Sport Diver - - Contents -

Monty Halls takes his fam­ily to the world-fa­mous Wakatobi Dive Re­sort.

Dr Oliver Firth has gained con­sid­er­able ex­pe­ri­ence in the field of div­ing and hy­per­baric medicine since join­ing LDC in 2006. He is an Ap­proved Med­i­cal Ex­am­iner of Divers for the UK HSE, and a med­i­cal ref­eree for the UK Sport Div­ing Med­i­cal Com­mit­tee. He is in­volved in the man­age­ment of all types of div­ing-re­lated ill­ness, in­clud­ing re­com­pres­sion treat­ment, as well as pro­vid­ing hy­per­baric oxy­gen ther­apy for non-div­ing con­di­tions. He re­mains a pas­sion­ate diver and has par­tic­i­pated in var­i­ous ex­pe­di­tions and con­ser­va­tion projects through­out the globe.

Q: I’ve been ad­vised to con­tact you by my dive in­struc­tor about some strange symp­toms which oc­curred whilst I was div­ing a few days ago. Dur­ing my first dive, at about 21m, I started to feel odd and then ef­fec­tively ‘fainted’, for a few min­utes. I had no vi­sion or mem­ory dur­ing this time. My in­struc­tor was with me and brought me to the sur­face. Dur­ing the as­cent I re­gained my senses, so we de­cided it could have been brought on by ni­tro­gen nar­co­sis. The same thing hap­pened on a sub­se­quent dive, but I was un­able to fo­cus or con­cen­trate and did not feel my­self even dur­ing the safety stop at the end of the dive. We de­cided per­haps it was due to oxy­gen star­va­tion, as I typ­i­cally breathe very lightly. Since then I have made a con­scious ef­fort to breathe more slowly and deeply and have felt fine, at sim­i­lar depths. I take no med­i­ca­tion, and am in good health as far as I am aware.

A: Ac­tu­ally, rather than it be­ing a lack of oxy­gen, I think the most likely ex­pla­na­tion for this is an ex­cess of an­other, of­ten over­looked, gas: car­bon diox­ide (CO2). As well as be­ing very use­ful in the fizzy drinks world, CO2 is the end prod­uct of cel­lu­lar res­pi­ra­tion, but is hand­ily used by pho­to­syn­the­sis­ing or­gan­isms to pro­duce oxy­gen. In the div­ing world, the fo­cus on ni­tro­gen nar­co­sis of­ten diverts at­ten­tion from the fact that CO2 is many times more nar­cotic, and even small in­creases in blood lev­els can cause po­ten­tially dan­ger­ous symp­toms of this sort. Ini­tially, mod­est rises in CO2 lev­els sig­nif­i­cantly re­duce cog­ni­tive per­for­mance, eg. sim­ple arith­metic and colour nam­ing, as well as phys­i­cal skills, eg. manual dex­ter­ity and hand-eye co-or­di­na­tion. So nar­co­sis is not al­ways due to ni­tro­gen… Fur­ther in­creases in CO2 cause dizzi­ness, headaches, nausea and even­tu­ally loss of con­scious­ness. Or­di­nar­ily, ris­ing CO2 lev­els stim­u­late the res­pi­ra­tory cen­tres in the brain, giv­ing rise to the sen­sa­tion of breath­less­ness and trig­ger­ing hy­per­ven­ti­la­tion. Para­dox­i­cally, how­ever, when CO2 lev­els get to the point of af­fect­ing con­scious­ness, they act as a res­pi­ra­tory de­pres­sant, re­duc­ing lung ven­ti­la­tion and there­fore caus­ing fur­ther CO2 re­ten­tion. At this point a down­ward spi­ral is dif­fi­cult to avoid. So the trick is ob­vi­ously to avoid get­ting to this point in the first place. As­cent, avoid­ance or re­duc­tion of stren­u­ous phys­i­cal ef­fort, and slow/mea­sured breathing rates should re­duce the risk of CO2 buildup.

Q: I need to do a PADI re­fresher course be­fore I go to Barbados next year. I have my advanced Open Wa­ter Div­ing cer­ti­fi­ca­tion, but I also have a query. I have mild bronchiec­ta­sis which I have had for about 16 years. I am told my lung ca­pac­ity is good for my height and age, and I do a lot of al­ti­tude hik­ing with no prob­lems. But my res­pi­ra­tory con­sul­tant has said I should get advice about whether it is OK for me to dive again, and if so whether I should re­strict this to 12m, or go for 45m. I con­trol ex­ac­er­ba­tions by tak­ing Azithromycin on a reg­u­lar ba­sis. Can you ad­vise please?

A: As I’m sure you are aware, bronchiec­ta­sis is char­ac­terised by per­ma­nent en­large­ment of parts of the air­ways of the lung, with vari­able symp­toms in­clud­ing breath­less­ness, mu­cus pro­duc­tion, chest pains, cough­ing up blood, and fre­quent lung in­fec­tions. The div­ing-spe­cific risks pri­mar­ily in­volve trap­ping of air in the af­fected lung tis­sue, which can cause lung dam­age on as­cent as the gas ex­pands. For these rea­sons most physi­cians would not rec­om­mend div­ing with the con­di­tion once it be­comes symp­to­matic or im­pairs lung func­tion. How­ever, in very mild cases, with no ab­nor­mal­i­ties on lung func­tion test­ing, then care­ful and con­trolled div­ing might still be pos­si­ble. I don’t per­son­ally be­lieve in ar­bi­trary depth re­stric­tions, but I would ad­vise keep­ing dives on the shal­lower end of the spec­trum.

For more Q&AS from Dr Oli, check out: www.sport­diver.co.uk/dive­doc­tor

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