Face immersion, especially in cold water, can abruptly slow heart rate, thereby prolonging cardiac filling time and increasing the volume of blood pumped into the lungs with each beat.
A tight wetsuit around the chest and neck could further raise breathing resistance, as well as deregulate blood pressure. Failure to warm up and redistribute blood to the extremities before the swim could worsen the increase in central blood volume with immersion.
Heightened mental stress because of an unfamiliar swim venue or poor visibility might raise stress hormones that increase blood pressure. In addition, drinking just before the swim will enlarge the abdominal fluid volume and thus augment the amount of blood that shifts into the chest upon immersion.
More: Open Water Worst Case Scenarios
Based on these proposed mechanisms of PE in open-water swims, the following seven precautionary steps are recommended to lessen the risk of respiratory failure:
1. Avoid wearing a wetsuit that restricts breathing or feels tight around the neck.
2. Do preliminary exercise before immersion to promote blood flow to the extremities.
3. Submerge gradually and become comfortable with face immersion without competitive stress. If breathing difficulty is experienced, get out and recover.
4. Do an easy swim warm-up after immersion to help redistribute the increased central blood volume. Note: a 10-minute warm-up has become mandatory in the Auburn Triathlon. Also, encourage race directors to follow this example as well as to provide a suitable warm-up area.
5. Don't overdrink within minutes before the swim start.
More: Race Day Fuel
6. In the event of a panic attack discontinue the competitive effort, back float and signal for help. Do not resume the swim until normal breathing is restored.
7. If possible, become habituated to the swim venue in advance, as this might attenuate race-morning anxiety and its associated hyperventilation.
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