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T Shaffer

Publications and source records attributed to T Shaffer.

5 recordsLinked to original sources
PubMed1990

Theoretical model of ventricular interdependence: pericardial effects.

One ventricle can influence the filling characteristics of the opposite ventricle directly through the myocardium and indirectly through the pericardium. Based on definitions of compliances and volumes, we developed a theoretical analysis that indicated that the magnitude of interdependence was related to the relative compliances of the left and right ventricular free walls, septum, and pericardium. This analysis was verified in postmortem canine hearts. Balloons were inserted into each ventricle, and left ventricle pressure (delta Pl) and volume (delta Vl) changes caused by increasing right ventricular pressure (delta Pr) and volume (delta Vr) or pericardial pressure (delta Pp) were recorded. For delta Pl/delta Pr, delta Pl/delta Pp, delta Pl/delta Vr, delta Vl/delta Pr, delta Vl/delta Pp, and delta Vl/delta Vr measurements, the standard error of estimates was small and the predicted and measured values were significantly related (P less than 0.05); the values were 0.88 +/- 0.16, 0.87 +/- 0.17, 0.93 +/- 0.05, 0.95 +/- 0.09, 0.96 +/- 0.05, and 0.96 +/- 0.04, respectively. These coupling coefficients (delta Pl/delta Pr, delta Pl/delta Pp, etc.) a direct measurement of interdependence, indicated that pericardial-to-ventricular coupling is greater than ventricular-ventricular coupling (delta Pl/delta Pp greater than delta Pl/delta Pr, 0.91 +/- 0.09 vs. 0.23 +/- 0.09, P less than 0.01; delta Vl/delta Pp greater than delta Vl/delta Pr, -1.04 +/- 0.35 vs. -0.19 +/- 0.05, P less than 0.05). This study, by developing a theoretical analysis and by direct measurements, provides a better understanding of ventricular interdependence and may help to predict effects of cardiac tamponade and constrictive pericarditis on ventricular interdependence.

Blood Pressure↗
PubMed1988

Predictive changes in ventricular interdependence.

Based on the balance of forces across the interventricular septum, we developed a theoretical analysis to explain how one ventricle can directly influence the filling characteristics of the other ventricle. The analysis indicated that the pressure and volume transfer were related to the relative compliances of the interventricular septum and ventricular free walls. The present study examined whether the theoretical analysis could be used to predict changes in ventricular interdependence caused by altering regional compliance. To examine this hypothesis, hearts were removed from 18 dogs and placed in cool cardioplegic solution. Balloons were inserted into each ventricle, and the left and right pressure (delta P1, delta Pr) and volume (delta V1, delta Vr) changes caused by changing the pressure and volume of the other ventricle were recorded. After the initial measurements, acute changes in left ventricular free wall compliance (n = 6), septal compliance (n = 6), and right ventricular free wall compliance (n = 6) were induced by glutaraldehyde injections. As predicted by the theoretical analysis, decreasing left ventricular free wall compliance increased delta P1/delta Pr, delta P1/delta Vr, delta Pr/delta V1, and delta Vr/delta V1 significantly (P less than 0.05) by 89 +/- 15, 155 +/- 33, 282 +/- 65, and 112 +/- 22% (mean +/- SEM), respectively. Decreasing septal compliance decreases delta P1/delta Pr, delta V1/delta Pr, delta V1/delta Vr, delta Pr/delta P1, delta Vr/delta P1, and delta Vr/delta V1 significantly (P less than 0.05) by 48 +/- 7, 71 +/- 10, 69 +/- 14, 48 +/- 7, 62 +/- 8, and 57 +/- 13%, respectively. Decreasing right ventricular free wall compliance increased delta P1/delta Vr, delta V1/delta Vr, delta Pr/delta P1, and delta Pr/delta V1 significantly (P less than 0.05) by 97 +/- 25, 79 +/- 20, 57 +/- 18, and 59 +/- 23%, respectively. Furthermore, these alterations in ventricular coupling were predictable: The actual and predicted percentage changes in the transfer functions were in close agreement. The results of these studies show predictable alterations in the mechanical coupling between the ventricles following changes in right ventricular, septal, and left ventricular free wall compliances.

Animals↗
PubMedDate not supplied

A theoretical and experimental model of ventricular interdependence.

Because of the close anatomical association between the ventricles, the volume of one ventricle can directly affect the volume and pressure within the other ventricle. To study the mechanical coupling between the ventricles, we modeled the right and left ventricles as a two-compartment model with right wall (Crw), septal (Cs), and left wall (Clw) compliances. Based on the balances of forces across the septum, four equations were obtained to predict the transfer of pressure (P) and volume (V) information from one ventricle to another. The validity of the theoretical analysis was tested first in a physical model and then in a post-mortem heart preparation. The standard errors of estimate comparing the predicted to measured values were low for both the physical model and the post-mortem heart data. All values were significantly related (P less than 0.05) with r greater than 0.89. The results show excellent correlation between predicted and measured values. This model provides a better understanding of ventricular interdependence and may help to predict effects of hypertrophy and/or myocardial ischemia on ventricular interdependence.

Animals↗