Viagra: good or bad for the diver?

By Caren Liebscher

It is quite possible that some men in their 40s, 50s or 60s take viagra and are also divers. These should be warned that taking viagra before diving is likely to increase the risk of DCS, while this drug may be a cure if taken afterwards.

When researchers decide to administer drugs to small rodents and then put them into a hyperbaric chamber, the divers know the researchers hope to find a cure for decompression sickness. But such a study attracts even more attention when the drug in question is Viagra, which is well-known.

The active substance in Viagra, perhaps less well known, is sildenafil. This was originally tested as a drug against hypertension. Its beneficial effects on male sexuality were sort of a side effect, which was subsequently marketed widely by Pfizer, as we all know.

Today, sildenafil is an approved treatment for pulmonary hypertension and other vascular diseases. It has also been used off the leaflet to treat pulmonary immersion edema (SIPE, swimming induced pulmonary edema) in triathletes. The main difference with Viagra is its administration in a lower dose.

Inhibitors of PDE5, exogenous and endogenous NO, vasodilation

Generally speaking, sildenafil acts on the endothelium or inner wall of blood vessels and dilates them by simply enhancing the vasodilator effect on the relaxation of smooth muscles. This phenomenon involves the inhibition of an enzyme called phosphodiesterase type 5 (PDE5). Sildenafil can therefore be defined as a PDE5 inhibitor. It produces a drop in blood pressure by dilating the blood vessels. This is a similar effect to that of nitric oxide (NO), which also produces vasodilation. This is why scientists thought that a vasodilator such as sildenafil (or viagra) could protect divers against decompression sickness (DCS). MDD develops from bubbles forming at micronuclei present in blood vessels after decompression. However, substances that release NO have the ability to reduce this bubble formation and therefore prevent serious forms of private label.

Sildenafil Preventive Treatment Study

However, all hopes for a new cure for private label collapsed when scientists - Blatteau, Brubakk, Gempp, Castagna, Risso and Vallée - examined the effect of preventative treatment with sildenafil in an animal model and found that not only did it not protect against private label, but on the contrary it could be harmful and divers should be warned.

In order to assess the clinical effects of sildenafil, the researchers administered it as a preventive treatment to small rodents at a dose of 10 mg / kg one hour before exposure. They then placed the rodents in a hyperbaric chamber and simulated a 90 m deep dive for 45 min before performing a stepwise decompression. Half an hour after the dive, they assessed the symptoms of neurological MDD, the level of blood cells and the level of bubbles circulating in the right chamber of the heart. The control group did not receive sildenafil, but the same volume of water, before diving under identical conditions.

Negative results

As noted above, the scientists' hopes were refuted: there were more cases of MDD in the group that received sildenafil than in the control group that received no treatment. In addition, they observed a reduction in the level of blood platelets in the group with sildenafil, a biological marker of decompression stress. This is because in MDD gas bubbles damage the vascular endothelium and cause an inflammatory reaction resulting in activation of leukocytes. The latter transmigrate into the vascular endothelium after MDD, which explains the decrease in the level of leukocytes observed by researchers.

Beneficial effects in the swimmer

Although these results seem disappointing with regard to MDD, let us not forget to mention the beneficial effects of sildenafil on immersion pulmonary edema (SIPE) among triathletes, in whom a reduction in blood pressure has been observed. symptoms of SIPE when the drug was taken before the onset of activity. Although it is also a water sport, swimming is very different from scuba diving. The main difference is the greater depths and higher pressures achieved while diving. What may have a beneficial effect in one activity may be detrimental in the other.

How to explain these facts?

According to the researchers, the increased risk of MDD after taking sildenafil before diving is explained by the increased cerebral blood flow caused by the vasodilator effect of sildenafil in the central nervous system, which is accompanied by a much higher load of inert gas when exposed to higher pressures. This could result in increased bubble formation that can cause severe DC in neurological tissue.

What is the current knowledge on this subject?

Sildenafil and nitric oxide (NO), whether endogenous or exogenous, are both potent vasodilators. In studies of preventative treatments, NO has been shown to be an effective substance against DCS. But that doesn't mean that taking any vasodilator reduces the risk of DCS. There is certainly a difference between endogenous / exogenous NO donors and a drug like the PDE5 inhibitor sildenafil. An endogenous NO donor is released following exercise, while an exogenous NO donor can be taken as food. In the study mentioned above, sildenafil was found to be unable to reduce bubble formation in an animal model. On the other hand, several studies on preventive treatments (see Balestra et al.) Have shown that NO reduced the formation of bubbles in rodents as well as in humans. This means that the NO donors must have properties and involve different mechanisms than those associated with sildenafil. It can therefore be thought that the presence of gaseous micronuclei on the vascular walls is not directly influenced by the vasodilator effect linked to the relaxation of smooth muscles. NO appears to have specific effects involved in reducing the number of gaseous micronuclei adhering to the surface of the endothelium. It can also diffuse towards the luminal surface of the endothelium and cause important physiological effects such as neutralization of superoxide radicals, inhibition of platelet aggregation, modulation of the permeability of the endothelial layer, as well as attenuation of leukocyte function.

Sildenafil, on the other hand, does not appear to have any of these specific effects.

A potential cure after decompression

However, what is not beneficial in one situation may be beneficial in other circumstances: increased cerebral blood flow and improved functional recovery of ischemic tissues have been shown to be beneficial in the treatment of stroke when taking sildenafil 24 hours after the onset of ischemic stroke. This raises new hope for the usefulness of sildenafil as an adjuvant (i.e. supportive) treatment for ischemic neurologic DCS in divers who have not recovered after initial treatment with ischemic disease. hyperbaric oxygen.

What can we learn from all of this?

SCUBA DIVERS:

Preventive methods such as sauna or moderate exercise are beneficial when implemented before diving. They trigger the release of endogenous NO, which neutralizes the micronuclei present on the inner wall of blood vessels, and are therefore likely to reduce the risk of MDD.

Intense physical exercise or sauna performed 24 to 48 hours after diving increases the risk of DCS, as such practices increase blood flow to most tissues and lead to increased bubble formation from the nitrogen accumulated in the body.

In animal model, sildenafil increases risk of DCS when taken before diving. (We do not know of any cases of this medication being taken by divers.)

In the event of declared MDD and treatment in a hyperbaric chamber, sildenafil may prove to be beneficial after diving and hyperbaric treatment, as it may might alleviate symptoms of neurologic DCD by increasing cerebral blood flow. This is a hypothesis based on studies of stroke in rodents, and requires further research.

SWIMMERS, TRIATHLETES AND OTHER EXTREME DISCIPLINES:

Off-label use of the medicine has shown that taking low-dose sildenafil can cure symptoms of immersion edema (SIPE) and other altitude-related illnesses.

Disclaimer

The researchers in this study concluded that preventive treatment with sildenafil (Viagra), or other drugs with similar action (PDE5 inhibitors), promoted the onset and worsened neurological MDD. This is an important finding that needs to be shared among the diving community.

When taking medication while scuba diving, it is always necessary to consult your (diving) doctor beforehand. Especially if it is viagra. Indeed, it is important to clarify the possible interactions with other drugs and the interference with other underlying diseases in the context of diving.

The future will tell us more ...

Research has shown that further studies on markers of oxidative stress in the central nervous system are needed to better understand the mechanisms underlying sildenafil in DCS.