Research Continued...

Energy Balance and Oxidative Stress in Wildland Firefighters: A Preliminary Study
Brent Ruby, Ph.D., University of Montana

Our laboratory has been conducting field studies to determine the unique energy and nutritional concerns of the wildland firefighter during wildfire suppression. We have demonstrated that wildland firefighters may expend between 3,500 and 6,500 kcal per day for up to 7 days. Because of the physical demands of the job, energy intake must be adequate to maintain performance during each incident and over the course of the fire season. The data presented in this summary are a portion of those from a study funded by the Women's Health Research Initiative (Department of Defense). From previously collected data, a subset of subject data was analyzed for urinary markers of oxidative stress. Subjects were tested during a 5- to 7-day period of wildfire suppression. Urine samples were collected on day 1 before fire suppression, and on subsequent days up to the final day of firefighting activity. In addition, measures of body weight and skinfolds were obtained to estimate changes in body composition during the work period.

Data for 10 male subjects indicated an average weight loss of 1.2 kg (2.64 lb) and a 1.7 kg (3.74 lb) loss of fat-free (lean body) mass. Six female subjects lost an average of 0.6 kg (1.32 lb), but did not lose fat-free mass. Measures of oxidative stress are shown in Table 1. Although the group data did not demonstrate significant differences from early to late fire exposure, there was a significant effect for gender, with females demonstrating significantly higher values for oxidative stress. Furthermore, when individual subjects were evaluated, 4 of 10 males and 4 of 6 females exhibited elevated levels of oxidative stress.

Table 1—Markers of oxidative stress during 5 to 7 days of wildfire suppression.

	Pre	Mid	Late	Mean
Males
Total alkenals (um)/ creatinine (mM)	0.51	0.73	0.61	0.61
8-OHDG (ng/ml)/ creatinine (mM)	1.22	1.36	1.29	1.28
Females
Total alkenals (um)/ creatinine (mM)	0.86	0.99	0.82	0.89*
8-OHDG (ng/ml)/ creatinine (mM)	2.20	1.61	1.22	1.68

* p = 0.023, significant difference for gender (females
demonstrated higher oxidative stress than males).

These results indicate that wildland fire suppression is associated with nutritional stresses that may lead to a loss of body weight and lean body mass. However, the relationship between the maintenance of energy balance and oxidative stress remains unclear. The results do indicate considerable variability in response to occupational environments that cause oxidative stress. Males and females may respond differently. Although the results are preliminary, females may be more sensitive to oxidative stress, even when energy balance is maintained. Further research should be conducted with wildland firefighters to document the potential for oxidative stress and compromised immune function that may be associated with this work. Additional emphasis should be placed on the possibility of a gender-specific or individual response to the working environment and physical stress. Finally, if studies document the need, field studies could determine effective ways to supplement the antioxidant defenses of wildland firefighters.

Total Energy Expenditure and Hydration Demands in the Wildland Firefighter
Brent Ruby, Ph.D., and Brian Sharkey, Ph.D., University of Montana

This investigation used doubly-labeled water methodology to calculate the total energy expenditure (TEE) of wildland fire suppression in a group of male and female firefighters (Hotshots). In addition, rates of evaporative water loss (rH2O) were calculated from D2O elimination. Measurements of total body water (TBW) and body weight were used to evaluate changes in energy balance. Before wildland fire suppression duties, each subject was given an oral dose of doubly labeled water (2H2O and H218O) adjusted for body weight. Morning urine samples were collected during the 5 to 7 days of fire suppression. Samples were analyzed using isotope-ratio mass spectrometry for 18O and 2H enrichment, and fitted using a linear elimination curve (Table 2). From prior research, TEE can range from 3000 to 6300 kcal/day, depending on assignment, conditions, and job detail. However, the environmental conditions associated with the work detail appear to affect evaporative water loss more than the rate of energy expenditure.

Table 2—Energy expenditure and water loss.

Location	Total Energy Expenditure (kcal/day)	Evaporative Water Loss (liters)
Florida	2960-4175	8.0 +/- 1.0
California, Idaho, Washington	3076-6260	6.8 +/- 1.6

This paper was presented at the International Association of Wildland Fire's third annual Safety Summit, Sydney, Australia, Nov. 5, 1999. Dr. Ruby is Director of the University of Montana Human Performance Laboratory. (Supported by DAMD17-96-1-63290; B. Ruby, principal investigator).

Death from Hyponatremia as a Result of Acute Water Intoxication in an Army Basic Trainee
T. Garigan and D. Ristedt

Several reports during the past 15 years have described hyponatremia (abnormally low concentration of sodium in the blood) as a result of excessive water intake by athletes during endurance races. The high rates of fluid consumption have been attributed to the desire of athletes to prevent heat injury. The military has adopted guidelines for programmed drinking to maintain performance and minimize the risks of heat casualties. As military personnel increase their fluid intake, their risk of hyponatremia as a result of water overload increases. A potentially life-threatening complication is acute water intoxication. This paper reports the first known death of an Army basic trainee as a result of acute water intoxication. The misrepresentation of his symptoms as those of dehydration and heat injury led to continued efforts at oral hydration until catastrophic cerebral and pulmonary edema developed (Military Medicine 164: 234-238, 1999).

Note: Wildland firefighters require about 1 liter of fluid per hour, which is consistent with the revised military hydration guidelines. See the Field Notes section for more on hydration.