Plunging into cold water during hot weather can cause heart attacks, even in young, fit and healthy individuals, according to new research.
Scientists are warning that entering cold water suddenly, without taking time to acclimatise, may cause abnormal heart rhythms that can be fatal. In the study, published in the Journal of Physiology, they explain how rapid submersion in cold water, combined with holding ones breath, automatically activates two powerful responses in the body which may interact and cause conflict at the level of the heart.
The scientists, from the University of Portsmouth and Kings College London, explain how the body’s Cold Shock Response, which speeds up the heart rate and causes hyperventilation, may conflict with the Diving Response, which does the opposite and which acts to conserve oxygen.
Normally these responses are not activated at the same time, but sudden immersion into cold water can activate both, and cause what they term ‘Autonomic Conflict’; resulting in the heart going into abnormal rhythms and, on occasions, causing sudden death.
Professor Mike Tipton, who runs the Extreme Environments Laboratory in the Department of Sport and Exercise Science, said that entering cold water should be done with caution.
He said: “As the recent sad spate of immersion deaths confirm, we have entered the most dangerous time of the year for water-related deaths. As air temperatures rise dramatically, people start to go into water that remains dangerously cold. The body’s responses to immersion in cold water are profound, uncontrollable and can result in drowning and heart problems within seconds.”
Professor Tipton and his colleague Professor Mike Shattock of King’s College London, explain that sudden cooling of the skin evokes the cold shock response; the faster the change in skin temperature the bigger the response. Immersion of the face with breath holding evokes the diving response: therefore submersion, even periodic submersion due to wave splash, can produce Autonomic Conflict.
Professor Tipton said: “Those wanting to enter the water should do so in a slow and controlled fashion to minimise these hazardous responses. Individuals should also realise the water they felt comfortable in at the end of last year is colder, and they are less prepared for it at the start of the summer.
“The prevalence of heart problems on immersion in water tends to be underestimated because electrical disturbances to the heart are undetectable post-mortem. The incapacitation caused by cardiac arrest, such as gasping for breath and breathing in water, means that death is often ascribed to drowning, but we believe a significant number of these cases could have a basis in Autonomic Conflict”.
Professor Shattock said, “These heart rate irregularities caused by Autonomic Conflict occur quite frequently on immersion in cold water but may only become lethal when other predisposing factors exist such as a large heart, pre-existing heart disease or a subtle and otherwise benign genetic mutation. We also think that Autonomic Conflict may be a cause of sudden death in other, non water-related situations.”
Immersion-related deaths are the second most common cause of accidental death in the UK and other countries. One child a week is lost from this cause in the UK. There is a peak in these deaths during early summer as people return to water-based activities.
The scientists say that a few simple precautions, such a slow entry and taking time to habituate to the cold water, will save lives at this critical time.