Hematological response and diving response during apnea and apnea with face immersion
Authors: Erika Schagatay, Johan P. A. Andersson, Bodil Nielsen
DOI / Source: 10.1007/s00421-007-0483-y
Date: 01 June 2007
Reading level: Beginner
Why This Matters for Freedivers
Freedivers often notice that the first few breath-holds feel “worse,” then suddenly things get easier. This paper explains a big part of that: after a few apneas, your spleen squeezes extra red blood cells into circulation, boosting your oxygen-carrying capacity for a short window. It also reinforces that cold face immersion mainly improves oxygen conservation through the classic dive response (slower heart rate and tighter blood vessels), not by giving you “more blood boost” than apnea alone.
Synopsis
Humans have a hidden “turbo button” during repeated breath-holds: the spleen can contract and push extra red blood cells into circulation, which slightly increases hematocrit (Hct) and hemoglobin (Hb). More red blood cells means more oxygen-carrying capacity—so this effect could help you hold your breath longer during repeated attempts. At the same time, apnea triggers the classic diving response (slower heart rate and reduced blood flow to the skin/limbs), and that response becomes stronger when you add cold water on the face.
This study asked two practical questions:
1) Does face immersion make the spleen response stronger, or is apnea alone enough to trigger it.
2) Is the better oxygen saturation seen with face immersion explained by the spleen response, or by the cardiovascular dive response.
What they did
Seven trained male breath-hold divers performed two series of five apneas, each apnea being a fixed “near-maximal” time for that person (about 2½ minutes on average). One series was apneas in air, the other was apneas with face immersion in 10°C water. Apneas were separated by 2-minute rests, and the two series were separated by 20 minutes of rest.
They measured: - Hct and Hb from venous blood samples before/after each apnea, - heart rate and skin blood flow (a marker of peripheral vasoconstriction), - arterial oxygen saturation (SaO₂), - venous oxygen measures and lactate (to see where oxygen was being used and whether anaerobic metabolism increased).
The spleen / blood-boost result
Hct and Hb increased progressively across the first few apneas and then leveled off, reaching about a ~4% rise by the fifth apnea. The key point: this happened the same way with or without face immersion. In other words, apnea (or what apnea does to your body) seems to be the main trigger for splenic contraction—not the cold face stimulus. After the series ended, Hct and Hb returned to baseline within about 10 minutes.
The diving response result
Face immersion produced a clearly stronger cardiovascular diving response than apnea in air: heart rate dropped more, and skin blood flow tended to drop more (stronger vasoconstriction). Importantly, heart rate recovered back toward baseline during the rest intervals between apneas—so the cardiovascular response switches on and off quickly.
Oxygen conservation and the “who pays the bill” effect
SaO₂ dropped after every apnea in both conditions, but it stayed higher with face immersion. At the same time, venous oxygen measures fell more with face immersion, and lactate rose a bit more too. That pattern fits a classic diving-response trade: the body protects arterial/lung oxygen (good for brain and heart) by restricting blood flow to the periphery—so the tissues/venous side gets “spent” more, and anaerobic metabolism increases slightly.
Because the Hct/Hb increase was identical in both series, the improved SaO₂ with face immersion cannot be explained by “more spleen boost.” It’s explained by the stronger cardiovascular diving response.
Takeaway in freediver terms
Two different helpers kick in during repeated breath-holds: - A slow-building “blood boost” (spleen contraction) that ramps up over the first 3–4 apneas and lingers into the recovery period. - A fast on/off diving response that gets stronger with cold face immersion and helps conserve arterial oxygen—at the cost of greater peripheral oxygen depletion and a bit more lactate.
Together, they help explain why repeated apneas can start to feel easier after a few rounds, and why cold face immersion is so effective for oxygen conservation even if your spleen response is already doing its thing.
Abstract
Increased hematocrit (Hct) attributable to splenic contraction accompanies human apneic diving or apnea with face immersion. Apnea also causes heart rate reduction and peripheral vasoconstriction, i.e., a cardiovascular diving response, which is augmented by face immersion. The aim was to study the role of apnea and facial immersion in the initiation of the hematological response and to relate this to the cardiovascular diving response and its oxygen conservation during repeated apneas. Seven male volunteers performed two series of five apneas of fixed near-maximal duration: one series in air (A) and the other with facial immersion in 10°C water (FIA). Apneas were spaced by 2 min and series by 20 min of rest. Venous blood samples, taken before and after each apnea, were analysed for Hct, hemoglobin concentration (Hb), lactic acid, blood gases and pH. Heart rate, skin capillary blood flow and arterial oxygen saturation were continuously measured non-invasively. A transient increase of Hct and Hb by approximately 4% developed progressively across both series. As no increase of the response resulted with face immersion, we concluded that the apnea, or its consequences, is the major stimulus evoking splenic contraction. An augmented cardiovascular diving response occurred during FIA compared to A. Arterial oxygen saturation remained higher, venous oxygen stores were more depleted and lactic acid accumulation was higher across the FIA series, indicating oxygen conservation with the more powerful diving response. This study shows that the hematological response is not involved in causing the difference in oxygen saturation between apnea and apnea with face immersion.