Abstract
BACKGROUND: Cardiac transplantation (CTX) improves exercise tolerance, but CTX recipients still achieve only 50% to 70% of normal values for exercise capacity. Among the factors suggested to explain the reduced exercise tolerance in CTX recipients is deconditioning. Little is known about the relation between physical activity patterns and exercise test responses in CTX patients.
METHODS: Forty-seven CTX patients (mean age 47 +/- 12 years; mean 4.8 +/- 3.0 years after CTX) underwent maximal exercise testing and assessment of current and past physical activity patterns using a questionnaire. Energy expenditure from recreational and occupational activities over the last year and for adulthood were expressed in kcal/week and correlated with peak oxygen consumption (VO2), VO2 at the ventilatory threshold, and the percentage of age-predicted peak VO2 achieved.
RESULTS: The patients reported expending a mean of approximately 1100 kcal/week in recreational activity, suggesting a moderate level of physical activity is maintained after CTX. The mean peak VO2 achieved for the group was 17.2 +/- 5.2 mL/kg/min, corresponding to 59% +/- 14% of age-predicted exercise capacity. Significant but modest associations were observed between recreational energy expenditure during the last year and percentage of age-predicted peak VO2 achieved (r = 0.34, P < .01), and VO2 at the ventilatory threshold (r = 0.45, P < .01). Energy expenditure from blocks walked and stairs climbed per week was modestly associated with peak VO2 (r = 0.36, P < .05), percentage of predicted peak VO2 achieved (r = 0.39, P < .01), and VO2 at the ventilatory threshold (r = 0.42, P < .01). Exercise capacity was poorly related to occupational and recreational activities when expressed as average weekly energy expended throughout adulthood.
CONCLUSION: Post-CTX patients maintain a moderately active lifestyle. Measures of exercise tolerance generally are related to recent daily recreational activities in CTX patients, but these associations are modest. The many physiologic factors unique to CTX recipients likely play a more important role than deconditioning in determining exercise tolerance in these patients.
Over the last three decades, cardiac transplantation (CTX) has become a successful and widely accepted treatment for patients with end-stage chronic heart failure, and this procedure improves exercise tolerance. 1,2 However, for reasons that are not completely understood, CTX only partially restores exercise capacity to normal; transplant recipients achieve only about 50% to 70% of values predicted for age and gender. 1,3,4 Although the factors that have been suggested to explain persistent exercise intolerance in CTX recipients include immunosuppressive therapy, a low chronotropic reserve associated with denervation, decreased skeletal muscle strength, decreased capillary density, and characteristics associated with rejection, 2,4-9 one of the most important may be deconditioning associated with physical inactivity. 9-12 In part for this reason, regular physical activity is now widely recommended for CTX patients. Favorable effects of exercise rehabilitation in these patients include improvements in peak oxygen consumption (VO2), reduced blood lactate concentration, reduced perceived effort for the same work demands, improved submaximal endurance, lessened symptoms of dyspnea and fatigue, and increased muscle strength and lean body mass. 10-13
Habitual physical activity is an important determinant of exercise capacity among healthy individuals. 14,15 In CTX patients, physical activity patterns may be limited by comorbidities, fear on the part of the patient, or concerns by the treating physician about limitations imposed by CTX. Information on the relationship between habitual activity and peak VO2 may provide insight into the extent to which deconditioning contributes to reduced exercise tolerance in CTX patients. At present, little is known about physical activity patterns among CTX recipients. The purpose of the current study was to: 1) describe daily occupational and recreational physical activity patterns in CTX recipients, and 2) determine the association between physical activity patterns and exercise test performance in these patients. We hypothesized that an association would exist between physical activity patterns and exercise performance in this population.