Dov Jaron

Left ventricular afterload and systemic hydraulic power during in-series cardiac assistance: studies using intraaortic balloon pumping in dogs.

The effects of in-series mechanical assistance on left ventricular (LV) afterload and aortic power dissipation were studied in four groups of open chest mongrel dogs: control, acute myocardial ischemia, cholinergic and beta-adrenergic blockade, and combined ischemia and blockade. Aortic root pressure, flow, power, and impedance and LV pressure and power were obtained. Assistance was provided by intraaortic balloon pumping. Times of inflation and deflation of the balloon were controlled to maintain a phase difference of 180° between the fundamental components of aortic root pressure and flow. Differences in hemodynamic parameters before and after 2–5 min of cardiac assistance were calculated. The results confirm other observations regarding effects of in-series assistance on LV and aortic pressure, cardiac output, and peripheral resistance. No consistent changes were obtained in the pulsatile components of aortic input impedance. A significant decrease (14–20%) was observed in the dc component of the impedance in all animals. The results reported here contradict previous reports regarding decreased LV power generation. It was found that LV power generation and aortic power dissipation increased significantly during assistance (LV, 3–17%; aortic, 4–19%). The results of this investigation also appear to conflict with previous reports regarding the role of cardiovascular control in “counteracting” the effects of assistance in the normal experimental preparation. They suggest that the short term effects are attributable directly to the device and are not mediated by the autonomic nervous system.

The Design of a Piezoelectric Heart Assist Device

A piezoelectric heart assist device was designed, and preliminary tests were performed in vitro and in vivo. The device has the advantages of simple construction, low power consumption (approximately one watt), electrical rather than pneumatic drive, and noiseless operation. The device consists of piezoelectric bender elements forming two cantilevers. A unique feature of the device is that two tungsten alloy masses, 0.44 kg each, were added to the free ends of the cantilevers to reduce the resonant frequency to 2.5 Hz. The driving voltage was a 320 V peak-to-peak square wave synchronized with a paced heartbeat.

RELATIONSHIP BETWEEN CORONARY ARTERY STENOSIS AND LEFT VENTRICULAR ASYNERGY: A COMPUTERIZED STUDY TO EVALUATE LV WALL MOTION

Publisher Summary This chapter reviews the relationship between coronary artery stenosis and left ventricular asynergy. Although global left ventricular function can be well quantified, analysis of regional wall motion has been limited mainly for lack of a satisfactory method of measuring segmental motion. Radiographic cine left ventriculography has been used for evaluating left ventricular function. The goals of this investigation were l) to establish a computerized system to quantify left ventricular wall motion and then apply this system to delineate those factors determining ventricular asynergy; and 2) to assess the feasibility of characterizing normal patients from those suffering from single vessel coronary artery stenosis on the basis of that wall motion. In the study described in the chapter, two groups of patients who underwent single plane anterior oblique cine left ventriculography and coronary cineangiography were utilized. One group was composed of 34 patients lacking any significant coronary artery stenosis or other ventricular abnormalities. These were defined to be normal. The second group of 22 patients had significant left anterior descending (LAD) coronary artery stenosis. Data from all patients were stored on magnetic disk and were used through-out the analysis. The results of the study showed that for the ventricular region contained between 30° and 170°, the mean percent change of the chords for normal patients varied between 30% and 40% increasing to mean values varying between 55% and 65% for the region between 190° and 300°. The entire population of LAD patients had significantly reduced percent shortening as compared to normals for left ventricular regions between 60° to 2I5°. In evaluating LAD patients as to the extent of stenosis, those with complete occlusion had greater impairment of shortening than those with stenotic but patent vessels.

ANALYSIS OF THE DIASTOLIC PRESSURE-VOLUME RELATIONSHIP USING AN ELLIPSOIDAL REPRESENTATION OF THE LEFT VENTRICLE

Publisher Summary This chapter presents an analysis of the diastolic pressure–volume relationship using an ellipsoidal representation of the left ventricle. It presents a time domain representation of the left ventricle. Previously, this model was used to analyze the isovolumic contraction phase and the ejection phase of the cardiac cycle. Results obtained from the simulation agreed with results from animal experiments. The chapter explores the properties of the model under conditions where the distributed strain in the ventricular wall was replaced by strain concentrated along a single surface within the myocardium. In the study described in the chapter, the left ventricle was modeled by two ellipses of revolution that represent the endocardial and epicardial surfaces of the chamber. The ellipsoids were truncated perpendicular to their long axis by a plane corresponding to the base of the left ventricle. The ellipsoids were approximated by a series of cylindrical shells. The model was tested utilizing 10 cylindrical segments. The stress in the walls of the cylindrical shells at end diastole was found from the end-diastolic pressure and end-diastolic configuration. The corresponding strain in the walls of the cylindrical shells was calculated from the stress–strain relationship of the model. As the assumed location of the strain is allowed to shift toward the epicardium, the results obtained from the model indicate that left ventricular internal pressure sensitivity to changes in chamber volume diminishes.

THEORETICAL ASSESSMENT OF A VALIDATION TECHNIQUE FOR NONLINEAR PHYSIOLOGICAL MODELS**Supported in part by NSF Grant ENG 77-06411

Publisher Summary This chapter presents theoretical assessment of a validation technique for nonlinear physiological models. These models were validated by comparing data obtained from the model with in-vivo data using time domain and frequency domain techniques to analyze the observed hemodynamic waveforms. These measures of validity imply that the most desirable model is that which best reproduces the waveforms observed in-vivo. To quantify the ability of the model to follow trends exhibited by the natural system, a state of the model that corresponds to a state of the natural system is specified. The state is defined by the hemodynamic parameters of interest, such as mean pressures, cardiac output, peak pressures, etc. The difference or the distance between the state of the model and the state of the natural system is defined as a metric. With the exception of the effect on cardiac output, the least sensitive parametric variat on in the model is occlusion of branch vessels.