Effects of lung volume and involuntary breathing movements on the human diving response
Authors: Johan Andersson, Erika Schagatay
DOI / Source: https://doi.org/10.1007/s004210050294
Date: 01 January 1998
Reading level: Intermediate
Why This Matters for Freedivers
This paper suggests a surprising idea: a bigger breath isn’t always “more dive reflex.” Very full lungs can mechanically interfere with the early response (by affecting blood return to the heart), and the strongest bradycardia/vasoconstriction in this study actually showed up at a smaller starting lung volume. It also reassures you about contractions: the involuntary breathing movements during the struggle phase didn’t meaningfully change the dive response, so they’re more about discomfort than suddenly “breaking” your physiology.
Synopsis
Freedivers usually assume that starting with more air means a better breath-hold: more oxygen in the lungs, more buoyancy, and (in theory) more time. But the body’s dive response isn’t only driven by “how much oxygen you have.” It’s also shaped by mechanics (pressure inside the chest) and by sensors in the lungs that respond to stretch. This study looked at how starting lung volume and involuntary breathing movements (contractions) change the human diving response.
Seventeen trained male breath-hold divers performed both maximal apneas and “simulated dives” (apnea plus cold face immersion) at three starting lung volumes: about 60%, 85%, and 100% of prone vital capacity. The researchers measured breath-hold time, heart rate, blood pressure, and skin blood flow, and they also tracked end-expired CO₂ and O₂ in a subset. They identified the “breaking point” as the moment the first involuntary breathing movement appeared, splitting each breath-hold into an easy phase and a struggle phase.
What lung volume changed
The simulated dives were shortest at 60%, mainly because CO₂ built up faster at lower lung volume, pushing divers into the struggle phase earlier. Interestingly, even though the higher-volume breath-holds lasted longer, the end-expired CO₂ and O₂ values at the end were very similar across lung volumes—suggesting people tend to quit around a fairly consistent “chemical limit,” just reached faster or slower depending on volume.
The cardiovascular story is where it gets really interesting:
- At 100% lung volume, there was a noticeable drop in arterial pressure in the first ~20 seconds of face-immersed apnea. The authors interpret this as a mechanical effect: very full lungs increase pressure inside the chest, which can reduce venous return to the heart, lowering stroke volume and briefly dropping blood pressure.
- The diving response (bradycardia + vasoconstriction) was actually most pronounced at 60% lung volume. At larger lung volumes, the relationship wasn’t linear—meaning “more air” didn’t simply mean “stronger response.” The paper argues this is because lung stretch receptors and chest mechanics push the cardiovascular system in competing directions when you’re near full vital capacity.
Do contractions change the dive response
A lot of freedivers feel like something “changes” once contractions start. In this study, when they compared the easy phase to the early struggle phase (around the breaking point), they found no meaningful change in the pattern of blood pressure, heart rate, or skin blood flow that could be attributed to the involuntary breathing movements themselves. The contractions were simply too small to create big enough pressure swings in the chest to change venous return and therefore the dive response.
Practical takeaway
Starting lung volume changes breath-hold duration mainly through CO₂ dynamics, but it can also change the shape of the early cardiovascular response through chest pressure and lung stretch receptors. And while contractions feel dramatic, they didn’t appear to “switch off” the dive response. For freedivers, this supports a more nuanced view: maximal inhalation is great for oxygen stores, but it doesn’t automatically mean a stronger dive reflex, especially at the start.
Abstract
The effects of lung volume and involuntary breathing movements on the human diving response were studied in 17 breath-hold divers. Each subject performed maximal effort apnoeas and simulated dives by apnoea and cold water face immersion, at lung volumes of 60%, 85%, and 100% of prone vital capacity (VC). Time of apnoea, blood pressure, heart rate, skin capillary blood flow, and fractions of end-expiratory CO2 and O2 were measured. The length of the simulated dives was the shortest at 60% of VC, probably because at this level the build up of alveolar CO2 was fastest. Apnoeas with face immersion at 100% of VC gave a marked drop in arterial pressure during the initial 20 s, probably due to high intrathoracic pressure mechanically reducing venous return. The diving response was most pronounced at 60% of VC. We concluded that at the two larger lung volumes both mechanical factors and input from pulmonary stretch receptors influenced the bradycardia and vasoconstriction, resulting in a non-linear relationship between the breath-hold lung volume and magnitude of the diving response in the near-VC range. Furthermore, the involuntary breathing movements that appeared during the struggle phase of the apnoeas were too small to affect the diving response.