Hemodynamic responses to exercise in normal children

A consensus approach to the classification of pediatric pulmonary hypertensive vascular disease: Report from the PVRI Pediatric Taskforce, Panama 2011

Current classifications of pulmonary hypertension have contributed a great deal to our understanding of pulmonary vascular disease, facilitated drug trials, and improved our understanding of congenital heart disease in adult survivors. However, these classifications are not applicable readily to pediatric disease. The classification system that we propose is based firmly in clinical practice. The specific aims of this new system are to improve diagnostic strategies, to promote appropriate clinical investigation, to improve our understanding of disease pathogenesis, physiology and epidemiology, and to guide the development of human disease models in laboratory and animal studies. It should be also an educational resource. We emphasize the concepts of perinatal maladaptation, maldevelopment and pulmonary hypoplasia as causative factors in pediatric pulmonary hypertension. We highlight the importance of genetic, chromosomal and multiple congenital malformation syndromes in the presentation of pediatric pulmonary hypertension. We divide pediatric pulmonary hypertensive vascular disease into 10 broad categories.

The Fontan circulation: who controls cardiac output?

In a Fontan circuit the mechanisms involved in control of cardiac output at rest and during exercise differ significantly from normal. The classical model presumes an unlimited preload which is not available in the Fontan circuit. This review critically analyses the role of contractility, heart rate, and afterload and highlights the importance of pulmonary vascular resistance (PVR) in determining adequate preload and, therefore, cardiac output in these patients. A conceptual model of the determinants of cardiac output in Fontan patients is presented.

Doppler echocardiography for the estimation of cardiac output with exercise

Insights into both normal and pathological cardiac responses to exercise have been hampered by lack of a safe, accurate, feasible means of estimating cardiac output (Q) during high-intensity and maximal exercise. Doppler ultrasound noninvasively measures blood velocity as it exits the heart and can be performed during exhaustive exercise without interference of the subject or need for steady state. From the product of aortic blood velocity and cross-sectional area of the aorta, stroke volume (SV) can be calculated. Despite these advantages of the Doppler technique, a number of potential sources of error have raised concern regarding the accuracy of this method. These include transducer angulation, change in aortic cross-sectional area during exercise, turbulence and alteration of a flat velocity profile in the aorta with increased Q, and uncertainties regarding the proper location for measurement of aortic outflow area. The magnitude of the influence of these potentially confounding variables on the accuracy of SV measurements determined by the Doppler technique is unknown. Estimates of both construct and concurrent validity suggest that the overall error may be small. Test-retest studies have indicated a high level of reliability with this technique.

Cardiorespiratory response during exercise in patients with cyanotic congenital heart disease with and without a Fontan operation and in patients with congestive heart failure

To clarify the different cardiorespiratory response to exercise in patients with congenital heart disease and patients with chronic congestive heart failure, we investigated the effect of a progressive exercise test in 30 patients aged 10 to 24 years, including 9 patients with cyanotic congenital heart disease (group A), 13 patients who had undergone a Fontan operation (group B), and 8 patients with reduced left ventricular function (group C), and 18 healthy controls (group D). There was no difference in peak oxygen uptake among patient groups and all group A, B, and C values were lower than those in group D (P<0.001). Although peak heart rate was lower in patient groups than in group D, heart rate at a given exercise intensity was highest in group C. The oxygen pulse (oxygen uptake divided by heart rate=stroke volume x arterial venous oxygen difference), as an indicator of stroke volume, was lower in patients groups, especially in group C, than in group D. There was no difference in tidal volume between groups A and D, but the respiratory rates at any given exercise intensity were higher in group A than in the other patient groups, thus minute ventilation and the ventilatory equivalent were highest in group A. The increased respiratory rate and low tidal volume in group C resulted in rapid and shallow respiration. There was no difference in exertional symptoms at peak exercise among the groups. In addition to impaired responses of stroke volume during exercise in patients with reduced exercise capacity, there was little limitation of increase in ventilation in group B and excessive ventilation in group A. The present results suggest that relationship between ventilatory and cardiac responses during exercise in patients with cyanotic congenital heart disease with and without a Fontan operation is different from the relationship in patients with chronic congestive heart failure; however, these pathological differences did not influence exertional symptoms.

Enalapril does not enhance exercise capacity in patients after Fontan procedure

BACKGROUND

Angiotensin-converting enzyme inhibitors improve exercise capacity in adults with congestive heart failure by decreasing systemic vascular resistance and improving ventricular diastolic function. Patients who have undergone the Fontan procedure have decreased cardiac output, increased systemic vascular resistance, abnormal diastolic function, and decreased exercise capacity compared with normal people.

METHODS AND RESULTS

To test the hypothesis that afterload reduction therapy alters hemodynamic variables and augments exercise capacity in patients after a Fontan procedure, we compared the results of graded exercise with maximal effort from 18 subjects (14.5+/-6.2 years of age, 4 to 19 years after Fontan procedure) in a randomized, double-blind, placebo-controlled crossover trial using enalapril (0.2 to 0.3 mg x kg[-1] x d[-1], maximum 15 mg). Each treatment was administered for 10 weeks. Diastolic filling patterns at rest were assessed by Doppler determination of the systemic atrioventricular valve flow velocity at the conclusion of each therapy. No difference was detected in resting heart rate, blood pressure, or cardiac index. Diastolic filling patterns were also similar. Exercise duration was not different (6.4+/-2.6 [enalapril] versus 6.7+/-2.6 minutes [placebo]). The mean percent increase in cardiac index from rest to maximum exercise was slightly but significantly decreased in subjects after 10 weeks of enalapril therapy (102+/-34% [enalapril] versus 125+/-34% [placebo]; P<.02). At maximal exercise, cardiac index (3.5+/-0.9 [enalapril] versus 3.8+/-0.9 L x min[-1] x m2 [placebo]), oxygen consumption (18.3+/-9 [enalapril] versus 20.5+/-7 mL x min[-1] x kg[-1] [placebo]), minute ventilation (57.5+/-17 [enalapril] versus 55.4+/-19 L/min [placebo]), and total work (247+/-181 [enalapril] versus 261+/-197 W [placebo]) were not different.

CONCLUSIONS

We conclude that enalapril administration for 10 weeks does not alter abnormal systemic vascular resistance, resting cardiac index, diastolic function, or exercise capacity in patients who have undergone a Fontan procedure.

Cardiorespiratory response to exercise after modified Fontan operation: determinants of performance

OBJECTIVES

This study sought to measure the cardiorespiratory responses to exercise and to identify the perioperative determinants of exercise performance in children, adolescents and young adults who underwent the modified Fontan operation.

BACKGROUND

Several studies of the cardiorespiratory responses to exercise after the Fontan operation have demonstrated subnormal maximal oxygen uptake and exercise heart rate, but the perioperative variables that ultimately affect exercise responses have not been assessed systematically.

METHODS

The study included 59 of the 548 patients who underwent a modified Fontan operation between January 1, 1984 and December 31, 1993 at the Mayo Clinic. Spirometry was performed at rest in all patients before exercise testing. The patients then exercised using a previously calibrated cycle ergometer and a 3-min incremental cycle exercise protocol. Multiple linear regression analysis was used to determine a subset of variables associated with oxygen uptake at peak exercise (VO2max), blood oxygen saturation (O2sat) and heart rate at peak exercise (HRmax).

RESULTS

VO2max ranged from 29% to 95% of normal value; O2sat at peak exercise ranged from 77% to 96%; and HRmax ranged from 39.7% to 97.4% of normal value. Multivariate analysis showed that log VO2max/kg2/3 was associated with age at exercise, male gender, body surface area, preoperative confluent pulmonary arteries and rest VO2max/kg2/3. Preoperative left pulmonary artery stenosis, the presence of a classic Glenn anastomosis at exercise and rest O2sat were associated with O2sat at peak exercise. Age, body surface area at exercise, heart rate at rest and diastolic blood pressure were associated with HRmax at exercise.

CONCLUSIONS

Subnormal VO2max and HRmax values were demonstrated at peak exercise. Several perioperative variables were associated with VO2max and O2sat at peak exercise. The presence of a classic Glenn anastomosis was associated with decreased O2sat at peak exercise, suggesting intrapulmonary shunting with the classic Glenn anastomosis.

Cardiovascular responses to dynamic submaximal exercise in children previously treated with anthracycline

This study assessed the long-term (5-year) outcome of pediatric low-dose anthracycline therapy on the circulatory response to moderate exercise. Thirteen patients (13 +/- 4 years old) and 15 age-matched control subjects completed a maximal cycle ergometer protocol as well as two 5-minute cycling tests at 33% and 66% maximal oxygen uptake (V(O2)max) for determination of cardiac index (carbon dioxide rebreathing). V(O2)max was lower in patients than in control subjects (1.3 +/- 0.5 L/min vs 2.3 +/- 0.6 L/min) (p< 0.05). Smaller relative increases in cardiac index for similar increases in relative exercise intensities were found in patients (33% V(O2)max, 73% vs 116%; 66% V(O2)max, 115% vs 192%), as a result of smaller increases in stroke index from rest (33% V(O2)max, 33% vs 54%; 66% V(O2)max, 33% vs 69%; p< 0.05). Similarly, despite normal resting systolic function, patients exhibited a lower stroke index and higher heart rate for any given value of oxygen uptake (milliliters per minute per square meter). Children who had survived cancer exhibited stroke index impairment during exercise similar in intensity to that of recreational activities or play, attesting to a limited inotropic reserve.

Pulmonary vascular resistance during exercise late after repair of large ventricular septal defects. Relation to age at the time of repair

Postoperative pulmonary artery pressure and resistance were assessed during exercise in 32 patients late after repair of large ventricular septal defect with pulmonary hypertension. Nineteen patients had a preoperative pulmonary-to-systemic resistance ratio of between 0.15 and 0.50 (group 1) and 13 had a ratio between 0.50 and 0.96 (group 2). Age at the time of operation was 0.9 to 13.0 years (4.6 +/- 3.6) in group 1 and 0.8 to 15.8 years (4.3 +/- 4.2) in group 2. Age at the time of restudy was 9 to 21 years (14.5 +/- 3.0) in group 1 and 9 to 22 years (13.5 +/- 4.1) in group 2. Pulmonary artery pressure was measured in the supine position at rest and during exercise, as were the measurements underlying the calculations of pulmonary vascular resistance. Mean pulmonary artery pressure was 13 to 21 mm Hg (17 +/- 2) and 10 to 26 mm Hg (20 +/- 5) in groups 1 and 2, respectively, at rest, and this increased to 17 to 27 mm Hg (22 +/- 3) and 14 to 39 mm Hg (27 +/- 7) in groups 1 and 2, respectively, during exercise (p < 0.05). Pulmonary vascular resistance was 0.51 to 3.40 U.m2 (1.93 +/- 0.63) and 0.79 to 3.31 U.m2 (2.05 +/- 0.65) in groups 1 and 2 at rest. It was 0.58 to 2.24 U.m2 (1.36 +/- 0.57) and 0.81 to 3.85 U.m2 (2.18 +/- 0.97) in groups 1 and 2 during exercise (p < 0.01). Postoperative pulmonary vascular resistance during exercise correlated well with age at the time of repair in both groups (r = 0.65, p < 0.05 in group 1; r = 0.86, p < 0.001 in group 2). These data suggest that 85% of patients with a preoperative pulmonary-to-systemic resistance ratio of between 0.15 and 0.50 would have normal pulmonary vascular resistance during exercise when operated on at younger than 3.8 years old and 85% of those with a preoperative pulmonary-to-systemic resistance ratio of more than 0.50 would have normal pulmonary vascular resistance during exercise when operated on at younger than 1.1 years.

Left ventricular function in asthmatic children chronically treated with theophylline evaluated by exercise Doppler echocardiography

To evaluate the chronic effects of theophylline on cardiac function, M-mode and pulsed Doppler derived variables were measured at rest and the suprasternal continuous wave Doppler measurement of ascending aortic flow was used during treadmill exercise testing. Subjects consisted of 13 children with stable asthma (mean 11.7 +/- 2.2 years) who were treated with theophylline for at least one year and 16 age-matched, untreated normal volunteers. In the resting state, the chronic administration of theophylline seemed to produce a slight increase in percent fractional shortening, outflow peak velocity and atrial contribution to ventricular filling in the asthmatic children as compared to normals, but these changes were not statistically significant. The asthmatic children showed significantly lower values than the controls in exercise induced changes in the peak velocity, stroke index and cardiac index, but not in the heart rate. Therefore, chronic administration of theophylline appears to have a minimal effect on resting cardiac function, but a possibly deleterious effect on the cardiac response to exercise testing.

Guidelines for exercise testing in the pediatric age group. From the Committee on Atherosclerosis and Hypertension in Children, Council on Cardiovascular Disease in the Young, the American Heart Association

Exercise testing of children differs from adult exercise testing in many ways beyond the technical issues related to test performance that are addressed in this report. Disease processes that produce myocardial ischemia are relatively rare in children compared with adults. Exercise testing may be useful in these cases, but the use of testing to assess functional capacity or cardiac rhythms will be encountered more often. Although the precise role of exercise testing in patient evaluation or long-term management of the cardiac patient will vary somewhat from center to center, exercise testing is often essential to diagnose and to direct treatment in a wide variety of clinical problems. An understanding of the role of exercise testing for children with known or suspected heart abnormalities is an essential part of the training of pediatric cardiologists. The staff of the pediatric exercise laboratory should be available to discuss with the clinician when a test might be of value in a specific case in addition to providing advice about the specifics of the performance of the test and offering age- and size-appropriate normal data from the laboratory with test interpretation.

Maximal hemodynamic response after the Fontan procedure: Doppler evaluation during the treadmill test

After undergoing the Fontan procedure for congenital heart disease, 16 young patients performed a maximal treadmill test according to the Bruce protocol. The peak velocity of the blood flow in the ascending aorta, stroke index, and cardiac index were measured by continuous-wave Doppler echocardiography at rest and at each stage of the test. The results were compared with those from 18 normal children. The body surface area was similar in the two groups. The endurance time was 37% shorter in the Fontan group than in the control group. From the beginning of exercise until the sixth minute, the increase in stroke index was lower in the Fontan group (NS). After that point, the stroke index was maintained at a high level in the control group but decreased toward its original level in the Fontan group. The response of cardiac index to exercise in the two groups was comparable until the sixth minute, after which the Fontan group failed to maintain an ascending curve. All the hemodynamic values were significantly higher in the control group at maximal exercise; at this point the cardiac index had increased 79% in the Fontan group and 170% in the control group. The subnormal response of the stroke volume at submaximal exercise and the subsequent decrease at maximal exercise following the Fontan procedure are important hemodynamic findings.

Treadmill exercise in Neopolitan children and adolescents

Two hundred and eighty healthy children from Naples, Italy (140 boys and 140 girls) aged 4-17 years were studied using Bruce walking treadmill protocol to voluntary exhaustion. Endurance time and double product increased with age. Systolic blood pressure increased linearly during the test. Multivariate analysis showed that body weight and age were the best predictors of endurance time. Endurance time averaged 15.2 +/- 2.8 min in boys and 13.7 +/- 2.3 min in girls (p = 0.00001). Mean +/- SD double product at peak exercise was 264.3 +/- 63 (boys) and 242 +/- 44 (girls) (p = 0.01). Sinus arrhythmia was present in 78% of the children and disappeared at a mean heart rate of 112 +/- 16 beats/min during exercise. The voltage of the R wave on V4 lead decreased in all but four children during the test (delta R = -0.25 +/- 0.24 mV). The P and T waves increased in almost all children. No ST depression or upward sloping was detected. The voltage of the PR isoelectric line remained constant. The J point was displaced downwards in 78% of children, unchanged in 11% and displaced upwards in the remaining 11% of the children. The present study gives reference parameters for a walking treadmill test in Southern European children.

Selective pulmonary and systemic vasodilator effects of amrinone in children: new therapeutic implications

OBJECTIVES

The present study was performed to determine the systemic and pulmonary hemodynamic effects of amrinone in infants and children with a cardiac left to right shunt to determine if there is a beneficial effect on the pathophysiology of this condition.

BACKGROUND

Amrinone is a bipyridine derivative with inotropic and vasodilator effects that have not been systematically evaluated in the pediatric patient with increased pulmonary blood flow.

METHODS

Nineteen patients (aged 2 months to 8.3 years) with one or more left to right shunts were evaluated during cardiac catheterization with direct hemodynamic measurements made before and 10 min (peak effect) after administration of a bolus injection of amrinone, 3 mg/kg body weight. The Fick method was used to calculate pulmonary and systemic blood flow, and resistances were then calculated.

RESULTS

In group A, five patients with normal pulmonary artery pressure and resistance, amrinone significantly reduced mean pulmonary artery pressure by 19%, mean left atrial pressure by 39% and systemic vascular resistance by 17%. In group B, seven patients with pulmonary artery hypertension (mean pulmonary artery pressure > 20 mm Hg) and normal pulmonary vascular resistance (total pulmonary resistance < or = 3 Wood U.m2), amrinone significantly reduced the pulmonary artery pressure by 27%, systolic aortic pressure by 5%, mean aortic pressure by 12%, pulmonary arteriolar resistance by 36% and total pulmonary vascular resistance by 26%. In group C, seven patients with pulmonary artery hypertension (mean pulmonary artery pressure > 20 mm Hg) and elevated pulmonary vascular resistance (total pulmonary resistance > 3 Wood U.m2), amrinone significantly reduced the pulmonary arteriolar resistance by 49%, total pulmonary resistance by 47% and pulmonary arteriolar/systemic vascular resistance ratio by 45% and increased the heart rate by 15%.

CONCLUSIONS

In children with a cardiac left to right shunt, amrinone 1) appears to have selective vasodilator effects depending on the pulmonary artery pressure and resistance, 2) has a beneficial hemodynamic effect in children with normal pulmonary artery pressure and resistance, and 3) may have a role in the treatment of patients with pulmonary artery hypertension without causing systemic hypotension.

Heart rate and oxygen uptake response to exercise in children with low peak exercise heart rate

Normal children achieve the same increase of oxygen uptake (VO2) in response to exercise even though resting and submaximal exercise heart rates vary greatly as a function of age, body size and physical conditioning. To determine whether the VO2 response to exercise is altered when heart rate is significantly reduced by heart disease, we compared 78 children who achieved a peak exercise heart rate of less than or equal to 150 beats/min to 201 controls of similar body size and normal peak exercise heart rates of greater than or equal to 180 beats/min. All performed incremental (16.4 Watts/min) maximal cycle exercise. Separate analysis of males and females included heart rate, power (kg-m/min, Watts/kg), VO2 (ml/min, ml/min per kg), O2 pulse (VO2/heart beat), VE (l/min) and R (VCO2/VO2) at rest and during the 1st, 4th and last minute of exercise. Patients with low peak exercise heart rates had also lower resting submaximal exercise heart rates than controls. VO2 at comparable exercise levels did not differ from controls and consequently O2 pulse was greater in the patients than controls at rest and at all levels of exercise. A consistent gender difference was only found in controls where males achieved a higher VO2 and lower heart rates at comparable levels of exercise. The data show a normal exercise VO2 despite significantly lower heart rates. These findings cannot be explained by an increased arteriovenous difference alone and suggest that the patients retained the ability to effectively modulate stroke volume.

Exercise responses in patients with congenital heart disease after Fontan repair: patterns and determinants of performance

After a Fontan repair for congenital heart disease, 42 patients underwent graded supine bicycle exercise tests at levels relevant to normal daily activities. Results were compared with those of 28 age-matched normal control subjects. At rest, the cardiac index, stroke index and systolic blood pressure were comparable in both groups, but increases with exercise were smaller in the patients with a Fontan circulation. The heart rate at rest was higher in the Fontan group, but this difference disappeared as soon as exercise started. To determine whether there are limitations intrinsic to the Fontan circulation at these levels of exercise, the 10 best performers were compared with 10 age-matched control subjects; no differences were found in cardiac index, stroke index, heart rate or blood pressure at any exercise level. Analysis of the determinants of cardiac output showed that at the other end of the spectrum poor performance after a Fontan operation did not result from inadequate levels of heart rate, but from an inability to increase or maintain stroke volume. Multivariate analysis demonstrated that impairment of ventricular contractility, only when severe, predicted limited performance. There was no evidence of increased afterload, particularly in the poor performers. Therefore, ventricular filling, which is determined primarily by the pulmonary vascular bed, appears to be a major determinant of functional result after a Fontan repair.

Hemodynamic responses to isolated increments in heart rate by atrial pacing after a Fontan procedure

The physiologic role of the right ventricle has long been a subject of interest to physiologists. The Fontan operation provides a human model for studying the circulation in series devoid of a subpulmonic right ventricle. The hemodynamic response to isotonic exercise in this setting has been established, and differs appreciably from normal. However, the physiologic response to an increase in heart rate (atrial pacing) as an isolated variable has not been examined and compared to atrial pacing in hearts with two concordant subarterial ventricles. Accordingly, we compared the supine bicycle exercise response to rate-equivalent right atrial pacing in nine patients after atriopulmonary anastomoses (the Fontan operation) for single ventricle or tricuspid atresia. Cardiac index increased 77% with exercise (rest 2.6 L/min/m2; exercise 4.6 L/min/m2) but decreased 12% with atrial pacing (rest 2.5 L/min/m2; pacing 2.2 L/min/m2). Pulmonary arterial oxygen saturation declined significantly during exercise (rest 68%; exercise 31%) and during atrial pacing (control 72%; pacing 64%). The mean increment in pulmonary arterial pressure was 1.3 times greater with exercise (rest 14 mm Hg; exercise 20 mm Hg) than with pacing (control 12 mm Hg; pacing 16 mm Hg). Peak systemic arterial systolic pressure increased 14% with exercise but was unchanged by pacing. Systemic and pulmonary vascular resistances fell with exercise but changed insignificantly during atrial pacing. Stroke volume rose slightly with exercise but fell significantly with pacing.(ABSTRACT TRUNCATED AT 250 WORDS)

Noninvasive assessment of hemodynamic responses to exercise in pulmonary regurgitation after operations to correct pulmonary outflow obstruction

The influence of pulmonary regurgitation (PR) on exercise capacity is unknown. The hemodynamic responses to exercise in postoperative patients with PR was determined using Doppler-measured regurgitant fraction to indicate PR severity. Maximal heart rate, oxygen consumption and workload capacity were measured during upright cycle ergometry. Cardiac output was measured at rest and during submaximal supine cycle ergometry by pulsed Doppler echocardiography. Oxygen consumption was simultaneously measured and exercise factor was calculated as the change in cardiac output per change in oxygen consumption. Twenty-seven patients were compared with 17 age-, size- and sex-matched control subjects. Patients with PR had larger right ventricles (p less than or equal to 0.001), lower heart rate response (p less than or equal to 0.05), lower maximal oxygen consumption (p less than or equal to 0.005) and lower workloads (p less than or equal to 0.005) when compared with normal control subjects during maximal exercise testing. Exercise factor was the same for both groups. Patients with PR were then separated into mild, moderate and severe groups. Patients with mild PR had a normal response to exercise. However, patients with moderate and severe PR had lower maximal oxygen consumptions and maximal workloads than control subjects. Control, mild and moderate PR groups had similar exercise factors. Patients with severe PR had markedly low cardiac output responses. PR is associated with reduced exercise capability, which is related to the severity of the PR.

Measurement of cardiac output and exercise factor by pulsed Doppler echocardiography during supine bicycle ergometry in normal young adolescent boys

The purposes of this study were to determine the ability of pulsed Doppler echocardiography to consistently and accurately measure cardiac output during exercise, and to measure the exercise factor by Doppler methodology when oxygen consumption was simultaneously measured. Thirty-four healthy young adolescent male volunteers (mean age 13 years) were recruited. Submaximal exercise was performed by supine bicycle ergometry. Cardiac output was calculated as mean velocity X cross-sectional area. Successful rest and exercise determinations of cardiac output were obtained in 81% (n = 52) of the studies. Mean cardiac output increased from 4.6 to 8.9 liters/min (p less than 0.001) during exercise and mean oxygen consumption increased from 212 to 899 ml/min (p less than 0.001). Doppler-estimated rest and exercise cardiac outputs correlated well with simultaneously measured oxygen consumption (r = 0.89, SEE = 1.2 liters/min; y = 0.006 X 3.2 liters/min). Mean exercise factor was 6.4 (1.2 SD). Twenty-six pairs of rest and exercise cardiac output determinations by Doppler technique and indirect Fick method were simultaneously compared in a subset population (r = 0.86, SEE = 1.4 liters/min; slope = 0.93, y intercept = 1.4 liters/min). Results of this study demonstrate that cardiac output and exercise factor can be estimated by pulsed Doppler echocardiography during exercise.

Effects of activity on ascending aortic velocity in children with valvar aortic stenosis

The peak velocity of aortic blood flow was measured in 12 normal children and 20 children with valvar aortic stenosis (AS) by continuous-wave Doppler ultrasound (CWD). Measurements were made at rest, after 2 forms of exercise and, in the 11 children who underwent cardiac catheterization, while under sedation. The exercise was both formal cycle ergometry and a 200-meter jog. The peak velocity in normal children was 1.5 +/- 0.2 m/s at rest, increasing to 2.1 +/- 0.4 m/s (p less than 0.01) after running and to 1.9 +/- 0.4 m/s (p less than 0.01) after cycling. Peak velocity in children with AS was 3.5 +/- 0.8 m/s at rest, increasing to 4.4 +/- 0.8 m/s (p less than 0.01) after running and to 4.5 +/- 0.5 m/s (p less than 0.01) after cycling. The increase in peak velocity was greater in children with AS than in normal children. Measurements of left ventricular (LV) aortic pressure differences by cardiac catheterization were compared to those made by CWD, using the modified Bernoulli equation. The best correlation of the CWD prediction of LV aortic pressure differences was achieved when the children were sedated. The peak velocity of blood flow in the ascending aorta varied with level of activity, and this variability must be considered when using the Bernoulli equation to predict LV aortic pressure differences. CWD prediction of the LV aortic pressure difference was best when the child was sedated (r = 0.98). It is therefore prudent to consider the velocity measurement proximal to the AS to calculate LV aortic pressure differences more accurately unless the child is sedated.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise radionuclide ventriculography in children: normal values for exercise variables and right and left ventricular function

Thirty two children (aged 5-19 years) with no clinical evidence of significant cardiovascular disease undertook continuous staged supine exercise on a bicycle ergometer. Multigated radionuclide ventriculography was performed at rest and during each exercise stage. Exercise duration and total workload both increased with age. Aerobic work correlated better with age than did total work. In most children the ejection fraction for both ventricles increased by at least 5% with exercise. Right ventricular ejection fraction did not decrease with exercise in any subject but left ventricular ejection fraction decreased by 2% and 9% in two. The response of end diastolic volume to exercise was variable, but there was a consistent decrease in mean (SD) end systolic volume of the left (29(22)%) and right (30(19)%) ventricles. Cardiac index (mean (SD)) increased by 234(65)% with exercise. The left ventricular:right ventricular end diastolic volume ratio (mean (SD)) at rest was 1.26(0.26). It is concluded that exercise radionuclide ventriculography is an excellent technique for a combined assessment of exercise capacity and an evaluation of ventricular size and performance in children. These values for supine bicycle exercise in children without significant cardiovascular disease will be useful for future comparisons with other groups.

Rest and exercise hemodynamics in pulmonary stenosis: comparison of children and adults

To better understand the hemodynamics of pulmonary stenosis (PS), 24 adults and 53 children with similar degrees of PS who had undergone cardiac catheterization at rest and during supine exercise were retrospectively studied. Three groups were defined. Group I consisted of 9 adults and 18 children with a pulmonary valve area of less than 0.5 cm2/m2; group II, 6 adults and 25 children with a pulmonary valve area of 0.5 to 1.0 cm2/m2; and group III, 9 adults and 10 children with pulmonary valve area of more than 1.0 cm2/m2. The mean ages of the adults were 29, 26 and 22 years for groups I, II, and III, respectively. The mean ages of the children were 11, 10 and 9 years for groups I, II and III, respectively. The pertinent data collected from catheterization included oxygen consumption, cardiac rate and index, arterial venous oxygen difference, stroke index, right ventricular (RV) systolic pressure and RV end-diastolic pressure. Adults and children in groups II and III had an appropriate response to exercise. Group I children responded abnormally by increasing their RV end-diastolic pressure and decreasing their stroke index. In group I adults both of these variables increased. Group I adults exhibited a significantly lower cardiac index at rest and exercise secondary to a significantly lower absolute cardiac rate. Long-standing severe PS results in hemodynamic compromise. Hence, early relief of PS is recommended.

Hemodynamic determinants of exercise-induced ST-segment depression in children with valvar aortic stenosis

To evaluate the hemodynamic factors associated with treadmill-induced ST-segment depression in children with valvar aortic stenosis, 12 patients (mean age 13 years) with ST-segment depression during treadmill exercise and 5 patients (mean age 13 years) without ST-segment depression during treadmill exercise underwent exercise testing during cardiac catheterization. The left ventricular (LV) systolic pressure and LV outflow tract gradient at rest (177 +/- 25 vs 138 +/- 8 mm Hg and 59 +/- 18 vs 23 +/- 7 mm Hg, respectively) and corresponding pressures during maximal supine exercise (248 +/- 37 vs 189 +/- 17 mm Hg and 112 +/- 34 vs 52 +/- 14 mm Hg) were significantly greater (p less than 0.01) in the patients with exercise-induced ST-segment depression, although overlap existed. The LV-O2 supply-demand ratio during maximal supine exercise was significantly less (6.4 +/- 2.7 vs 11.8 +/- 0.7; p less than 0.005) in patients with than in those without exercise-induced ST-segment depression. In fact, an LV-O2 supply-demand ratio less than 11.0 was 100% sensitive and specific in predicting treadmill-induced ST-segment depression. These results suggest that although the development of ST-segment depression during treadmill exercise is related to LV systolic pressure and LV outflow gradient, its major hemodynamic determinant is the LV-O2 supply-demand ratio.

Hemodynamic effects of dynamic exercise in children and adolescents with moderate-to-small ventricular septal defects

We studied the hemodynamic effects of dynamic exercise during cardiac catheterization in 35 children and adolescents with small-to-moderate ventricular septal defects. Eighteen of them exercised at 25% and 50% of their maximum workload and 17 exercised at 60%. There was no significant difference between the two groups with respect to age and body mass, height, and surface area. The changes evoked by exercise showed the same pattern at the different workloads, although they were more marked at the higher than at the lower percentage of maximum workload. During exercise the pulmonary vascular resistance did not change, in contrast to the systemic vascular resistance, which decreased. The pulmonary and systemic blood flows both increased, while the left-to-right shunt flow did not change, which led to a decrease of the left-to-right shunt fraction. As the heart rate increased and the shunt flow did not change, the shunt volume per beat decreased during exercise. We conclude that in patients with small-to-moderate ventricular septal defects the hemodynamic effects of dynamic exercise are favorable because the normal rise in systemic blood flow occurs without a corresponding increase in left-to-right shunt flow. Consequently, children and adolescents with such defects should not be restricted in their dynamic exercise activities.

Sympathetic nervous system and exercise tolerance response in normotensive and hypertensive adolescents

Comparative evaluation of isometric and dynamic exercise performance in normotensive, borderline hypertensive and hypertensive adolescents was made. Hemodynamic changes were correlated with level of adrenergic sympathetic nervous system activity as measured by plasma epinephrine and norepinephrine values. No significant intergroup differences were found with respect to isometric exercise with the exception of high peak isometric exercise heart rates and plasma epinephrine levels in the patients with significant hypertension. During dynamic treadmill testing, patients with the most marked hypertension demonstrated a statistically significantly greater tachycardia response to exercise that correlated with highest peak exercise epinephrine levels. The most hypertensive systolic dynamic exercise response was evidenced in the borderline hypertensive group in which peak exercise norepinephrine values were significantly higher than in other groups. Maximal exercise serum lactate levels were higher in hypertensive patient groups than in normotensive subjects. Altered hemodynamic response to peak dynamic exercise appears to exist in adolescents with borderline and significant hypertension and is in part mediated by altered activity of the sympathetic nervous system.

Exercise induced pulmonary vasoconstriction

Pulmonary vascular resistance normally falls or remains unchanged during exercise. Seven children with pulmonary hypertension were exercised during cardiac catheterisation after operative correction of ventricular septal defect (6) and truncus arteriosus (1). Except for the presence of moderate pulmonary hypertension, resting haemodynamics in these seven children were similar to those of normal children of equal age, but during exercise the postoperative patients showed a rise rather than a fall (+2% vs -18%) in total pulmonary vascular resistance. Two of the seven children had a substantial increase in pulmonary arteriolar resistance during exercise (from 509 to 715 dyne s cm-5 in one patient and from 606 to 828 dyne s cm-5 in the other). These two patients did not differ from normal children in respect of arterial or mixed venous oxygen saturations or of pH with exercise, nor was left atrial pressure related to the rise in pulmonary resistance. These two patients, however, had only a small rise in cardiac output during exercise (6.8% and 43.1%) in spite of a substantial increase in oxygen consumption (121% and 373%). One of the patients with exercise-induced pulmonary vasoconstriction had an 82% increase in resting pulmonary vascular resistance over a five year period subsequent to her first exercise study. Analysis of these data, and those previously reported, suggests that exercise induced pulmonary vasoconstriction may occur in 10 to 25% of patients who survive correction of certain congenital cardiac defects. The vasoconstriction cannot be attributed to abnormal changes in blood gases or left atrial pressure, and may be an early sign of progressive pulmonary hypertension.

Responses to ergometer exercise in a healthy biracial population of children

To determine normal values for the exercise variables heart rate, blood pressure, maximal workload, physical working capacity index, J point displacement, and ST segment slope, we stress tested 405 healthy children. We analyzed the data for four body surface area-determined groups, to discover whether there were any racial differences between healthy white children and black children. There were numerous racial differences in blood pressure, maximal workload, and physical working capacity index; there were no differences in the heart rate values. The incidence of false-positive J point displacement was less than or equal to 3% when the PR isoelectric line method was used. The ST segment slope in healthy children was always greater than zero at maximal exercise. Thus, norms for exercise variables must be expressed in relation to both sex and race. The nomograms presented in this report provide an easy-to-use set of normative data for cycle ergometer stress testing in children.

Rest and exercise hemodynamics after the Fontan procedure

Sixteen consecutive patients (12 with tricuspid atresia) underwent a Fontan procedure, with no operative deaths. There were three late deaths. Eleven of the survivors were electively catheterized 4-25 months postoperatively. Rest and exercise hemodynamics were measured in five patients, and resting hemodynamics alone were measured in three. All exercised patients were New York Heart Association class I Cardiac index was low at rest (2.3 +/- 0.61/min/m2) and during exercise (4.9 +/- 1.11/min/m2) due to a low stroke index both at rest (28 ml) and exercise (35 ml). Accordingly, mixed venous oxygen saturations were decreased (66% at rest and 31% during exercise). These values are significantly lower than those at rest and during exercise from 23 control patients of similar age and size. Heart rates, pulmonary vascular resistances, and left ventricular filling pressures appeared normal both at rest and during exercise. High right atrial pressure at rest (15 mm Hg) was associated with minimal conduit gradient (2 mm Hg). However, exercise increased the mean conduit gradient to 8 mm Hg, demonstrating significant functional conduit obstruction. As expected, the cardiovascular response to exercise is abnormal after the Fontan procedure, even in asymptomatic patients. This abnormal response may be exacerbated by conduit obstruction, and conduit obstruction may not be apparent during resting studies.

Assessment of right ventricular function during supine bicycle exercise after Mustard's operation

Right ventricular (RV) performance during supine bicycle exercise was evaluated by gated equilibrium nuclear angiography in 19 clinically well children with d-transposition of the great arteries (d-TGA), 6.4 +/- 2.7 years after Mustard's operation. Comparisons were made between rest and peak exercise. The mean resting ejection fraction was 44 +/- 12% (range 30-75%) and was unchanged at peak exercise. Eight children had a normal ejection fraction response, whereas 11 children had either no increase or a decrease in ejection fraction. Relative end-diastolic volumes decreased from resting values in all patients who had an abnormal ejection fraction response. Among patients whose ejection fraction increased, the end-diastolic volume increased in three, decreased in four and was unchanged in one at peak exercise. Heart rate increased 84% (range 52-135%) and systolic blood pressure increased 16% (range 0-28%) at peak exercise. There was no correlation between exercise response and age at surgery or interval since surgery. These data indicate that clinically well children after Mustard's procedure may have abnormal right ventricular function under stress, raising concerns about the ability of the right ventricle to function as the systemic ventricle.

Blood pressure response to dynamic exercise in healthy children--black vs white

In order to determine normal values for systolic blood pressure response to cycle ergometer stress testing in children, we performed 405 studies in subjects from 6 to 15 years of age, of whom 184 were black and 221 were white. We analyzed the data in relation to sex, color, age, and body surface area. Resting systolic blood pressure showed no differences between groups of black and white children, analyzed either by age or surface area. Peak exercise blood pressures were higher in the black females, in comparison to their white counterparts, only when separated into groups by body surface area. The black males had higher exercise blood pressure values than the whites, both by age and surface area evaluation. Our data suggest a difference in the blood pressure response to dynamic exercise within the black population. Further studies are needed to define the mechanism of this difference and whether this difference may provide a clue to the identification of children at increased risk for developing hypertension later in life.

Hemodynamic abnormalities in response to supine exercise in patients after operative correction of tetrad of Fallot after early childhood

The exercise hemodynamic values in two groups of patients with repaired tetrad of Fallot (eight patients with some residual pulmonary insufficiency and seven patients without insufficiency) were compared with values in seven patients with trivial pulmonary stenosis who had not been operated on. The patients with tetrad of Fallot underwent surgery after age 8 years and all had a good hemodynamic repair (no shunts and a right ventricular systolic pressure at rest of less than 60 mm Hg). Exercise increased the right ventricular outflow tract gradient by the same magnitude in all three groups of patients. However, both surgically treated groups experienced impaired cardiac pump function on supine exercise (that is, a lower than anticipated cardiac index for the amount of oxygen consumed and a significant decrease in stroke index). Exercise also caused both groups with repair to have a decrease in stroke index and a concomitant increase in right ventricular end-diastolic and pulmonary wedge pressures; in contrast, the patients with pulmonary arterial stenosis had an increase in stroke index and a concomitant decrease in right ventricular end-diastolic and pulmonary wedge pressures. These findings indicate that an impaired cardiac response to supine exercise can occur in patients in whom intracardiac repair of tetrad of Fallot was performed after early childhood, even though they have had a good hemodynamic repair. In addition, the impaired cardiac response to supine exercise in these patients was probably due largely to an altered myocardial compliance rather than to either residual pulmonary stenosis or pulmonary insufficiency.

Hemodynamic responses to supine exercise in children with left-sided cardiac disease

Exercise, a physiologic stress, has been used in adults to unmask abnormalities of left ventricular hemodynamics not detectable at rest. Similar data in children are not available. An evaluation was made of the feasibility, safety and value of a graded upright and supine ergometer stress test to assess exercise hemodynamics during cardiac catheterization in 21 children with left-sided cardiac disease. The catheterization technique involved the simultaneous recording of intracardiac and great vessel pressures, thermodilution cardiac index and M mode echocardiograms of the left ventricular cavity. The method appears practical and safe. Although hemodynamic responses varied among clinical groups, the lack of control data currently prevents assessment of the value of this technique for long-term management.