Edward L. Yellin

Laminar-Turbulent Transition Process in Pulsatile Flow

A controlled ex-vivo study of a simple, sinusoidally oscillating flow in a rigid, constant-area, smooth tube, has produced significant insight into the laminar-turbulent transition phenomenon. The development of turbulence was studied by analyzing the dynamic characteristics of the transition process; i.e., the velocity, growth rate, and intermittency which describe the generation and propagation of turbulent slugs. A new concept, the relaxation time, has been introduced to interpret the effect of a periodic flow component superposed on a mean flow. Classical stability concepts, such as the point of inflection criterion and the Reynolds number, which have been derived from steady-flow analysis, are shown to require modification when applied to an oscillatory flow. Neither the mean nor the instantaneous Reynolds number is a sufficient criterion for determining the transition of laminar to turbulent flow in a pulsatile system. Other necessary criteria are: (1) a source of disturbances, (2) the relaxation time, and (3) the distance from the fluid under observation to the source of disturbance. The concept of relaxation time indicates that slowly oscillating flows of large amplitude tend to suppress or destroy turbulence downstream from sources of disturbance. Qualitative observations are presented which indicate that systolic acceleration may be laminar regardless of the large value of the instantaneous Reynolds number, while diastolic deceleration probably produces disturbed, but not turbulent or highly dissipative, flow.

Dynamic Determinants of Left Ventricular Filling: An Overview

The left ventricle fills through dynamic changes in its compliance as it relaxes (by altering its wall stress), through elastic recoil from a nonequilibrium shape, and through passive acceptance of blood during diastole. The driving force necessary to accelerate the blood and to overcome dissipative energy losses is provided by the pressure in the left atrium which acts as a passively compliant reservoir (whose potential energy is provided by the right ventricular contraction), and by the active generation of force during atrial systole. The efficiency of ventricular filling, and its ability to determine the subsequent stroke volume, is in part determined by the ability of the valve to open widely and to stay open during filling, to close competently at systole, and to remain closed without leakage.

The influence of left ventricular filling on postextrasystolic potentiation in the dog heart.

We studied the role of left ventricular filling on postextrasystolic potentiation (PESP) in the intact dog heart by calculating changes in end-systolic and end-diastolic volumes on a beat-to-beat basis from electromagnetic measurements of phasic mitral inflow and aortic outflow. In all, 161 extrasystolic sequences with compensatory pauses in 13 dogs were analyzed. The first postextrasystolic cycle showed an increased end-diastolic volume (EDV) in 94%, a decreased end-systolic volume (ESV) in 50%, and an estimated increased ejection fraction in 85% of the sequences. In the 91 sequences with a coupling index ⩽0.7, despite a 76% increase in filling time, there was during the compensatory pause only a 6% increase in filling volume when compared to control. The net filling volume, stroke volume, and diastolic filling period for the sum of the extra- and postextrasystolic cycles were, respectively, 78%, 80%, and 116% of the sum of two control cycles. This retarded filling rate is attributed to a lower left atrial pressure, a reduced left ventricular relaxation rate, and a relaxation to a higher pressure minimum, all of which decrease the amplitude of the atrioventricular pressure gradient. Nevertheless, in 98% of the postextrasystolic cycles, stroke volume was augmented when compared to control (ratio, 1.49 ± 0.26; mean ± SD), due in part to intrinsic mechanisms, to increased preload (EDV), and to decreased afterload. As a first approximation, the effects of increases in preload were separated from intrinsic increases in contractility following an extrasystole by defining potentiation in terms of decreased ESV and/or increased ejection fraction. With the former criterion, 50% of the sequences showed PESP; with the latter, PESP occurred in 85% of the sequences. Circ Res 44: 712-722, 1979

UL-FS 49 (Zatebradine) does not affect arterial baroreflex in conscious normal or aortic-constricted rats

Heart-rate reduction is an important element of patient management during cardiac bypass surgery and in therapeutic measures for combating ischemia and relieving pain in patients with angina. UL-FS 49 is a novel bradycardic agent that purportedly acts solely on the sinoatrial node without potentially deleterious effects on arterial pressure and cardiac inotropism. However, little is known about influences of this agent on neuronal tissue and cardiovascular reflexes. Moreover, left ventricular hypertrophy, which often accompanies cardiovascular disease, is known to attenuate the arterial baroreflex and could have effects interactive with those of UL-FS 49. In this study, the effects of UL-FS 49 on the arterial baroreflex were tested in normal rats (N), rats with left ventricular hypertrophy 14 days after abdominal aortic constriction (AC), and sham-operated controls (SH). Arterial baroreflex sensitivity (BRS) was estimated as the slope of the relation between mean arterial pressure (independent variable) and the RR interval (dependent variable). At the time of study, the AC group had significantly greater mean arterial pressure than either SH or N (159 +/- 2, 122 +/- 3, and 124 +/- 3 mm Hg, respectively; mean +/- SEM, p < 0.01) and significantly greater left ventricular mass to body mass ratio than did SH (3.73 +/- 0.11, 2.33 +/- 0.11 mg/g; p < 0.01). As expected, BRS was significantly depressed in AC, compared with either SH or N (0.52 +/- 0.16, 1.48 +/- 0.12, 1.69 +/- 0.25 ms/mm Hg, respectively; p < 0.01). Despite its potent dose-dependent bradycardic effects in all three groups, UL-FS 49 did not affect BRS significantly in any group. These results show that the arterial baroreflex is largely unaffected by UL-FS 49 in both normal rats and rats with systemic hypertension and left ventricular hypertrophy.

Hemodynamic effects of high-frequency jet ventilation in dogs with a chronically banded pulmonary artery.

Two to seven weeks after banding the main pulmonary artery, the hemodynamic effects of high-frequency jet ventilation (HFJV) and conventional mechanical ventilation (CMV) were studied in dogs with and without PEEP. In comparison with CMV, HFJV significantly increased cardiac index, stroke index (SI), left ventricular stroke work index, and oxygen delivery index, and decreased pulmonary vascular resistance index both with and without PEEP; however, there were significant decreases in PaO2 and increases in intrapulmonary physiologic shunt ratio in HFJV without PEEP. SI without PEEP was significantly greater with HFJV when the peak airway pressure was synchronized with the diastole in pulmonary arterial pressure (PAP) than with CMV and with HFJV synchronized with the systole in PAP. These findings suggest that HFJV has hemodynamic advantages over CMV in dogs with chronically banded pulmonary artery and dilated right ventricle.

Pressure-Flow Relations and Energy Losses Across Prosthetic Mitral Valves: In Vivo and In Vitro Studies

The use of the Gorlin equation (1) to estimate the area of a prosthetic mitral valve has received widespread acceptance despite frequently questionable results. We have found, for example, that intra-operative studies on patients undergoing valve replacement with mitral bioprostheses sometimes yield exceptionally small valve areas during low cardiac output states. This study was designed to analyse the pressure-flow relations across prosthetic mitral valves and to determine the in vivo conditions which would lead to inaccurate area calculations when using the Gorlin equation.

Cardiac Mechanics and Function in the Normal and Diseased Heart

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Effect of left ventricular shape on diastolic pressure-flow relationship

Srdian Nikolic PhD, Edward L Yellin PhD, Manfred Dahm MD, Octavia Pajaro MS, Robert W.M. Frater, MD FACC. Albert Einstein College of Medicine, Bronx, NY To determine if elastic restoring forces and changes in diastolic shape influence the diastolic pres?iure-flow relation we instrumented 8 anesthetized dogs to measure mitral flow, LVP, LAP, LW from major and minor diameters, and with electronically controlled artificial mitral valve to stop filling in diastole. We determined LV shape in normal filling (F) and nonfilling (NF) beats in the presence (+ER) or absence (-ER) of elastic recoil. Development of negative LVP in NF indicated +ER. Midwall eccentricity (ECC) was related to end-diastolic (ED) and end-systolic (ES) volumes: in NF at ED: EC&,,,=-0.004OV,,,+O.98 (n=72, r=0.95) in F at ES: EC&=-0.0010V,+0.90 (n=72, r=0.93) in F at ED: EC&,=-0.0033V,,+0.99 (n=72, r=OSY) Intersection of the ES and ED lines in F (transitional volume, V,) divides ECC-V plane into two regions: for VcV, elliptical shape change and +ER: for V>V, spherical shape change and -ER. We calculated the slope (dissipative coefficient) of the linear regression through the origin of peak mitral flow squared (Q?) and the corresponding atrio-ventricular pressure gradient (PC,&. (Note that mitral ring is fixed). In F: V>V, and (-ER) PGruD= 0.00063Q~ (n==48, r=0.94) VcV, and (+ER) PGRAD= 0.000370? (n=24, r=0.96) (pcO.001) Thus, filling is more efficient in a smaller, ellipsoidal LV, in which the flow is assisted by the restoring forces.