Dive & Hyperbaric Medicine


January 19th 2021

5:00PM - 6:00PM EST

The Physiology of Freediving

Dr. M. Peter Sayers

December 17th 2020

7:00PM - 8:00PM EST

Introduction to Undersea and Hyperbaric Medicine

Dr. Derek Covington

The Physiology of Freediving


Introduction to Undersea and Hyperbaric Medicine



You've talked a lot about rapid decompression. Is there any risk of rapid compression?

The main risks of rapid compression are an increased likelihood of difficulty with equalizing air spaces (like your middle ear) and possibly an increased chance of inert gas narcosis.

Do you think sat divers that undergo the correct amount of decompression still run the risk of having health issues with their bones? I heard some sat divers get air pockets?

Yes, there are certainly long-term health risks with significant and chronic exposures to hyperbaric environments. One of the most commonly encountered long-term health risk of saturation divers is dysbaric osteonecrosis, also known as DON. A type of avascular necrosis, DON usually presents in the hip joint (proximal femur) and increases a patient's risk for fracture.

What is the rate of increasing hearing recovery in sudden lost of hearing with HBO (vs no HBO)?

The effectiveness of HBO treatment for idiopathic sudden sensorineural hearing loss (ISSHL) is still be described. However, the best outcomes with HBO tend to occur in those patients with severe to profound hearing loss.

Any idea for the mechanism behind the transient myopia with HBO treatment? You mentioned lens swelling (which optically makes sense), but there are no blood vessels feeding the lens. Perhaps increased gas dissolved in the aqueous of the anterior chamber, but curious how that would like to swelling of the lens. Do you see the transient myopia often? Lens cells are not very metabolically active, perhaps the excess O2 is not effectively consumed?

Prevailing hypotheses describe oxidative damage of lens proteins leading to changes in lenticular refraction. However, some studies supporting these mechanisms stem from work in guinea pigs in the 1990s. I'm sure additional work investigating this physiology would be welcome from the undersea medicine community!

Where can we learn about what is going on physiologically in detail during decompression?

Lots of places! Diving courses, the internet, books (Deco for Divers is excellent!), and of course during your future undersea medicine fellowship. đŸ˜‰

Can you talk a little more about the use of HBO for traumatic brain injury? How extensive is the literature and medicine supporting the use of HBO for TBI? Do you think that it is close to becoming an indicated use for HBO?

I'm attaching an excellent review of HBO for TBI. It covers the history of this likely to be approved condition and the mechanisms of HBOT for TBI very well. The literature is quickly accumulating, and yes, I believe close to approval. (See Below)

For someone susceptible to DCS in a location where the nearest hyperbaric chamber is a flight away or 3 hour boat ride, besides O2, what are some other ways immediately help with symptoms/improve outcome while you get to the chamber?

In this case, surface oxygen and supportive care are your best bet. So, remove the diver from the water, administer oxygen, maintain normothermia, and hydrate the patient. You should also limit the altitude of any flight to reduce exposure to a hypobaric environment, which could make the DCS worse.