SHORT COMMUNICATION Changes in Manual Dexterity Following Short-Term Hand and Forearm Immersion in 10°C Water Stephen S. Cheung, Diane L. Montie, Matthew D. White, and David Behm CHEUNG SS, MONTIE DL, WHITE MD, BEHM D. Changes in manual dexterity following short-term hand and forearm immersion in 10°C water. Aviat Space Environ Med 2003; 74:990 –3. Background: Following accidental immersion in cold water, the chance of survival through the initial short-term period may depend on manual dexterity for survival tasks. We aimed to study the time course of impairment of manual dexterity during the initial stages of immersion. Methods: We investigated gross (manipulating harness buckles) and fine (Purdue Pegboard Assembly) manual dexterity of 11 male and 15 female subjects with either no immersion (Control) or after immersion of right and left hand and forearm in 10°C water for 30, 120, and 300 s. Exposure lengths were presented in a counter-balanced order in a single session. Results: Mean local skin temperature decreased significantly with cold-water immersion, with the amount of cooling proportional to the length of exposure. Buckle test times increased significantly from 9.1  3.0 s during Control to similar values of 19.5  11.1 s and 18.14  12.1 s after 120 and 300 s of immersion. Pegboard scores were significantly lower at 40.2  7.6 pieces following 300 s of immersion compared with Control and 30 s values of 49.0  6.4 and 47.2  6.9 pieces, respectively. Conclusions: It is concluded that fine and gross manual dexterity were rapidly and progressively impaired with short- term cold-water immersion. Therefore, efforts must be made to protect the hands/forearms from cold and to ensure survival equipment manip- ulation requires as little dexterity as possible. Keywords: marine survival, heat loss, hands, manual dexterity, time course. S IXTY PERCENT of deaths in lakes and oceans occur within 3 m of a safe refuge, and of these victims, two-thirds are regarded as good swimmers (10). Imme- diately post-immersion into cold water, one of the pri- mary concerns is the threat of drowning from the cold- induced hyperventilation and tachycardia; victims should strive to control their breathing and heart rate over the first 3–5 min prior to systematically attempting escape. However, manual dexterity remains extremely important for various survival tasks during this initial phase of immersion, in particular for tasks such as releasing buckles from safety harnesses or gripping a safety line from a boat. Short-term cold immersion could significantly impair the performance of these sur- vival tasks by causing rapid decrements in manual dexterity, placing the victim in greater risk of prolonged exposure. Therefore, an understanding of the degree and time course of manual dexterity impairment is crucial in the design of survival equipment and protec- tive clothing for use in marine environments. Many authors have studied the effects of long-term cold exposure on manual dexterity through either pro- longed cooling of the forearms and/or the whole body. These protocols typically exceed 30 min of exposure and/or feature significant body core cooling. Exposure of the forearm to cold temperatures resulting in cooling of the hand has been shown to have a negative effect on manual dexterity (5) and tactile sensitivity (8). Studies investigating the relative contributions of core vs. local arm cooling confirmed that the decrement in gross mo- tor performance was primarily due to the effects of local arm cooling (4). Compared with the plethora of research on the effects of long-term (30 min) local and/or whole-body cool- ing on manual function, the time-course of manual dexterity impairments during the first survival phase of cold-water immersion has not been documented. There- fore, the purpose of our study was to investigate the time course of fine and gross manual dexterity over the first 5 min of cold-water immersion, with a hypothesis of a progressive impairment over time. METHODS Subjects The experimental protocol was approved by Dalhou- sie University’s Health Sciences Research Ethics Board. Participating in the study were 11 men and 15 women with a mean ( SD) age of 24.8  9.4 yr; hand and forearm volume measured by water displacement of 339  69 ml and 863  229 ml, respectively; and fore- arm circumference measured halfway between the wrist and elbow of 23.7  2.3 cm. Age limits were set at 18 – 60 yr to capture as wide a subject pool as possible, though the majority of subjects were drawn from the From the Environmental Ergonomics Laboratory, School of Health and Human Performance, Dalhousie University, Halifax, Nova Sco- tia, Canada (S. S. Cheung, D. L. Montie); and the School of Human Kinetics and Recreation, Memorial University, St. John’s, Newfound- land, Canada (M. D. White, D. Behm). This manuscript was received for review in June 2002. It was revised in November 2002, and January, February, and March 2003. It was accepted for publication in March 2003. Address reprint requests to: Stephen S. Cheung, Ph.D., Associate Professor, School of Health and Human Performance, 6230 South Street, Halifax, Nova Scotia, Canada B3H 3J5; stephen.cheung@dal.ca. Reprint & Copyright © by Aerospace Medical Association, Alexan- dria, VA. 990 Aviation, Space, and Environmental Medicine • Vol. 74, No. 9 • September 2003