Immersion deaths and deterioration in swimming performance in cold water.

BACKGROUND: General hypothermia (deep body temperature <35 degrees C) has been implicated in immersion-related deaths, but many deaths occur too quickly for it to be involved. We investigated changes in swimming capability in cold water to find out whether such changes could lead to swim failure and drowning.
METHODS: Ten volunteers undertook three self-paced breaststroke swims in a variable-speed swimming flume, in water at 25 degrees C, 18 degrees C, and 10 degrees C, for a maximum of 90 min. During each swim, we measured oxygen consumption, rectal temperature, swim speed and angle, and stroke rate and length. Swim failure was defined as being unable to keep feet off the bottom of the flume.
FINDINGS: All ten swimmers completed 90 min swims at 25 degrees C, eight completed swims at 18 degrees C, and five at 10 degrees C. In 10 degrees C water, one swimmer reached swim failure after 61 min and four were withdrawn before 90 min with rectal temperatures of 35 degrees C when they were close to swim failure. Swimming efficiency and length of stroke decreased more and rate of stroke and swim angle increased more in 10 degrees C water than in warmer water. These variables seemed to characterise impending swim failure.
INTERPRETATION: Impaired performance and initial cardiorespiratory responses to immersion probably represent the major dangers to immersion victims. Consequently, treatment should be aimed at symptoms resulting from near-drowning rather than severe hypothermia.