Effects of Forearm vs. Leg Submersion in Work

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However,. LS ratings of thermal comfort (RTC) at Minute 14 (p = 0.03) .... leg cooling or the forearm cooling on the first trial, and in ... During submersion the tank temperature was measured every. 2 min to .... during 45 min of combating a fire.
Journal of Occupational and Environmental Hygiene, 8: 473–477 ISSN: 1545-9624 print / 1545-9632 online c 2011 JOEH, LLC Copyright DOI: 10.1080/15459624.2011.590743

Effects of Forearm vs. Leg Submersion in Work Tolerance Time in a Hot Environment While Wearing Firefighter Protective Clothing Charles P. Katica,1 Robert C. Pritchett,2 Kelly L. Pritchett,2 Andrew T. Del Pozzi,1 Gytis Balilionis,1 and Tim Burnham2 1 2

The University of Alabama, Tuscaloosa, Alabama Central Washington University, Ellensburg, Washington

This study compared physiological responses and total work tolerance time following forearm submersion (FS) or leg submersion (LS) in cool water, after performing work in a hot environment while wearing fire fighting protective clothing (FPC). Participants walked at 3.5 mph on a treadmill in a hot environment (WBGT 32.8 ± 0.9◦ C) until a rectal temperature (Trec ) of 38.5◦ C was reached. Participants were then subjected to one of two peripheral cooling interventions, in a counterbalanced order. Forearms or lower legs were submerged in water (16.9 ± 0.8◦ C) for a total of 20 min, followed by a work tolerance trial. Results indicated no significant difference (p = 0.052) between work tolerance time (LS = 21.36 ± 5.35 min vs. FS = 16.27 ± 5.56 min). Similarly, there was no significant difference for Trec (p = 0.65), heart rate (HR) (p = 0.79), mean skin temperature (Tsk ) (p = 0.68), and rating of perceived exertion (RPE) (p = 0.54). However, LS ratings of thermal comfort (RTC) at Minute 14 (p = 0.03) were significantly lower for LS (10 ± 1) vs. FS (12 ± 1). Results indicate little difference between FS and LS for physiological measures. Despite a lack of statistical significance a 5-min (24%) increase was found during the work tolerance time following LS. Keywords

heat stress, peripheral cooling, thermal comfort

Correspondence to: Charles P. Katica, Department of Kinesiology, University of Alabama, 201Moore Hall, Box 870312, Tuscaloosa, AL 35487 ; e-mail: [email protected].

INTRODUCTION

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irefighters work in extreme environmental conditions, performing much of their occupational responsibilities in temperatures exceeding 200◦ C, subjecting them to lifethreatening consequences. Technology of fire fighting protective clothing (FPC) has improved throughout the years. However, the susceptibility of heat stress still exists due to the nonpermeable garments worn by firefighters. Time spent in

extreme heat for firefighters may vary from 30 min to an hour depending on the size and severity of the fire.(1) In 2003, the National Fire and Protection Association’s (NFPA) revised standards for firefighters to combat heat stress.(2,3) These revisions were designed to remove the fire fighters from extreme temperatures during incidents and training exercises, mandating a recovery protocol to combat hyperthermia and dehydration as well as the assessment of vital signs.(2,3) Over the past several decades researchers have looked at various cooling interventions to combat hyperthermia during these recovery periods. Some of these interventions have included whole body cooling, limb cooling, liquid air cooling systems, and intermittent microclimate cooling.(4–9) Some cooling methods have a noteworthy impact on reducing heat strain and in some cases increase work tolerance time.(4–9) Limb cooling may improve heat dissipation and increase work tolerance time for firefighters.(8,9) Studies have looked at the impact of hand and forearm submersion in cold water for heat dissipation in firefighters. Forearm submersion has been shown to significantly increase tolerance time and total work time when compared with liquid air cooling and passive cooling strategies.(9) However, investigators have neglected to determine the response of lower leg submersion on work tolerance time and physiological variables. It may be hypothesized that the larger musculature in the legs compared with the forearms may increase heat storage for active firefighters. Therefore, the purpose of this investigation was to evaluate the physiological responses and work tolerance time, following forearm and leg submergence for cooling the body, during recovery between work bouts in a hot environment while wearing FPC. METHODS Participants Following approval by the Central Washington University Human Subjects Committee, 10 healthy male volunteer

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firefighters were recruited (age 22.6 ± 3.2 yr, height 177.7 ± 5.8 cm, weight 86.6 ± 16.8 kg, body fat 12.9 ± 9.6%, VO2max 53.0 ± 7.8 ml × kg−1 × min−1). All thermal testing was conducted in a climactic chamber between January and March of 2009, which meant the volunteers were not acclimatized to the heat during the testing procedures. All participants were informed of the nature of the study and provided written consent and health history questionnaire prior to participating in the study. Participants were asked to refrain from heavy exercise, caffeine, and alcohol 24 hr before each trial. Participants were instructed to drink an adequate amount of water to ensure normal hydration the day before the work trials. First Lab Session Following the consent and health history forms, participant’s descriptive data were then assessed (age, height, weight, and body fat percentage). Weight was measured seminude (underwear and shorts) on a calibrated scale (DetectoMedic Scales Inc., Brooklyn, N.Y.). Body fat percentage was determined using the three-site skin fold measurements (chest, abdomen, and thigh), using Lange Skinfold Calipers (Beta Technology Inc., Cambridge, Md.).(10) Furthermore, VO2peak was determined for all participants during the first lab session. Participants were tested in a thermal neutral environment of ∼22◦ C with a relative humidity of 17 ± 2%. VO2peak was determined by open circuit spirometry (Parvo Medics, Sandy, Utah) on a treadmill (Quinton Instrument Company, Seattle, Wash.) using a modified Bruce Protocol. VO2peak and HRmax were defined as the highest observed 30-sec value when the participants reached volitional fatigue. Heart rate (HR) was monitored and recorded every minute during the treadmill protocol, using a transmitter telemetry unit (Polar, Stamford, Conn.). Protocol Each participant performed two experimental cooling sessions, in a counterbalanced order, in a climactic chamber that was temperature-controlled at ∼ 32.8 ± 0.9◦ C WBGT. Each volunteer was chosen randomly to undergo either the leg cooling or the forearm cooling on the first trial, and in the second session to receive the other cooling procedure. Experimental sessions included forearm submersion (FS) or leg submersion (LS) in cool water. Participants were required to have a minimum of 72 hr rest between trials. On arrival, seminude weight was collected using a DetectoMedic calibrated scale. Participants were then asked to self-insert a flexible rectal thermocouple (Yellow Springs Instrument Company Inc., Yellow Springs, Ohio), which was inserted approximately 12 cm beyond the anal sphincter. The rectal probe was then securely taped to the gluteus maximus, below the waist band of the shorts. Skin temperature (Tsk ) was continuously monitored from thermocouples placed at the right bicep, right forearm, right calf, right thigh, and the right pectoralis. Thermocouples were attached to the skin using prewrap and adhesive tape. The pre-wrap was wrapped around 474

the head of the thermocouple, and adhesive athletic tape was wrapped above and below the head of the thermocouple, to secure the thermocouple in place without adding insulation. This technique allowed the maintenance of an appropriate skin-to-thermocouple interface. Rectal temperatures (Trec ) and Tsk were recorded using the YSI precision 4000, a thermometer computerized system (Yellow Springs Instrument Company). Heart rate was recorded using a Polar heart rate monitor. After thermocouples were securely fastened, participants then began putting on the FPC. After the participants were fully dressed in FPC, clothed weight was recorded. Baseline Trec , Tsk and HR were recorded prior to the work phase, and every 2 min during the work phase. Furthermore, ratings of thermal comfort (RTC) were estimated by participants verbally communicating the score to the investigators. The RTC scale was a modified version of Selkirk et al.(9) and Gagge et al.(11) scales used in previous studies. The RTC scale ranged from 7 (Cool) to 13 (So hot I am sick and nauseated). Furthermore, Tsk was combined as a weighted mean. The weighted Tsk was calculated using the following equation:(12) T sk = T chest 0.5 + T forearm 0.07 + T bicep 0.07 + T calf 0.18 + T thigh 0.18

Fire Fighting Protective Gear During the thermal testing, participants wore NFPAapproved fire fighting clothing that consisted of jacket and pants (Fire Gear Incorporated, Aspen, Colo.), gloves (The Glove Corporation, Alexandria, Ind.), Nomex flash hood (Quest Fire Apparel Inc., Saratoga Springs, N.Y.), protective rubber steel-toed boots (Servus Firefighter, Rock Island, Ill.), helmet (Cairns Helmets, Pittsburgh, Pa.), and SCBA (Magnum, Lawrence, Pa.). The FPC and SCBA were donated by the Ellensburg Fire Department. Each participant wore underwear, shorts, a cotton t-shirt, and socks underneath the FPC. During all trials, individuals breathed room air, as opposed to SCBA air. However, a full SCBA was carried to keep the weight of the tank consistent for every participant. Work Phase The work phase consisted of walking on a treadmill at 0% incline at 3.5 mph while wearing FPC and SCBA. Participants walked until they reached volitional exhaustion or a core temperature of 38.5◦ C. Tre , Tsk , HR, RPE, and RTC were measured every 2 min during the work phase. Cooling Phase Following termination of the work phase, participants were allowed 5 min to safely exit the climactic chamber and remove their helmet, flash hood, gloves, jacket, boots, and SCBA tank. After removing the FPC, participants received one of two 20min cooling strategies (LS or FS) followed by a second 5-min transition period to redress in the FPC.

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Cooling Strategies Forearm Submersion Forearm submersion was accomplished by using two plastic tanks (16 in. height × 18 in. width × 28 in. length) placed in a thermal-neutral environment. Water in the tank was temperature controlled at 16.96 ± 0.81◦ C prior to submersion and during submersion. Participants sat in a chair and submerged hands and forearms up to the elbow joint for 20 min. During submersion the tank temperature was measured every 2 min to make sure the temperature remained around 17◦ C. For both FS and LS, participants moved their arms and legs to circulate the water and prevent a warm water buffer around the skin.

Leg Submersion The protocol was exactly the same as FS; however, participants sat in a chair and submerged feet and lower legs up to the knee joint for 20 min. During every cooling session HR, Tsk , Trec and RTC were collected every 2 min. Work Tolerance Phase The work tolerance phase used the same protocol as the work phase and consisted of walking on a treadmill at 0% incline at 3.5 mph while wearing FPC and SCBA. The work tolerance phase continued until the participant signaled for the termination of the test or when one of the following end point criteria was achieved: Trec of 38.5◦ C, dizziness, or nausea occurred, subjects were exhausted or experienced discomfort, or the investigator terminated the test. Statistical Analysis Statistical comparisons using SPSS 16.0 (SPSS Inc., Chicago, Ill.) were made between trials for each dependent variable, using a repeated-measures ANOVA. A post hoc analysis was administered to assess the differences between trials where necessary. Furthermore, independent t tests were employed on a survival basis to allow for the diminishing N. Participants reached either volitional fatigue or a Trec of 38.5◦ C at different times. Furthermore, t tests were employed at different time points during the work tolerance phase to assess if there was statistical significance between the two cooling procedures. All statistical analyses had a set alpha level (P ≤ 0.05). A control of no cooling was not used in this study, because of such a low Trec cut-off deemed safe by the Human Subjects Committee. During pilot studies participants were not able to lower Trec below 38.5◦ C within the 20 min provided for the other cooling interventions. RESULTS Total Work Tolerance Time A dependent paired sample t test revealed no significant difference between FS (16.27 ± 5.56 min) and LS (21.36 ± 5.35 min) for work tolerance time (p = 0.052). However, participants walked 5.1 ± 0.3 min (24% longer) post LS when compared with FS in cold water ( Table I).

TABLE I. Means and Standard Deviations Between LS and FS for all Variables during the Work Tolerance Phase Variables

LS

Work Tolerance Time (min) HR (bpm) Trec (◦ C) Tsk (◦ C) RTC RPE

FS

21.36 ± 5.35 16.27 ± 5.56 142 ± 22 147 ± 24 38.3 ± 2.3 38.2 ± 2.1 35.3 ± 1.3 35.7 ± 1.2 12 ± 1 10 ± 1 12.2 ± 3.5 12.5 ± 3.3

Heart Rate There was no significant difference between FS and LS during the cooling phases and at the beginning of the work tolerance phase. However, mean HR remained slightly lower during the 20-min cooling phase for FS. A repeated-measures ANOVA showed that following the cooling phase, there was no significant difference between work tolerance trials (P = 0.79). However, following LS, HR was attenuated (142 ± 22 vs. 147 ± 24 bpm) during the work tolerance phase. Rectal Temperature A repeated-measures ANOVA indicated no significant difference for Trec between FS and LS (38.2 ± 2.1◦ C vs. 38.3 ± 2.3◦ C) during the cooling phases (P = 0.52) and work tolerance phases (P = 0.65). However, Trec remained slightly lower during the 20 min cooling phase and the work tolerance phases when participants underwent FS. Mean Skin Temperature A repeated measures ANOVA indicated there was no significant difference between the weighted skin measurements during the work tolerance phase for FS (P = 0.43) and LS (P = 0.68). However, following LS, the mean Tsk was slightly cooler when compared with FS (35.28 ± 1.31◦ C vs. 35.76 ± 1.29◦ C). Ratings of Thermal Comfort The mean RTC during the entire cooling phase remained slightly lower for LS than for FS (10 ± 1 vs. 12 ± 1). Although RTC was slightly lower during the cooling phase, no significant difference was detected (P = 0.67). However, during the work tolerance phase, RTC was found to be significantly lower following LS at Minute 14 (P = 0.031) when compared with FS. At minute 6 RTC was approaching significance for LS (P = 0.051) when compared with FS (Figure 1).

Ratings of Perceived Exertion The average RPE during the work tolerance phase remained slightly lower for LS than for FS (12.2 ± 3.5 vs. 12.5 ± 3.3). No significance was found for RPE during the work tolerance phase (P = 0.54).

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FIGURE 1. At all time points there is a common mean. The upper error bar corresponds to the common mean plus one standard of the aggregate values, and the lower error bar corresponds to the common mean minus one standard of the aggregate values. However, at the 14-minute time point, because there is no common mean value, your upper error bar corresponds to the forearm mean plus one standard deviation of the forearm values, and the lower error bar corresponds to the leg mean minus one standard deviation of the leg mean values. There is a depleting N throughout the work tolerance phase because of participants reaching volitional exhaustion or reaching a Trec of 38.5◦ C. Values are means ± SD. ∗ Represents significance at 14 min (p = 0.031).

DISCUSSION

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his study examined the physiological responses and work tolerance time following FS and LS for cooling the body between work bouts in a hot environment while wearing FPC. The main finding of this study was a 24% extended work tolerance time following LS. The main study finding was that the increase in work tolerance time due to LS was 24% greater than the increase due to FS, although the difference was just shy of statistical significance (p = 0.052). However, the practicality of increasing work tolerance by this magnitude could mean an improvement in exposure time of approximately 10 min during 45 min of combating a fire. Furthermore, if we expand that to a 12-hr shift it can really help exposure time for active firefighters. The current study indicated little difference between FS and LS when comparing physiological measurements of heart rate and Trec between trials, despite the difference in active muscle mass submerged. Both FS and LS in cool water of ∼ 17◦ C should produce vasoconstriction throughout the submerged limbs because of centrally controlled receptors, located within the skin, that maintain an adequate temperature.(11–15) A study conducted by Kakigi and Watanabe(16) suggests that peripheral cooling in cool water produces significant changes in the amplitude of pain. This decline in pain can be caused by a delay in neural feedback to the dorsal horn of the spinal cord. Because of the attenuation in neural feedback, it is suggested that participants would indicate lower thermal comfort scores following peripheral cooling. Anecdotally, it was noted that during the current study, 75% of the participants commented on how cool their legs felt on the initiation of the work tolerance 476

phase following LS. Furthermore, there were no differences detected for RPE between trials. In the 10 study participants, the increase in work tolerance time was, on average, approximately 5 min greater for LS compared with FS, although this difference was just shy of statistical significance based on alpha = 0.05. This result seems contradictory to the lack of physiological variation between trials noted previously. The lack of Trec attenuation might be explained by a localized muscular cooling in the lower extremities. These results are in accordance with Giesbrecht et al.,(17) who studied the effects of cooling firefighters by forearm and hand immersion. In that study, participants performed three 20min exercise bouts (40◦ C ambient temperature), each followed by a 20-min cooling period. During the cooling period, fire fighting FPC was removed and subjects immersed either their hands or forearms in cold water (10–20◦ C). The authors found that both hand immersion and hands/forearm immersion cooled the firefighters better when compared with the control condition. Because of the conduction properties of water, it can be assumed that forearm and lower leg immersion will increase heat loss after exercise. Furthermore, it is commonly generalized that an excessive increase in core temperature limits the body’s ability to sustain high levels of work or endurance exercise. The converse of this generalization is that the extraction of heat from the body should increase its capacity to do work. The lower perceptual response found in this current study may be related to the large active musculature of the lower leg being cooled and therefore creating a localized negative metabolic heat sink. This local effect, however, did not translate to a decrease in Trec , between trials. These results are

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supported by Cheung and Sleivert,(18) who examined upper body cooling in a thermoneutral environment. Participants (N = 10) completed a 30-min, high-intensity intermittent cycling bout. The protocol consisted of 30 min at 50% VO2 peak with 10-sec Wingate tests on a 5-min interval. Results suggest that there was little benefit of cooling the upper body during high-intensity, intermittent cycling. These results help to solidify the finding of the current investigation where there was little effect of upper arm peripheral cooling prior to the work tolerance phase when compared with the larger active musculature of the lower legs being cooled. CONCLUSION

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his investigation has highlighted the positive effect of peripheral cooling by water submersion. While just shy of statistical significance (for alpha = 0.05), lower leg submersion increased work tolerance by 24%. Once again, the practicality of increasing work tolerance by this magnitude could mean an improvement in exposure time of approximately 10 min during 45 min of combating a fire. In addition, results indicate that RTC scores are diminished during lower leg submersion when compared with forearm submersion. The current study revealed a positive work tolerance time for lower leg submersion and could be a viable cooling mechanism for first responders wearing FPC. ACKNOWLEDGMENTS

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pecial thanks go out to the Ellensburg Fire Department and all the volunteers for their help and hard work during this study. Also, special thanks go to the rest of Central Washington University’s Exercise Science faculty for their support and help with this project. REFERENCES 1. Crockford, G.W., and D.E. Lee: Heat-protective ventilated jackets: A comparison of humid and dry ventilating air. Br. J. Ind. Med. 24:52–59 (1967).

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