Influence of Intermittent Hand Cooling and Fluid Replacement on Inflammatory Cytokines During Uncompensable Heat Stress

Abstract

The effect of whole-body cooling on circulating inflammatory cytokines is well established, however the effects of peripheral hand cooling during uncompensable heat stress are unclear. PURPOSE: To examine how circulating inflammatory cytokines (interleukin (IL)-6, IL-12, IL-1B, IL-8, IL-10, tumor necrosis factor (TNF)-α, IL-12p70) respond to hand cooling with fluid replacement (HCF), hand cooling with fluid restricted (HC), and control (C), no cooling and fluid restricted. METHODS: Twelve males (mean ± SD; age: 24 ± 3y, height: 179 ± 5cm, body mass: 82.64 ± 9.77kg) completed three randomized 90 minute bouts of treadmill exercise (4.0-5.6 km·hr-1; 5% grade) while wearing a full American football uniform in a hot environment (39°C, 40% RH). HCF and HC cooled one hand every 12th minute of exercise using the CoreControl™ device for 3 minutes. Rectal temperature (TRE) was measured before (PRE), during (every 12th min), and after (POST) exercise. Percent body mass loss (%BML) and delta (Δ) plasma cytokine concentration were calculated using PRE and POST values. Cytokine concentrations were measured via multiplexed cytometric bead array. Two-way repeated measures ANOVA (condition x time) with Bonferroni post-hoc tests were conducted (α = 0.05). RESULTS: HCF had lower %BML (1.6 ± 0.53%) than HC (3.08 ± 0.59%; p = 0.001) and C (3.29 ± 0.68%; p = 0.001). From minute 57 through POST, HCF TRE was lower than C (p ≤ 0.05). TRE for HC was not different from HCF or C at any time point (p ≥ 0.05). Independent of condition, inflammatory markers IL-8 (p = 0.001) and IL-6 (p = 0.001) were elevated over time. A significant condition x time interaction was observed for IL-8 (p = 0.001). ΔIL-8 for HCF was significantly lower than HC (p = 0.001) and C (p = 0.050). ΔIL-8 for HC and C were similar (p = 0.133). ΔIL-6 for HCF was reduced compared to HC (p = 0.005) but not C (p = 0.118). ΔIL-6 for HC and CON were similar (p = 0.963). IL-12, IL-1B, IL-10, TNF-α, IL-12p70 showed no significant differences between any of the conditions over time (p > 0.05). CONCLUSIONS: During uncompensable heat stress while wearing football equipment, hand cooling with fluid replacement had a greater effect than hand cooling alone and resulted in lower TRE, lower %BML, and lower ΔIL-8 and ΔIL-6. Further research on the effects of peripheral cooling may elucidate the inflammatory cytokine response.