Biomechanical and Hemodynamic Measures of Right Ventricular Diastolic Function: Translating Tissue Biomechanics to Clinical Relevance

Figure 1. Diastolic function was determined by fitting the diastolic phase of a pressure–volume loop with an exponential function. Eed (end‐diastolic elastance) is the slope of this exponential curve at the end of diastole or at EDV. β indicates diastolic stiffness; dP/dV, change in pressure per change in volume; EDP, end‐diastolic pressure; EDV, end‐diastolic volume; P, pressure; V, volume.

Figure 2. The E1 region represents the elastic modulus in the low‐strain, linear portion of the stress–strain curve at which collagen fibers have not yet been recruited and the behavior of the tissue is predominantly determined by myofibers. The E2 region represents the elastic modulus in the high‐strain, linear portion of the curve after all collagen fibers have straightened. Elb indicates the lower boundary of the exponential transition region; Eub, upper boundary of the exponential transition region.

Figure 3. A, Representative pressure–volume loops for control and PAB demonstrate the significantly different diastolic pressure–volume relationship after 3 weeks of PAB. Triangular and circular points were representative diastolic points to fit the exponential curve to P=α (eβV−1). B, Pressure overload on the right ventricle significantly increased end‐diastolic elastance. C, PAB significantly increased end‐diastolic pressure and (D) RV systolic pressure. Bar graphs represent mean values with error bars representing standard error. β indicates diastolic stiffness; Eed, end diastolic elastance; P, pressure; PAB, pulmonary artery banding; RV, right ventricular; V, volume.

Figure 4. Plot of Eed vs β showing a positive linear correlation with R=0.5954, P=0.04. Eed indicates end‐diastolic elastance; PAB, pulmonary artery banding; β, diastolic stiffness.

Figure 5. A, Average stress–strain curves in the PAB rats are shifted up and to the left in the longitudinal direction. Error bars represent standard error. B, There are no differences in the stress–strain curves in the circumferential direction. C, Longitudinal low‐strain elastic modulus (E1) was significantly increased in PAB rats. D, There was no significant difference in longitudinal high‐strain elastic modulus (E2). Bar graphs represent mean values with error bars representing standard error. PAB indicates pulmonary artery banding.

Figure 6. Integrating the hemodynamic changes in diastolic function with biomechanical changes in diastolic stiffness shows that PAB rats have both increased E1 and Eed with R=0.3856. Box represents mean Eed and longitudinal E1. Error bars represent standard error. E1 indicates low‐strain elastic modulus; Eed, end‐diastolic elastance; PAB, pulmonary artery banding.

Figure 7. A, Plot of the measured pressure values against the calculated estimated wall stress using the Laplace model of a representative control animal. The black asterisks represent diastolic filling points, and the red circles represent the systolic ejection points. The rest of the cardiac cycle is labeled and progresses in a clockwise direction. B, Corresponding stress–strain curve of a representative control animal with black asterisks representing diastolic filling points. The purple dashed line indicates the Elb and Eub boundaries. E1 and E2 are represented by red lines in low‐ and high‐strain regions, respectively. In this control animal, diastolic filling points overlap in both the E1 and the exponential transitional area, suggesting predominant myofiber stretch involved in early diastolic filling followed by combined myofiber and collagen strengthening in late diastolic filling. E1 indicates low‐strain elastic modulus; E2, high‐strain elastic modulus; Elb, lower boundary of the exponential transition region; Eub, upper boundary of the exponential transition region.

Figure 8. A, Plot of stress–pressure loops of all control animals. B, Plot of stress–pressure loops of all PAB animals. Black asterisks represent data points during diastolic filling, whereas red dots represent data points during systolic ejection. The cardiac cycle progresses in a clockwise direction. PAB indicates pulmonary artery banding.