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The ability of our bodies to adjust to different environments is one of the many reasons that we can explore the underwater world. Yes, we need to use diving equipment to do this, but the body’s ability to adapt is critical.
You get into the water and your body immediately experiences a decrease in ambient temperature. This decrease in temperature causes blood vessels in your arms and legs to narrow and the body then concentrates heat towards the core rather than the extremities. When the body temperature drops sufficiently, in an attempt to offset further cooling your breathing rate will increase, you may start to shiver, or even experience true hypothermia.
Further descent induces a change in the ambient pressure which also shifts blood circulation from peripheral to central areas. As shallow as 2 meters it has been estimated that this volume shift is around 700 mL of blood. To counteract this the heart pumps harder.
The increase in pressure is felt in your ears. There is a need to equalize these pressures as the increased ambient pressure pushes on the ear drum. Equalizing the ears occurs by moving air from the mouth via the Eustachian tubes into the middle ear. The pressure changes can stimulate the ear canal causing coughing.
Your body starts to on-gas with the increase in partial pressure of your breathing gas. Nitrogen, will be the first gas to have adverse physiological consequences: nitrogen narcosis.
Our body continues to adjust to the decreased ambient light and visibility, our weightlessness, as we continue our dive.
The original article ‘The Body - Descending’ by Derek Covington was published in the June 2014 edition of Tech Diving Mag is available here.