Prediction of Water Requirements to Replace Sweat Losses

The Shapiro sweat prediction equation (OSE) was formulated more than two decades ago as: msw (g•m -2 •h -1 ) = 27.9 • Ereq • (Emax) -0.455 , where Ereq is required evaporative heat loss and Emax is maximum evaporative power of the environment. Although OSE was developed for a limited set of conditions, in practice it is often used outside its boundaries to estimate fluid requirements and generate guidance in military, public health, occupational and sports medicine settings. Military (NATO) and public health (IOM) reports have expressed a need for improved sweating rate prediction models that calculate hourly and daily water needs. Purpose The purposes of this study were to 1) determine the accuracy of OSE when widening its boundaries to include cooler environments (2h) and very prolonged exercise (8h), and 2) improve the accuracy of OSE and/or develop a de novo sweat prediction equation with improved accuracy. Methods OSE prediction accuracy was determined by comparing measured (msw) and predicted sweating rates in 39 volunteers during 15 trials that included intermittent treadmill walking for 2h (300 to 600 W, 15 to 30 o C; n = 21) or 8h (300 to 420 W, 20 to 40 o C; n = 18). Accuracy was first assessed by comparing msw and predicted sweating rates (211 observations) using least-squares regression. Mean and 95% confidence intervals for group differences were compared against a ± 0.125 L/h prediction error theshold. The 2h and 8h data were then combined with archived data (total of 101 volunteers, >500 observations), using a variety of metabolic rates over a range of environmental conditions, clothing and equipment combinations and work durations, in an effort to correct OSE and develop a new sweat prediction equation using fuzzy piecewise regression. The corrected and de novo equations were then crossvalidated against independent data (30 volunteers; >200 observations). Results OSE accounted for more than 70% of the variance in msw and the SEE was small and uniform around the line of best fit. However, the OSE error was always > 0.125 L/h during 2h and 8h of exercise. A corrected equation (OSEC): msw = 147•exp (0.0012•OSE) and a new equation (PW): msw = 147+1.527•(Ereq) 0.87•(Emax) were derived. OSEC and PW were 58% and 65% more accurate (P<0.01) than OSE, respectively, for conditions both within and outside the original OSE domain of validity. Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE OCT 2010 2. REPORT TYPE N/A 3. DATES COVERED 4. TITLE AND SUBTITLE Prediction of Water Requirements to Replace Sweat Losses 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) U.S. Army Research Institute of Environmental Medicine Thermal and Mountain Medicine Division Kansas Street, Building 42 Natick, MA 01760-5007 USA 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release, distribution unlimited 13. SUPPLEMENTARY NOTES See also ADA564696. Human Modelling for Military Application (Applications militaires de la modelisation humaine). RTO-MP-HFM-202 14. ABSTRACT The Shapiro sweat prediction equation (OSE) was formulated more than two decades ago as: msw (gm-2h-1) = 27.9 Ereq (Emax)-0.455, where Ereq is required evaporative heat loss and Emax is maximum evaporative power of the environment. Although OSE was developed for a limited set of conditions, in practice it is often used outside its boundaries to estimate fluid requirements and generate guidance in military, public health, occupational and sports medicine settings. Military (NATO) and public health (IOM) reports have expressed a need for improved sweating rate prediction models that calculate hourly and daily water needs. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18. NUMBER OF PAGES 8 19a. NAME OF RESPONSIBLE PERSON a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 Prediction of Water Requirements to Replace Sweat Losses P6 2 RTO-MP-HFM-202 Conclusion OSEC and PW provide for more accurate sweat predictions over a broader range of conditions. Applications overlap multiple HFM domains and military needs scenarios. Authors’ views; not official U.S. Army or DoD policy.