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What's New In What’s new in DCS a review for techies and diving docs Mattijn Buwalda Anaesthesiologist-intensivist & Diving Medicine 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 temperature • depends on partial pressure • depends on partial pressure 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 perfusion 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/ambient pressure 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 pressures 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 Surfactant • bubbles get coated by a lipid/ 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 surface tension > smaller critical radius > more bubbles grow – diffusion 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 . 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 decompression stress • bubble stress • tired! • disrupted endothelium with immunological, and biochemical effects • unknown long term effects: – dysbaric osteonecrosis – 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, weight, 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 decompression sickness 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 oxygen 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 > diuresis > 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
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