Signal Variability Comparative Analysis of Healthy Early- and Late-Pubertal Children during Cardiopulmonary Exercise Testing

Abstract

ABSTRACT Purpose The kinetics of physiological responses to exercise have traditionally been characterized by estimating exponential equation parameters using iterative best-fit techniques of heart rate (HR) and gas exchange [respiratory rate, RR; oxygen uptake, ; carbon dioxide output, ; and ventilation, V̇E]. In this study, we present a novel approach to characterizing the maturation of physiological responses to exercise in children by accounting for response uncertainty and variability. Methods Thirty-seven early-pubertal (17 females, 20 males) and 44 late-pubertal (25 females, 19 males) participants performed three multiple brief exercise bouts (MBEB). MBEB consisted of ten 2-min bouts of cycle ergometry at constant work rate interspersed by 1-min rest. Exercise intensity was categorized as low, moderate, or high, corresponding to 40%, 60%, and 80% of peak work rate, and performed in random order on three separate days. We evaluated sample entropy (SampEn), approximate entropy, de-trended fluctuation analysis, and average absolute local variability (AALV) of HR and gas exchange. Results SampEn of HR and gas exchange responses to MBEB was greater in early- compared to late-pubertal participants (e.g., V̇O2 early-pubertal 1.70 ± 0.023 versus late-pubertal 1.41 ± 0.027, p = 2.97 × 10−14), and decreased as MBEB intensity increased [e.g., HR for low-intensity: 0.37 ± 0.01 compared to 0.21 ± 0.014 for high intensity, p = 3.56 × 10−17]. Females tended to have higher SampEn than males (e.g., V̇O2 for females: 1.61 ± 0.025 versus 1.46 ± 0.031 for males, p = 1.28 × 10−4). AALV was higher in younger participants for both gas exchange and HR (e.g., early-pubertal V̇O2: 17.48 ± 0.56% versus 10.24 ± 0.34% late-pubertal, p = 1.18 × 10−21). Conclusions The greater entropy in signal response to a known, quantifiable exercise perturbation in the younger children might represent maturation-dependent, enhanced competition among physiological controlling mechanisms that originate at the autonomic, subconscious, and cognitive levels.