Info Decompression & Treatment Simplified

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1: Introduction​


“ Everything should be made as simple as possible, but not simpler ”

Albert Einstein (paraphrased)

I probably violated the "But Not Simpler" part, but I tried to include enough Hyperlinks to make amends. Clicking on them should allow any interested diver to "drill-down" as far as curiosity takes them. I also have faith that replies from the ScubaBoard community will keep me from disappointing Dr. Einstein.

What is Decompression?​

In diving physiology, decompression occurs when the ambient pressure is reduced causing body tissues to release dissolved gas; like when a diver ascends. This dissolved gas is the key concept that divers need to understand.

Normally, all of our tissues are fully equalized (saturated) with Nitrogen at the altitude (pressure) where we live. This phenomenon matters to divers because changing the ambient pressure changes the gas equilibrium in tissues. Tissues will absorb more Nitrogen (ingas) when pressure increases and release it (outgas) when pressure decreases. The ingassing part is fairly benign; it is outgassing that causes all the problems.

Divers often refer to gasses that can dissolve in tissues as diluent. Diluent is one or more biologically inert gasses used to dilute Oxygen in breathing mixtures; typically Nitrogen and Helium. For example, Nitrogen is the major diluent gas in air comprising about 78%. Oxygen metabolizes in the body so doesn't materially contribute to excessive outgassing during ascent.

An important but less dramatic force acting on tissue saturation is the Partial Pressure of Oxygen (PPO2). Increasing Oxygen reduces diluent absorption and accelerates transfer from the blood stream into the lungs.

For perspective, it is worth noting that diluent outgassing occurs in all of these scenarios:
  • Natural drops in Barometric Pressure (too small to impact decompression calculations)
  • Hospital patients wearing an Oxygen cannula tube
  • Driving up a mountain side
  • Ascending in an aircraft*
  • Recreational divers ascending (whether decompression stops were required or not)
  • Saturation divers returning to the bell after a deeper lockout/excursion
* The cabin pressure inside commercial passenger aircraft is typically between 0.55 and 0.62 ATM at cruising altitude; 6000-8000' or 1830-2440M. That is why decompression tables and computers account for altitude and recommend against flying too soon after diving.

Different Rates
OK, that's not too complicated. The perplexing parts begin with the fact that different tissues, from blood to bone, ingas and outgas at different rates. It gets even more challenging because different diluent gasses also ingas and outgas at different rates. That is one reason that Trimix* dive computers cost more.

* Trimix is a breathing mixture of Oxygen, Nitrogen, and Helium that is typically used on dives deeper that recreational limits to minimize Nitrogen Narcosis.​

It is very common for slower tissues to still be ingassing during a decompression stop while faster tissues are outgassing. It all has to be calculated to limit bubble formation to prevent blocking your bloodstream. You might be asking yourself about now: Why not just breathe pure Oxygen and avoid the whole diluent and decompression mess? You could, but going below about 20'/6M will cause Oxygen Toxicity, which can be much worse.

Residual Nitrogen (or Diluent)
Another complicating factor is that all decompression procedures are designed for you to safely return to the surface, but with higher tissue saturation (super-saturation) than before you started diving. The US Navy Diving Manual refers to this as "Residual Nitrogen", though it applies to all diluents. It basically shifts the starting point for calculating the next dive.

Fortunately, divers don’t need to do the math or sort out all the convoluted interactions; over 100 years of hyperbaric research figured that out for us. However, that doesn’t mean that blindly following your computer is your best strategy. There are a number of more minor factors that influences decompression, which are discussed in Post #3.

Vague on DCS? (DeCompression Sickness)
Divers that haven’t been trained in decompression procedures might be a little unsure what DCS really is; other than they don't want it. To confuse matters even more, it goes by several different names:
  • DCS (DeCompression Sickness)
  • DCI (DeCompression Illness) which includes AGE (Arterial Gas Embolism)
  • The Bends, from the name of a popular dance when the Brooklyn Bridge was under construction, the Grecian Bend.
  • Caissons Disease, because Caisson workers or Sandhogs also suffered DCS
  • Divers' Disease
  • Divers' Condition
  • Diver's Palsy
  • Decompression Disease
  • Compressed Air Illness
  • Dysbaric Illness
  • Tunnel Disease
I'll use DCS because that is the US Navy's preferred term, although "Bends" may slip in the conversation once in a while. The following quote provides a useful perspective to begin exploring this subject:

“ Ask a new diver what causes DCS and he'll say he doesn't know. Ask an instructor on ScubaBoard and he'll go on for days about micro bubbles, M-values, tissue stress, etc. Ask a research scientist who has studied DCS at Duke for many years and he'll say he doesn't know. ”

Unknown

Contents​

  1. Decompression & Treatment Simplified (this post)
  2. Visualizing Decompression
  3. What exactly is DCS?
  4. DCS Treatment
  5. DCS Diagnosis
  6. Recognizing DCS Symptoms
  7. Type I DCS
  8. Type II DCS
  9. OK, I might be bent
  10. Soapbox
  11. DCS Treatment History
  12. Still Too Simple?

Click on the "Share this thread" icon to copy the link to any post and paste into your post:

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The link will "unfurl" like this:


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DCS Treatment History​


DCS was a mysterious affliction for decades after Augustus Siebe invented the first successful surface-supplied diving rig in 1837. Greek sponge divers, caisson workers or "Sand Hogs", and salvage divers all noted debilitating effects of deep and long duration dives, but only guessed at procedures to prevent and treat them. Decompression tables weren't developed until the British Admiralty commissioned John Scott Haldane around 1907.

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This illustration is of one of the earliest chambers I have seen.

Rules of thumb for DCS treatment were a little more codified by around World War I. John Scott Haldane and Chief George D. Stillson's work on decompression tables were recently completed and, as you might expect, a lot of animals and divers were bent during human trials.

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Rosemary is ready for her test dive in Siebe Gorman's chamber, circa early 1900s

Here is a modern day version. Note the comment "by animal I mean a Navy Diver". Some things never change. :facepalm:

Experience treating these DCS cases is reflected in the US Navy's 1916 Diving Manual:

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That's all there was, about three-quarters of a 6x8½" (152x216mm) page. This part would make me very nervous:

No hard and fast rule can be laid down for a decompression rate, which will depend on the condition of the patient, how he stands decompression, and also the pressure at which he was saturated. If the patient becomes ill again while the pressure is falling, decompression must be stopped, and, if necessary, the pressure raised; when the patient is better, pressure may be allowed to fall again, but at a slower rate. If after decompression the patient again develops symptoms, the process of recompression and subsequent decompression must be repeated.

In contrast, the latest US Navy Diving Manual, Rev 7A devotes 44 pages 8½x11" (216x280mm) Pages to DCS treatment.

Doctor Albert Behnke suggested using Oxygen to treat DCS in the 1930s while at the US Navy Experimental Diving Unit. The first treatment table using Oxygen was introduced in the 1943 Diving Manual. The Royal and French Navies developed similar tables.

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This is a photo of the EDU from the 1930s where most of the decompression, treatment and Sur-D-O2 tables were developed.

Personal Sidebar​

I was in a commercial diving company's "bone yard" in the 1970s when I noticed an old riveted single lock chamber. It was heavily rusted, but some haze-gray remnants were visible. On closer inspection I found a barely readable certification plate indicating that it was US-made in 1923.​
There was no Oxygen system, a barely readable pressure gauge that was calibrated only in PSI, and the piping was lead — seriously. I guess they figured a few more damaged brain cells wouldn't matter! I think it was built for the US Navy, but can't be certain. The door seal was a narrow rubber gasket (flat, not O-rings). Viewports were about 3"/750mm in diameter and not completely clear. I think they were made of Quartz. The over-size valves looked like something out of a World War I submarine.​

US Navy Treatment Tables 5 & 6 were introduced in 1965 and quickly grew to be the most widely used in the world.

ScubaBoard Footnotes

US Navy Experimental Diving Unit
A Brief History of Diving (before 1943)


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Continued from previous post



Still Too Simple?​


Here are some links for divers that are interested in learning more:

Recommended Hardcopy Publications

Deco for Divers: A Diver's Guide to Decompression Theory and Physiology by Mark Powell

Deep Into Deco: The Diver's Decompression Textbook by Asser Salama

Online Reading Resources


The Rubicon Foundation maintains a Research Repository, probably the best digital repository of Diving and Environmental Physiology Research on the Internet.

Alert Diver Magazine
Tech Diving Magazine Issue 29, 6.3 MB free download, 33 pages, Dealing with Denial, Getting Bends Out of the Closet, Page 6.

Gradient Factors by Matti Anttila, Ph.D.

Gradient Factors… a simplified primer by @Doppler

Online Video Resources

DAN (Diver's Alert Network) Video Lecture Series
DAN Online Seminars are a series of video lectures including many directly related to decompression and treatment. Video Lecture Series is open to all while the Online Training Seminars requires logging in.

Khan Academy
The Khan Academy is an exceptional resource, especially for those who prefer an academic lecture-style environment.

Of particular interest:
Biology Membranes and Transport, Diffusion and osmosis 7-part series

YouTube

Decompression Controversies DAN Southern Africa, Published on May 9, 2016, Dr Simon Mitchell — ScubaBoard's @Dr Simon Mitchell and Medical Moderator

Diffusion and Osmosis explained in 5 minutes

Thoughtful management of decompression stress - Dr Neal Pollock at BSAC’s Diving Conference 2016

Keywords for Internet Search Engines

  • Bubble mechanics
  • Bubble nucleation
  • Bubble models
  • Diffusion
  • Dissolved phase gas dynamics
  • Gradient factors
  • Isobaric counter-diffusion
  • M-values
  • Tissue compartments

ScubaBoard Footnotes

Oxygen Toxicity Limits & Symptoms

Diving at Altitude

What is Saturation Diving?

US Navy Experimental Diving Unit


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