DEN HUMANE DYKKERESPONS VARIASJON OG INTERINDIVIDUELLE FORSKJELLER

Abstract

This paper presents the different expressions of the human diving response in 57 young healthy individuals. The mammalian diving response is what makes the seals and whales survive hours under water. It is initiated by apnéa and consists of bradycardia and peripheral vasoconstriction with a reduced cardiac output, redistribution of regional blood flows and lactate accumulation in unperfused muscles. The respons was discovered in man in the 1950s. The aim of the response is to contribute to minimised oxygen consumption during long-duration apneas and is our primary defence against apneainduced hypoxia. The most powerful stimulator of the response is hypothermia, especially of the face. Exercise prior to a dive has also been shown to modulate the response. Thus, our subjects peformed apneas with their faces in ice cold water riding an ergometercycle. Their heart rate was continually monitored. The aim of our study was to see how the diving response is expressed in a large population to get an idea of the diversity of it. We wanted to find the extremes and also try to generate thesis that could explain the variety. Our study showed a huge diversity in the diving respons. The extremes were markedly gender associated, the males being able to hold their breath longer and tolerating the effect of the diving respons better. Trained breath-holders had a stronger response showing extreme apné duration and a persistent bradykardia during the dive similar to underwater mammals. But to our surprise we also had a young man who showed a “seal-like” diving response with no previous breath-hold training, mimicing the response of those experienced freedivers. This may give us new information about the importance of genes for the diving response. The variation also semes to be caused by size, physics, lungvolume, gender and psychological state. Why some people are more likely to survive near-drowning accidents with a long period of hypoxia than others, is not explained by these findings.