The Physiology and Pathophysiology of Human Breath-Hold Diving
Authors: Peter Lindholm, Claes E. G. Lundgren
DOI / Source: https://doi.org/10.1152/japplphysiol.90991.2008
Date: 30 October 2008
Reading level: Intermediate
Why This Matters for Freedivers
If you want one paper that connects almost everything in freediving physiology—diving reflex, blackout risk, lung squeeze, packing, even decompression illness—this is it. It’s a “big map” that helps you understand why certain rules exist (no excessive hyperventilation, careful depth progression, conservative repetitive deep diving), and why some problems can appear in surprising ways (like sudden vertigo on ascent, or cough/blood after a deep session).
Synopsis
This review is a wide-angle tour of what happens to the human body during breath-hold diving—what helps you perform, what limits you, and what can go wrong. The authors frame freediving around two main challenges: time (staying conscious while oxygen falls and CO₂ rises) and depth (surviving lung compression and pressure effects). A third challenge is high gas pressure itself, which can cause effects more familiar to scuba divers, like nitrogen narcosis or decompression sickness in specific situations.
The diving response (your built-in “economy mode”)
The paper explains the classic diving response: peripheral vasoconstriction (blood vessels tighten), blood pressure rises, and heart rate drops (bradycardia), lowering cardiac output. In many people this helps conserve oxygen for the brain and heart. But it’s highly variable between individuals and can be strongly influenced by face cooling, hypoxia later in the breath-hold, stress, and exercise.
It also highlights a fascinating piece many freedivers love: spleen contraction. Early in a breath-hold, the spleen can squeeze out stored red blood cells, briefly increasing hemoglobin concentration—essentially a small “natural blood boost.” It’s real, but how much it matters long-term is still debated.
Arrhythmias and the “autonomic tug-of-war”
A key warning in this review is that the diving response can combine strong parasympathetic braking (slow heart rate) with sympathetic stimulation (stress chemistry), which is a setup for ectopic beats and rhythm disturbances—especially in cold water or in people with underlying susceptibility. The paper notes reports of dramatic bradycardia and rhythm changes in deep chamber dives, and even ECG patterns that could suggest temporary strain on the heart after dives.
Blackout: why it happens (and why it can feel sudden)
The review walks through the major, preventable pathways to hypoxic loss of consciousness:
- Hyperventilation: it mainly lowers CO₂ stores, which delays the urge to breathe far more than it increases oxygen stores. That means you can “feel okay” right up until you don’t.
- Ascent blackout: the physics matters. As you rise, pressure drops, so the oxygen partial pressure in the lungs drops sharply near the surface. A diver can be “functional” at depth but cross the unconsciousness threshold in the last meters.
- Fasting / depleted glycogen: after prolonged exertion or a long day, the body relies more on fat metabolism, which uses more oxygen and produces less CO₂—so you become hypoxic sooner while also getting a weaker CO₂ warning signal.
This section is especially relevant to spearfishers and anyone doing repetitive dives with fatigue, currents, stress, or long surface swims.
Lung squeeze and chest stress (what “too deep” can do)
The authors describe three main outcomes when pressure stress overwhelms the chest–lung system: 1) partial lung collapse (atelectasis), 2) fluid leaking into air spaces (pulmonary edema), 3) rupture/bleeding across the membrane (alveolar hemorrhage → blood/cough).
They emphasize that even surface swimming and immersion can contribute to lung fluid issues, and that individual susceptibility varies a lot—some divers get symptoms at modest depths while others tolerate very deep dives.
Lung packing and its trade-offs
Glossopharyngeal insufflation (“lung packing”) is covered as a performance tool that increases starting lung volume, but the review stresses it is not free: it raises intrathoracic pressure, can reduce venous return and cardiac output, and has been linked to fainting and pressure-related complications in some cases. The “reverse” technique (exsufflation) is also mentioned in relation to equalization strategies at very low lung volumes.
Nitrogen: decompression sickness and narcosis (yes, even in freediving)
The review highlights that under certain patterns—especially repetitive deep dives with short surface intervals—nitrogen can accumulate enough to create decompression sickness, and cases have been reported. Narcosis is discussed too: despite the extreme depths reached in some disciplines, reports are rare, possibly because exposure is short or because episodes are forgotten.
Overall, this paper is a cornerstone overview: it ties together performance physiology and real-world failure modes, and it makes a strong case that freediving safety is less about bravado and more about understanding the handful of mechanisms that can “flip the table” quickly.
Abstract
This review summarizes physiological responses, performance limits, and key injury mechanisms in human breath-hold diving. It covers cardiovascular aspects of the diving response (vasoconstriction, hypertension, bradycardia, oxygen conservation), including arrhythmias and splenic contraction. It reviews respiratory consequences of lung compression and descent stress, including pulmonary edema and hemorrhage, and discusses the benefits and risks of glossopharyngeal techniques used to increase lung volume. Mechanisms leading to hypoxic loss of consciousness are described, including the dangers of pre-dive hyperventilation, ascent-related hypoxia, fasting and increased oxygen cost after prolonged exertion. The potential for nitrogen-related problems such as decompression sickness and narcosis is also considered, along with accident patterns and risk factors in recreational and spearfishing populations.