Physiology of Drowning, A Review
Authors: Joost J. L. M. Bierens, Philippe Lunetta, Mike Tipton, David S. Warner
DOI / Source: https://doi.org/10.1152/physiol.00002.2015
Date: 17 February 2016
Reading level: Intermediate
Why This Matters for Freedivers
Freediving safety conversations often focus on hypoxia, blackouts, and rescue technique — but “drowning physiology” explains what actually happens to the body when water, cold, panic, and breathing reflexes collide. This review helps you understand why a situation can deteriorate fast (especially in cold water), why rescue priorities are what they are, and why prevention (buddying, calm exits, avoiding risky conditions) is usually the real lifesaver.
Synopsis
This review separates drowning into two linked but different events: immersion (your airway is above water) and submersion (your airway is under water). That distinction matters because many drownings start before anyone actually goes underwater.
During immersion, the paper explains how water temperature and stress can trigger a cascade that sets people up for failure. In hot-water immersion (like tubs), heat-related blood-vessel widening and changes in blood pressure can increase risk, especially when standing up to exit. In cold-water immersion, the most dangerous early threat is cold shock: an involuntary gasp and rapid breathing that can destroy any attempt to breath-hold and dramatically increase the chance of inhaling water. Cold shock also spikes heart workload and, when combined with face immersion and breath-holding, can provoke rhythm disturbances. After the initial shock, cooling of nerves and muscles can cause physical incapacitation (loss of strength and coordination) even before deep body temperature drops into severe hypothermia. Later, deep cooling can lead to confusion and loss of consciousness, making self-rescue impossible.
During submersion, the review maps the competing forces that determine outcome: panic and sympathetic “fight-or-flight,” the diving response (heart rate slowing and blood-vessel tightening), and what the authors call autonomic conflict — when strong sympathetic drive and strong vagal drive act at the same time, raising the risk of arrhythmias, especially around the moment breath-holding stops and breathing restarts. It also examines upper airway reflexes (including the debated role of laryngospasm) and emphasizes a practical point: regardless of the “dry drowning” myth, water usually reaches the lungs in true drowning, and the final common pathway is typically hypoxemia.
The paper then explains why aspirated water is so damaging. Freshwater and seawater affect the lungs differently, but both can disrupt surfactant and the air–blood barrier, leading to poor ventilation-perfusion matching, shunt, foam, and an ARDS-like picture. Swallowing water and vomiting are discussed mainly as complications that can worsen aspiration and complicate resuscitation. It also addresses electrolyte disorders, concluding that in most real-world drownings they are not the main driver (except in unusual circumstances), and that lack of oxygen is the key problem.
Finally, the review covers brain injury: asphyxia causes progressive cerebral hypoxia before arrest, and cold-water dynamics can either worsen things (hyperventilation-driven low CO₂ reducing brain blood flow) or, in rare cases, help via rapid cooling. The authors end by pointing out how many gaps still exist and where research could improve prevention and treatment.
Abstract
This review summarizes the physiology underlying drowning by separating the process into immersion (airway above water) and submersion (airway under water). Immersion can trigger cardiorespiratory stress responses related to temperature and exertion, including hot-water and cold-water effects, cold shock, physical incapacitation, and hypothermia as precursors to collapse and submersion. Submersion physiology includes fear and sympathetic activation, breath-holding and the diving response, autonomic conflict and arrhythmias, upper airway reflexes, aspiration and swallowing of water, emesis, and potential electrolyte disturbances. Outcomes are determined primarily by hypoxemia and resultant cardiac, pulmonary, and neurological injury. The review highlights major knowledge gaps and suggests areas where improved understanding could enhance prevention, treatment, and forensic interpretation of drowning events.