Viscoelastic properties of the diastolic left ventricle in the conscious dog.

Abstract

SUMMARY The mechanical properties of the normal left ventricular wall during diastole were studied in 15 chronically instrumented, conscious dogs. Left ventricular minor and major axis diameters and equatorial wall thickness were measured with implanted pulse-transit ultrasonic dimension transducers. Left ventricular and pleural pressures were measured with high fidelity micromanometers. Circumferential mural stress was calculated by using an ellipsoidal shell theory; circumferential strain was calculated by using a natural strain definition. The static elastic properties of the myocardium were estimated by fitting the stress-strain values at the points of diastasis during a vena caval occlusion to an exponential function. A modified creep test was used to evaluate the series viscous properties of the myocardium. Acute increases in systolic and diastolic loading were produced by inflating implanted aortic occluders for 15 minutes in five dogs. In these dogs, the static stress-strain curves were not altered significantly after this period of pressure loading, indicating tbat short-term series viscous properties are negligible. Parallel viscous properties were evaluated in 10 dogs by means of the variable rate stretch test of dynamic diastolic filling. A viscoelastic model incorporating a parallel viscous element fit the dynamic stress-strain data better and predicted the static elastic properties more accurately than a simple exponential model. Thus, the mechanical characteristics of the diastolic left ventricle can be represented most precisely by a viscoelastic model that includes a parallel viscous element.AN EXPONENTIAL relationship between ventricular pressure and volume during diastole was first demonstrated by Frank.1 Influenced by Blix, 2 Frank concluded that this observation represented a fundamental relationship between diastolic force and length within the ventricular wall. During the past two decades there has been a renewed interest in describing the mechanical properties of diastolic myocardium, and numerous investigators have confirmed Frank's observations in a variety of experimental preparations. "5 On the basis of these studies it generally has been accepted that, in both the isolated and the intact heart, an exponential relationship exists between left ventricular pressure and volume during diastole. 6 However, several authors recently have suggested that fitting pressure-volume or pressure-dimension data from a single diastolic filling period with a simple exponential function may be an oversimplification. "12 Indeed, previous experiments that demonstrated exponential pressure-dimension curves in the intact heart utilized static measurements during induced volume changes.13 So far as we are aware, there are no directly measured data in the literature which indicate that ventricular pressure and di- Received July 9,1976; accepted for publication December 10,1976. mensions are exponentially related during the dynamic filling of a single diastole. The diastolic mechanical properties of isolate...

Diastolic stiffness and myocardial structure in aortic valve disease before and after valve replacement.

“…This difference between chamber and myocardial properties is important because chamber properties are dependent on the size and geometry of the left ventricle (not normalized data), but are directly related to clinical symptoms and diastolic compliance failure, whereas myocardial properties reflect mechanical and structural factors of the myocardium per se (normalized data for size and geometry) and are not necessarily related to clinical symptoms and diastolic compliance failure. A viscoelastic model for the determination of chamber and myocardial properties was used since it has been demonstrated that the diastolic stress-strain relationships are characterized more adequately by a viscoelastic than a simple elastic relationship with a monoexponential curve fit.4 12 Our data show only minor viscous effects for the whole ventricle when chamber properties are studied, but increased viscous effects in patients with aortic valve disease before surgery when myocardial properties are examined (table 3). Thus, overall viscous effects seem to be small, but myocardial viscous effects seem to be important in patients with myocardial hypertrophy.…”

The effects of airway pressure on cardiac function in intact dogs and man.

“…The accuracy of this technique was illustrated by the finding that subtracting pleural pressure from intracavitary left ventricular pressure virtually eliminated respiratory variation in the diastolic pressuredimension relationship. 10 Thus, using the pleural pressure on the surface of the heart as the external pressure, decreased transmural filling pressures of both ventricles were observed with PEEP in all animal preparations and in man. Therefore, the increased filling pressures reported previously must have been artifactual, possibly because of inaccurate pleural pressure measurements or the use of mean atrial pressure as the absolute index of ventricular filling.…”

“…Thus, the prolate spheroid model and the results of the group 1 experiments appear to be valid. The right ventricular o 0 PEEP septal-free wall diameter remained relatively constant o 10 PEEP as the airway pressure was increased. To more fully 20PEEP understand these observations, the experiment illus-3OPEEP trated in figure 8 was performed.…”

Myocardial preservation: A comparison of oxygenated crystalloid and blood cardioplegia.

“…Co was measured during maximum vena caval occlusion. Emax and the static diastolic curve were generated by selecting data from 10 to 20 cycles during an approximately 20 sec vena caval occlusion (Rankin et al 1977;Sodums et al 1984). DP/ dE and da/de correspond to the instantaneous chamber and myocardial stiffness of the LV at a specific LVP and stress (Alyono et al 1984).…”