PubMed Health⌕ Search

Biomedical subjects

S E Moskowitz

Publications and source records attributed to S E Moskowitz.

13 recordsLinked to original sources
PubMed1986

USMGs versus FMGs. Are there performance differences in the ambulatory care setting?

Several earlier studies compared performance differences between USMGs and FMGs in inpatient care settings, mainly hospitals. This study compares performance differences between USMGs and FMGs in ambulatory care settings. The sample consisted of 14,203 patient episodes treated by 1,156 physicians (pediatricians, obstetricians/gynecologists, internists, and other specialty physicians). The study setting was a midwestern state. Little evidence was found to support the hypothesis that the medical school origin (U.S. and foreign) had influenced physicians' technical quality in practice. Mean differences between the USMGs and FMGs were either not significant or contrary to the general assumption. The FMGs provided equal care to the USMGs, and sometimes the FMGs provided even marginally better care than the USMGs.

Black or African American↗
PubMed1985

Constitutive stress--strain relations for the myocardium in diastole.

The importance of stress-strain myocardial constitutive relations is that they provide a criterion for behavior in vivo. Our purpose was to develop constitutive equations which are valid in diastole. The myocardium was assumed to be composed of a nonlinear viscoelastic, inhomogeneous, anisotropic (transversely isotropic) and incompressible material operating under adiabatic and isothermal conditions. The expressions contain five moduli. Two are fixed by the restriction of incompressibility, one is estimated, the remaining two refer to directions along and perpendicular to a fiber. Both possess a bimodal variation with intermodal switching occurring in late rapid filling and diastasis. They are functions of time and material constants. These constants can be observed. A dynamic test is suggested. Constitutive statements complete a set of equations sufficient for the solution of a class of boundary value problems. One type is formulated. They also permit the determination of stress from measured strain. Examples are given.

Heart↗
PubMed1982

Passive stress-strain relation for the right ventricle in diastole.

Wall thickness and medial line radii of an in vitro canine heart are measured. These data are assumed to be characteristic of the in vivo ventricles subject to zero pressure, and in the absence of filling. The myocardium is taken to be homogeneous, isotropic, non-linearly elastic, and incompressible. The right ventricular free wall is modeled as a circular arch of constant thickness, fixed at the interventricular groove. Circumferential stress is determined from thrust, and circumferential strain from displacement, both at the crown of the midwall. Our purpose was to obtain a stress-strain relationship without inertia and ventricular filling, termed passive. The passive circumferential stress-strain relation for the right ventricle in diastole is shown to be an exponential equation with two parameters. These parameters are related to the product of material constants of in vivo heart, and functions of right ventricular geometry in terms of the ratio of wall thickness to arch radius, and the terminal value of the central angle. Using mean values of observations, right and left ventricular passive curves are plotted over the same representative strain interval in an example from lowest diastolic pressure to the start of atrial contraction.

Animals↗
PubMed1980

Computer simulation: a diagnostic method in comparative studies of valve prostheses.

Computer simulation was used to compare flow characteristics through Starr-Edwards and Björk-Shiley valves in the mitral and aortic positions. Pressure and velocity determinations were mathematically computed with the use of a model based on the recognition that blood is a non-Newtonian fluid. The results were displayed in two-dimensional graphic form. In both the mitral and aortic positions the Björk-Shiley prosthesis showed a more favorable laminar flow pattern, producing fewer eddies and smaller pressure and velocity gradients through the occluder. Computer simulation is a valuable adjunct in the comparative testing of the hemodynamic properties of artificial heart valves and offers several advantages over physical simulators.

Aortic Valve↗
PubMed1979

Selection of saphenous vein bypass gradt diameter to support patency of the stenosed coronary artery.

Injudicious selection of a saphenous vein graft can adversely affect the the late postoperative patency of the proximal coronary artery which it bypasses. The purpose of this investigation was to deduce an upper bound for graft diameter, at small angle of distal anastomosis, below which the stenosed artery will remain patent, from a mathematical model of aortocoronary bypass haemodynamics.

Coronary Artery Bypass↗
PubMed1978

Computer prediction of left ventricular complicance throughout diastole in normal patients.

This study deals with the development of a computer program to predict instantaneous left ventricular complicance, as defined by the tangent modulus E, throughout diastole. Diastole is divided into discrete time intervals according to the major events which occur: the start of isovolumic relaxation (aortic valve closure), mitral valve opening, the point of minimum left ventricular pressure, the junction of the rapid and slow filling phases, the start of atrial systole, and the peak of the 'a' wave. Each interval is separated into subintervals. Over each subinterval two mechanisms are assumed to operate: myocardial relaxation or contraction producing a pressure change without an accompanying volume change, followed by explansion of the left ventricle at constant pressure. Although these mechanisms occur simultaneously in the intact heart, they are treated sequentially in a multistage computer program that employs the finite element technique to determine the displacements within a thick-walled ellipsoidal shell. The smaller the time interval between successive stages, the closer is the approximation to the actual continous process of myocardial relaxation, contraction, and distension. Diastolic determinants revealed in this investigation are the mechanical properties of the myocardium, the state variables of pressure and volume, and the control variables of wall thickness and cavity size. In isovolumic relaxation, the myocardium relaxes and the ventricular wall thickens to reduce intracavitary pressure. The relaxation process continues and intraventricular pressure falls to a minimum (0-point) while ventricular volume increases after mitral valve opening. In the succeeding phases, excluding atrial systole, ventricular filling pursues, the properties of the myocardium change, there is an increase in tone (possibly due to myocardial contraction), the wall thins and intraventricular pressure rises. Computer prediction shows that at the start of diastole the tangent modulus is approximately 6 times the enddiastolic value, and is nearly 0 at the onset of the slow filling phase. Tangant modulus is a useful index by which to distinguish normal from abnormal patients provided the characteristics of E as a function of time are recognized and compared throughout diastole.

Compliance↗
PubMed1978

Left ventricular wall thickness during the isovolumic relaxation period.

Left ventricular (LV) wall thickness was measured by echocardiography at the onset and at the end of the isovolumic relaxation period (IRP) in a group of normal young subjects. Measured LV minor diameter was constant during the IRP in these patients and there was no change in interventricular septal thickness. Posterior LV wall thickness increased by 12 +/- 6 (SD)% (P less than 0.001) and mean LV wall thickness by 6 +/- 4% (P less than 0.01). An increase in LV wall thickness during the IRP is consistent with simple fluid dynamic principles.

Adolescent↗