Drugs such as Cialis or Viagra belong to a family of drugs called PDE5 inhibitors. This family of drugs may cause vasodilation in the brain and thus increase the risk of oxygen toxicity. In this DAN-funded study, researchers used an animal model to test whether animals using PDE5 inhibitor drugs would experience accelerated seizure development due to increased cerebral blood flow when compared to the control group that did not receive the drug.
This study concluded that rats treated with PDE5 inhibitors had a faster onset of CNS oxygen toxicity resulting in oxygen seizures than rats not treated with PDE5 inhibitors.
This study was completed in 2009.
DAN was contacted by a diver who experienced symptoms of oxygen toxicity after using EAN at an oxygen partial pressure of 1.3 ATA. He had done similar dives many times before without any problems. His exposure to oxygen was within limits usually considered safe, but this time he had used Cialis (a PDE-5 inhibitor) the night before his dive. These drugs cause widening of the arteries responsible for erection, but theoretically they may cross from the circulation into the brain and may increase sympathetic activity. However, it was not known whether this could affect a diver’s risk of oxygen toxicity. To explore this, DAN funded an animal study conducted by Dr. Ivan Demchenko and his team at Duke University. They demonstrated that PDE-5 inhibitors can cause vasodilatation in the brains of rats at normal and hyperbaric conditions, while untreated animals maintain vasoconstriction for some time. Because of increased blood flow in brain of animals receiving PDE-5, under hyperoxic conditions they may seize sooner than untreated animals.
The lesson for divers is that PDE-5 inhibitors, which may have lifetime from five to over 24 hours, may not be safe to use the night before diving, especially if they have prolonged exposure to gas mixes rich in oxygen like in technical and nitrox diving. Attention should be given to the effective duration of the chosen medication and the partial pressures of oxygen likely to be encountered on planned dives. The diver should discuss dive plans with a DAN medic, or a doctor trained in dive medicine.
Additional Reading and References
Publications
- Demchenko I, Ruehle A, Allen B, Vann R, Piantadosi C. Phosphodiesterase-5 inhibitors oppose hyperoxic vasoconstriction and accelerate seizure development in rats exposed to hyperbaric oxygen. J Appl Physiol. 2009; 106: 1234-42.