Viagra and diving: Risk reduction

Viagra tablet
(Audrey Disse)

Awareness is everything in diving, and BOB COLE has advice for divers who, for whatever reason, take PDE5 inhibitors

I recently met an old friend who, because of a heart condition and hypertension, no longer dives. He told me that he had been prescribed sildenafil (sold as Viagra) to open up his blood vessels and get more blood to his heart.

This medication has the effect of increasing blood flow (perfusion) not only to the heart but to other places too – and that does not fit well with diving.

Researchers have concluded that the use of sildenafil and other drugs with similar effects (PDE5 inhibitors) can, by dilating the blood vesels, promote the onset of decompression illness (DCI).

Wider blood vessels not only increase blood/oxygen delivery but in the process allow more inert gas to be taken up by the diver’s body – possibly exceeding the inert gas design limits of your dive computer or tables.

This means that you’re off the map and effectively unable to determine your decompression obligation accurately. The designer of your computer’s decompression algorithm would not have taken Viagra into account, so you’re likely to find yourself on the wrong side of safety.

Case studies

I tried to find reported cases of DCI in the British Sub-Aqua Club’s national Annual Diving Incident Reports, but could find none. 

It was no different back in 1994 when doctors Wilmshurst, Davidson, O’Connell and Byrne reported the link between neurological DCI and the heart condition patent foramen ovale (PFO) – the small hole that can be left from birth between the two upper chambers of the heart. 

There were no reports of unexplained cases of DCI linked to PFOs either, and many people at the time were sceptical about the potential for a link, including some hyperbaric doctors. Not any more.

It could be beneficial – and would certainly do no harm – to be cautious and take steps to reduce your potential risk of a DCI hit caused by Viagra. 

Know when to stop

If you are taking Viagra for a heart condition you should NOT be diving unless you have a positive diving medical certificate from a cardiologist with experience of diving, and a hyperbaric doctor. 

For those using Viagra purely in connection with erectile disfunction, no clear message is provided by researchers as to when to stop taking the drug and go diving. However, such users should contact a diving medical referee rather than their GP, because it would be wise to be checked out properly and, one hopes, obtain the answer yes, it’s OK to dive. 

However, bear in mind that the half-life of sildenafil (Viagra) is 4 hours, vardenafil (Levitra) 4-6 hours and tadalafil (Cialis) 17.5 hours, meaning that the strength of the drug has reduced by 50% only by the end of the period shown. 

To completely clear these drugs from your system takes six half-lives: that means for Viagra 24 hours, Levitra 36 hours and Cialis 105 hours.

Micro-bubble reduction

Recent research has shown that taking a sauna and light exercise no closer than 24 hours before diving is beneficial in reducing the risk of DCI. It seems that it causes a release of endogenous nitric oxide (NO), which helps to clean out micro-bubbles from the inner surface (endothelium) of your blood vessels. 

On the other hand, taking heavy exercise or a sauna within 48 hours after diving increases the risk of DCI, and this also includes snorkelling between dives and after diving. The reason for this is the increase in  perfusion in many of your bodily tissues, which leads to increased micro-bubble formation during the off-gassing of nitrogen and/or helium. 

Your best move is to be like me: I’m a lounge lizard. I rest in a soft chair out of direct sunlight, do as little as possible and sup a soft drink or two. 

This is simple advice that my dive-buddy Johnny Jones failed to follow in Belize. The result? A massive skin bend in the form of bright red rings on his stomach and the loss of four days’ diving – expensive! 

Note that skin bends are often associated with PFOs, so a diver should get advice from a diving medical referee if one occurs. It is also recommended that the possibility of a PFO be considered following an inner ear or significant neurological DCI.

The usual warning

A number of drugs, whether prescribed by a doctor or over the counter (OTC), can affect your blood flow, and that is not good when you go diving. 

My tip: seek the advice of a UKDMC medical referee (not your GP) as to whether particular prescription or OTC medications, other than the contraceptive pill, are suitable for diving. 

This is especially true for Viagra. Also check for possible interactions with other drugs, and the possible effects on underlying diseases of diving at pressure should always be discussed and clarified upfront.

Having a general understanding of gas movement through the body is important for divers. Perfusion is the key to this understanding, but it is equally important to identify what it is that might increase or reduce blood flow. 

When you plan your diving, take into account all aspects that might cause your perfusion rates to move outside the upper and lower limits set by the algorithm of the computer or tables you’re using. 

This means assessing your work-rate, skin-cooling, breathing patterns and micro-bubble generation; then adjusting your behaviour, computer settings or both to mitigate the additional risk. If tables are your preferred decompression guide, you might need to adjust their use in accordance with the rules of your chosen system.

Your decompression health is also linked to your diving skills. Keep in mind that the most difficult part of your dive profile to control correctly is the ascent. 

The ascent is, potentially, the most dangerous time during any dive. For some, the required skills are used only during the annual summer holiday, so time taken to brush up on them is worthwhile.

Viagra and oxygen toxicity

Divers Alert Network funded a study into the risk of O2 toxicity in rats, to find out whether Viagra would cause an O2 hit because of increased blood flow in the brain. Dr Ivan Demchenko and his team at Duke University concluded that the onset of O2 toxicity in rats given Viagra was faster than in those not given the drug. 

I know a few rats that dive, but I’m sure they weren’t used in this study. However, this is an important pointer to what not to do when diving. 

Also on Divernet: Viagra: Curse Or Blessing For Divers?

Bob Cole on deck of boat
Bob Cole on deck of boat

Bob Cole left school at Easter 1955, took a week off and started work. At a London open-air pool he bumped into a man with an Aqualung. On exiting the water 45 minutes later, he was told that surgery would be the only way to remove the smile from his face. He hasn’t stopped diving since.

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