Marine Survival in the Mediterranean: A Pilot Study on the Cognitive and Cardiorespiratory Response to Sudden Cool Water Immersion

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 (V˙E, L∙min−1), oxygen consumption (V˙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.

How does cold water impact on human physiology? Recent research discoveries

“…There are suggestions that even 18-degree water can cause an acute decrease in cognitive function [34]. That is crucial because it escalates the risk of drowning.…”

“…That is crucial because it escalates the risk of drowning. Researchers linked changes in cognitive function with heart rate [34] and not with respiratory changes as was presumed. That study was conducted on active males which may suggest that changes in overall populations can be higher.…”

“…Other researchers examined the impact of cold water on cognitive function and the cardiorespiratory system. The cross-over study included 10 healthy males [34]. They examined cognitive function, heart rate, minute ventilation, and oxygen consumption [34].…”

“…The cross-over study included 10 healthy males [34]. They examined cognitive function, heart rate, minute ventilation, and oxygen consumption [34]. The studied group was examined during immersion in an 18-degree portable pool in a seating position which excluded the impact of strain of buoying on organism response.…”

“…It is worth pointing out that the temperature of the water was higher than in another study on cold water immersion previously mentioned. The control group was examined in a dry environment (25•C) [34]. The limitation of that research what is marked by researchers is that the study does not count hydrostatic impact on organisms because of the environment of the control group.…”