What Maintains the Metabolic Cost at Maximal Exercise in Heart Transplant Recipients and Coronary Artery Disease Patients? (original) (raw)
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AJP: Heart and Circulatory Physiology, 2008
The cardiovascular response to exercise in heart transplant recipients (HTR) has been compared with that of healthy individuals matched to the recipient age (RM controls). However, no study has compared HTR with donor age-matched (DM) controls. Moreover, the cardiovascular response to sustained submaximal exercise in HTR requires further evaluation. We therefore examined cardiovascular responses during incremental exercise and sustained (1 h) submaximal aerobic exercise in 9 clinically stable HTR [63 +/- 10 yr of age, 24.2 +/- 10.9 ml x kg(-1) x min(-1) peak O(2) uptake (Vo(2peak))] and 11 healthy age-matched controls (60 +/- 11 yr of age and 36.3 +/- 10.7 ml.kg(-1) x min(-1) Vo(2peak) for 6 RM controls and 35 +/- 8 yr of age and 51.1 +/- 10.4 ml x kg(-1) x min(-1) Vo(2peak) for 5 DM controls). Heart rate (HR) and left ventricular systolic and diastolic volumes (2-dimensional echocardiography) indexed to body surface area [end-systolic and end-diastolic volume indexes (EDVI and ESVI)], cardiac output (CI), ejection fraction (EF), systemic vascular resistance (SVRI), end-systolic elastance index, and arterial elastance index were determined. Although systolic function was maintained during incremental exercise, peak CI was significantly reduced (6.7 +/- 2.4 vs. 11.6 +/- 1.4 l x min(-1) x m(-2)), secondary to blunted HR, EDVI, and increased peak SVRI, in HTR compared with DM controls. The lower peak CI in HTR than in RM controls was due to blunted peak EDVI (54.1 +/- 13.2 vs. 68.6 +/- 5.7 ml/m(2)). During sustained submaximal exercise, HTR exhausted their preload reserve, a response for which changes in ESVI, HR, or EF did not fully compensate. Thus it appears that HTR are limited by impaired preload reserve, HR reserve, and vascular reserve during exercise conditions.
International Journal of Cardiology, 2010
One way of defining an individual's heart effort is to calculate the maximum heart rate to be expected given their age, but the reinnervation seen in patients who have received heart transplants makes for different calculations from patients who have suffered heart failure. The purpose of this study is to evaluate heart rate dynamics (rest, peak and percentage of predicted heart rate for age) in heart transplant patients compared to optimized beta-blocked heart failure patients during a treadmill cardiopulmonary exercise test.
Aerobic Capacity in Patients Entering Cardiac Rehabilitation
Circulation, 2006
Background-Symptom-limited treadmill testing is commonly performed on entry to cardiac rehabilitation (CR) for its prognostic value and to design a safe and effective exercise program. Normative values for this evaluation are not available. The primary goals of this study were to establish normative values for peak aerobic capacity (peak V O 2 ) for patients entering CR and to create nomograms for conversion of peak V O 2 to a percentage of predicted exercise capacity, stratified by age, gender, and diagnosis.
American Journal of Transplantation, 2012
Heart transplant (HTx) recipients usually have reduced exercise capacity with reported VO 2peak levels of 50-70% predicted value. Our hypothesis was that highintensity interval training (HIIT) is an applicable and safe form of exercise in HTx recipients and that it would markedly improve VO 2peak. Secondarily, we wanted to evaluate central and peripheral mechanisms behind a potential VO 2peak increase. Forty-eight clinically stable HTx recipients >18 years old and 1-8 years after HTx underwent maximal exercise testing on a treadmill and were randomized to either exercise group (a 1-year HIIT-program) or control group (usual care). The mean ± SD age was 51 ± 16 years, 71% were male and time from HTx was 4.1 ± 2.2 years. The mean VO 2peak difference between groups at follow-up was 3.6 [2.0, 5.2] mL/kg/min (p < 0.001). The exercise group had 89.0 ± 17.5% of predicted VO 2peak versus 82.5 ± 20.0 in the control group (p < 0.001). There were no changes in cardiac function measured by echocardiography. We have demonstrated that a long-term, partly supervised and community-based HIIT-program is an applicable, effective and safe way to improve VO 2peak , muscular exercise capacity and general health in HTx recipients. The results indicate that HIIT should be more frequently used among stable HTx recipients in the future.
Effects of an Enhanced Heart Rate Reserve on Aerobic Performance in Patients with a Heart Transplant
American Journal of Physical Medicine & Rehabilitation, 2002
The aim of this study was to investigate whether a high-intensity warm-up at the start of a graded, symptom-limited exercise test would enhance heart rate reserve and thus improve the aerobic performance of orthotopic heart transplant patients. Design: Adrenal and cardiorespiratory responses were compared in 10 orthotopic heart transplant patients who performed two graded, symptom-limited exercise tests on an ergocycle. Results: At the start of the graded, symptom-limited exercise test, high intensity increased the norepinephrine level more than usual intensity between rest and the third minute of exercise. This higher norepinephrine level was followed by a higher heart rate response from the fourth minute of exercise. Heart rate reserve was enhanced during high-intensity exercise, without any significant change in peak oxygen uptake. Conclusions: This specific warm-up enhanced heart rate reserve during a graded, symptom-limited exercise test on an ergocycle. Mechanisms more important than limited heart rate reserve are involved in the limitation of exercise tolerance in orthotopic heart transplant patients.
Circulation, 1984
The purpose of this study was to examine the relationship between maximal O2 uptake (VO2max) and left ventricular systolic function in patients with coronary artery disease. We studied 27 patients, age 50 +/- 10 years (mean +/- SD), who were asymptomatic and able to attain true VO2max. VO2max was defined by the leveling-off criterion and/or a respiratory exchange ratio of 1.15 or greater. Left ventricular ejection fraction was determined by gated cardiac blood pool imaging. In patients whose ejection fraction decreased with exercise, VO2max was 21 +/- 4 vs 27 +/- 4 ml/kg/min in those whose ejection fraction increased (p less than .001). Systolic blood pressure/end-systolic volume relation was shifted upward and to the right in the former group in response to peak exercise. In contrast, the pressure-volume relation was shifted upward and to the left in patients whose ejection fraction increased with exercise. Ejection fraction at rest did not correlate with VO2max. There was a signif...
Influence of the Exercise Protocol on Peak Vo2 in Patients After Heart Transplantation
The Journal of Heart and Lung Transplantation, 2005
The protocol and the duration of an exercise test have considerable influence on peak oxygen consumption (VO 2 ). On a bicycle ergometer, the use of a ramp protocol with a target exercise duration of 8 to 12 minutes is recommended to reliably measure maximal oxygen uptake. Because of cardiac denervation, heart transplant recipients have a delayed heart rate adaptation to exercise, and oxygen uptake kinetics are altered.