Determination of a Constitutive Relation for Passive Myocardium: II.—Parameter Estimation

1990 ◽  
Vol 112 (3) ◽  
pp. 340-346 ◽  
Author(s):  
J. D. Humphrey ◽  
R. K. Strumpf ◽  
F. C. P. Yin
Keyword(s):  
Constitutive Relation ◽  
Functional Form ◽  
Nonlinear Least Squares ◽  
Transversely Isotropic ◽  
Least Squares Regression ◽  
Material Parameters ◽  
Biomechanical Behavior ◽  
Best Fit

In the first paper of this series, we proposed a new transversely isotropic pseudostrain-energy function W for describing the biomechanical behavior of excised noncontracting myocardium. The specific functional form of W was inferred directly from biaxial data to be a polynomial function of two coordinate invariant measures of the finite deformation and five material parameters. In this paper, best-fit values of the material parameters are determined from biaxial data using a nonlinear least-squares regression. These values of the parameters are shown to be well-determined, and the final constitutive relation is shown to have good predictive capabilities. Since the proposed constitutive relation describes much broader classes of in-vitro biaxial data than previously proposed relations, it may be better applicable to analyses of stress in the passive heart.

Determination of a Constitutive Relation for Passive Myocardium: I. A New Functional Form

1990 ◽  
Vol 112 (3) ◽  
pp. 333-339 ◽  
Author(s):  
J. D. Humphrey ◽  
R. K. Strumpf ◽  
F. C. P. Yin
Keyword(s):  
Constitutive Relation ◽  
Invariant Measures ◽  
Functional Form ◽  
Transversely Isotropic ◽  
The Other ◽  
Material Symmetry ◽  
Material Parameters ◽  
Experimental Protocols ◽  
Theory And Experiment

The specific aim of this study is to determine a constitutive relation for non-contracting myocardium in terms of a pseudostrain-energy function W whose form is guided by both theory and experiment. We assume that the material symmetry of myocardium is initially and locally transversely-isotropic, and seek a W which depends upon only two coordinate invariant measures of the finite deformation. The specific functional form of such a W is inferred directly from experimental protocols in which one invariant is held constant while the other is varied, and vice versa. On the basis of data from families of these “constant invariant” tests on thin slabs of myocardium taken from the mid-walls of six canine left ventricles, we propose a new polynomial form of W containing only five material parameters.

A Constitutive Theory for Biomembranes: Application to Epicardial Mechanics

1992 ◽  
Vol 114 (4) ◽  
pp. 461-466 ◽  
Author(s):  
J. D. Humphrey ◽  
R. K. Strumpf ◽  
F. C. P. Yin
Keyword(s):  
Constitutive Relation ◽  
Experimental Approach ◽  
Functional Form ◽  
Biological Membrane ◽  
Left Ventricular ◽  
Constitutive Theory ◽  
Material Parameters ◽  
Biomechanical Behavior ◽  
The Right

We present a new theoretically motivated experimental approach for identifying the functional form of a constitutive relation for any nonlinear, anisotropic pseudoelastic biological membrane. The utility of this approach is illustrated by identifying, from biaxial data, a new constitutive relation for excised ventricular epicardium. Values of the associated material parameters are calculated and compared for right and left ventricular specimens. Based on our findings, we suggest that there are no significant differences in the biomechanical behavior of epicardium excised from the right and left ventricular free walls of canine hearts.

On Constitutive Relations and Finite Deformations of Passive Cardiac Tissue: I. A Pseudostrain-Energy Function

1987 ◽  
Vol 109 (4) ◽  
pp. 298-304 ◽  
Author(s):  
J. D. Humphrey ◽  
F. C. P. Yin
Keyword(s):  
Energy Function ◽  
Cardiac Tissue ◽  
Functional Form ◽  
Structural Information ◽  
Constitutive Relations ◽  
Three Dimensional ◽  
Transversely Isotropic ◽  
Limited Range ◽  
Material Parameters ◽  
Data Result

A three-dimensional constitutive relation for passive cardiac tissue is formulated in terms of a structurally motivated pseudostrain-energy function, W, while the mathematical simplicity of phenomenological approaches is preserved. A specific functional form of W is proposed on the basis of limited structural information and multiaxial experimental data. The material parameters are determined in a least-squared sense from both uniaxial and biaxial data. Our results suggest that (1) multiaxially-loaded cardiac tissue is nearly transversely-isotropic with respect to local muscle fiber directions, at least for a limited range of strain histories, (2) material parameters determined from uniaxial papillary muscle data result in gross underestimates of the stresses in multiaxially-loaded specimens, and (3) material parameters determined from equibiaxial tests predict the behavior of the tissue under various nonequibiaxial stretching protocols reasonably well.

scholarly journals Pharmacokinetic-Pharmacodynamic Characterization of Omadacycline against Haemophilus influenzae Using a One-Compartment In Vitro Infection Model

2020 ◽  
Vol 64 (6) ◽  
Author(s):  
Brian D. VanScoy ◽  
Elizabeth A. Lakota ◽  
Haley Conde ◽  
Jennifer McCauley ◽  
Lawrence Friedrich ◽  
...  
Keyword(s):  
Haemophilus Influenzae ◽  
Antimicrobial Agents ◽  
Nonlinear Least Squares ◽  
Infection Model ◽  
Least Squares Regression ◽  
Total Drug ◽  
Time Curve ◽  
Content Type ◽  
Concentration Time

ABSTRACT Omadacycline is a novel aminomethylcycline with activity against Gram-positive and -negative organisms, including Haemophilus influenzae, which is one of the leading causes of community-acquired bacterial pneumonia (CABP). The evaluation of antimicrobial agents against H. influenzae using standard murine infection models is challenging due to the low pathogenicity of this species in mice. Therefore, 24-h dose-ranging studies using a one-compartment in vitro infection model were undertaken with the goal of characterizing the magnitude of the ratio of the area under the concentration-time curve (AUC) to the MIC (AUC/MIC ratio) associated with efficacy for a panel of five H. influenzae isolates. These five isolates, for which MIC values were 1 or 2 mg/liter, were exposed to omadacycline total-drug epithelial lining fluid (ELF) concentration-time profiles based on those observed in healthy volunteers following intravenous omadacycline administration. Relationships between change in log10 CFU/ml from baseline at 24 h and the total-drug ELF AUC/MIC ratios for each isolate and for the isolates pooled were evaluated using Hill-type models and nonlinear least-squares regression. As evidenced by the high coefficients of determination (r2) of 0.88 to 0.98, total-drug ELF AUC/MIC ratio described the data well for each isolate and the isolates pooled. The median total-drug ELF AUC/MIC ratios associated with net bacterial stasis and 1- and 2-log10 CFU/ml reductions from baseline at 24 h were 6.91, 8.91, and 11.1, respectively. These data were useful to support the omadacycline dosing regimens selected for the treatment of patients with CABP, as well as susceptibility breakpoints for H. influenzae.

Determination of in vitro „anti-aging„-effects of Ganoderma pfeifferi

Planta Medica ◽  
2010 ◽  
Vol 76 (12) ◽  
Author(s):  
W Jülich ◽  
J Pörksen ◽  
H Welzel ◽  
U Lindequist
Keyword(s):  
Aging Effects

In vitro determination of the skin anti-aging potential of eleven South African plants

Planta Medica ◽  
2013 ◽  
Vol 79 (13) ◽  
Author(s):  
GN Ndlovu ◽  
G Fouche ◽  
W Cordier ◽  
V Steenkamp ◽  
M Tselanyane
Keyword(s):  
South African ◽  
South African Plants ◽  
African Plants
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