What’s new in DCS a review for techies and diving docs

Mattijn Buwalda Anaesthesiologist-intensivist & Physician Content

• review tissue saturation • from Haldane to Wienke • origin of bubbles • bubble stress • factors influencing bubble stress

Slides will be available online www.mattijnb.nl Henry’s law On (or off) gassing

How much gas? How fast? • depends on • depends on partial • depends on difference (gradient) difference (gradient) • depends on specific gas • depends on specific gas • depends on specific tissue • depends on tissue • depends on tissue volume • depends on of the specific tissue • half times! Fast & slow tissues

Blood vessels

Fast tissue Slow tissue

Brain Fat Cartilage

Not real tissues but virtual compartments! Half time

• time needed to double or half the tissue pressure gradient • Gradient: ambient (= inspiratory) <> tissue pressure

surface fast tissue PN2 = 0.8 bar inspiratory T1/2 = 4 min PN2 = 0.8 bar air diver

30 msw inspiratory PN2 = 0.8 bar PN2 = 2 bar PN2 = 2.6 bar PN2 = 3.19 bar PN2 = 3.2 bar T=0 T=4 min T=8 min T=40 min 8 compartment model

John Scott Haldane 1860-1932

• ascending:

– Pambient < P tissue – super saturation • no symptoms or bubbles if tissue/ ratio < 2 • the basis for the first Haldanian tables (published 1908) – ascend up to a super sat ratio of 2 – 60 > 25 m = 7 > 3.5 bar or – 20 > 5 m = 3 > 1.5 bar – then wait for tissue to fall – and ascend again – 5 compartments (5, 10, 20, 40 and 75) • used by the US Navy 1912 - 1956

Boycott AE, Damant GCC, Haldane JS. The prevention of compressed-air illness. Journal of Hygiene. Cambridge 1908 Workman

• < 1960’s: variation in number of compartments • Robert Workman MD 1965 • Haldane’s tables too conservative for longer and deeper dives • tolerable super saturation not the same for all compartments and depth’s! – faster compartment: more super saturation – increasing depth: less super saturation • the M-value!

– maximum tolerated partial pressure of He or N2 – for each compartment – linear relation to depth • equation rather then a table!

BÜhlman

• Also worked with M-values • But based on absolute pressure • Mountain lakes in Switzerland! • 1983: ZH-L12 1990: ZH-L16 • Zurich-Limits, number of compartments • ZH-L16A: not conservative enough in middle compartments • ZH-L16B: more conservative, used in tables • ZH-L16C: more conservative, real time deco computations

M-values M-value and gradient factors Gradient factors

• GF low: depth of first stop • GF high: length of last stop “silent” bubbles?

• 1976 Dr Merrill Spencer • venous bubbles without symptoms • below your M-line!

Clip with doppler study Bubbles and DCS

Even undetectable bubbles (< 20µm) cause damage DAN project save dive • 1418 monitored recreational dives – 25% low bubbles – 14% high bubbles – 61% no bubbles • Repetitive dives: – 67% high bubbles – 18% low bubbles – 15% no bubbles • Bubbles correlated with: – Negatively with remaining no deco time – depth

DAN project save dive

• As fraction (percentage) of the M-value • < 0.8 →no or low bubbles • 0.8-0.9 → high bubbles • > 0.9 → very high bubbles

• There appear to be divers who are low or high bubblers!

Bubble models

• bubble researchers: • Brian Hills • Val Hempleman • Tom Hennessy • David Yount • Erik Baker • Eric Maiken • critical volume hypothesis: – bubbles are always present • can grow • can coalesce – the body can only tolerate a certain total volume of bubbles – the challenge: how to keep the bubble (total volume) small?

Bubble dynamics I

Pint = Pamb + P surf tens

La Place law: Psurf = 2y:r

large radius → low psurf → bubble will grow

small radius → high psurf → bubble will shrink

critical radius → stable bubble Bubble dynamics II

Bubble will grow or shrink depending on the relation of ambient pressure (depth) and radius

But also because of the tissue saturation. If partial pressure in tissue > bubble internal pressure then the bubble will grow and v v How to minimize bubbles?

Tissue saturation • ‘sucking’ • Haldanian • largest tolerable gradient between partial pressure in tissue and lung

Bubble dynamics • ‘crushing’ • < crit radius • highest possible ambient pressure = deep stops

• bubbles get coated by a / protein mono layer • after some hours bubbles are coated by a strong layer due to the body’s immunological reaction (foreign body) • surfactant further complicates things! – lowers > smaller critical radius > more bubbles grow – barrier: increases when the surfact molecules are pressed together due to bubble compression Dual phase models

• bubbles appear as soon as we start ascending (minimal supersaturation) • bubble model: keep the bubbles small! • dual phase = ‘bubble’ model • dual phase = Haldanian model + bubble dynamics

VPM (varying permeability model) RGBM (Reduced gradient Bubble model) – micronuclei – Bruce Wienke – surfactant – protected – variable diffusion rate – repetitive, reverse profiles, – open software crushing of micro nuclei – V-planner – used in many recreational dive computers

AP diving vision: Buhlman Where do the bubbles come from? Origin of bubbles

• tissues: cavitation (autochthones bubbles) – formation and then immediate implosion of cavities in a liquid – i.e. small liquid-free zones ("bubbles") • rapid pressure changes • musculoskeletal activity (tribonucleation) • veins: micro nuclei sticking to the vessel wall – micro bubbles are already there (< 1.2 µm) – most bubbles are formed in the venous blood

• CO2 bubble can absorb N2

Blatteau JE, et al. Gas nuclei, their origin, and their role in bubble formation. Aviat Space Environ Med 2006;77:1068-1076 cavitation Micronuclei < 1.2 µm

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High tissue PN2 or PHe micronuclei • irregularity in glass or floating particles • bubbles formation in clean water requires very high partial N2 pressure (> 1000 bar)

• micronuclei continuously appear and disappear • always present, also in non-divers Direct effect of too much bubbles

In the tissues In the veins • spinal cord > paraplegia • filtered by lungs • in or around bone > • Right > left shunt bends/ DON – PFO • inner ear > vestibular – pulmonary bends arterialisation – • right side heart > neurological DCS chokes – skin signs – constitutional ?? DCS signs Stripping the veins.....

Bubbles get coated by white blood cells & platelets

SIRS “generalized inflammatory reaction without bugs”

Bubbles damages Micro particles the inside of little 0.1 – 1 µm veins

fluid shift Leakage circulation > tissues dehydration! Bubble or stress

• bubble stress • tired! • disrupted endothelium with immunological, and biochemical effects • unknown long term effects: – – mild neurocognitive changes – neurodegenerative changes brain and spinal cord – inner ear/ deaf

Counting bubbles

• Post dive venous bubbles are correlated to decompression stress and the risk of DCI

40-60 min post-dive bubbles are big enough to be detected

After surfacing there is still tissue supersaturation

Nishi RY, et al. Bubble detection. In; Brubakk AO, Neuman (eds) Bennett and Elliot’s physiology and medicine of diving, 5th edn. WB Saunders, London, pp501-529 How to minimize bubbles

• general factors, age, , fitness • pre-dive optimization • during dive • post dive measures

Personal factors

• gender: no effect/ females slightly more • obesity: no effect but...... • physical condition: protective – more capillaries • Age > 40 yrs: more susceptible – +1% risk for every 10 yrs above 40 • PFO: OR 2.5 for neurological DCS

Bove AA. Risk of with patent foramen ovale. Undersea Hyperb Med 1998;25:175-8 Physical fitness

• 50 divers, mixed group • Two open water air dives, 25min @ 35m, 3min @ 6m, 15 min @ 3m • doppler bubble score @ 60 min

• VO2 max > or < 40 ml/min/kg

Fitness is measured by maximum O2 consumption during cycle or tredmill exertion

FIT NOT FIT Average untrained: male: 35-40 ml/kg/min Female: 27-31 ml/kg/min

Spencer bubble grade: 0 = no bubbles 4 = a lot of bubbles

Caturan D, et al. Ascent rate, age, maximal uptake, adiposity and circulating venous bubbles after diving. JAP 2002;93:1349-1356 Dehydration and DCS

• dehydration > vasoconstriction > decreased perfusion of the tissues > less on-gassing during TBT • but it also causes decreased off-gassing during ascent/deco/ at the surface > less venous bubbles

• no robust study linking dehydration to DCI! • conflicting animals studies, no human studies • mainly anecdotal reports: DCI patients appear to be dehydrated

• immersion > > post-dive dehydration • prehydration attenuates post-dive dehydration Immersion diuresis

• Physiologic response to pressure and cold • can be blocked by 40 mcg intranasal desmopressine (healthy military divers)

Nyquist, PA; Schrot, J; Thomas, JR; Hyde, DE; Taylor, WR. Desmopression Prevents Immersion Diuresis and Improves Physical Performance After Long Duration Dives. NMRC 2005-001, March 2005 Hydration and VGE Pre-dive hydration

• 8 military divers , cross-over trial • Protocol 1: 1300 ml (hypertonic) in 60 min • Protocol 2: no prehydration • Air: 30 min @ 30msw > 9 min @ 3 msw

Gempp E, et al. Preventive effect of pre-dive hydration on bubble formation in divers. Br J Sports Med 2009;43:224-228 Urine and fluid balace

• Protocol 1: urinated 810 ml post dive balance: -140 ml • Protocol 2: urinated 500 ml post dive balance: -859 ml

Gempp E, et al. Preventive effect of pre-dive hydration on bubble formation in divers. Br J Sports Med 2009;43:224-228 Post-dive bubbles (VGE)

• VGE = venous gas embolie • TTE for 3 min every 30 min 3x postdive • no clinical signs of DCI

Gempp E, et al. Preventive effect of pre-dive hydration on bubble formation in divers. Br J Sports Med 2009;43:224-228 Pre-dive exercise • leads to reduced bubble formation • mechanism not clear – elimination of gaseous nuclei (via NO pathway) – heat shock proteins – dehydration...... – altered tissue perfusion • 24 hours before dive • 12 divers (dry) • High intensity treadmill • Reduced post-dive bubbles • 2 hours before dive • high intensity • medium intensity • 15 divers (dry) • 32 divers (wet) • duration of protective effect unknown – regeneration of micronuclei 10-100 H

Dujic Z, et al. Aerobic exercise before diving reduces venous gas bubble formation in humans. J Physiol (Lond) 2004;555:637-42 Blatteau JE, et al. Aerobic exercise 2 hours before a dive to 30 msw decreases bubble formation after decompression. Aviat Space Environ Med 2006;76:666-669 Jurd KM, The effect of pre-dive exercise timing, intensity and mode on post-decompression venous gas emboli. Diving and hyperb med 2011;41:183-188 Pre-dive vibration

• 14 male military divers – 30 min whole body vibration ending 1 hour pre-dive – 2 dives, 1 week interval – 30 min 30 msw dive , 9 min deco @ 3msw • less bubbles after vibration-dive • probable mechanism: elimination of micronuclei

Germonpré P. et al. Pre-dive vibration effect on bubble formation after a 30-m dive requiring a decompression stop. Aviat Space Environ med 2009;80:1044-48 Pre-dive sauna

• leads to reduced bubble formation • 30 min sauna 1 hour pre dive • 16 ‘divers’ simulated dive • hyperbaric chamber 25 min 4 bar • mechanism not clear: – heat shock proteins – NO-pathways – dehydration!

Blatteau JE, et al. Predive sauna and venous gas bubbles upon decompression from 400 kPa. Aviat Space Environ Med 2008;79:1100-1105 Pre-dive oxygen • routinely used in aviation and space (preparation for EVA) • studied in animals: reduced DCS • possible mechanisms:

– Denitrogenation (lower tissue N2 pressure) • should be used immediately before the dive • not much difference: fast tissues are quickly saturated

• but works in space! (100% O2) – elimination of gas micronuclei • prolonged protective effect

Katsenelson K, et al. Hyperbaric oxygen pretreatment reduces the incidence of decompression sickness in rats. Eur J Appl Physiol 2007;101:571-576 Pre-dive oxygen

• 30 min pre-dive normobaric oxygen (100%) • up to 15 min before dive • 30 min @ 30 msw, 6 min @ 3 msw • 21 divers, two dives/ day, 100 min SI, several days • significant reduction in bubble stress!

Castagna O, Gempp E, Blatteau JE. Pre-dive normobaric oxygen reduces bubble formation in scuba divers. Eur J Appl Physiol 2009; 106:167-172 Exertion during deco phase

• Mild exercise during decompression • 10 military divers • 30 min @ 30 msw with moderate exertion during bottom phase • Two dives: one with and one without exercise during the 3 min deco stop. • Reduced venous gas bubbles after the exercise dive.

Dujic Z. Et al. Exercise during a 3-min decompression stop reduces postdive venous gas bubbles. Med Sci Sports Exerc 2005;37:1319-23 Post-dive oxygen

• 19 military divers • 3 dives, 3 days apart • doppler study

Blatteau J, Pontier JM. Effect of in-water recompresiion with oxygen to 6 msw versus normobaric oxygen on bubble formation in divers. Eur J Appl Physiol 2009;106:691-695 Post-dive oxygen

• post dive oxygen: – strenuous dive – Jo-Jo profile – multi /repetitive diving – – and everything that makes you worry • the oxygen hang tank @ 5 msw? Future

• cardio : – measurement of activity level during the various phases of a dive

– exertion > increased hart freq/ flow > smaller T1/2 • personalized bubble profile, advice and dive computer settings – high or low bubbler (echocardiography) – pulmonary arterialization (echocardiography) – biomarkers of decompression stress (blood test) – age & fitness – biomarkers of pulmonary otox (analysis of exhaled air) – susceptibility for (flicker fusion test)

Hypes & trends

• Reduction of time to recompression in remote locations (serious DCS) – revival of in water recompression – portable recompression chamber Top tip Thank you for listening!

Contact: [email protected] medicine for scuba divers. Carl Edmonds et al. 2012 edition free download http://www.divingmedicine.info/ Lectures: www.mattijnb.nl