing. The method was used to establish the in vivo negative inotropic effect of 1% end-tidal isoflurane in eight patients with ischaemic heart disease during positive pressure ventilation (IPPV). Stroke volume measured during steady-state isoflurane anaesthesia and IPPV with preload, afterload, and heart rate kept constant was 23% below awake control. The decrease in myocardial oxygen consumption was 22% and correlated well (r = 0.891) with the fall in left ventricular performance (stroke volume).

Left ventricular wall motion improvement after phentolamine: a case report

Left ventricular wall motion abnormalities are commonly seen in coronary artery disease patients. The differentiation between reversibly ischemic areas an irreversibly damaged areas is 1 was of predicting which patient might gain improved ventricular function from surgical correction. One patient with coronary artery disease is presented here who showed poor septal movement on his echocardiogram. After the IV administration of phentolamine, the septal movement became normal. Thus, phentolamine should be considered as an agent that can detect reversible areas of wall motion abnormalities.

A flow microcalorimeter system for the measurement of dynamic energy variables of isolated perfused hearts

An isothermic flow microcalorimeter system for fluid rates of 1-50 cm3 min -1 has been developed to measure the total heat flow produced by isolated perfused small animal hearts and its rate of change. The heat, which is absorbed by the perfusion fluid flowing through the coronary capillary system, is detected by passing the coronary effluent through a plate heat exchanger mounted in intimate contact with the internal surface of a gradient layer calorimeter. By employing electrical calibration, this heat flow detector gives a precision of +/- 0.2 m W for average effluent rates of about 15 cm3 min-1. The method provides direct comparison of the biologically produced heat flow with electrically generated energy flows. The response time to step changes in heat flow is 1 min to 90% of the total change. Possible systematic errors are analysed and quantified, using a heart bypass flow technique and a thermoelectric differential temperature meter. The accuracy of the measurement of constant heat sources with the complete system over the range of 5-40 mW is +/- 2% for fluid rates up to 40 cm3 min-1. Measurements with small rat hearts have given absolute values between 17 and 36 mW measured with an accuracy of +/- 3%. The rate of total myocardial energy turnover can be studied with the system.

Intropic and electrophysiological action of humoral factors released in cardiogenic shock after acute myocardial infarction

The inotropic and electrophysiological effects of plasma obtained from patients and experimental dogs during cardiogenic shock following acute myocardial infarction were studied. Changes in the isometric contraction and the intracellular action potential were determined in isolated papillary muscles of rabbits. Control plasma collected from normal subjects produced no significant changes in the contraction or the electrical parameters. Plasma from shock patients decreased peak force by 42% and the maximum rate of force development by 38% in comparison to control values; the time to peak of contraction, the relaxation time and the action potential parameters were not significantly altered. Corresponding results were obtained with plasma from dogs before and during experimental cardiogenic shock. Biochemical determinations failed to identify a single specific "myocardial depressant factor" in the plasma of patients and dogs with cardiogenic shock. The results suggest that (1) various humoral factors released during cardiogenic shock may depress the contractile function of cardiac muscle and (2) that the observed negative intropic effect is not due to electrical changes in the cell membrane.

[The calcium metabolism of myocardial mitochondria and sarcoplasmic reticulum in experimental potassium deficiency (author's transl)]

Mechanical Parameters of the whole, Langendorff-perfused cat heart and of isolated right ventricular papillary muscles are depressed in chronic potassium deficiency. 45Ca binding of sarcoplasmic reticulum (SR) was found to be diminished and correlated with a reduced contractility of the perfused hearts. 45Ca uptake of sarcoplasmic reticulum isolated from potassium deficient hearts was also reduced. The mitrochondrial 45Ca binding and endogenous Ca concentration were increased and there was a positive correlation between these two parameters. The data suggest that a reduced SR Ca binding plays a role in the depression of myocardial contractility in chronic potassium deficiency. Increased mitochondrial 45Ca binding in the presence of reduced 45Ca binding and uptake of sarcoplasmic reticulum suggests the possibility that mitochondria are an additional myocardial calcium pool in chronic potassium deficiency.

Improvement in left ventricular wall motion following nitroglycerin

Coronary artery disease patients frequently have left ventricular wall motion abnormalities. Though nitroglycerin is commonly used in ischemic heart disease, its effects on wall motion abnormalities is unknown. In this study we have evaluated the effects of nitroglycerin on wall motion abnormalities and on ejection fraction in 25 patients. Sixteen had coronary artery disease (greater than 70% luminal narrowing). Six had no evidence of heart disease and three had congestive cardiomyopathies with normal coronary arteries. Left ventricular angiography was performed prior to and six minutes after administration of 0.4 mg of sublingual nitroglycerin. Twelve of the 16 coronary artery disease patients had wall motion abnormalities, and in seven of these, segmental wall motion improved after nitroglycerin. In five, all motion did not change. The initial heart rate, left ventricular systolic and end-diastolic pressure, and left ventricular end-diastolic volumes were not different for those whose wall motion improved versus those whose did not. The increase in the former and fall in the latter three hemodynamic parameters were significant (P less than 0.01) and similar for the two groups. In those whose wall motion abnormalities improved after nitroglycerin, ejection fraction (mean plus or minus se) increased significantly (P less than 0.05), from 0.47 plus or minus 0.025 to 0.62 plus or minus 0.046. In those without improvement, the ejection fraction went from 0.55 plus or minus 0.056 to 0.58 plus or minus 0.051 (NS). Three patients with congestive cardiomyopathy showed no improvement in ventricular wall motion or ejection fraction after nitroglycerin. Left ventricular wall motion abnormalities and ejection fraction improved in some coronary artery disease patients following nitroglycerin. The mechanism for this is unknown; however, ventriculography before and after nitroglycerin may be of potential usefulness for identifying areas of reversible wall motion abnormalities.

A simulation of human heart function

A simulation of the function of the human heart and heart muscle has been developed in the form of a digital computer code. For a given set of values for the input variables, realistic values of the cardiac output variables are predicted. A detailed discussion of the simulation and some results obtained from its application are presented. This simulation represents a unique combination of what was known in muscle mechanics, muscle thermodynamics, and of the structure, size, and shape of the heart, into an engineering model to improve the understanding of human heart muscle function. The left ventricle (LV) is treated as a thick-walled sphere whose wall is composed entirely of muscle fibers. Force-length velocity relationships are used to determine the tension in each fiber. The pressure in the LV is computed from fiber tension and fiber structure in the LV. A lumped-parameter simulation of the arterial tree provides a load impedance for the LV. Results are presented for simulation of normal human LV performance.

Flow directed-pulmonary artery catheterization in surgical patients: indications and modifications of technic

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Changes in left ventricular performance from early after acute myocardial infarction to the convalescent phase

Left ventricular performance was assessed in 22 patients early (within the first 2 days) after acute myocardial infarction (AMI) and again during the convalescent phase (3-5 weeks later). Left ventricular end-diastolic pressure (LVEDP) fell from the early to the late study by an average of 10.7 mm Hg in the 12 (55%) group A patients. In these patients, cardiac index (CI) and left ventricular stroke work (LVSW) increased by an average of 0.65 liters/min/m 2 and 63.8 g-m, respectively, and the mean right atrial pressure fell by 2.4 mm Hg. These changes were statistically significant ( P < 0.05). Left ventricular (LV) function was improved in this group of patients.

LVEDP increased in the other 10 patients and they were subdivided into groups B and C depending on whether CI increased or decreased. In six patients (27%), LVEDP increased by 5 mm Hg and CI increased by 0.4 liters/min/m 2 (group B); the P value for these changes was < 0.05. Group B patients also had an increase of mean arterial pressure and left ventricular ejection time, and thus the alterations in LVEDP and CI could have resulted from an increase of arterial pressure. In four patients (18%), LVEDP increased by 11.5 mm Hg, CI decreased by 0.9 liter/min/m 2 , and LVSW was reduced by 34.5 g-m (group C). Although the decreases of CI and LVSW were not statistically significant in group C patients, LV function had deteriorated. In the follow-up period, three of the four patients in group C died and the fourth patient is in functional class IV.

Therefore, in the convalescent period ventricular function had improved in 55%, and had deteriorated in 18% of cases. The changes in LV function could not have been predicted on the basis of the clinical features, systolic time intervals, or the initial hemodynamic findings. Patients whose ventricular function deteriorated during convalescence had a very poor prognosis.

Lactate dehydrogenase isozymes: kinetic properties at high enzyme concentrations

The kinetic properties of lactate dehydrogenase (LDH) isozymes have been determined at high enzyme concentrations. Spectrophotofluorometric assays revealed that the extent of substrate inhibition of LDH-1 and LDH-5 depends on enzyme concentration. At high enzyme concentrations, in the range of those that exist in most mammalian cells, no inhibition by pyruvate occurred. Pyruvate concentrations up to and including 20.0 millimoles per liter were used for each isozyme at 25 degrees and 40 degrees C at pH 7.0 and 7.4. These results suggest that substrate inhibition of LDH may not occur in vivo but only in vitro after appreciable dilution from physiologic enzyme concentrations. These experiments provide further evidence against the theory that substrate inhibition of LDH-1 in vivo accounts for the distribution of LDH isozymes within various tissues. They raise the possibility that, for other enzymes, kinetic properties determined at highly dilute concentrations in vitro may also be quite different from kinetic properties at the much higher concentrations that exist in vivo.