Reliability of Heart Rate Variability by Sample Entropy at Rest and During Light Exercise in Children.

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Variations in heart rate period are attributed to the dynamic balance of sympathetic and parasympathetic modulation. This balance may be assessed by determining sample entropy (SampEn) of heart rate variability (HRV) data, but little is know about the reliability of SampEn measures in children. PURPOSE: Assess the reproducibility of SampEn during rest and light exercise in children. METHODS: Nine healthy children (age= 12.9 ± 0.3 yrs, mean ± SD) agreed to participated in the study. All abstained from caffeinated beverages and physical activity for 24 hours prior to testing. Resting data were obtained on two separate days using a Polar Vantage telemetry system (Polar Electro Inc., Kemple, Finland). During both resting studies subjects rested in a quiet room for 8 minutes and then resting data was collected for the next 5 minutes while breathing was paced at 12 breaths/minute. On subsequent visits, subjects completed two 5 minute bouts of light exercise. Each bout of light exercise consisted of a constant work rate of unloaded cycling representing an intensity of 25% VO2peak at a cadence of 70 rpm, during which HRV data were collected. Sample entropy scores for variability were determined for each 5 minute data set (Matlab, The MathWorks, Inc., Natick, MA). The same R-R intervals were analyzed using m=5 and m=2; where m is the length of data points in a template for matching. All statistical procedures were performed using SPSS 14.0 (SPSS Inc., Chicago, IL). RESULTS: Intraclass correlations coefficients (ICC) were calculated with m=5 and m=2 for rest and exercise: A. resting with m=5 ICC = 0.56 (95% Confidence Interval (CI) −0.11 to 0.88) ; with m=2, ICC = 0.64 (95% CI 0.01 to 0.90) B. during exercise with m=5, ICC = 0.19 (95% CI −0.50 to 0.73 ; with m=2, ICC = 0.29 (95% CI −0.42 to 0.78). CONCLUSIONS: These data suggest that the reliability of HRV using SampEn analysis at rest are weak to moderate, but are weak during light exercise in children. Caution should therefore be taken in interpreting HRV data with children, but particularly during excise. Due to small number of subjects, future studies are needed to confirm these findings.