Facial immersion in cold water enhances cerebral blood velocity during breath-hold exercise in humans
Authors: Thomas Kjeld, Frank C. Pott, Niels H. Secher
DOI / Source: 10.1152/japplphysiol.90370.2008
Date: 29 January 2009
Reading level: Intermediate
Why This Matters for Freedivers
When you’re breath-holding—especially while moving—your brain is the organ you most want to protect. This paper shows that cold face immersion doesn’t just slow your heart rate; it can also boost blood flow to the brain beyond what CO₂ alone would predict. That helps explain why “cold face in water” can feel more stable and controlled during hard apneas, and it supports using face immersion (and calm technique) as part of safer training.
Synopsis
Freedivers often talk about the “diving reflex” as if it’s mainly a heart-rate thing: face in cold water, heart rate drops, you feel calmer, oxygen gets conserved. But there’s another important piece—what happens to blood flow to the brain. If breath-holding lowers oxygen and raises CO₂, does the brain automatically get more blood. And does cold face immersion add anything extra on top of that, especially when you’re exercising.
This study tested that question in nine healthy, trained male subjects. The researchers measured cerebral perfusion indirectly using transcranial Doppler ultrasound on the middle cerebral artery (reported as mean flow velocity, MCA Vmean). They also measured arterial blood gases through an arterial line, plus heart rate, blood pressure, stroke volume and cardiac output.
The experiments were designed to separate three influences that can all change brain blood flow: 1) Breath-holding (apnea), 2) Exercise (cycling), 3) Facial immersion in cold water (10°C).
At rest, a maximum-duration breath-hold massively increased MCA Vmean. The main driver was the expected one: CO₂ rose during the breath-hold, and CO₂ is a powerful signal that dilates brain blood vessels. So the longer the breath-hold, the more CO₂ accumulated, and the more cerebral blood velocity climbed toward the end.
During moderate exercise (100 W), adding a 30-second breath-hold again produced a big rise in MCA Vmean. The key finding is what happened when they added cold face immersion: MCA Vmean rose even more than with breath-hold exercise alone. In other words, cold face immersion appeared to provide an additional “push” toward brain perfusion, not simply explained by changes in CO₂.
They also tested harder exercise (180 W) without breath-holding. Exercise alone slightly raised MCA Vmean, but when the same exercise was combined with cold face immersion (breathing through a snorkel), MCA Vmean increased much more—even though CO₂ did not significantly change. That’s the cleanest evidence in this paper that cold face immersion can influence cerebral blood velocity independently of CO₂.
The recordings also show a distinctive pattern at the start of each breath-hold: an early spike in MCA Vmean followed by a sharp drop, likely related to mechanical effects of a deep inhale and a brief Valsalva-like strain (changes in intrathoracic pressure can transiently affect blood pressure and cerebral blood flow). After that early wobble, MCA Vmean climbed steadily toward a maximum near the end of the breath-hold as CO₂ accumulated.
The practical takeaway is that breath-holding strongly redirects support toward the brain (largely via CO₂-driven dilation), and cold face immersion adds an extra boost that may help preserve cerebral perfusion during breath-hold exercise. For freedivers, this fits the lived experience: face immersion can make demanding apneas feel “more controlled,” and it reinforces why training that combines movement with breath-holding should respect the brain as the limiting organ—especially near the end of efforts, where decisions and motor control matter most.
Abstract
The diving response is initiated by apnea and facial immersion in cold water and includes, besides bradycardia, peripheral vasoconstriction, while cerebral perfusion may be enhanced. This study evaluated whether facial immersion in 10°C water has an independent influence on cerebral perfusion evaluated as the middle cerebral artery mean flow velocity (MCA Vmean) during exercise in nine male subjects. At rest, a breath hold of maximum duration increased the arterial carbon dioxide tension (PaCO2) from 4.2 to 6.7 kPa and MCA Vmean from 37 to 103 cm/s (mean; +178%). Similarly, during 100-W exercise, a breath hold increased PaCO2 from 5.9 to 8.2 kPa and MCA Vmean from 55 to 113 cm/s (+105%), and facial immersion further increased MCA Vmean to 122 cm/s. MCA Vmean also increased during 180-W exercise (from 47 to 53 cm/s), and this increment became larger with facial immersion (76 cm/s, +62%), although PaCO2 did not significantly change. These results indicate that a breath hold diverts blood toward the brain with a 100% increase in MCA Vmean, largely because PaCO2 increases, but the increase in MCA Vmean becomes larger when combined with facial immersion in cold water independent of PaCO2.