Originally posted 2018-11-05 06:10:48.

Types of Decompression Sickness (DCS)

by Andy Davis

Decompression sickness is caused by inert gases leaving solution inside the body and forming bubbles. If allowed to grow sufficiently large, those bubbles present signs and symptoms, which allow DCS to be diagnosed, such as;

Type 1:  Minor. Localized pain, skin itching (Pruritis) and skin rash (Cutis marmorata)

Type 2: Cardiovascular/Pulmonary and Neurological.  Severe pain, organ failure, decreasing levels of consciousness, cognitive ability, communication, mobility, dexterity, sensation and bodily control (including; breathing, bladder and bowel control).

Type 3: Vestibular.  Inner-Ear bubble, generally due to Isobaric Counter-Diffusion when using Trimix for dives below 100m depth; presenting as severe vertigo, nausea and localized ear/head pain.

Type 4: Osteopathic. Dysbaric Osteo-Necrosis (DON); a long-term condition where frequent and repeated exposure to hyperbaric conditions (increased pressure) and variation(pressure changes) causes necrosis (death/brittleness) of the skeletal bones.

We can see that the severity and type of DCS diagnosed is related to the frequency (number) and, most importantly, size of the bubbles that occur in the body.

Sub-Clinical Decompression Sickness

It is proven that (micro-) bubbles always do occur in our bodies on the ascent from scuba dives,  We can also accept that those bubbles may not grow to sufficient size to cause us harm and present diagnoseable / clinical symptoms of decompression sickness.

Medically, the frequency of stable (not growing) micro-bubbles is largely irrelevant to decompression sickness., Unless they are able to accumulate and ‘merge’ to form larger bubbles, those micro-bubbles will not cause a sufficiently intense problem to register on the victim.  Higher frequencies of micro-bubbles indicate what is known as ‘decompression stress’, something only identified via doppler ultra-sound charting of micro-bubble size. and frequency.

However, even if bubbles are below that symptomatic/clinical size, the decompression stress may still have a noticeable (if not harmful) general impact upon us. It can be proposed that post-dive fatigue, reduced vitality and drowsiness are symptoms of the increased frequency of non-symptomatic micro-bubbles. This is called “sub-clinical” DCS.

About the Author

andy davis technical diving philippines

Andy Davis is a RAID, PADI TecRec, ANDI, BSAC and SSI qualified independent technical diving instructor who specializes in teaching advanced sidemount, trimix and wreck exploration diving courses across South East Asia.  Currently residing in ‘wreck diving heaven’ at Subic Bay, Philippines, he has amassed more than 9000 open circuit and CCR dives over 27 years of diving across the globe.

Andy has published many magazine articles on technical diving, has written course materials for dive training agency syllabus, tests and reviews diving gear for major manufacturers and consults with the Philippines Underwater Archaeology Society.

He is currently writing a series of books to be published on advanced diving topics.  Prior to becoming a professional technical diving educator in 2006, Andy was a commissioned officer in the Royal Air Force and has served in Iraq, Afghanistan, Belize and Cyprus.


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