2016 Jun

Decompression Sickness – The Problem

June 3, 2016

Taravana syndrome, a disorder that is often reported in Polynesian divers. These divers make 50 m dives just by holding their breath. Taravana sickness is later deciphered to be decompression sickness. The sickness has something do with their profession. The symptoms of this sickness include joint pains, paralysis, vertigo, nausea and in rare cases death. The sickness is also observed in people who carry oxygen equipment. How does deep sea diving cause something fatal and why does artificially carried oxygen fail to help? How a, seemingly, problem of biology or medicine found its solution in physics? The answers are discussed below.

A solvent absorbs gases when placed in a gaseous environment. The oceans absorb carbon dioxide and in fact form a major sink for large amounts of CO2 in the atmosphere in the same way. The extent of absorption is a function of a quantity called partial pressure. ‘Partial pressure’ is a concept that is invoked when there is more than one type of gas in the gaseous environment under study. Partial pressure of a particular gas is the pressure contribution of the gas to the total pressure. Suppose if there are two gases and the total pressure exerted by them is ‘P’ and the partial pressures of the gases are given by ‘p1’ and ‘p2’, then the total pressure P is equal to sum of ‘p1’ and ‘p2’. Partial pressure of a particular gas depends on the number of moles of the gas present in the environment.

This absorption of gases is explained using Henry’s law. Henry’s law states that the amount of a particular gas absorbed depends on the partial pressure of that gas. When the pressure exerted by the gas is high then the absorption of the gas in the solvent is also high. When you suddenly decrease the pressure of the gas in the environment. The dissolved gas molecules come out of the solution increasing the pressure of the gas in the environment. How is this related to decompression sickness?

As we go deep into water the pressure exerted on our bodies varies. We have learnt during our Physics tuition classes that the deeper one dives, more is the pressure exerted on his/her body. This is due to the fact that as one goes deep into the water the weight of the water above exerts force increasing the pressure. But how exactly this increase in pressure is related to decompression sickness? The details are discussed in the next article.

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