DCS and the Immune Response

The Complement System and Diving

   by Dr. Ernest Campbell FACS

[Blog note:  I reproduced this article from ScubaDoc, as I thought it valuable for understanding the wider implications of  sub-clinical DCS, especially the issue of ‘post-dive fatigue’ that indicates unhealthy decompression stress.

This article ‘The Complement System and Diving’ illustrates that bubbles cause an immune-system response (with predicted damaging consequences in the long term), and also shows how individual tolerances can play a big role in the degree of immune-system (complement system) activation.

From my (very limited) medical understanding, the frequency (number) of bubbles would have a much more direct impact on an immune-system response. Therefore, sub-clinical DCS doesn’t present the size of bubbles needed to provoke the symptoms (pain, rash etc) that justify chamber rides; but the quantity of (micro) bubbles can still bring about harmful changes in blood/brain chemistry. The symptoms of these changes is unusual post-dive fatigue, lethargy, sleepiness and decreased vitality.

Preventing the formation of microbubbles, or resolving them at the earliest possible opportunity, may have significant health impacts for divers. | Andy Davis]


Considerable research over the past 10 years has been directed toward elucidation of the complement system and it’s effect on the body in association with bubbles. Reviewed nicely in 1997 by Andrea Zaferes in the magazine ‘Immersed’, the complicated but important field of how bubbles cause damage is slowly but clearly being brought to light. 

Long thought to be a simple process of blockage of vessels and infarction, it has now been shown that there is a tripping of the complement system and the immune system (T- and B- leucocytes) when bubbles form from decompression. This immune response has a domino effect on blood chemistry that leads to marked changes in the tissues long after the bubbles are gone.

Work has also been done that shows the importance of early treatment. The longer the period of waiting after a decompression incident, the more blood chemistry changes occur and the greater the damage done, emphasizing the importance of early recompression in the treatment of decompression illness.

Very interesting studies have also shown that activation of the complement system may acclimate you to the effects of a decompression accident. This might be a ‘using up’ process of multiple shallow dives with sub clinical bubbling causing complement activation and having little or none present when a subsequent deeper dive is done. This same process might be the explanation of the excessive fatigue that many divers describe after diving – the fatigue actually being the complement activation damage that is know to occur distant from local bubble sites and the hemoconcentration that occurs.

Individuals who have greater sensitivity to complement activation may be at greater risk for DCS manifestation and more severe DCS injury. Conversely, those with chronically ‘used up’ complement may be a lesser risk, as in the chronic asthmatic or the atopic patient.

Finally, there might be individual variation in the sensitivity to DCS. Divers who are complement sensitive have a higher rate of DCS. Sensitivity is defined by the level of C5a increase following plasma incubation with bubbles in vitro. However, Lundgren and associates were unable to show this effect in their report in 1997.

Interestingly, workers have also found that cobra venom factor ends the manifestations of DCS in rabbits.

Read more highly educational diving medical articles at scuba-doc.com

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Shastri KA, Logue GL, Lundgren CERelated Articles
In vitro activation of human complement by nitrogen bubbles.
Undersea Biomed Res. 1991 May;18(3):157-65.

Bergh K, Hjelde A, Iversen OJ, Brubakk AO.
Variability over time of complement activation induced by air bubbles in human and rabbit sera.
J Appl Physiol. 1993 Apr;74(4):1811-5.

Ward CA, McCullough D, Fraser WD.
Relation between complement activation and susceptibility to decompression sickness.
J Appl Physiol. 1987 Mar;62(3):1160-6.

Shastri KA, Logue GL, Lundgren CE, Logue CJ, Suggs DF.
Diving decompression fails to activate complement.
Undersea Hyperb Med. 1997 Jun;24(2):51-7.

Ward CA, McCullough D, Yee D, Stanga D, Fraser WD.
Complement activation involvement in decompression sickness of rabbits.
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Complement activation in divers after repeated air/heliox dives and its possible relevance to DCS.
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Katuntsev VP, Kozlov LV, Shcherbakova MA, Ageev VP, Sizoi MN.
[Effect of decompression on the compliment system].
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Stevens DM, Gartner SL, Pearson RR, Flynn ET, Mink RB, Robinson DH, Dutka AJ.
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Undersea Hyperb Med. 1993 Dec;20(4):279-88.

Zhang J, Fife CE, Currie MS, Moon RE, Piantadosi CA, Vann RD.
Venous gas emboli and complement activation after deep repetitive air diving.
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Activation of complement and neutrophils increases vascular permeability during air embolism.Aviat Space Environ Med. 1997 Apr;68(4):300-5.

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