Quiz - 21 - Diving Knowledge Workbook - Diving Physiology

[Pedro Burrito]

From the Diving Physiology Section of the PADI Diving Knowledge Workbook Version 2.02 © PADI 2009:

Objective 2.7 - Explain the physiological mechanism of decompression sickness (DCS), and list the common susceptibility factors that can contribute to its occurrence.

Question 3

Divers succumb to decompression sickness because in humans any amount of supersaturation of the tissues with nitrogen will result in significant bubble formation.

a. True

b. False​

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Thank you for your patience while we try to give people something to discuss other than Covid-19 and/or Politics. I will post the answer covered by the spoiler tag later today.

 

[Brett Hatch]

I like this question, thanks Pedro

 

[helodriver87]

Supersaturation is your friend (up to a point). Different tissue compartments can handle different levels of supersaturation at different depths. A limited amount of supersaturation promotes off gassing on ascent. It's the m value (or critical supersaturation level) that we're concerned with. That's where bubbling theoretically begins, and it corresponds to a GF of 100/100. Most people use more conservative settings to provide a buffer and account for unknown variables that may promote DCS.

 

[Brett Hatch]

Supersaturation is your friend (up to a point). Different tissue compartments can handle different levels of supersaturation at different depths. A limited amount of supersaturation promotes off gassing on ascent. It's the m value (or critical supersaturation level) that we're concerned with. That's where bubbling theoretically begins, and it corresponds to a GF of 100/100. Most people use more conservative settings to provide a buffer and account for unknown variables that may promote DCS.

That's true. Supersaturation just means that the tissues contain more nitrogen than they would at the saturation point for your depth and breathing gas, ie they are off-gassing. Practically speaking, all dives will achieve some supersaturation, by definition. At the surface your body's tissues will all be saturated with about 79% nitrogen. Even a short, shallow dive on air will increase the tissues' saturation of nitrogen (think 5 minutes at 5 meters). Once you begin ascending, all tissues will become supersaturated to some degree. To what degree is a function of depth, time, and breathing gas; the goal being to keep the supersaturation level below the critical level.

The question is a bit ambiguous and tricky, it hinges on the meaning of the word "significant". If you take it to mean something like "measurable bubble formation", or "non-zero bubble formation", then True is a good answer. Maybe some of the responders were thinking along these lines?

However in the context of the question asking about DCS, I think it's clear that "significant bubble formation" means "formation of bubbles above tissue critical supersaturation", so I chose False.

 

[Pedro Burrito]

Spoiler: Answer

b. False

Humans can tolerate some degree of supersaturation. Otherwise, we would get the bends by merely going to the top of a skyscraper in an elevator, or driving up a mountain. The important factor is determining how much supersaturation can be tolerated without the formation of nitrogen bubbles. This is what decompression models seek to explain.