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Aggravated hypoxia during breath-holds after prolonged exercise
Swedish Defence Research Agency.
2005 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 93, no 5-6, 701-707 p.Article in journal (Refereed) Published
Abstract [en]

Hyperventilation prior to breath-hold diving increases the risk of syncope as a result of hypoxia. Recently, a number of cases of near-drownings in which the swimmers did not hyperventilate before breath-hold diving have come to our attention. These individuals had engaged in prolonged exercise prior to breath-hold diving and it is known that such exercise enhances lipid metabolism relative to carbohydrate metabolism, resulting in a lower production of CO(2) per amount of O(2 )consumed. Therefore, our hypothesis was that an exercise-induced increase in lipid metabolism and the associated reduction in the amount of CO(2) produced would cause the urge to breathe to develop at a lower P O(2), thereby increasing the risk of syncope due to hypoxia. Eight experienced breath-hold divers performed 5 or 6 breath-holds at rest in the supine position and then 5 or 6 additional breath-holds during intermittent light ergometer exercise with simultaneous apnoea (dynamic apnoea, DA) on two different days: control (C) and post prolonged sub-maximal exercise (PPE), when the breath-holds were performed 30 min after 2 h of sub-maximal exercise. After C and before the prolonged submaximal exercise subjects were put on a carbohydrate-free diet for 18 h to start the depletion of glycogen. The respiratory exchange ratio ( RER) and end-tidal P CO(2), P O(2), and SaO(2) values were determined and the data were presented as means (SD). The RER prior to breath-holding under control conditions was 0.83 (0.09), whereas the corresponding value after exercise was 0.70 (0.05) ( P <0.01). When the three apnoeas of the longest duration for each subject were analysed, the average duration of the dynamic apnoeas was 96 (14) s under control conditions and 96 (17) s following exercise. Both P O(2) and P CO(2) were higher during the control dynamic apnoeas than after PPE [PO(2) 6.9 (1.0) kPa vs 6.2 (1.2) kPa, P <0.01; P CO(2) 7.8 (0.5) kPa vs 6.7 (0.4) kPa, P <0.001; ANOVA testing]. A similar pattern was observed after breath-holding under resting conditions, i.e., a lower end-tidal P O(2) and P CO(2) after exercise (PPE) compared to control conditions. Our findings demonstrate that under the conditions of a relatively low RER following prolonged exercise, breath-holding is terminated at a lower P O(2) and a lower P CO(2) than under normal conditions. This suggests that elevated lipid metabolism may constitute a risk factor in connection with breath-holding during swimming and diving.

Place, publisher, year, edition, pages
2005. Vol. 93, no 5-6, 701-707 p.
Keyword [en]
Apnoea, Drowning, Hypoxemia, Metabolism
National Category
Physiology
Identifiers
URN: urn:nbn:se:kth:diva-45331DOI: 10.1007/s00421-004-1242-yISI: 000228525100026PubMedID: 15778900OAI: oai:DiVA.org:kth-45331DiVA: diva2:452338
Note
QC 20111116Available from: 2011-10-28 Created: 2011-10-28 Last updated: 2017-12-08Bibliographically approved

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