Review
Extremity cooling for heat stress mitigation in military and occupational settings

https://doi.org/10.1016/j.jtherbio.2013.03.010Get rights and content

Highlights

  • Numerous work settings may cause heat stress that increases injury risk.

  • Extremity cooling in cold water can accelerate body cooling from 0.4 to 1.0 °C/10 min.

  • Immersing the hands and forearms is preferable to just the hands or the feet only.

  • Arm immersion can reduce cardiovascular strain.

  • The Arm Immersion Cooling System provides cooling in the field training environment.

Abstract

Physical work, high ambient temperature and wearing protective clothing can elevate body temperature and cardiovascular strain sufficiently to degrade performance and induce heat-related illnesses. We have recently developed an Arm Immersion Cooling System (AICS) for use in military training environments and this paper will review literature supporting such an approach and provide details regarding its construction. Extremity cooling in cool or cold water can accelerate body (core temperature) cooling from 0.2 to 1.0 °C/10 min vs. control conditions, depending on the size/surface area of the extremity immersed. Arm immersion up to the elbow results in greater heat loss than hand- or foot-only immersion and may reduce cardiovascular strain by lowering heart rate by 10–25 beats/min and increase work tolerance time by up to 60%. The findings from studies in this paper support the use of AICS prototypes, which have been incorporated as part of the heat stress mitigation procedures employed in US Army Ranger Training and may have great application for sports and occupational use.

Introduction

Numerous commercial and industrial occupational settings, as well as military operational and training exercises, expose individuals to considerable heat stress due to high environmental heat and/or a high rate of metabolic heat production (Carter et al., 2005, Centers for Disease Control and Prevention, 2008). As a result body heat storage and associated cardiovascular strain limit exercise performance and increase the risk of exertional heat illness (EHI) (Carter et al., 2005, Sawka et al., 2012). In a number of occupational and military settings it may be biophysically difficult to dissipate body heat due to very hot ambient conditions and/or wearing needed protective clothing or equipment. Clothing/equipment limiting heat loss is common in numerous military, firefighting, hazmat incident, law enforcement, and sporting endeavors (e.g., American Football) (Cheuvront et al., 2003). When physiological cooling is insufficient, active cooling countermeasures may be capable of extending work performance time and reducing EHI incidence and severity (O’Hara et al., 2008).

The purpose of this paper is to review literature on extremity cooling and present a prototype Arm Immersion Cooling Systems (AICS) which we have developed and successfully implemented at military training sites. We will also present information demonstrating that extremity immersion cooling is highly effective and well received by users.

Section snippets

Exertional heat injury epidemiology

In the active duty military, there are typically over 300 cases of exertional heat stroke and over 2000 cases of other reportable heat illness hospitalizations in the training environment per year (Army Medical Surveillance Activity, 2012). In the civilian sector the incidence of EHI is more difficult to determine, as the diagnosis of heat stroke is not required to be reported in any US state (Howe and Boden, 2007). It has been reported, however, that exertional heat stroke is the third leading

Extremity immersion in cold water

Extremity immersion can be an effective method for reducing core temperature and extending work for the following reasons: the heat transfer coefficient of water is approximately 25 times greater than air; the extremities have relatively large surface area to mass ratios compared to the torso; and blood flow through the cutaneous vasculature is very high when core temperature is elevated.. As a result of these characteristics, a number of investigators have examined the use of extremity

Arm immersion cooling system

Over the past several years, in an attempt to take advantage of the well-documented efficacy of extremity immersion for reducing core temperature, the US Army Research Institute of Environmental Medicine and the Natick Solider Research, Development and Engineering Command have been jointly developing an Arm Immersion Cooling System (AICS) for use by Soldiers in the training environment (Fig. 2). The goal was to develop a solution that was suitable for use by multiple soldiers at once, that was

Summary

From research studies (Giesbrecht et al., 2007, House, 1998, House et al., 1997, Selkirk et al., 2004) it can be concluded that (1) hand or hand and forearm immersion in cool water is preferable to foot immersion due to greater rate of cooling and/or convenience factors regarding removing footwear; (2) 10 °C and 20 °C water provides greater cooling power than 30 °C water; (3) 20 °C water is still effective and allowing colder water to warm to 20 °C through repeated use may reduce logistical demands;

Disclaimer

This study is approved for public release, distribution is unlimited. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the U.S. Army or the Department of Defense. Any citations of commercial organizations and trade names in this report do not constitute an official U.S. Department of the Army endorsement of approval of the products or services of these organizations.

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    Present Address: US Army Public Health Command, 5158 Blackhawk Rd, Aberdeen, MD 21010, United States.

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