Q : Why are some divers more susceptible to DCS?

A: You may have heard of divers who fly less than 12 hours after diving with no negative impact and others that wait a longer period who end up with symptoms of DCI and wondered why this happens.

Dr John Parker, a diving physician and Senior Dive Medical Consultant for DAN, advises that there is no conclusion as to why some individuals are more susceptible to DCS. However, increasing age and BMI have been shown to be associated with increased post-dive bubble, and the presence of a patent foramen ovale (PFO) is known to increase the risk up to sixfold, depending on the size and characteristics of the PFO.

There may be some genetic factors affecting susceptibility. However, individual susceptibility can also vary from day to day depending on factors such as exercise, hydration, alcohol, smoking and anxiety.

As a general rule, DAN AP recommends that divers wait at least 24 hours before flying after diving.

Q:  What about diving after flying?

A: It can often take a long time, and several flights, to get to some dive destinations but some divers are known to begin diving immediately when they arrive to maximize the time they have available. The question is: Does doing so put them at greater risk for decompression illness?

Mild dehydration can occur on long flights, especially when travelers cross several time zones; alcohol consumption can also contribute to dehydration. Generally speaking, dehydration is thought to predispose a diver to decompression illness because the washout of inert gas (nitrogen, in diving) is less effective in a dehydrated individual.

If there were a relationship between diving after flying and DCI, we would expect to see a great deal of decompression illness on the very first day of diving; this has not been verified to date, and many DCI cases occur after several days of diving.

Although no one can insist upon a 24-hour waiting period after flying, such a conservative approach to diving after flying is a reasonable idea as it gives divers an opportunity to rehydrate, adjust to a new climate and time zone, and rest up after a long flight.