Abstract
Background and Aim: The Mediterranean is one of the major gateways of human migratory fluxes from Northern Africa, the Middle East, and Central Asia to Europe. Sea accidents have become an urgent humanitarian crisis due to the high number of migrants on the move, but data on the physiological effects to sudden cool water immersion are not as extensive as cold-water studies. We wanted to evaluate to what extent cool water immersion (~18 °C) may detrimentally affect cognitive ability and cardiorespiratory strain compared to the more prevalent cold-water (<10–15 °C) studies. Methods: In this case, 10 active, healthy men participated in this study which consisted of completing one familiarization trial, and then a control (CON) or experimental (EXP) trial in a randomized, repeated-measures, cross-over fashion, separated by at least 7-days. Cognitive function was assessed via the Symbol Digit Modalities Test (SDMT), a code substitution test, performed at baseline, then repeated in either a thermoneutral (~25 °C room air) dry environment, or when immersed to the neck in 18 °C water. Testing consisted of six “Step” time-blocks 45-s each, with a 5-s pause between each Step. Cardiorespiratory measures, continuously recorded, included heart rate (beats per minute), minute ventilation (E, L∙min−1), oxygen consumption (O2, L∙min−1), and respiratory frequency (fR, count∙min−1). Results: Initial responses to cool water (<2 min) found that participants performed ~11% worse on the code substitution test (p = 0.025), consumed 149% greater amounts of oxygen (CI: 5.1 to 9.1 L∙min−1, p < 0.0001) and experienced higher cardiovascular strain (HR CI: 13 to 38 beats per minute, p = 0.001) than during the control trial. Physiological strain was in-line to those observed in much colder water temperature. Conclusion: Sudden, cool water immersion also negatively affects cognitive function and cardiorespiratory strain, especially during the first two minutes of exposure. The magnitude increase in heart rate is strongly associated with poorer cognitive function, even in (relatively) warmer water consistent with temperatures found in the Mediterranean Sea environment.
Highlights
IntroductionAccidental water immersion represents a common cause of death in many countries, with cold water representing a further risk due to the combination of drowning, cold shock response, and hypothermia [1–3]
The mechanism(s) underlying improper decision-making during maritime disasters are likely to include anxiety and panic, it is hypothesized that altered physiological responses have a role to play in the reduced cognitive capacity observed
Previous findings have shown that even warm water immersion might induce a small but significant increase in plasma catecholamines [32,33], which have been found to be potentially associated to poor cognitive function [34]
Summary
Accidental water immersion represents a common cause of death in many countries, with cold water representing a further risk due to the combination of drowning, cold shock response, and hypothermia [1–3]. Between 1978 and 1998 more than 5300 passengers were killed in ferry accidents around the world, making ferry travel. 10 times more dangerous than air travel [4]. Cold water can be defined as water temperature less than 15 ◦ C, and it represents an extremely hazardous scenario, physiologically speaking, since tachycardia, hyperventilation, tachypnea, increased blood pressure, and possible arrhythmias are likely with sudden, cold-water immersion [5,6]. In 1981, Golden and Harvey identified four stages of water immersion, each associated with their own specific
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