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

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, oxygen uptake (V̇O 2 ), carbon dioxide output, and ventilation). 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 3 separate days. We evaluated sample entropy (SampEn), approximate entropy, detrended fluctuation analysis, and average absolute local variability of HR and gas exchange. RESULTS: SampEn of HR and gas-exchange responses to MBEB was greater in early- compared with late-pubertal participants (e.g., V̇O 2 early-pubertal vs late-pubertal, 1.70 ± 0.023 vs 1.41 ± 0.027; P = 2.97 × 10 -14 ), and decreased as MBEB intensity increased (e.g., 0.37 ± 0.01 HR for low-intensity compared with 0.21 ± 0.014 for high intensity, P = 3.56 × 10 -17 ). Females tended to have higher SampEn than males (e.g., 1.61 ± 0.025 V̇O 2 for females vs 1.46 ± 0.031 for males, P = 1.28 × 10 -4 ). Average absolute local variability was higher in younger participants for both gas exchange and HR (e.g., early-pubertal vs late-pubertal V̇O 2 , 17.48 % ± 0.56% vs 10.24 % ± 0.34%; 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.

Relationship Between Central Venous Catheter Protein Adsorption and Water Infused Surface Protection Mechanisms.

Central venous catheters (CVCs) are implanted in the majority of dialysis patients despite increased patient risk due to thrombotic occlusion and biofilm formation. Current solutions remain ineffective at preventing these complications and treatment options are limited and often harmful. We present further analysis of the previously proposed water infused surface protection (WISP) technology, an active method to reduce protein adsorption and effectively disrupt adsorbed protein sheaths on the inner surface of CVCs. A WISP CVC is modeled by a hollow fiber membrane (HFM) in a benchtop device which continuously infuses a saline solution across the membrane wall into the blood flow, creating a blood-free boundary layer at the lumen surface. Total protein adsorption is measured under various experimental conditions to further test WISP performance. The WISP device shows reduced protein adsorption as blood and WISP flow rates increase (P < 0.040) with up to a 96% reduction in adsorption over the no WISP condition. When heparin is added to the WISP flow, protein adsorption (0.097[+0.035/-0.055] µg/mm2 ) is reduced when compared to both bolus administration and nondoped WISP, 0.406(+0.056/-0.065) µg/mm2 (P = 0.001) and 0.191 (+0.076/-0.126) (P = 0.029), respectively. Additionally, when heparinized WISP is applied to a preadsorbed protein layer, 0.375(+0.114/-0.164) µg/mm2 , it displays the ability to reduce the previously-adsorbed protein, 0.186(+0.058/-0.084) µg/mm2 (P = 0.0012), suggesting aptitude for intermittent treatments. The WISP technology not only shows the ability to reduce protein adsorption, but also the ability to remove preadsorbed material by effectively delivering drugs to the point of adsorption; functionalities that could greatly improve clinical outcomes.