Exercise induced pulmonary vasoconstriction

Variable Hemodynamic Responses during Diastolic Stress Echocardiography in Patients Who Have Relaxation Abnormality with Possible Elevated Filling Pressure

BACKGROUND AND OBJECTIVES

The clinical characteristics of patients with diastolic dysfunction characterized by a relaxation abnormality with possible elevated filling pressure is remain to be determined. We sought to test whether diastolic stress echocardiography (DSE) is useful for characterization of these patients.

METHODS

A total of 120 patients (58 men, mean age of 64±7 years) with E/A ratio <1.0 (mean±SD, 0.7±0.1) and 10≤ E/e' <15 at rest echocardiography was enrolled prospectively for supine bicycle exercise up to 50 W.

RESULTS

During exercise, 47 patients (39%) showed high left ventricular filling pressure (E/e' >15, hLVFP) and 40 (30%) developed exercise-induced pulmonary hypertension (systolic pulomary arterial pressure >50 mmHg, EiPH) without hLVFP. The remaining 33 patients did not show hLVFP or EiPH. The incidence of EiPH with hLVFP was 21% (25/120). By multivariate analysis, age (odds ratio [OR], 1.07; 95% confidence interval [CI], 1.00-1.13; p=0.039) and systolic pulmonary artery pressure at rest (OR, 1.14; 95% CI, 1.02-1.27; p=0.02) were associated with EiPH, whereas late diastolic transmitral velocity (OR, 1.04; 95% CI, 1.00-1.08; p=0.03) and diastolic blood pressure (OR, 0.94; 95% CI, 0.90-0.99; p=0.02) were associated with hLVFP during exercise.

CONCLUSIONS

Patients with relaxation abnormality and possibly hLVFP showed markedly heterogeneous hemodynamic changes during low-level exercise and DSE was useful to characterize these patients.

Pulmonary Hypertension in Congenital Heart Disease: Beyond Eisenmenger Syndrome

Patients with adult congenital heart disease have an increased risk of developing pulmonary hypertension. There are several mechanisms of pulmonary hypertension in patients with adult congenital heart disease, and understanding them requires a systematic approach to define the patient's hemodynamics and physiology. This article reviews the updated classification of pulmonary hypertension in patients with adult congenital heart disease with a focus on pathophysiology, diagnostics, and the evaluation of pulmonary hypertension in special adult congenital heart disease populations.

Impaired exercise capacity following atrial septal defect closure: an invasive study of the right heart and pulmonary circulation

Patients with early repair of an isolated atrial septal defect (ASD) are expected to have unremarkable right ventricular (RV) and pulmonary circulation physiology. Some studies, however, suggest persistent functional impairment. We aimed to examine the role of abnormal RV and pulmonary vascular response to exercise in patients who had undergone ASD closure. Using a previously published data set, we reviewed invasive exercise cardiopulmonary testing with right-sided hemodynamic data for 12 asymptomatic patients who had undergone ASD closure. The 5 (42%) patients with impaired maximal oxygen uptake ([Formula: see text]) were older and exhibited a lower peak cardiac index (5.6 ± 0.8 vs. 9.0 ± 1.2 L/min/m(2); P = .005) because of abnormal stroke volume augmentation (+3.2 ± 3.9 vs. +17.4 ± 10.2 mL/m(2); P = .02). While all resting hemodynamic variables were similar, patients with low [Formula: see text] tended to have abnormal total pulmonary vascular resistance change during exercise (+11% ± 41% vs. -28% ± 26%; P = .06) and had a steeper relation between mean pulmonary arterial pressure and cardiac index (5.8 ± 0.6 vs. 2.2 ± 0.1 L/min/m(2); P = .02). The increase in peak mean RV power during exercise was also significantly lower in the impaired-[Formula: see text] patients (4.7 ± 1.6 vs. 7.6 ± 2.1 J/s; P = .04). As described in the original study, despite normal resting hemodynamics, a subset of asymptomatic patients with repaired ASD had diminished exercise capacity. Our analysis allows us to conclude that this is due to a combination of abnormal pulmonary vascular response to exercise and impaired RV function.

A new multiparameter approach to computational simulation for Fontan assessment and redesign

INTRODUCTION

Despite an abundance of prior Fontan simulation articles, there have been relatively few clinical advances that are a direct result of computational methods. We address a few key limitations of previous Fontan simulations as a step towards increasing clinical relevance. Previous simulations have been limited in scope because they have primarily focused on a single energy loss parameter. We present a multi-parameter approach to Fontan modeling that establishes a platform for clinical decision making and comprehensive evaluation of proposed interventions.

METHODS

Time-dependent, 3-D blood flow simulations were performed on six patient-specific Fontan models. Key modeling advances include detailed pulmonary anatomy, catheterization-derived pressures, and MRI-derived flow with respiration. The following performance parameters were used to rank patients at rest and simulated exercise from best to worst performing: energy efficiency, inferior and superior vena cava (IVC, SVC) pressures, wall shear stress, and IVC flow distribution.

RESULTS

Simulated pressures were well matched to catheterization data, but low Fontan pressure did not correlate with high efficiency. Efficiency varied from 74% to 96% at rest, and from 63% to 91% with exercise. Distribution of IVC flow ranged from 88%/12% (LPA/RPA) to 53%/47%. A "transcatheter" virtual intervention demonstrates the utility of computation in evaluating interventional strategies, and is shown to result in increased energy efficiency.

CONCLUSIONS

A multiparameter approach demonstrates that each parameter results in a different ranking of Fontan performance. Ranking patients using energy efficiency does not correlate with the ranking using other parameters of presumed clinical importance. As such, current simulation methods that evaluate energy dissipation alone are not sufficient for a comprehensive evaluation of new Fontan designs.

Three-dimensional hemodynamics in the human pulmonary arteries under resting and exercise conditions

The biomechanical forces associated with blood flow have been shown to play a role in pulmonary vascular cell health and disease. Therefore, the quantification of human pulmonary artery hemodynamic conditions under resting and exercise states can be useful in investigating the physiology of disease development and treatment outcomes. In this study, a combined magnetic resonance imaging and computational fluid dynamics approach was used to quantify pulsatile flow fields, wall shear stress (WSS), oscillations in WSS (OSI), and energy efficiency in six subject-specific models of the human pulmonary vasculature with high spatial and temporal resolution. Averaging over all subjects, WSS was found to increase from 19.8±4.0 to 51.8±6.7 dynes/cm2, and OSI was found to decrease from 0.094±0.016 to 0.081±0.015 in the proximal pulmonary arteries between rest and exercise conditions (p<0.05). These findings demonstrate the localized, biomechanical effects of exercise. Furthermore, an average decrease of 10% in energy efficiency was noted between rest and exercise. These data indicate the amount of energy dissipation that typically occurs with exercise and may be useful in future surgical planning applications.

Use of bicycle exercise echocardiography for unexplained exertional dyspnea

Unexplained exertional dyspnea is a common and perplexing clinical problem. Myocardial ischemia and left ventricular systolic dysfunction are important cardiac causes, but are often not detected in these patients. Recently, exercise-induced left ventricular diastolic dysfunction and exercised-induced pulmonary hypertension have emerged as common alternative mechanisms. While conventional exercise treadmill echocardiography effectively diagnoses left ventricular systolic dysfunction and myocardial ischemia, it has limited ability to detect exercise-induced diastolic dysfunction or pulmonary hypertension. The latest advances in exercise echocardiography, including utilization of tissue Doppler imaging and harmonic imaging, make noninvasive evaluation of both conventional and alternative cardiac causes of exertional dyspnea possible. These advancements, when coupled with newly designed supine exercise platforms for bicycle exercise echocardiography (BE), facilitate the detection of exercise-induced diastolic dysfunction and pulmonary hypertension. Moreover, BE using supine ergometry additionally permits the dynamic evaluation of valvular function and interatrial shunting and detection of pulmonary arteriovenous fistula, uncommon but important causes of unexplained exertional dyspnea. Therefore, we propose that because of its superior diagnostic capabilities, BE should be included as part of a comprehensive cardiac evaluation of patients with unexplained exertional dyspnea.

Evaluation of a novel Y-shaped extracardiac Fontan baffle using computational fluid dynamics

OBJECTIVES

The objective of this work is to evaluate the hemodynamic performance of a new Y-graft modification of the extracardiac conduit Fontan operation. The performance of the Y-graft design is compared to two designs used in current practice: a t-junction connection of the venae cavae and an offset between the inferior and superior venae cavae.

METHODS

The proposed design replaces the current tube grafts used to connect the inferior vena cava to the pulmonary arteries with a Y-shaped graft. Y-graft hemodynamics were evaluated at rest and during exercise with a patient-specific model from magnetic resonance imaging data together with computational fluid dynamics. Four clinically motivated performance measures were examined: Fontan pressures, energy efficiency, inferior vena cava flow distribution, and wall shear stress. Two variants of the Y-graft were evaluated: an "off-the-shelf" graft with 9-mm branches and an "area-preserving" graft with 12-mm branches.

RESULTS

Energy efficiency of the 12-mm Y-graft was higher than all other models at rest and during exercise, and the reduction in efficiency from rest to exercise was improved by 38%. Both Y-graft designs reduced superior vena cava pressures during exercise by as much as 5 mm Hg. The Y-graft more equally distributed the inferior vena cava flow to both lungs, whereas the offset design skewed 70% of the flow to the left lung. The 12-mm graft resulted in slightly larger regions of low wall shear stress than other models; however, minimum shear stress values were similar.

CONCLUSIONS

The area-preserving 12-mm Y-graft is a promising modification of the Fontan procedure that should be clinically evaluated. Further work is needed to correlate our performance metrics with clinical outcomes, including exercise intolerance, incidence of protein-losing enteropathy, and thrombus formation.

Characterization of Hemodynamics in Patients with Idiopathic and Thromboembolic Pulmonary Hypertension

Demographic and hemodynamic data from patients with idiopathic pulmonary arterial hypertension (IPAH) and chronic thromboembolic pulmonary hypertension (CTEPH) have not been systematically characterized to identify differences related to gender, age, race, disease severity, and drug response. Our goal was to define the distribution and relation of IPAH and CTEPH based on these criteria. Hemodynamic and demographic data from 242 IPAH patients and 90 CTEPH patients were collected and compared. IPAH incidence was greater in women, but men had a higher basal mean pulmonary arterial pressure (mPAP). mPAP was comparable among all IPAH ethnic groups. IPAH patients with no history of fenfluramine-phentermine use had a higher mPAP than users. Exercise-induced IPAH was apparent in 14.5% of IPAH patients. Only 9% of IPAH patients responded to inhaled nitric oxide with a ≥20% decrease in mPAP. Compared to CTEPH patients, mPAP was greater but average age of diagnosis was lower in IPAH patients. mPAP negatively correlated with age of diagnosis in IPAH patients only. These results indicate that elevated CO is not the main determinant of mPAP in both IPAH and CTEPH patients. However, the two patient groups differ in terms of their demographic and hemodynamic distributions, and according to the correlation between mPAP and other clinical hemodynamics and demographics.

Effects of Exercise and Respiration on Hemodynamic Efficiency in CFD Simulations of the Total Cavopulmonary Connection

Congenital heart defects with a single functional ventricle, such as hypoplastic left heart syndrome and tricuspid atresia, require a staged surgical approach to separate the systemic and pulmonary circulations. Ultimately, the venous or pulmonary side of the heart is bypassed by directly connecting the vena cava to the pulmonary arteries with a modified t-shaped junction. The Fontan procedure (total cavopulmonary connection, TCPC) completes this process of separation. To date, computational fluid dynamics (CFD) simulations in this low pressure, passive flow, intrathoracic system have neglected the presumed important effects of respiration on physiology and higher "stress" states such as with exercise have never been considered. We hypothesize that incorporating effects of respiration and exercise would provide more realistic estimates of TCPC performance. Time-dependent, 3D blood flow simulations are performed by a custom finite element solver for two patient-specific Fontan models with a novel respiration model, developed to generate physiologic time-varying flow conditions. Blood flow features, pressure, and energy efficiency are analyzed at rest and with increasing flow rates to simulate exercise conditions. The simulations produce realistic pressure and flow data, comparable to that measured by catheterization and echocardiography, and demonstrate substantial increases in energy dissipation (i.e. decreased performance) with exercise and respiration due to increasing intensity of small scale vortices in the flow. As would be expected, these changes are highly dependent on patient-specific anatomy and Fontan geometry. We propose that respiration and exercise should be incorporated into TCPC CFD simulations to provide increasingly realistic evaluations of TCPC performance.

Exercise after surgical repair of congenital cardiac lesions

Congenital heart defects arise in approximately 1% of all live births, independent of ethnic and geographical considerations. With the development of new surgical procedures and current technologies a large number of these heart lesions can be surgically corrected in infancy. In the majority of cases patients evaluated some 10 to 20 years after surgery are asymptomatic and can lead a normal life. Despite their satisfactory clinical outcome patients may, nevertheless, show an abnormal pattern of physiological responses when submitted to dynamic exercise. This paper reviews the scientific literature concerning the exercise capabilities and the cardiorespiratory adjustments to exercise in patients surgically corrected for 4 of the most common congenital heart lesions: isolated atrial septal defect, isolated ventricular septal defects, pulmonary stenosis and tetralogy of Fallot. The maximal exercise tolerance of postoperative congenital heart defect patients may usually be related to: (a) the age of the patients at the time of surgery; (b) the severity of the lesions remaining after surgery; and (c) the age of the patients at the time of investigation. Although normal maximal exercise capabilities may be found in a good number of patients operated for either of the 4 lesions considered, this does not imply normal exercise haemodynamics. A general observation made in these 4 groups of patients is that of a subnormal exercise cardiac output which may or may not be fully compensated by an increase in peripheral oxygen extraction. The limitation in exercising cardiac output may, in turn, be attributed to either a subnormal stroke volume or a limitation in the chronotropic response to exercise or a combination of both factors. Residual pulmonary stenosis, increased pulmonary vascular resistance, increased myocardial stiffness are all factors that may contribute to the cardiac output limitation. A thorough explanation of underlying causes for the abnormal haemodynamic response to exercise, however, still remains to be provided.

Modification of pulmonary hypertension secondary to congenital heart disease by prostacyclin therapy

We have shown that PGI2 is a powerful but not selective pulmonary vasodilator, and we believe that there is a role for PGI2 in pulmonary vascular disease secondary to congenital heart disease, but much work remains to be done, including comparisons of PGI2 with other vasodilators. The role of PGI2 in altering the cellular and chemical events producing pulmonary vascular disease secondary to congenital heart disease, and any role in long-term treatment, is largely unexplored.

Recreational and sports recommendations for the child with heart disease

Although there is widespread acceptance that some children with congenital or acquired heart disease need exercise proscription, there is little data on which to base recommendations. In this article, the author, after reviewing the hemodynamic burdens of the common cardiac anomalies in children, gives his personal recommendations for recreational and sports activities.