The mechanical properties of ventricular muscle are a critical determinant of cardiac function. The mechanical properties can be quantified in terms of the muscle's stress-strain relationships, where the stresses and strains are the normalized forces and displacements. The objective of this project is to determine how the mechanical properties of reperfused myocardium are related to the level of flow, to mechanical interventions, and to administered pharmacologic agents. The investigators will first study the mechanical properties of reperfused myocardium in an isolated ventricular septal preparation, where the stresses, strains, and level of flow can be directly measured and controlled. The investigators will first study the mechanical properties of reperfused myocardium in an isolated ventricular septal preparation, where the stresses, strains, and level of flow can be directly measured and controlled. The investigators then intent to obtain an index of wall stress in intact hearts so that they can study the mechanical properties of reperfused muscle in intact hearts. These studies in intact hearts can provide information that is not available from the isolated septum, such as data about ischemic border zones, the influence of ischemic and reperfused areas on nonischemic areas, and the effect of geometry. These studies will require accurate estimates of regional ventricular wall stress, but with currently available methods, it is not possible to accurately quantify wall stress in the intact heart. Our recent studies have shown, however, that the mechanical properties in the plane of the tissue are related to those in the direction perpendicular to the plane of the tissue. They are, therefore, developing a probe for measuring these perpendicular (or transverse) properties. They will verify the close correlation between the in-plane wall stress and the transverse (across the wall) stiffness. The transverse stiffness is determined by transversely indenting the muscle, and is defined as the ratio of the indentation stress to indentation strain. Since the transverse stiffness can be measured in both isolated muscle and intact hearts, once it is validated in the isolated septum that the close correlation between in-plane stresses and transverse stiffness pertains during reperfusion and its attendant interventions, transverse stiffness can be used in the intact heart to estimate in-plane properties.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL044092-03
Application #
3362850
Study Section
Surgery and Bioengineering Study Section (SB)
Project Start
1990-01-01
Project End
1994-12-31
Budget Start
1992-01-01
Budget End
1992-12-31
Support Year
3
Fiscal Year
1992
Total Cost
Indirect Cost
Name
Johns Hopkins University
Department
Type
Schools of Medicine
DUNS #
045911138
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Blair, D M; Halperin, H R (1996) Hand-held, dynamic indentation system for measuring myocardial transverse stiffness. Biomed Instrum Technol 30:517-25
Livingston, J Z; Halperin, H R; Yin, F C (1994) Accounting for the Gregg effect in tetanised coronary arterial pressure-flow relationships. Cardiovasc Res 28:228-34
Halperin, H R; Tsitlik, J E; Rayburn, B K et al. (1993) Estimation of myocardial mechanical properties with dynamic transverse stiffness. Adv Exp Med Biol 346:103-12
Resar, J R; Judd, R M; Halperin, H R et al. (1993) Direct evidence that coronary perfusion affects diastolic myocardial mechanical properties in canine heart. Cardiovasc Res 27:403-10