What Dive Computers Don't Know

BY DENNIS GUICHARD

1. TEMPERATURE

Dive computers might measure water temperature to display on your screen readout. Still, almost none of them actually incorporate that data into their decompression algorithm calculations.

Fluctuations in temperature may affect diving safety by increasing the risk of developing decompression sickness (DCS). The reason for this is two fold if the body is cold, it can retain more inert gas Then, when the diver warms up after a dive, the recovery to normal body temperature may bring bubbles out of solution. Hot showers or baths and exercise may have the same effect: This is why exercise is not recommended within 24 hours of diving. If the diver is adamant about keeping to their exercise routines, then 4 hours before and after diving should be considered the bare minimum due to the influence of exercise and increased body heat on blood perfusion and gas solubility

After the dive, exposure to sudden and excessive heat, such as in a hot shower, produces increased superficial blood flow and lower solubility of gas, which could induce decompression sickness.

As mentioned previously, cold tissues in-gas more and have a higher affinity to hold excess nitrogen Active movement may help eliminate nitrogen during decompression before bubbles are likely to form Suppose a diver becomes mildly hypothermic during the ascent phase of a dive in that case, the ability to eliminate excess nitrogen is decreased, and DCS can become more likely in some studies, the perfusion rate was halved, thus doubling the required duration of decompression.

2. BODY FAT CONTENT

Some say that fat is only important as an indicator of physical condition and efficient gas exchange and is of no consequence to sport divers being a slow tissue, unlikely to affect those who stay within accepted NDT dive time limits as it in gasses relatively little on regular sports dives. We know that fat has a much higher affinity for nitrogen than other tissues, but how this impacts the risk of DCS is still uncertain. ‘Chubbier’ subjects may be at slightly greater risk of DCS, as nitrogen is 5 6x more soluble in fatty tissues than aqueous ones Also, chubbier individuals may have elevated blood lipid levels that may increase susceptibility to DCS.

3.OURADVANCINGAGE

Theageingprocesscausesadecreaseintheefficiency of all biological systems. Generally, the older the person, especially over 40 years, the greater the susceptibility to DCS. A 28 year old has twice the likelihoodofan18 year oldinaviationdecompression sickness.

The number and area of ‘Active Hydrophobic Spots’ (AHS) in our blood vessels, a known seed source for producing the microbubbles, might lead to neurologicalDCSwithincreasingage.AHSareformed by(DPPC)surfactantswhichleakovertimefromour lungs and settle on the walls of the blood vessels in ourvascularsystem.

4.DIVEEXERTION

Exerciseperformedatdepthislikelytoincreasethe bloodsupplytothemusculartissuesandtherateof inert gas absorption at that site. It can increase decompression requirements by a factor of three. During or after decompression, strenuous exercise increases the speed of bubble development and the number of bubbles, perhaps due to increased cavitation from tribonucleation of tissues or turbulence, similar to shaking a bottle of fizzy juice. Mild exercise during decompression is of value in increasing the rate of gas elimination, perhaps by increasing tissue perfusion, if supersaturation and bubblegrowthhavenotoccurred.

5.HYDRATIONSTATUS

Influencedbytheenvironment,exercise,respiration, immersion, and alcohol consumption, dehydration remainsoneoftheprimarycausesofdecompression sickness worldwide. Dehydration is a loss of body fluidsthatinadvertentlyleadstoa‘thickening’ofthe blood, reducing the efficiency of circulation and gas eliminationandinducingbubblecoalescence.Oneway to monitor your hydration level is to observe the colourofyoururine itshouldbevirtuallycolourless. If it’s dark or cloudy, you’re dehydrated! It has been recommendedthatdiversdrink500mlofwaterbefore and after a dive to maintain adequate levels lost throughdiving

6.ALCOHOL

Alcoholisadiureticandinducesbodyfluidloss.Itis also a vascular dilator, causing peripheral blood vessels to expand, increasing blood flow, nitrogen absorption,andheatloss.Italsoreducesbloodserum surface tension, which can cause bubbles to form more easily. Alcohol also appears to reduce surface tension in bubbles that might remain too small to causeDCS.NeurologicalDCSseemstobetheprimary ‘target’ofdehydrationandalcoholabuse.Itisoneof themostsevereandcommontypesofDCSweseein thechamber.Afewsocialdrinkscanbefunthenight before,butnoonewantstodivehungover.

7.ADAPTATION

Repetitive recent exposure to scuba diving has been showntoreducethelikelihoodofDCS.Itisbelieved that frequent diving removes the naturally occurring gas nuclei that are precursors to bubble formation. Regeneration times for these classes of micronuclei are estimated to be near a week, so a lay off of this periodputsyoubackatsquareone.

Detached ‘Active Hydrophobic Spot’ microbubbles stripawaythephospholipidAHScellstructureinour blood vessels which may also contribute to acclimation in repetitive diving. A rest day is recommendedafter3 daysofcontinuousdiving.

8.DRUGUSE

The many variables in diving complicate drug use. Quite apart from the unknown effect of many therapeuticdrugsinthehyperbaricenvironment,itis often the condition for which these drugs are taken thatrendersdivingunwise.DrugscanaffectDCSrisk, particularly if they impact circulation or blood chemistry.Sedativescanaggravatenitrogennarcosis, whilst stimulants, excessive caffeine, decongestants, and many weight loss products, can cause fatal arrhythmias of the heart, provoke heart attacks, and may precipitate oxygen seizures. So, generally speaking, all drugs affecting the central nervous system,theautonomicnervoussystem,andtheheart arecontra indicatedindiving.

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