Exercise testing in children with primary pulmonary hypertension.

Cardiopulmonary exercise testing is a useful noninvasive tool to assess physiological changes associated with exercise. Developing noninvasive methods to assess the severity of cardiopulmonary disorders, as well as the response to therapeutic interventions, is useful in conditions, such as primary pulmonary hypertension, in which invasive procedures carry significant risks. The 6-minute walk test is a simple measure of exercise endurance. Exercise studies that measure both hemodynamic and ventilatory responses provide additional information regarding the interaction of the circulatory and pulmonary systems. Subtle changes in exercise capacity may suggest deterioration prior to clinical manifestations. This may lead to an earlier reevaluation, including repeat cardiac catheterization, and subsequently changes in medical and/or surgical therapy.

Effect of provocative maneuvers on heart rate variability in subjects with quadriplegia.

This study investigated heart rate variability (HRV) in individuals with quadriplegia who have disruption of autonomic control of the heart. Seven male subjects with neurological complete quadriplegia and seven with incomplete quadriplegia were studied at rest and during provocation. HRV was measured by power spectral analysis using a fast Fourier transform. Two spectral components were generated: 1) the high-frequency (HF) peak, a reflection of parasympathetic activity, and 2) the low-frequency (LF) peak, primarily sympathetic activity with some parasympathetic input. Results of the provocative maneuvers were grouped into one composite variable. Significant differences in the LF spectral component were found between the groups with complete and incomplete lesions in the supine position and after provocation (LF supine: P = 0.01; LF provocation: P = 0.002). After provocation, significant differences were demonstrated in the HF spectral component between these groups (P = 0.005). In contrast to previous findings, a LF component in subjects with complete quadriplegia was observed; this LF component decreased after provocation, suggesting the parasympathetic component withdrew during stressful maneuvers. There also appeared to be general downregulation of parasympathetic activity to the heart in subjects with complete quadriplegia. The presence of an increased LF spectral component during provocation in those with incomplete lesions implies sympathetic stimulation of the heart and may be used as a marker of sympathetic activity in individuals with quadriplegia.

Exercise performance after pediatric heart transplantation.

BACKGROUND: Children awaiting heart transplantation have severe limitations in their ability to exercise. The purpose of this study was to assess exercise capacity after pediatric heart transplantation and to identify factors influencing exercise performance. METHODS AND RESULTS: Progressive cycle ergometry testing was performed in 31 patients at 1.3 +/- 0.8 years after transplantation, and in 16 patients, follow-up studies were performed at 3.3 +/- 1.3 years after transplantation. Maximum work load (Wmax), peak oxygen consumption (VO2), and maximum heart rate (HRmax) were measured. Exercise capacity was defined as normal if Wmax was > or = 75% of predicted values and decreased if Wmax was < 75% of predicted values. Differences in age at transplantation, sex, diagnosis, duration of heart failure, New York Heart Association class before transplantation, resting cardiac index, body mass index, and rejections per patient month were compared between patients with normal and decreased exercise capacity. At initial study, Wmax was 62 +/- 38 W or 61% of that predicted, peak VO2 was 20 +/- 6 mL.kg-1 x min-1 (63% of that predicted), and HRmax was 136 +/- 22 beats per minute (66% of that predicted) for all 31 patients. Six patients had normal exercise capacity, and 25 patients had decreased exercise capacity. Peak VO2 was significantly higher in the normal versus the decreased exercise capacity patients (26 +/- 5 vs 19 +/- 5 mg.kg-1 x min-1). The mean age at transplantation was significantly less in patients with normal exercise capacity: 8.2 +/- 4.6 versus 12.5 +/- 3.6 years for patients with decreased capacity. On follow-up study, no significant differences in Wmax, peak VO2, or HRmax were found from the initial test. CONCLUSIONS: Similar to results obtained in adult patients, exercise capacity was decreased but stable in pediatric patients after heart transplantation.

Hemodynamic correlates of exercise function in patients with primary pulmonary hypertension.

The purpose of this investigation was to study the hemodynamic correlates of exercise function in patients with primary pulmonary hypertension and to further define the role of exercise testing in the evaluation of these individuals. Data from the progressive exercise tests and subsequent cardiac catheterization in 16 consecutive patients, aged 16.9 +/- 10.4 years (range 6 to 35), with primary pulmonary hypertension were prospectively collected and analyzed. Exercise capacity averaged 40 +/- 36% (range 0 to 117%) of that predicted for age, height and gender. Statistically significant correlations existed between exercise capacity and 10 invasively measured hemodynamic variables. Mean right atrial pressure, a variable previously noted to be one of the best predictors of survival in patients with primary pulmonary hypertension, correlated best with exercise capacity (r = -0.83, p less than 0.0001). Exercise capacity greater than 75% of the predicted value identified the two patients who had a positive response to acute pulmonary vasodilator drug testing. Poor exercise capacity (less than 10% of the predicted value) identified the three patients who died during or soon after cardiac catheterization. The ability of exercise testing to identify patients at high risk for cardiac catheterization was superior to that of other noninvasive variables. Results of exercise testing may help guide decisions regarding the optimal timing of heart-lung or single lung transplantation.

Ventilatory response to exercise after intracardiac repair of tetralogy of Fallot.

Previous radionuclide studies have shown residual maldistribution of lung perfusion after intracardiac repair of Tetralogy of Fallot (TF). Maldistribution of perfusion may also be detectable by measurements of gas exchange during exercise. Thus, we used exercise to test for maldistribution of perfusion in 13 children (8 to 18 yr of age) who were clinically well (New York Heart Association Class 1) 7 to 14 yr after repair of TF. Sixteen children, matched to the study group by age, size, and sex, served as control subjects. Peak oxygen consumption during progressive exercise on a cycle ergometer was 28.7 +/- 6.6 (SD) ml/kg/min for the study group compared with 35.7 +/- 6.9 for the control subjects (p less than 0.05). During steady-state exercise at a VCO2 of 0.6 L/min, ventilation (VE) and the ventilatory equivalents for oxygen (VE/VO2) and carbon dioxide (VE/VCO2) were high (VE/VCO2 = 35.9 +/- 4.4 versus 32.0 +/- 3.5, p less than 0.05), whereas mixed expired and end-tidal CO2 concentrations were low (PETCO2 = 34.0 +/- 2.4 versus 39.2 +/- 3.0 mm Hg, p less than 0.001). Indices of pulmonary function were normal; FVC values were 96 +/- 17% and FEV, values were 96 +/- 16% of predicted values. Therefore, children who are clinically well may exhibit gas exchange abnormalities compatible with mild maldistribution of lung perfusion 7 to 14 yr after repair of TF.

Effect of right ventricular anatomy on the cardiopulmonary response to exercise. Implications for the Fontan procedure.

Incorporation of the right ventricle (RV) into the pulmonary circulation of patients with tricuspid atresia undergoing a Fontan procedure has been advocated. The consequences of this approach on the exercise function of these patients was studied by examining the effects of progressive and steady-state bicycle exercise tests performed by 11 patients with right atrial (RA)-RV Fontan anastomoses, seven patients with RA-pulmonary artery (PA) Fontan anastomoses, 13 patients after repair of tetralogy of Fallot, and 34 normal control patients. All patients were in New York Heart Association class I. The exercise function of the patients undergoing RA-RV and RA-PA Fontan procedures were similar. The achieved peak work loads 60% and 67% of control and peak oxygen consumptions 60% and 64% of control, respectively. Both groups also displayed excessive ventilation, elevated dead space/tidal volume ratios, and depressed cardiac output during steady-state exercise. In contrast, tetralogy of Fallot patients achieved peak work loads and oxygen consumptions 83% of control and maintained normal cardiac outputs and dead space/tidal volume ratios during steady-state exercise. These results suggest that the presence of an RV within the pulmonary circulation of the Fontan patient does not result in improved exercise function. This may be due to the development of obstructive gradients across the RA-RV conduits during exercise or to the RV's negative effect on left ventricular compliance. Moreover, in contrast with the postoperative tetralogy of Fallot patient, the hypoplastic RV of tricuspid atresia may not have sufficient myocardium to assume the active pumping function required by exercise.

Cardiorespiratory response to exercise after the Fontan procedure for tricuspid atresia.

Noninvasive exercise testing was used to assess gas exchange in 13 patients age 6-25 yr who had undergone Fontan procedures for tricuspid atresia, five of whom had preexisting Glenn shunts. The results were compared to 28 age- and sex-matched controls. Oxygen saturation was measured by ear oximetry at rest and after exercise. Ventilation, oxygen consumption (VO2), carbon dioxide production (VCO2), and heart rate were measured during progressive exercise. The ventilatory equivalents for oxygen (VE/VO2) and carbon dioxide (VE/VCO2), mixed expired pCO2 (PECO2) end-tidal pCO2 (PETCO2), and dead space to tidal volume ratio (VD/VT) were determined during steady state exercise on a cycle ergometer. Heart rate was higher for VO2 by 15% (p less than 0.02) and ventilation was higher for both VO2 (by 37%, p less than 0.001) and VCO2 (by 27%, p less than 0.002) in the patients than the controls. Mean VE/VO2 was 35.4 +/- 7.8 (SD) compared to 25.8 +/- 3.1 (p less than 0.001) and mean VE/VCO2 was 41.7 +/- 9.0 compared to 31.6 +/- 4.3 (p less than 0.001). Mean PECO2 was 21.4 +/- 4.4 torr with controls at 27.9 +/- 3.8 (p less than 0.001) and mean PETCO2 was 33.0 +/- 5.3 torr compared to 40.0 +/- 3.3 (p less than 0.001). The patients had a mean oxygen saturation of 92 +/- 5% at rest and abnormal saturation after exercise (87 +/- 9, p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)