Case studies highlight dangers of hyperventilating before breath-holding underwater

Dr Kishore Kumar and Dr Karl Ng, of the Department of Neurology at Royal North Shore Hospital, NSW, report the cases of two medical students who experienced seizure-like activity while competing in a breath-hold dive competition. In both cases, the students hyperventilated before the dive.

“The seizure-like activity that occurred in the two university students was probably convulsions secondary to cerebral hypoxia induced by breath-holding,” Dr Kumar said.

Swimmers often hyperventilated before breath-holding to reduce the urge to breathe from hypercapnia (too much carbon dioxide in the blood), Dr Kumar said. This may result in prolonged breath-holds with consequent hypoxaemia (decreased partial pressure of oxygen in the blood).

“Loss of consciousness may ensue without forewarning because the respiratory stimulus from hypoxaemia is weak and easily overridden,” Dr Kumar said.

“Vigorous exercise, such as underwater swimming, may exacerbate hypoxia by increasing oxygen consumption.

“These factors are likely to result in syncope occurring late in the dive, as in our two cases.”

Dr Kumar said that anecdotal observations suggested that underwater breath-holding was a relatively common practice in Australia, with breath-hold practitioners often skilled male swimmers who were not closely watched by lifeguards.

“The practice is particularly dangerous if coupled with prior hyperventilation,” he said.

“This report provides further evidence that hyperventilating before breath-holding should be discouraged.”

The Medical Journal of Australia is a publication of the Australian Medical Association.

The statements or opinions that are expressed in the MJA  reflect the views of the authors and do not represent the official policy of the AMA unless that is so stated.

CONTACT:     Dr Karl Ng     9467 5900/ 9926 7111