Hand immersion in cold water alleviating physiological strain and increasing tolerance to uncompensable heat stress

Abstract

The current study examines the use of hand immersion in cold water to alleviate physiological strain caused by exercising in a hot climate while wearing NBC protective garments. Seventeen heat acclimated subjects wearing a semi-permeable NBC protective garment and a light bulletproof vest were exposed to a 125 min exercise-heat stress (35 degrees C, 50% RH; 5 km/h, 5% incline). The heat stress exposure routine included 5 min rest in the chamber followed by two 50:10 min work-rest cycles. During the control trial (CO), there was no intervention, whilst in the intervention condition the subjects immersed their hands and forearms in a 10 degrees C water bath (HI). The results demonstrated that hand immersion in cold water significantly reduced physiological strain. In the CO exposure during the first and second resting periods, the average rectal temperature (T (re)) practically did not decrease. With hand immersion, the mean (SD) T (re) decreased by 0.45 (0.05 degrees C) and 0.48 degrees C (0.06 degrees C) during the first and second rest periods respectively (P < 0.005). Significant decreases in skin temperature, sweat rate, heart rate, and heat storage was also noted in the HI vs. the CO trials. Tolerance time in the HI exposure were longer than in the CO exposure (only 12 subjects in the CO trial endured the entire heat exposure session, as opposed to all 17 subjects in the HI group). It is concluded that hand immersion in cold water for 10 min is an effective method for decreasing the physiological strain caused by exercising under heat stress while wearing NBC protective garments. The method is convenient, simple, and allows longer working periods in hot or contaminated areas with shorter resting periods.

Extremity cooling for heat stress mitigation in military and occupational settings

“…Khomenok and colleagues asked participants to rate their hand discomfort using a 0-10 scale during immersion in 10 1C water (Khomenok et al, 2008). During hand immersion the discomfort ratings were 3.25 70.3 and 4.0 70.4 for the first and second recovery periods, which was not significantly different from the ratings during the nonimmersion recovery periods (4.24 70.4 and 4.687 0.6, respectively).…”

“…While some investigations have reported that heart rate was 10-25 bpm less than during non-cooling control (Khomenok et al, 2008;Selkirk et al, 2004) others have reported no difference in heart rate between conditions (Giesbrecht et al, 2007). Postural differences may explain the discrepancy, as subjects were seated or leaning over the cooling apparatus in the former studies (Khomenok et al, 2008;Selkirk et al, 2004) but remained standing in the latter (Giesbrecht et al, 2007). It should be noted, however, that heart rate differences persisted into subsequent work bouts in the aforementioned studies (Khomenok et al, 2008;Selkirk et al, 2004), suggesting that more than postural differences are involved.…”

“…In addition to being impractical in a military training environment (Khomenok et al, 2008;Selkirk et al, 2004), data suggest that the rate of core temperature cooling during foot immersion is inferior compared to hand or hand and forearm immersion (House, 1998;Livingstone et al, 1995). Similar to hand or combined hand and forearm immersion, when immersing the feet, heat loss was greatest in the 10 1C water condition, such that heat loss was $3 times greater at that temperature compared to 30 1C (Livingstone et al, 1995).…”

“…An asterisk indicates a significantly greater cooling compared to a control trial. 1, (Giesbrecht et al, 2007); 2, ; 3, (Zhang et al, 2009); 4, (Kuennen et al, 2010); 5, (Grahn et al, 2009); 6, (Grahn et al, 2005); 7, (Barr et al, 2011); 8, (Khomenok et al, 2008); 9, (House, 1998); 10, (House, 1998). 35 1C) and the body segment immersed was smaller (1 hand vs. both hands and forearms) in the study by Amorim and colleagues (2010), likely contributing to the observed differences.…”

“…Postural differences may explain the discrepancy, as subjects were seated or leaning over the cooling apparatus in the former studies (Khomenok et al, 2008;Selkirk et al, 2004) but remained standing in the latter (Giesbrecht et al, 2007). It should be noted, however, that heart rate differences persisted into subsequent work bouts in the aforementioned studies (Khomenok et al, 2008;Selkirk et al, 2004), suggesting that more than postural differences are involved. No previous studies have reported changes in skin blood flow or stroke volume changes during extremity immersion cooling; however using cold air exposure or water-perfused suit models, it is well-established that skin temperature and skin blood flow are directly related (DeGroot and Kenney, 2006;Stephens et al, 2001).…”