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Biomedical subjects

I Mirsky

Publications and source records attributed to I Mirsky.

At least 55 records · Page 3Linked to original sources
PubMed1981

Prediction of postoperative performance in aortic valve disease.

A new direct method has been developed for predicting postoperative performance in patients undergoing aortic valve replacement. Employing micromanometry and cineangiography, a number of conventional hemodynamic and angiographic variables, including the peak value of the first derivative of ventricular pressure divided by ventricular pressure (dP/dt/P)max, were evaluated in 171 patients studied preoperatively and in 44 patients studied pre- and postoperatively with an additional 14 patients serving as control subjects. Normal contractile state relations (dP/dt/P)max versus end-diastolic pressure (over a range of 125 mm Hg or less to more than 15 mm Hg) were derived from patients whose preoperative ejection fraction and peak wall stress were equal to or more than control mean--2 standard deviations. Postoperative function was predicted to be abnormal (ejection fraction less than control mean--2 standard deviations) if preoperative values of (dP/dt/P)max and end-diastolic pressure fell below the 95 percent confidence bands of these contractile state relations. The method accurately predicted postoperative function in 40 of 44 patients with a sensitivity of 100 percent. This result was confirmed by a discriminant function analysis (based on preoperative ejection fraction, end-diastolic pressure and [dP/dt/P]max) that yielded correct classifications in 42 of 44 patients. These studies indicate that the preoperative contractile state of the myocardium is the major determinant of postoperative performance in aortic valve disease.

Aortic Valve↗
PubMed1981

The role of wall stress in the assessment of ventricular function.

Over the past decade there has been a steady proliferation of indices which have been proposed for assessing ventricular function. Many of these indices are based on single measurements and often are insensitive and have limited clinical utility. The present article focuses on the role of wall stress in assessing ventricular function from the point of view of the heart as a muscle. For many clinical applications (excluding coronary artery disease), average stress formulae developed by Falsetti et al. and Mirsky are adequate. Based on these formulae one may describe the mechanical properties of heart muscle in terms of stress-strain or stiffness-stress relations. Such analyses yield useful information with regard to the degree of fibrosis present and should be of importance in biopsy studies on the cardiomyopathies and in hypertrophied ventricles. Furthermore, regional muscle function may be simply quantitated by these methods, employing simultaneous measurements of pressure and wall thickness. Pressure-volume relations obtained during diastole or systole at best yield limited information on ventricular function and should be replaced by a corresponding stress-strain analysis. Finally, it is recommended that relationships (rather than single points) be developed for assessing both muscle and pump function. Furthermore, these relationships should first be based on invasive measurements before proceeding with the more attractive but less accurate noninvasive approach.

Biomechanical Phenomena↗
PubMed1980

Time course of changes in the mechanical properties of the canine right and left ventricles during hypertrophy caused by pressure overload.

We developed a mathematical model of the right and left ventricles to determine whether there is a change in the mechanical properties of muscle during the hypertrophy process resulting from pulmonary arterial banding. Pressure-volume data were obtained from 10 normal dog hearts and 8 dog hearts in which the pulmonary artery was banded for periods of 2--40 weeks. These data were applied to the model, and the time course of wall stress and muscle stiffness was quantified for both ventricles. The results demonstrate that (1) myocardial stiffness is increased in pressure-overload hypertrophy (2) normal right and left ventricular muscle exhibits similar mechanical properties and (3) the relationships between wall stresses and the volume/mass ratios to the period of banding are biphasic. We concluded that (1) increase in muscle stiffness is due to several factors. In the early stages of hypertrophy, it may be predominantly due to fibrosis and, in the later stages, to substantial increases in muscle mass. (2) The progressive increase in muscle stiffness concomitant with the increase in muscle mass may be due to the presence of myocardial cellular projections and fibrosis. (3) The appropriate timing for surgical/medical intervention should take place before low volume:mass ratios and, hence, low wall stresses are attained.

Animals↗
PubMed1980

Elastic properties of normal and hypertrophied cardiac muscle.

This brief review addresses itself to the following questions on normal and hypertrophied muscle. 1) What changes, if any, take place in the mechanical properties of cardiac muscle during pressure and volume overload hypertrophy? 2) What parameters may signal preoperatively irreversibility of hypertrophy and chamber enlargement? 3) Are the effects of age and hypertrophy on muscle stiffness similar? 4) What relationships exist between diastolic properties and systolic function? The analyses of the elastic properties of cardiac muscle based on several animal and clinical studies indicate that: a) Muscle stiffness in pressure overload is elevated and is normal in volume overload in the majority of the animal studies. However, the clinical studies support the hypothesis that muscle stiffness remains normal in mild to moderate degrees of valvular disease and is elevated in severe valvular disease. b) Wall stress, volume:mass, and radius:thickness ratios are useful prognostic indicators regarding reversibility of wall hypertrophy and/or chamber enlargement. c) Effects of age and hypertrophy on muscle stiffness are similar for the age range of young adult (6 mo) to old (90 wk) SHR and WKY rats. d) Increased muscle stiffness is invariably accompanied by decreased muscle shortening velocity but rate of force development and peak force may not be impaired.

Aging↗
PubMed1979

Myocardial contractile function in aortic stenosis as determined from the rate of stress development during isovolumic systole.

To assess myocardial contractile function in the chronically hypertrophied human left ventricle, the rate of stress development (dsigma/dt) as a function of developed stress (sigmaD) during isovolumic systole was examined. Results for eight patients with aortic stenosis were compared with those for seven subjects with normal left ventricular function and with those for five patients with idiopathic congestive cardiomyopathy. The rate of stress development (dsigma/dt) was nearly identical in patients with aortic stenosis and in normal subjects over a wide range of values of sigmaD but was significantly lower in patients with cardiomyopathy (P less than 0.01 versus control subjects and patients with aortic stenosis). Normal values for dsigma/dt held not only for patients with compensated pressure overload, but also for those patients with aortic stenosis with depressed left ventricular ejection fraction and overt congestive failure. Similar findings were obtained when the first derivative of left ventricular pressure (dP/dt) was examined as a function of developed left ventricular pressure in normal subjects and patients with aortic stenosis or cardiomyopathy. These results indicate that contractile function as characterized by the isovolumic rate of stress development is not necessarily impaired in chronic pressure overload hypertrophy.

Adult↗
PubMed1979

The effects of geometry, elasticity, and external pressures on the diastolic pressure-volume and stiffness-stress relations. How important is the pericardium?

The concept of an incremental elastic modulus is applied in the quantification of passive elastic stiffness-stress relations of intact heart muscle, and a transmural pressure-volume relation for the left ventricle is subsequently derived in terms of geometry, muscle elasticity, and external pressures to assess their importance. Physiological and clinical applications of this method indicate that: (1) stiffness-stress relations obtained on the basis of pressure-volume data from dog hearts are not significantly different from those obtained from muscle strips excised from these same hearts; (2) shape and the presence of right ventricular, pericardial, or pleural pressures are of secondary importance in an assessment of passive elastic stiffness; and (3) dramatic shifts in the left ventricular intracavity pressure-volume relations following drug interventions are primarily due to the presence of substantial pericardial pressures; however, the transmural pressure-volume relations are not markedly altered, implying no alteration in the intrinsic ventricular compliance.

Animals↗
PubMed1976

Effect of age on passive elastic stiffness of rat heart muscle.

A thick-wall spherical model for the rat left ventricle was used to deduce passive wall stiffness from diastolic pressure-volume data. This was done for rats in three age classes: young (1 mo), adult (17 mo) and old (17 mo). The model was based on finite deformation elasticity theory consistent with the magnitude of observed deformation. A least-squares procedure was used to determine elastic constants in postulated nonlinear stress-stretch relations for the myocardium. It was found that at a given level of stress, wall stiffness for ventricles in the young age class was consistently greater than wall stiffness in the other two classes. In addition, the difference in wall stiffness between rats in the adult and old age classes was found to be approximately 10%.

Aging↗