Apnea Diving - Long Term Neurocognitive Sequalae Of Repeated Hypoxemia
Authors: Lynne Ridgway and Ken McFarland
DOI / Source: https://doi.org/10.1080/13854040590947407
Date: February 2006
Reading level: Intermediate
Why This Matters for Freedivers
This paper is useful because it tackles a real worry head-on and offers a cautiously reassuring message: long-term freediving exposure, even in elite divers with a history of sambas/blackouts, did not show clear cognitive decline on common neuropsych tests in this study. At the same time, it reinforces a safety mindset: acute “weirdness” after a hard breath-hold may be temporary, but repeated adverse events still shouldn’t be normalized—avoiding blackouts and giving proper recovery remains the smart approach.
Synopsis
A lot of freedivers worry about the same thing: “If I keep doing breath-holds for years, am I slowly damaging my brain?” This paper looks directly at that fear by testing whether repeated exposure to low blood oxygen (hypoxemia) in elite breath-hold divers is linked to lasting problems with thinking, memory, attention, or speed. The authors also make an important distinction early on: low oxygen in the blood (hypoxemia) is not the same as ischemia (low blood flow). Ischemia is what causes rapid brain cell death in things like strokes or cardiac arrest. Hypoxemia, by itself, is often reversible because blood flow can be maintained or even increased, and the brain has several ways to compensate. 
To see what this looks like in real athletes, the researchers tested 21 elite freedivers (men and women, ages roughly 21–68) with 1–20 years of apnea experience. They used standard neuropsychological tests designed to detect subtle “brain insult” effects: reaction/processing speed, attention, working memory (digit span), response inhibition (a Stroop-style task), language fluency, and short-term recall. They also recorded each diver’s history of adverse events, including loss of consciousness (blackout), loss of motor control (“samba”), and past concussions. Importantly, the divers weren’t tested right after an incident; they had avoided breath-holds for about 12 hours and had no major events in the week before testing, so the focus here was on long-term, not “right-after-a-hard-breath-hold” effects. 
The main result is reassuring: as a group, these elite freedivers scored within the average range compared with published norms on all the tests, and the researchers did not find that more years of freediving, or more reported blackouts/sambas, was linked to worse test performance. The authors are careful about what this does and doesn’t mean: it doesn’t prove nobody ever has lasting issues, and it doesn’t rule out very subtle changes that might show up on MRI or with different tests. But it suggests that in this sample, even many years of repeated hypoxemia and occasional adverse events did not translate into obvious long-term deficits on standard, sensitive cognitive tests.
Abstract
This article examines the neurocognitive sequelae of repeated exposure to hypoxemia in apnea (breath-hold) divers. A brief review of the literature on the physiological and neuro- logical adaptations involved in the ‘‘human diving reflex’’ is presented. The results from a neuropsychological investigation of N¼ 21 elite apnea divers are evaluated. Standard neuropsychological tests, with known sensitivity to mild brain insults, included speed of visuo-motor responding, speed of language comprehension, response inhibition, and visual and verbal attention and recall tasks. Results indicated that the breath-hold divers performed tasks within the average range compared to norms on all tests, suggesting that 1–20 years of repeated exposure to hypoxemia including multiple adverse neurological events did not impact on performance on standard neuropsychological tasks. The results are discussed in relation to implications for clinical conditions such as sleep apnea, respir- atory disorders, altitude sickness, and recreational apnea activities.