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