The Semi-Cardinal Rule of Diving
by
Larry "Harris" Taylor, Ph.D.
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Most diving students are told the "Cardinal Rule of Diving" (Never hold your breath). But the reality is that divers when breathing underwater through a regulator essentially hold their breath on every single respiratory cycle. You can verify this by paying attention to how you breathe underwater with a regulator in your mouth.
Consider:
On land, without a regulator in the mouth, the normal respiratory cycle: inhale, exhale ... hold.
But underwater, while mouth breathing through a regulator, the respiratory cycle becomes: slowly inhale ... hold ... slowly exhale.
In essence, the "hold" portion of the underwater respiratory cycle is "holding your breath" (violating the Cardinal Rule?). This pattern is simply normal human respiratory physiology while breathing with pressure on the chest.
My "Semi-Cardinal Rule" is to not consciously extend (called "Skip breathing") the hold portion of the underwater respiratory breathing cycle.
Historically, some divers will "skip breathe" because the accumulated practice of consciously extending the normal underwater hold portion between inhale and exhale breathing pattern provides a longer bottom time. However, this can be a dangerous practice. Holding your breath at depth can slightly increase risk of lung barotrauma, but far more dangerous is the decreased respiration can lead to a CO2 build-up.
Many moons ago there was a local diving instructor who took "skip breathing" to the extreme. He often bragged about his extended bottom times this practice provided. His lifetime goal was to dive the Andrea Doria. He died there. He was found on the deck, not entangled, with ~ 1/3 of his gas supply remaining in his tanks. It is surmised that his practice of "skip breathing" at the wreck depth (~ 200 - 250 fsw) led to a toxic build-up of carbon dioxide such that he simply fell asleep (went unconscious) and died. (After incident analysis of the breathing mix found no toxic components and the tri-mix concentrations were appropriate for the diving depth.)
Bottom line: While underwater, breathe normally without a conscious effort to extend the hold portion of the respiratory cycle.
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About The Author:
Larry "Harris" Taylor, Ph.D. is a biochemist and Diving Safety Coordinator at the University of Michigan. He has authored more than 200 scuba related articles. His personal dive library (See Alert Diver, Mar/Apr, 1997, p. 54) is considered one of the best recreational sources of information In North America.
All rights reserved.
Use of these articles for personal or organizational profit is specifically denied.
These articles may be used for not-for-profit diving education