Diastolic ventricular interaction in normal and dilated heart during head-up tilting

Right Ventricular Myocardial Stiffness and Relaxation Components by Kinematic Model-Based Transtricuspid Flow Analysis in Children and Adolescents with Pulmonary Arterial Hypertension

We hypothesized that the kinematic model-based parameters obtained from the transtricuspid E-wave would be useful for evaluating the right ventricular diastolic property in pediatric pulmonary arterial hypertension (PAH) patients. The model was parametrized by stiffness/elastic recoil k, relaxation/damping c and load x. These parameters were determined as the solution of m⋅d²x/dt² + c⋅dx/dt + kx = 0, which is based on the theory that the E-wave contour is determined by the interplay of stiffness/restoring force, damping/relaxation force and load. The PAH group had a significantly higher k and c compared with the control group (182.5 ± 72.4 g/s vs. 135.7 ± 49.5 g/s², p = 0.0232, and 21.9 ± 6.5 g/s vs. 10.6 ± 5.2 g/s, p <0.0001, respectively). These results indicate that in the PAH group, the right ventricle had higher stiffness/elastic recoil and inferior cross-bridge relaxation. The present findings indicate the feasibility and utility of using kinematic model parameters to assess right ventricular diastolic function.

A cardiovascular mathematical model of graded head-up tilt

A lumped parameter model of the cardiovascular system has been developed and optimized using experimental data obtained from 13 healthy subjects during graded head-up tilt (HUT) from the supine position to . The model includes descriptions of the left and right heart, direct ventricular interaction through the septum and pericardium, the systemic and pulmonary circulations, nonlinear pressure volume relationship of the lower body compartment, arterial and cardiopulmonary baroreceptors, as well as autoregulatory mechanisms. A number of important features, including the separate effects of arterial and cardiopulmonary baroreflexes, and autoregulation in the lower body, as well as diastolic ventricular interaction through the pericardium have been included and tested for their significance. Furthermore, the individual effect of parameter associated with heart failure, including LV and RV contractility, baseline systemic vascular resistance, pulmonary vascular resistance, total blood volume, LV diastolic stiffness and reflex gain on HUT response have also been investigated. Our fitted model compares favorably with our experimental measurements and published literature at a range of tilt angles, in terms of both global and regional hemodynamic variables. Compared to the normal condition, a simulated congestive heart failure condition produced a blunted response to HUT with regards to the percentage changes in cardiac output, stroke volume, end diastolic volume and effector response (i.e., heart contractility, venous unstressed volume, systemic vascular resistance and heart rate) with progressive tilting.

Changes in ventricular twist and untwisting with orthostatic stress: endurance athletes versus normally active individuals

Endurance-trained individuals exhibit larger reductions in left ventricular (LV) end-diastolic volume in response to lower body negative pressure (LBNP) compared with normally active individuals. However, the relationship between LV torsion and untwisting and the LV volume response to LBNP in endurance athletes is unknown. Eight endurance-trained athletes [maximal oxygen consumption (V̇o2max): 66.4 ± 7.2 ml·kg−1·min−1] and eight normally active individuals (V̇o2max: 41.9 ± 9.0 ml·kg−1·min−1) (all men) underwent two cardiac magnetic resonance imaging (MRI) assessments, the first during supine rest and the second during −30 mmHg LBNP. Right ventricular (RV) and LV volumes were assessed, myocardial tagging was applied in order to quantify LV peak torsion and peak untwisting rate, and filling rates were measured with phase-contrast MRI. In response to LBNP, endurance-trained individuals had greater reductions in RV and LV end-diastolic volume and stroke volume ( P < 0.05). Endurance athletes had reduced untwisting rates (20.3 ± 8.7°/s), while normally active individuals had increased untwisting rates (−16.2 ± 32.1°/s) in response to LBNP ( P < 0.05). Changes in peak untwisting rate were significantly correlated with change in peak torsion ( R = −0.87, P < 0.05), with the change in early filling rate and V̇o2max, but not with changes in end-diastolic or end-systolic volume ( P > 0.05). We conclude that increased untwisting rates in normally active subjects may mitigate the drop in early filling rate with LBNP and thus may be a compensatory mechanism for the reduction in stroke volume with volume unloading. The opposite response in athletes, who showed a decreased untwisting rate, may contribute to their larger reductions in LV end-diastolic and stroke volumes with volume unloading and their orthostatic intolerance.

The potential role of the pericardium on diastolic filling in endurance-trained athletes under conditions of physiological stress

In this review, we examine the growing body of evidence suggesting that the pericardium plays an important role in modulating cardiac function during conditions of physiological stress. Specifically, we discuss the effects of the pericardium on left ventricular filling and compliance. Furthermore, we reveal that there is increasing evidence to support the contention that the pericardium is capable of adaptation in response to volume loading. We also provide data that suggests endurance-training is a good example of a physiological stressor capable of causing pericardial remodelling. These adaptations appear particularly beneficial during exercise and may explain (in part) the common finding of stroke volume increasing during exercise to a greater extent in endurance-trained athletes. However, this adaptation may also partially explain the increased susceptibility to orthostatic intolerance in endurance athletes.

Diastolic ventricular interactions in endurance-trained athletes during orthostatic stress

Enhanced left-ventricular (LV) compliance is a common adaptation to endurance training. This adaptation may have differential effects under conditions of altered venous return. The purpose of this investigation was to assess the effect of cardiac (un)loading on right ventricular (RV) cavity dimensions and LV volumes in endurance-trained athletes and normally active males. Eight endurance-trained (Vo(2max), 65.4 +/- 5.7 ml.kg(-1).min(-1)) and eight normally active (Vo(2max), 45.1 +/- 6.0 ml.kg(-1).min(-1)) males underwent assessments of the following: 1) Vo(2max), 2) orthostatic tolerance, and 3) cardiac responses to lower-body positive (0-60 mmHg) and negative (0 to -80 mmHg) pressures with echocardiography. In response to negative pressures, echocardiographic analysis revealed a similar decrease in RV end-diastolic cavity area in both groups (e.g., at -80 mmHg: normals, 21.4%; athletes, 20.8%) but a greater decrease in LV end-diastolic volume in endurance-trained athletes (e.g., at -80 mmHg: normals, 32.3%; athletes, 44.4%; P < 0.05). Endurance-trained athletes also had significantly greater decreases in LV stroke volume during lower-body negative pressure. During positive pressures, endurance-trained athletes showed larger increases in LV end-diastolic volume (e.g., at +60 mmHg; normals, 14.1%; athletes, 26.8%) and LV stroke volume, despite similar responses in RV end-diastolic cavity area (e.g., at +60 mmHg: normals, 18.2%; athletes, 24.2%; P < 0.05). This investigation revealed that in response to cardiac (un)loading similar changes in RV cavity area occur in endurance-trained and normally active individuals despite a differential response in the left ventricle. These differences may be the result of alterations in RV influence on the left ventricle and/or intrinsic ventricular compliance.

Load-independent index of diastolic filling: model-based derivation with in vivo validation in control and diastolic dysfunction subjects

Maximum elastance is an experimentally validated, load-independent systolic function index stemming from the time-varying elastance paradigm that decoupled extrinsic load from (intrinsic) contractility. Although Doppler echocardiography is the preferred method of diastolic function (DF) assessment, all echo-derived indexes are load dependent, and no invasive or noninvasive load-independent index of filling (LIIF) exists. In this study, we derived and experimentally validated a LIIF. We used a kinematic filling paradigm (the parameterized diastolic filling formalism) to predict and derive the (dimensionless) dynamic diastolic efficiency M, defined by the slope of the peak driving force [maximum driving force (kx(o)) proportional, variant peak atrioventricular (AV) gradient] to maximum viscoelastic resistive force [peak resistive force (cE(peak))] relation. To validate load independence, we analyzed E-waves recorded while load was varied via tilt table (head up, horizontal, and head down) in 16 healthy volunteers. For the group, linear regression of E-wave derived kx(o) vs. cE(peak) yielded kx(o) = M (cE(peak)) + B, r2 = 0.98; where M = 1.27 +/- 0.09 and B = 5.69 +/- 1.70. Effects of diastolic dysfunction (DD) on M were assessed by analysis of preexisting simultaneous cath-echo data in six DD vs. five control subjects. Average M for the DD group (M = 0.98 +/- 0.07) was significantly lower than controls (M = 1.17 +/- 0.05, P < 0.001). We conclude that M is a LIIF because it uncouples intrinsic DF (i.e., the pressure-flow relation) from extrinsic load (left ventricular end-diastolic pressure). Larger M values imply better DF in that increasing AV pressure gradient results in relatively smaller increases in peak resistive losses (cE(peak)). Conversely, lower M implies that increasing AV gradient leads to larger increases in resistive losses. Further prospective validation characterizing M in well-defined pathological states is warranted.

Relationship of diastolic intraventricular pressure gradients and aerobic capacity in patients with diastolic heart failure

We sought to elucidate the relationship between diastolic intraventricular pressure gradients (IVPG) and exercise tolerance in patients with heart failure using color M-mode Doppler. Diastolic dysfunction has been implicated as a cause of low aerobic potential in patients with heart failure. We previously validated a novel method to evaluate diastolic function that involves noninvasive measurement of IVPG using color M-mode Doppler data. Thirty-one patients with heart failure and 15 normal subjects were recruited. Echocardiograms were performed before and after metabolic treadmill stress testing. Color M-mode Doppler was used to determine the diastolic propagation velocity ( Vp) and IVPG off-line. Resting diastolic function indexes including myocardial relaxation velocity, Vp, and E/ Vp correlated well with V̇o2 max ( r = 0.8, 0.5, and −0.5, respectively, P < 0.001 for all). There was a statistically significant increase in Vp and IVPG in both groups after exercise, but the change in IVPG was higher in normal subjects compared with patients with heart failure (2.6 ± 0.8 vs. 1.1 ± 0.8 mmHg, P < 0.05). Increase in IVPG correlated with peak V̇o2 max ( r = 0.8, P < 0.001) and was the strongest predictor of exercise capacity. Myocardial relaxation is an important determinant of exercise aerobic capacity. In heart failure patients, impaired myocardial relaxation is associated with reduced diastolic suction force during exercise.

Effects of acute angiotensin-converting enzyme inhibition on diastolic ventricular interaction in the dilated heart

BACKGROUND

The normal and dilated heart behaves as a single functional unit during preload reduction: volume unloading in the setting of diastolic ventricular interaction allows for increased left ventricular (LV) filling.

HYPOTHESIS

We hypothesized that reduction of venous return induced by a physiologic stimulus (tilting) or by acute angiotensin-converting enzyme (ACE) inhibitors in dilated heart is likely to have a marked and similar effect on ventricular chamber geometry and filling. This study was designed to assess how the normal and dilated heart adapts to preload reduction.

METHODS

Twenty normal subjects and 20 patients with moderate heart failure due to dilated cardiomyopathy were studied with two-dimensional and Doppler echocardiography in supine position (B) and after 40 degrees of head-up tilting (T). The following day, patients repeated supine (C) and tilting test (TC) after administration of captopril (25 mg s.l.). Right ventricular (RV) and LV dimensions, LV geometry, and tricuspid, mitral, and pulmonary venous flow patterns were recorded at each step of the study.

RESULTS

In the two groups, T was associated with reduction of RV area and LV volumes; C and TC produced a similar effect on RV and LV. Changes in LV septal-lateral diameter and anterior-posterior diameter were different at each step of the study: during T (both groups) and after C and TC, the septallateral diameter increased slightly while the anterior-posterior diameter decreased. During T, mitral and tricuspid peak flow velocities decreased, peak late velocities were unchanged, and the deceleration time of mitral flow increased; the systolic forward flow of pulmonary venous flow decreased, the diastolic forward flow did not change, and the difference in duration between reverse pulmonary flow and mitral peak late flow decreased: C and CT induced similar changes.

CONCLUSION

Preload reduction induced by tilting or by ACE inhibitors induces profound and similar effects on LV and RV dimensions, LV geometry, and biventricular filling. Reduction of RV dimension is associated with adaptation of LV geometry and decrease of LV diastolic pressure, which facilitates LV filling and pulmonary venous drainage: ACE inhibition associated with tilting exerts an additional effect on these changes. These data confirm the role of ventricular interaction in modulating LV filling in heart failure.