Exercise-Induced Pulmonary Hypertension in Long-Term Survivors of Congenital Diaphragmatic Hernia.

OBJECTIVE: To determine the prevalence of exercise-induced pulmonary hypertension (PH) among long-survivors of congenital diaphragmatic hernia repair. STUDY DESIGN: This is a single-center, retrospective cohort study of CDH survivors who underwent exercise stress echocardiography (ESE) at Boston Children's Hospital from January 2006 to June 2020. PH severity was assessed by echocardiogram at baseline and after exercise. Patients were categorized by right ventricular systolic pressure (RVSP) after exercise: Group 1 - no or mild PH; and Group 2 - moderate or severe PH (RVSP ≥ 60 mmHg or ≥ ½ systemic blood pressure). RESULTS: Eighty-four patients with CDH underwent 173 ESE with median age 8.1 (4.8 - 19.1) years at first ESE. Sixty-four patients were classified as Group 1, 11 as Group 2, and 9 had indeterminate RVSP with ESE. Moderate to severe PH after exercise was found in 8 (10%) patients with no or mild PH at rest. Exercise-induced PH was associated with larger CDH defect size, patch repair, use of ECMO, supplemental oxygen at discharge, and higher WHO functional class. Higher VE/VCO2 slope, lower peak oxygen saturation, and lower percent predicted FEV1, and FEV1/FVC ratio were associated with Group 2 classification. ESE changed management in 9/11 Group 2 patients. PH was confirmed in all 5 Group 2 patients undergoing cardiac catheterization after ESE. CONCLUSIONS: Among long-term CDH survivors, 10% had moderate-severe exercise-induced PH on ESE, indicating ongoing pulmonary vascular abnormalities. Further studies are needed to optimally define PH screening and treatment for patients with repaired CDH.

Assessment of Exercise Function in Children and Young Adults with Hypertrophic Cardiomyopathy and Correlation with Transthoracic Echocardiographic Parameters.

Exercise function is well characterized in adults with hypertrophic cardiomyopathy (HCM); however, there is a paucity of data in children and young adults with HCM. Here we sought to characterize exercise function in young people with HCM, understand limitations in exercise function by correlating exercise function parameters with echocardiogram parameters and identify prognostic value of exercise parameters. We performed a retrospective, single-center cohort study characterizing exercise function in patients < 26 years old with HCM undergoing cardiopulmonary exercise testing (CPET). Patients with syndromic HCM or submaximal effort were excluded. We compared exercise function in this cohort to population normal values and measured changes in exercise function over time. We correlated exercise function parameters with echocardiographic parameters and investigated the relationship between exercise test parameters and a clinical composite outcome comprised of significant ventricular arrhythmia, death, or heart transplantation. We identified 229 CPETs performed by 117 patients (mean age at time of first CPET 15.6 ± 3.2 years). Mean %-predicted peak VO2, O2 pulse, and peak heart rate were statistically significantly depressed compared to population normal values and exercise function gradually worsened over time. Abnormal exercise testing correlated closely with echocardiographic indices of diastolic dysfunction. There was a trend toward increased incidence of poor clinical outcome in patients with abnormal exercise function. While adverse clinical outcomes were rare, normal exercise function appears to be a marker of low risk for adverse clinical outcomes in this population.

Activity During the COVID-19 Pandemic in Children with Cardiac Rhythm Management Devices.

Decreased physical activity is associated with cardiovascular, metabolic and mental health disease. While decreases in physical activity during the COVID-19 pandemic have been described in the general population, there is a paucity of data regarding children with underlying cardiovascular disease. We hypothesized there would be a decrease in physical activity at the onset of the COVID-19 pandemic. Performed a single-center, retrospective cohort study of children aged < 19 years with cardiac rhythm management devices. Patients were included if they had device-measured physical activity data from > 80% of dates from February 3, 2020 through June 30, 2020. Patients with significant neurologic/neuromuscular disease were excluded. We identified 144 patients with a median age of 15.4 years. 47% were female. 34% had congenital heart disease, 20% had cardiomyopathy, 19% had an inherited arrhythmia syndrome and 5% had atrioventricular block without congenital heart disease. 47% of patients had an implantable loop recorder, 29% had a permanent pacemaker and 24% had an implantable cardioverter-defibrillator. We observed a significant decrease in device-measured physical activity from baseline (February 3-March 9), with up to a 21% decrease in physical activity during mid-March through early May. Activity levels returned to pre-pandemic levels in June. Physical activity sharply declined in children with cardiac rhythm management devices at the onset of the COVID-19 pandemic. These data highlight the importance of finding strategies to maintain physical activity during the current pandemic and future public health crises.

Reducing radiation dose from myocardial perfusion imaging in subjects with complex congenital heart disease.

INTRODUCTION: The prevalence of defects and effective radiation dose from various myocardial perfusion imaging (MPI) strategies in congenital heart disease (CHD) is unknown. METHODS: We studied 75 subjects with complex CHD (ages 5 to 80 years) referred for MPI between 2002 and 2015. A rest and exercise or pharmacologic stress MPI was performed using 99mTechnetium sestamibi, 82rubidium or 13N-ammonia, and Sodium iodide SPECT (single-photon emission computed tomography), SPECT/CT or Cadmium zinc telluride (CZT) SPECT or PET (positron emission tomography)/CT scanners. Deidentified images were interpreted semi-quantitatively in three batches: stress only MPI, stress/rest MPI, and stress/rest MPI with taking into account a history of ventricular septal defect repair. Effective radiation dose was estimated for stress/rest MPI and predicted for 1-day stress-first (normal stress scans), and for 2-day stress/rest MPI (abnormal stress scans). RESULTS: The median age was 18.6 years. The most common type of CHD was transposition of the great arteries (63%). Rest/stress MPI was abnormal in 43% of subjects and 25% of the abnormal scans demonstrated reversible defects. Of the subjects with abnormal MPI, 33% had significant underlying anatomic coronary artery obstruction. Estimated mean effective radiation dose ranged from 2.1 ± 0.6 mSv for 13N-ammonia PET/CT to 12.5 ± 0.9 mSv for SPECT/CT. Predicted effective radiation dose was significantly lower for stress-first MPI and for 2-day stress/rest protocols. CONCLUSIONS: Due to the relatively high prevalence of abnormal stress MPI, tailored protocols with a stress-first MPI as well as the use of 2-day protocols and advanced imaging technologies including CZT SPECT, novel image reconstruction software, and PET MPI could substantially reduce radiation dose in complex CHD.

Exercise testing and spirometry as predictors of mortality in congenital heart disease: Contrasting Fontan physiology with repaired tetralogy of Fallot.

OBJECTIVE: Risk prediction using cardiopulmonary exercise testing (CPET) in complex congenital heart disease tends to either focus on single diagnoses or complete cohorts. We aimed to evaluate patients with two distinct anatomies cared for at a single institution over the same time period to determine CPET variables associated with mortality. DESIGN: All Fontan and tetralogy of Fallot (TOF) subjects with CPET between November 1, 2002 and December 31, 2014 and subsequently died were identified (cases). Cases were matched 1:3 to controls with similar age, underlying anatomy and timing of exercise test. RESULTS: Of the 42 cases, 27 had a Fontan circulation and 15 with TOF. All Fontan patients had a low peak VO2 but there was no significant difference between cases and controls (52.5 ± 14.7 v. 57.4% ± 13.5% predicted, P = .11). Spirometry values were significantly lower in Fontan cases than controls (eg, FVC 67.4 ± 19.1 v 77.6% ± 14.9% predicted, P = .007). Spirometry values were also lower in TOF cases than controls (% predicted FVC 62.8 ± 16.7 v 75 ± 14, P = .006). In contrast to the Fontan analysis, both %peak predicted VO2 and VE/VCO2 slope were worse in TOF cases than controls (50.1 ± 13.5 v. 68.5% ± 15.0% predicted VO2 , P = .0004; 33.9 ± 12.9 v 26.6 ± 4.4, P = .002). Multivariable analysis also identified different predictors of mortality among the anatomic subgroups. Spirometric data (FVC) correlated most strongly with mortality in Fontan patients while the VE/VCO2 slope was most associated with outcome in TOF patients. CONCLUSIONS: Variables most predictive of mortality in Fontan and TOF patients diverge but spirometry was abnormal and associated with mortality in both groups. When compared with age-matched controls, reduced FEV1 and FVC correlated most strongly with mortality in Fontan patients while VE/VCO2 slope correlated with mortality for TOF patients. These findings further support the importance of lung health in patients with complex congenital heart disease.

A Pilot Study of Inspiratory Muscle Training to Improve Exercise Capacity in Patients with Fontan Physiology.

While the Fontan procedure has improved life expectancy, patients with single ventricle physiology have impaired exercise capacity due to limited increase in pulmonary blood flow during activity. Enhancing the "thoracic pump" using inspiratory muscle training (IMT) may ameliorate this impairment. Adult nonsmokers with Fontan physiology were recruited through Boston Children's Hospital's outpatient clinic. Participants underwent cardiopulmonary exercise testing and pulmonary function testing, followed by 12 weeks of IMT and then repeat testing. The primary endpoint was change in % predicted peak oxygen consumption (VO2). Secondary endpoints were changes in other exercise metrics. Eleven patients (6 male) were enrolled. Median ages at time of enrollment and Fontan completion were 28.8 years (25.7, 45.5) and 7.8 years (3.9, 16.5), respectively. Average baseline maximal inspiratory pressure (MIP) was normal; only 2 patients had MIP <70% predicted. Peak work rate improved significantly from baseline after 12 weeks of IMT (116.5 ± 45.0 to 126.8 ± 47.0 W, P = 0.019). Peak VO2 tended to improve (baseline 68.1 ± 14.3, change + 5.3 ± 9.6% predicted, P = 0.12), as did VE/VCO2 slope (34.1 ± 6.7 to 31.4 ± 3.6, P = 0.12). There was no change in peak tidal volume or MIP. In a small cohort of Fontan patients with mostly normal MIP, IMT was associated with significant improvement in peak work rate and a trend toward higher peak VO2 and improved ventilatory efficiency. Larger studies are needed to determine if this reflects true lack of effect or whether this pilot study was underpowered for effect size, and whether IMT is more narrowly useful for patients with impaired MIP.

A Randomized Trial Comparing Cardiac Rehabilitation to Standard of Care for Adults With Congenital Heart Disease.

BACKGROUND: Cardiac rehabilitation (CR) improves exercise capacity and quality of life while reducing mortality in adults with acquired heart disease. Cardiac rehabilitation has not been extensively studied in adults with congenital heart disease (CHD). METHODS: We performed a prospective, randomized controlled trial (NCT01822769) of a 12-week clinical CR program compared with standard of care (SOC). Participants were ≥16 years old, had moderate or severe CHD, had O2 saturation ≥92%, and had peak O2 consumption ([Formula: see text]) < 80% predicted. We assessed exercise capacity, physical activity, quality of life, self-reported health status, and other variables at baseline and after 12 weeks. The prespecified primary end point was change in [Formula: see text]. RESULTS: We analyzed data on 28 participants (aged 41.1 ± 12.1 years, 50% male), 13 randomized to CR and 15 to SOC. [Formula: see text] averaged 16.8 ± 3.8 mL/kg/min, peak work rate = 95 ± 28 W, and median Minnesota Living with Heart Failure Questionnaire (MLHFQ) score = 27 (interquartile range: 11-44). Cardiac rehabilitation participants were older (48 ± 9 years vs 36 ± 12 years; P = .01), but there were no significant between-group differences in other variables. There were no adverse events related to CR. [Formula: see text] increased in the CR group compared with SOC (+2.2 mL/kg/min, 95% confidence interval: 0.7-3.7; P = .002, age-adjusted +2.7 mL/kg/min; P = .004); there was a nonsignificant improvement in work rate (+8.1 W; P = .13). Among the 25 participants with baseline MLHFQ > 5, there was a clinically important >5-point improvement in 72.7% and 28.6% of CR and SOC participants, respectively ( P = .047). Cardiac rehabilitation was also associated with improved self-assessment of overall health ( P < .04). CONCLUSIONS: Cardiac rehabilitation is safe and is associated with improvement in aerobic capacity and self-reported health status compared with SOC in adults with CHD.

Feasibility of exercise stress echocardiography and myocardial response in patients with repaired congenital heart disease.

BACKGROUND: Exercise stress echocardiography (ESE) can unmask ventricular dysfunction in asymptomatic patients with congenital heart disease (CHD), but its acquisition and interpretation is often challenging, and the method has not been validated in CHD. This study aimed to evaluate the feasibility of ESE using Doppler imaging and to assess myocardial response to exercise in patients with biventricular (BiV) and univentricular (UniV) circulation after CHD repair. METHODS: In this single-center prospective study, we recruited 55 participants (17 females), median age 14 years (8-22 years). Our analysis categorized participants in these three groups: with structurally normal hearts as controls (n=21), with BiV circulation (n=20) and with UniV circulation (n=14). We acquired ESE images of the systemic ventricle including pulsed-wave flow and spectral tissue Doppler imaging (TDI) of lateral free wall before and immediately after standard, symptom-limited exercise tests on an electronically braked cycle ergometer. RESULTS: During ESE we obtained inflow E-wave and TDI systolic (S') and early diastolic (E') velocities in 93% to 100% of participants at rest and in 90% to 100% of participants post exercise. Feasibility to obtain Doppler imaging parameter was the same across study groups. The myocardial response to exercise was increase in heart rate (HR), S' and inflow E-wave velocity in all participants. Patients with BiV circulation had preserved ventricular function at rest. While patients with UniV circulation had low S', E', and E-wave velocities at rest in comparison to controls and to BiV group (all P<.001), both patients with BiV and UniV circulation showed significant increases in HR, S' velocity and inflow E-wave velocity post exercise, with magnitudes of these increases higher in controls than in the BiV and UniV group. The S' and E' velocities were strongly associated with lower percent predicted peak oxygen consumption VO2 (rs=0.614 and rs=0.64, respectively, both P<.001). CONCLUSION: ESE with Doppler imaging is a practical noninvasive diagnostic method and sufficiently robust for the assessment of morphologic LV/systemic ventricles under exercise in patients after biventricular and univentricular CHD repair. Although patients with BiV and UniV circulation had both preserved myocardial response to exercise, the magnitude of this response was the lowest in patients with UniV circulation.

The effect of 1 year of Alagebrium and moderate-intensity exercise training on left ventricular function during exercise in seniors: a randomized controlled trial.

Sedentary aging leads to left ventricular (LV) and vascular stiffening due in part to advanced glycation end-products (AGEs) cross-linking of extracellular matrix proteins. Vigorous lifelong exercise ameliorates age-related cardiovascular (CV) stiffening and enhances exercise LV function, although this effect is limited when exercise is initiated later in life. We hypothesized that exercise training might be more effective at improving the impact of age-related CV stiffening during exercise when combined with an AGE cross-link breaker (Alagebrium). Sixty-two seniors (≥60 yr) were randomized into four groups: sedentary + placebo, sedentary + Alagebrium, exercise + placebo, and exercise + Alagebrium for 1 yr. Moderate-intensity aerobic exercise was performed 3-4 sessions/wk; controls underwent similar frequency of yoga/balance training. Twenty-four similarly-aged, lifelong exercisers (4-5 sessions/wk) served as a comparator for the effect of lifelong exercise on exercising LV function. Oxygen uptake (Douglas bags), stroke index (SI; acetylene rebreathing), and effective arterial elastance (Ea) were collected at rest and submaximal and maximal exercise. Maximum O2 uptake (23 ± 5 to 25 ± 6 ml·kg(-1)·min(-1)) increased, while SI (35 ± 11 to 39 ± 12 ml/m(2)) and Ea (4.0 ± 1.1 to 3.7 ± 1.2 mmHg·ml(-1)·m(-2)) were improved across all conditions with exercise, but remained unchanged in controls (exercise × time, P ≤ 0.018). SI or Ea were not affected by Alagebrium (medication × time, P ≥ 0.468) or its combination with exercise (interaction P ≥ 0.252). After 1 yr of exercise plus Alagebrium, exercise SI and Ea remained substantially below that of lifelong exercisers (15-24 and 9-22%, respectively, P ≤ 0.415). In conclusion, Alagebrium plus exercise had no synergistic effect on exercise LV function and failed to achieve levels associated with lifelong exercise, despite a similar exercise frequency.

Relationship between Exercise Parameters and Noninvasive Indices of Right Ventricular Function in Patients with Biventricular Circulation and Systemic Right Ventricle.

OBJECTIVES: In patients with systemic right ventricles (RVs) in a biventricular circulation, exercise capacity and RV function often deteriorate over time and echocardiographic assessment of systemic RV function is difficult. The purpose of this study was to examine the relationship between exercise capacity and RV function and to determine which noninvasive imaging parameters correlate most closely with exercise capacity. DESIGN: Patients with a systemic RV (D-loop transposition of the great arteries [TGA] after atrial switch procedure or physiologically "corrected" TGA) who underwent cardiopulmonary exercise testing (CPX) and noninvasive imaging (cardiac magnetic resonance [CMR] and echocardiography [echo]) within 1 year of CPX were identified. Regression analysis was used to evaluate the relationship between exercise variables and noninvasive indices of ventricular function. RESULTS: We identified 92 patients with 149 encounters (mean age 31.0 years, 61% men, 70% D-loop TGA) meeting inclusion criteria. Statistically significant correlations between % predicted peak oxygen uptake (%pVO2 ) and RV ejection fraction (EF) (r = 0.29, P = .0007), indexed RV end-systolic volume (r = -0.25, P = .002), and Tei index (r = -0.22, P = .03) were found. In patients without additional hemodynamically significant lesions, the correlations between %pVO2 and RV EF (r = 0.37, P = .0007) and the Tei index (r = -0.28, P = .03) strengthened and a correlation emerged between %pVO2 and dP/dtic (r = 0.31, P = .007). On multivariable analysis, Tei index was the only statistically significant correlate of %pVO2 (P = .04). CONCLUSIONS: In patients with systemic RVs in a biventricular circulation, CMR-derived RVEF and echo-derived Tei index correlate with %pVO2 . On multivariable analysis, the Tei index was the strongest predictor of peak %pVO2 response.

Purulent pericarditis after transbronchial biopsy.

A 28-year-old woman experienced hypotension and unresponsiveness. She had undergone bronchoscopy with needle biopsy 2 weeks before admission to evaluate hilar lymphadenopathy given suspicion of sarcoidosis. She had an elevated white blood cell count of 28,000/µL and a serum creatinine level of 4.0 mg/dL. Echocardiography showed a large pericardial effusion. Pericardiocentesis resulted in removal of 400 mL of yellow-green purulent material that grew Streptococcus milleri, Prevotella, Veillonella, and Peptostreptococcus species. Pericardiectomy and mediastinal washout were performed. Subsequently, her condition rapidly improved. She returned home after 26 days of admission. At 12-month follow-up, the patient had made a full recovery.

Cardiovascular effects of 1 year of alagebrium and endurance exercise training in healthy older individuals.

BACKGROUND: Lifelong exercise training maintains a youthful compliance of the left ventricle (LV), whereas a year of exercise training started later in life fails to reverse LV stiffening, possibly because of accumulation of irreversible advanced glycation end products. Alagebrium breaks advanced glycation end product crosslinks and improves LV stiffness in aged animals. However, it is unclear whether a strategy of exercise combined with alagebrium would improve LV stiffness in sedentary older humans. METHODS AND RESULTS: Sixty-two healthy subjects were randomized into 4 groups: sedentary+placebo; sedentary+alagebrium (200 mg/d); exercise+placebo; and exercise+alagebrium. Subjects underwent right heart catheterization to define LV pressure-volume curves; secondary functional outcomes included cardiopulmonary exercise testing and arterial compliance. A total of 57 of 62 subjects (67 ± 6 years; 37 f/20 m) completed 1 year of intervention followed by repeat measurements. Pulmonary capillary wedge pressure and LV end-diastolic volume were measured at baseline, during decreased and increased cardiac filling. LV stiffness was assessed by the slope of LV pressure-volume curve. After intervention, LV mass and end-diastolic volume increased and exercise capacity improved (by ≈8%) only in the exercise groups. Neither LV mass nor exercise capacity was affected by alagebrium. Exercise training had little impact on LV stiffness (training × time effect, P=0.46), whereas alagebrium showed a modest improvement in LV stiffness compared with placebo (medication × time effect, P=0.04). CONCLUSIONS: Alagebrium had no effect on hemodynamics, LV geometry, or exercise capacity in healthy, previously sedentary seniors. However, it did show a modestly favorable effect on age-associated LV stiffening. CLINICAL TRIAL REGISTRATION- URL: http://www.clinicaltrials.gov. Unique identifier: NCT01014572.

Effects of age and aerobic fitness on myocardial lipid content.

BACKGROUND: Aging and sedentary lifestyles lead to cardiac atrophy, ventricular stiffening, and impaired diastolic function. Both conditions are marked by increased adiposity, which can lead to ectopic fat deposition in nonadipocyte tissues including the myocardium. The effect of excess intramyocardial fat on cardiac function in nonobese individuals is unknown. METHODS AND RESULTS: Cardiac lipid content was measured by magnetic resonance spectroscopy in 153 healthy nonobese subjects with varying fitness levels quantified by peak oxygen uptake during treadmill exercise. Cardiac function (echo) and left ventricular (LV) filling pressures (right heart catheterization) were measured under varying preloads. LV stiffness was calculated from a curve fit of the diastolic portion of the pressure-volume curve. The strongest clinical predictors of lipid content were body mass index (ß=+0.03; 95% confidence interval, 0.001-0.06) and peak oxygen uptake (ß=-0.02; 95% confidence interval, -0.03 to -0.009; R(2)=0.14; P<0.001). Subjects in the highest quintile had smaller LV end-diastolic volumes (68±13 versus 58±12 mL/m(2); P<0.01) and decreased peak early mitral annular and increased peak late mitral inflow velocities. There were no differences in LV stiffness, but a leftward shift in the pressure-volume curve suggested a less distensible ventricle with increasing myocardial lipid levels. After adjusting for age, fitness, and body mass index, echocardiographic and morphometric differences among groups were attenuated and no longer significant. CONCLUSIONS: Body mass index and fitness levels are the strongest predictors of myocardial lipid content in nonobese humans. Cardiac lipid content is associated with decreased ventricular distensibility, and it may provide a causal mechanism linking changes in LV function related to age and fitness.

Hemodynamic responses to rapid saline loading: the impact of age, sex, and heart failure.

BACKGROUND: Hemodynamic assessment after volume challenge has been proposed as a way to identify heart failure with preserved ejection fraction. However, the normal hemodynamic response to a volume challenge and how age and sex affect this relationship remain unknown. METHODS AND RESULTS: Sixty healthy subjects underwent right heart catheterization to measure age- and sex-related normative responses of pulmonary capillary wedge pressure and mean pulmonary arterial pressure to volume loading with rapid saline infusion (100-200 mL/min). Hemodynamic responses to saline infusion in heart failure with preserved ejection fraction (n=11) were then compared with those of healthy young (<50 years of age) and older (≥50 years of age) subjects. In healthy subjects, pulmonary capillary wedge pressure increased from 10±2 to 16±3 mm Hg after ~1 L and to 20±3 mm Hg after ~2 L of saline infusion. Older women displayed a steeper increase in pulmonary capillary wedge pressure relative to volume infused (16±4 mm Hg·L(-1)·m(2)) than the other 3 groups (P≤0.019). Saline infusion resulted in a greater increase in mean pulmonary arterial pressure relative to cardiac output in women compared with men regardless of age. Subjects with heart failure with preserved ejection fraction exhibited a steeper increase in pulmonary capillary wedge pressure relative to infused volume (25±12 mm Hg·L(-1)·m(2)) than healthy young and older subjects (P≤0.005). CONCLUSIONS: Filling pressures rise significantly with volume loading, even in healthy volunteers. Older women and patients with heart failure with preserved ejection fraction exhibit the largest increases in pulmonary capillary wedge pressure and mean pulmonary arterial pressure.

The importance of the muscle and ventilatory blood pumps during exercise in patients without a subpulmonary ventricle (Fontan operation).

OBJECTIVES: The aim of this study was to determine the relative contribution of the muscle and ventilatory pumps to stroke volume in patients without a subpulmonic ventricle. BACKGROUND: In patients with Fontan circulation, it is unclear how venous return is augmented to increase stroke volume and cardiac output during exercise. METHODS: Cardiac output (acetylene rebreathing), heart rate (electrocardiography), oxygen uptake (Douglas bag technique), and ventilation were measured in 9 patients age 15.8 ± 6 years at 6.1 ± 1.8 years after Fontan operation and 8 matched controls. Data were obtained at rest, after 3 min of steady-state exercise (Ex) on a cycle ergometer at 50% of individual working capacity, during unloaded cycling at 0 W (muscle pump alone), during unloaded cycling with isocapnic hyperpnea (muscle and ventilatory pump), during Ex plus an inspiratory load of 12.8 ± 1.5 cm water, and during Ex plus an expiratory load of 12.8 ± 1.6 cm water. RESULTS: In Fontan patients, the largest increases in stroke volume and stroke volume index were during zero-resistance cycling. An additional increase with submaximal exercise occurred in controls only. During Ex plus expiratory load, stroke volume indexes were reduced to baseline, non-exercise levels in Fontan patients, without significant changes in controls. CONCLUSIONS: With Fontan circulation increases in cardiac output and stroke volume during Ex were due to the muscle pump, with a small additional contribution by the ventilatory pump. An increase in intrathoracic pressure played a deleterious role in Fontan circulation by decreasing systemic venous return and stroke volume.