Exercise Tolerance in Pediatric Patients on Regular Hemodialysis and Effect of L-Carnitine

ABSTRACT
Background: Peak ventilatory oxygen consumption (VO2 max), which is the maximum rate that oxygen can be taken up and consumed, is widely used to characterize exercise function and can be determined from analysis of respired gases during graded exercise. Renal failure patients undergoing chronic hemodialysis have severely impaired exercise tolerance. Severely factors have been suggested to be responsible for the impairment in exercise tolerance, including the loss of muscle cross-sectional area, renal anemia, inactivity, malnutrition, impaired muscle energy production or fatty acid oxidation and carnitine deficiency. Carnitine homeostasis is abnormal in hemodialysis patients. In maintenance hemodialysis, carnitine is lost through dialytic membranes, leading in selected patients to caritine depletion. Objectives: To determine exercise capacity among the studied group of patients in comparison to healthy controls, through non-invasive exercise testing. In addition, carnitine status will be evaluated among them together with detection of the effect of carnitine therapy on the exercise performance. Methods: The study was conducted in the Children′s Hospital, Ain-Shams University. It included 11 patients with chronic renal failure on regular hemodialysis. They were 6 males and 5 females with a mean age of 15.27 ± 2.32 years. They were compared to 20 healthy control subjects. They were 12 males and 8 females with a mean age of 12.8 ± 1.93 years. For all subjects clinical evaluation was done in addition to assay of hemoglobin, blood urea, serum creatinine, lipid profile, including total triglycerides (TC), total cholesterol (TC), HDL-cholesterol (HDL-C) and calculation of LDL-cholesterol (LDL-C). serum carnitine was also assayed by enzymatic ultraviolet test. All subjects underwent cardiopulmonary exercise testing using Bruce walking protocol. Data obtained were exercise duration, VO2  max , RER (ratio of ventilator CO2 production/O2 consumption) and anerobic threshold (AT). All patients received carnitine supplementation for 5 weeks, after which lipid profile and exercise testing were re-evaluated. Results: Serum carnitine was significantly lower in patients with ESRD on HD compared to controls. Supplementation of carnitine did not show any effect on lipid profile. However, carnitine therapy caused significant improvement in three of the four exercise parameters used in this study, namely exercise duration, AT and RER. A significant positive correlation between hemoglobin level and VO2 max was detected in the studied patients before therapy. Conclusions: ESRD pediatric patients on HD have significant impairment in exercise performance that can affect their style of life. Carnitine deficiency is considered an important contributing factor of this exercise intolerance. Carnitine therapy, although did not affect lipid profile in the studied patients, yet proved effective in improving their exercise tolerance.