Biaxial mechanical behavior of excised ventricular epicardium

1990 ◽  
Vol 259 (1) ◽  
pp. H101-H108 ◽  
Author(s):  
J. D. Humphrey ◽  
R. K. Strumpf ◽  
F. C. Yin
Keyword(s):  
Mechanical Behavior ◽  
Cardiac Mechanics ◽  
Left Ventricular ◽  
Biaxial Stress ◽  
Biomechanical Behavior ◽  
Highly Nonlinear ◽  
Nonlinear Stress ◽  
Parietal Pericardium ◽  
The Right

We present results from in vitro biaxial stress-strain experiments on epicardium excised from the right and left ventricular free walls of canine hearts. These data reveal that the biomechanical behavior of ventricular epicardium is qualitatively similar to atrial epicardium and parietal pericardium but different from noncontracting myocardium. In particular, ventricular epicardium exhibits a highly nonlinear stress-stretch behavior, being initially compliant but then very stiff near the limits of its extensibility. In addition, the epicardium appears to be initially isotropic but becomes markedly anisotropic upon rapid stiffening. Finally, specimens taken from the right and left ventricular free walls behaved similarly. We submit that excised ventricular epicardium is capable of carrying significant in-plane loads and that there is a need to investigate further its role in local and global cardiac mechanics and physiology.

Abstract 635: The Proximal AV Bundle in the Human Heart and Related Morbidity

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Darlene K Racker
Keyword(s):  
Human Heart ◽  
Lucifer Yellow ◽  
Ventricular Outflow Tract ◽  
Left Ventricular ◽  
Canine Heart ◽  
Sa Node ◽  
Electrode Potentials ◽  
The Right ◽  
Av Bundle

INTRODUCTION: The proximal AV bundle (PAVB) has been shown to be the only input to the AV node (AVN) in the canine heart in anatomoelectrical reports over the past 20 years. The anatomic studies utilized photographic correlations of epi- and endocardial aspects of whole hearts through blocking, and serial histologic parallel, perpendicular and transverse plane Goldner Trichrome stained sections of the flattened heart; Karnovsky’s fixative at pH 7.2 and sucrose buffer rinses; direct 3D and stereotaxic analysis. Electrical studies, under direct observation of in-vitro superfused hearts, delineated unique wire, catheter, and micropipet electrode potentials via high K, transections, Lucifer Yellow iontophoresis and photoablations during spontaneous and paced SA node rhythms and with simultaneous SA node, atrionodal bundles, PAVB, AVN and distal AV bundle recordings. HYPOTHESIS: The PAVB exists in the human heart. METHODS AND RESULTS: Explanted normal human hearts, deemed unsuitable for transplantation, processed as above with transverse sections, revealed that the AVN (Figs. A–C ) is joined by the PAVB at a 90-degree angle (Figs. B, C ). These “normal” hearts from older patients (57– 80 yr) had atrophic or absent atrial myocardium. In Figure C , most of the right medial atrial wall myocardium, but not the left atrium (LA), had been replaced by fat. CONCLUSIONS: PAVB is the only AVN input in the human heart. As in the canine heart, PAVB also runs away from the annulus and is apposed to LA. Knowledge of the PAVB should be helpful in decreasing morbidity associated with clinical procedures. Care must be taken in ablating the fast superior atrionodal bundle pathway input to the PAVB. Figures A and B are from the same 60 yr and C is from a 71 yr old heart. AVN (A) is apposed to the left ventricular outflow tract (LVOFT and dotted line) along with the PAVB ( B and C ). But as seen in C , PAVB assumes a position apposed to LA, And, as in the dog heart, thereafter (not shown here) PAVB is completely apposed to LA.

On the Biaxial Mechanical Response of Porcine Tricuspid Valve Leaflets

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Keyvan Amini Khoiy ◽  
Rouzbeh Amini
Keyword(s):  
Tricuspid Valve ◽  
Computational Models ◽  
Mechanical Response ◽  
Ex Vivo ◽  
Biaxial Stress ◽  
Strain Behavior ◽  
Highly Nonlinear ◽  
Rapid Transition ◽  
Biaxial Tensile Testing ◽  
The Right

Located on the right side of the heart, the tricuspid valve (TV) prevents blood backflow from the right ventricle to the right atrium. Similar to other cardiac valves, quantification of TV biaxial mechanical properties is essential in developing accurate computational models. In the current study, for the first time, the biaxial stress–strain behavior of porcine TV was measured ex vivo under different loading protocols using biaxial tensile testing equipment. The results showed a highly nonlinear response including a compliant region followed by a rapid transition to a stiff region for all of the TV leaflets both in the circumferential and in the radial directions. Based on the data analysis, all three leaflets were found to be anisotropic, and they were stiffer in the circumferential direction in comparison to the radial direction. It was also concluded that the posterior leaflet was the most anisotropic leaflet.

Influence of Acidosis on Cardiotonic Effects of Milrinone 

1998 ◽  
Vol 88 (3) ◽  
pp. 725-734 ◽  
Author(s):  
Makoto Tanaka ◽  
Tomohisa Ishikawa ◽  
Toshiaki Nishikawa ◽  
Katsutoshi Goto ◽  
Shigehito Sato
Keyword(s):  
Guinea Pig ◽  
Right Ventricular ◽  
Left Ventricular ◽  
Inotropic Effect ◽  
Control Group ◽  
Dependent Manner ◽  
Ph Values ◽  
The Right ◽  
Camp Formation

Background The present study was designed to determine whether augmentation of cardiac performance by milrinone is affected by acidosis in in vivo canine and in vitro guinea pig preparations, and to elucidate a mechanism in relation to the cyclic adenosine monophosphate (cAMP) formation. Methods Halothane-anesthetized, ventilated dogs were randomly assigned to a control group (arterial pH [pHa] approximately 7.4, base excess [BE] > -2 mM; n = 7), mild acidosis group (pHa approximately 7.2, BE < -9 mM; n = 7); or severe acidosis group (pHa < 7, BE < -20 mM; n = 6). Arterial blood pressure, left ventricular pressure (including maximum rate of increase, LV dP/dtmax), and pulmonary blood flow (PBF) were measured. Acidosis was induced by transient hypoxia and maintained with hydrogen chloride infusion. Hemodynamic responses to milrinone infusions at 2 and 5 microg x kg(-1) x min(-1) were then studied. In addition, left atria and right ventricular strips were dissected from guinea pig hearts and suspended in HEPES-Tyrode solution, with pH values adjusted to 7.4, 7, or 6.6. The concentration-response relation of isometric contractions for milrinone (10(-7) to 10(-4) M) and 8-bromo-cAMP (10(-4) to 10(-3) M) were determined. Results In the control group of dogs, significant increases in LV dP/dtmax (2,674 +/- 822 to 3,999 +/- 1,016 mmHg/s [means +/- SD]) and PBF (2.04 +/- 0.98 to 2.44 +/- 0.96 l/min [means +/- SD]) were seen with a milrinone infusion of 5 microg x kg(-1) x min(-1). In the mild acidosis group, 5 microg x kg(-1) x min(-1) milrinone also increased LV dP/dtmax and PBF. However, neither LV dP/dtmax nor PBF changed in the severe acidosis group. In in vitro experiments, milrinone exerted a positive inotropic effect in a concentration-dependent manner on the right ventricular preparations at pH 7.4, but not at pH 7 and 6.6, whereas no significant difference was observed in inotropic responses to 8-bromo-cAMP at pH values of 6.6, 7, and 7.4 on the right ventricular strips. In the right ventricular in vitro preparation, 10(-4) M milrinone was accompanied by a significant increase in intracellular cAMP content at apH of 7.4 but not 7. Conclusions These results indicate that the inotropic effect of milrinone is attenuated by acidosis due, at least in part, to decreased cAMP formation in acidotic muscle.

scholarly journals Lung tissue mechanics as an emergent phenomenon

2011 ◽  
Vol 110 (4) ◽  
pp. 1111-1118 ◽  
Author(s):  
Béla Suki ◽  
Jason H. T. Bates
Keyword(s):  
Mechanical Behavior ◽  
Lung Tissue ◽  
Computational Models ◽  
Tissue Mechanics ◽  
Dynamic Interactions ◽  
Strain Behavior ◽  
Tissue Resistance ◽  
Highly Nonlinear ◽  
Nonlinear Stress ◽  
Macro Scale

The mechanical properties of lung parenchymal tissue are both elastic and dissipative, as well as being highly nonlinear. These properties cannot be fully understood, however, in terms of the individual constituents of the tissue. Rather, the mechanical behavior of lung tissue emerges as a macroscopic phenomenon from the interactions of its microscopic components in a way that is neither intuitive nor easily understood. In this review, we first consider the quasi-static mechanical behavior of lung tissue and discuss computational models that show how smooth nonlinear stress-strain behavior can arise through a percolation-like process in which the sequential recruitment of collagen fibers with increasing strain causes them to progressively take over the load-bearing role from elastin. We also show how the concept of percolation can be used to link the pathologic progression of parenchymal disease at the micro scale to physiological symptoms at the macro scale. We then examine the dynamic mechanical behavior of lung tissue, which invokes the notion of tissue resistance. Although usually modeled phenomenologically in terms of collections of springs and dashpots, lung tissue viscoelasticity again can be seen to reflect various types of complex dynamic interactions at the molecular level. Finally, we discuss the inevitability of why lung tissue mechanics need to be complex.

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.

Mono and Bi-ventricular Assistance: Their Effect on Ventricular Energetics

2001 ◽  
Vol 24 (6) ◽  
pp. 380-391 ◽  
Author(s):  
G. Ferrari ◽  
K. Górczyńska ◽  
R. Mimmo ◽  
C. De Lazzari ◽  
F. Clemente ◽  
...  
Keyword(s):  
Right Ventricular ◽  
Peripheral Resistance ◽  
Mechanical Efficiency ◽  
Left Ventricular ◽  
External Work ◽  
Ventricular Elastance ◽  
The Right ◽  
Ventricular Assistance ◽  
Mechanical Assistance

When mono- and bi-ventricular mechanical assistance is used for heart recovery, its control strategy and circulatory variables affect ventricular energetics (external work-EW, oxygen consumption-VO2, cardiac mechanical efficiency-CME). This study is based on the data obtained in vitro and presents an analysis of the effects of the mono- and bi-ventricular mechanical assistance on ventricular energetics. The assistance was conducted on the principle of counterpulsation with atrio-arterial connection. It includes the following stages: 1) the characterisation of the isolated ventricle model in terms of EW, VO2 and CME as a function of the filling pressure and peripheral resistance, 2) modelling of left ventricular and pulmonary dysfunction, followed by left ventricular and bi-ventricular assistance. Experimental data enable us to draw the following conclusions: • in general, the greatest hemodynamic improvement does not correspond to the highest energetic improvement, • LVAD assistance deteriorates left ventricular CME while its effect on right ventricular energetics depends on the value of right ventricular elastance (Emax). Right ventricular CME is deteriorated by BVAD assistance irrespective of right Emax, • the energetics optimisation in bi-ventricular assistance is closely related to the right Emax, which could probably be a deciding factor in the choice of the assistance mode.

Evaluation of 99mTc-Label led Vitamin K4 as an Agent for Testicular Imaging

1991 ◽  
Vol 30 (01) ◽  
pp. 35-39 ◽  
Author(s):  
H. S. Durak ◽  
M. Kitapgi ◽  
B. E. Caner ◽  
R. Senekowitsch ◽  
M. T. Ercan
Keyword(s):  
Soft Tissue ◽  
Room Temperature ◽  
Normal Subjects ◽  
Left Testis ◽  
Wide Range ◽  
Activity Ratios ◽  
The Right ◽  
Radioactivity Levels

Vitamin K4 was labelled with 99mTc with an efficiency higher than 97%. The compound was stable up to 24 h at room temperature, and its biodistribution in NMRI mice indicated its in vivo stability. Blood radioactivity levels were high over a wide range. 10% of the injected activity remained in blood after 24 h. Excretion was mostly via kidneys. Only the liver and kidneys concentrated appreciable amounts of radioactivity. Testis/soft tissue ratios were 1.4 and 1.57 at 6 and 24 h, respectively. Testis/blood ratios were lower than 1. In vitro studies with mouse blood indicated that 33.9 ±9.6% of the radioactivity was associated with RBCs; it was washed out almost completely with saline. Protein binding was 28.7 ±6.3% as determined by TCA precipitation. Blood clearance of 99mTc-l<4 in normal subjects showed a slow decrease of radioactivity, reaching a plateau after 16 h at 20% of the injected activity. In scintigraphic images in men the testes could be well visualized. The right/left testis ratio was 1.08 ±0.13. Testis/soft tissue and testis/blood activity ratios were highest at 3 h. These ratios were higher than those obtained with pertechnetate at 20 min post injection.99mTc-l<4 appears to be a promising radiopharmaceutical for the scintigraphic visualization of testes.

Effects of Rest and Exercise on Cardiac Blood Volume Determinations

1997 ◽  
Vol 36 (08) ◽  
pp. 259-264
Author(s):  
N. Topuzović
Keyword(s):  
Radionuclide Ventriculography ◽  
Left Ventricular ◽  
Peak Exercise ◽  
Volume Determination ◽  
Group I ◽  
Lv Volumes ◽  
Group Ii ◽  
Lv Volume

Summary Aim: The purpose of this study was to investigate the changes in blood activity during rest, exercise and recovery, and to assess its influence on left ventricular (LV) volume determination using the count-based method requiring blood sampling. Methods: Forty-four patients underwent rest-stress radionuclide ventriculography; Tc-99m-human serum albumin was used in 13 patients (Group I), red blood cells was labeled using Tc-99m in 17 patients (Group II) in vivo, and in 14 patients (Group III) by modified in vivo/in vitro method. LV volumes were determined by a count-based method using corrected count rate in blood samples obtained during rest, peak exercise and after recovery. Results: In group I at stress, the blood activity decreased by 12.6 ± 5.4%, p <0.05, as compared to the rest level, and increased by 25.1 ± 6.4%, p <0.001, and 12.8 ± 4.5%, p <0.05, above the resting level in group II and III, respectively. This had profound effects on LV volume determinations if only one rest blood aliquot was used: during exercise, the LV volumes significantly decreased by 22.1 ± 9.6%, p <0.05, in group I, whereas in groups II and III it was significantly overestimated by 32.1 ± 10.3%, p <0.001, and 10.7 ± 6.4%, p <0.05, respectively. The changes in blood activity between stress and recovery were not significantly different for any of the groups. Conclusion: The use of only a single blood sample as volume aliquot at rest in rest-stress studies leads to erroneous estimation of cardiac volumes due to significant changes in blood radioactivity during exercise and recovery.

Enhanced Increases in Cytosolic Ca2+ in ADP-Stimulated Platelets from Patients with Delta-Storage Pool Deficiency – A Possible Indicator of Interactions between Granule-Bound ADP and the Membrane ADP Receptor

1997 ◽  
Vol 77 (02) ◽  
pp. 376-382 ◽  
Author(s):  
Bruce Lages ◽  
Harvey J Weiss
Keyword(s):  
Platelet Rich Plasma ◽  
Limited Range ◽  
Dense Granule ◽  
Receptor Desensitization ◽  
Fura 2 ◽  
Storage Pool ◽  
Low Levels ◽  
The Right

SummaryThe possible involvement of secreted platelet substances in agonist- induced [Ca2+]i increases was investigated by comparing these increases in aspirin-treated, fura-2-loaded normal platelets and platelets from patients with storage pool deficiencies (SPD). In the presence and absence of extracellular calcium, the [Ca2+]i response induced by 10 µM ADP, but not those induced by 0.1 unit/ml thrombin, 3.3 µM U46619, or 20 µM serotonin, was significantly greater in SPD platelets than in normal platelets, and was increased to the greatest extent in SPD patients with Hermansky-Pudlak syndrome (HPS), in whom the dense granule deficiencies are the most severe. Pre-incubation of SPD-HPS and normal platelets with 0.005-5 µM ADP produced a dose-dependent inhibition of the [Ca2+]i response induced by 10 µ M ADP, but did not alter the [Ca2+]i increases induced by thrombin or U46619. Within a limited range of ADP concentrations, the dose-inhibition curve of the [Ca2+]i response to 10 µM ADP was significantly shifted to the right in SPD-HPS platelets, indicating that pre-incubation with greater amounts of ADP were required to achieve the same extent of inhibition as in normal platelets. These results are consistent with a hypothesis that the smaller ADP-induced [Ca2+]i increases seen in normal platelets may result from prior interactions of dense granule ADP, released via leakage or low levels of activation, with membrane ADP receptors, causing receptor desensitization. Addition of apyrase to platelet-rich plasma prior to fura-2 loading increased the ADP-induced [Ca2+]i response in both normal and SPD-HPS platelets, suggesting that some release of ADP derived from both dense granule and non-granular sources occurs during in vitro fura-2 loading and platelet washing procedures. However, this [Ca2+]i response was also greater in SPD-HPS platelets when blood was collected with minimal manipulation directly into anticoagulant containing apyrase, raising the possibility that release of dense granule ADP resulting in receptor desensitization may also occur in vivo. Thus, in addition to enhancing platelet activation, dense granule ADP could also act to limit the ADP-mediated reactivity of platelets exposed in vivo to low levels of stimulation.

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