Oxygen irritates the lungs full stop - it's not the fact that you are asthmatic which will make this happen - it's the fact that you are a human and designed to breathe O2 at surafce pressures. See this, amongst many papers - it's not great but it is the first I googled and it sets out the basic facts.
http://medind.nic.in/jac/t03/i3/jact03i3p234.pdf Quote:
(B) Pulmonary toxicity – ‘Smith effect’
Pulmonary effects of oxygen toxicity can occur after
a prolonged exposure to oxygen > 0.5 ATA. Symptoms
appear after a latent period whose duration decreases
with increase in pO2. In normal humans, the first signs
of toxicity appear after 10 hours of oxygen at 1 ATA6.
Pathology and pathophysiology
Prolonged and/or high concentrations of oxygen may
damage the pulmonary epithelium, and inactivate the
surfactant, form intra-alveloar oedema and interstitial
thickening, and later fibrosis, leading to pulmonary
atelectasis5,11. The lung lesions resemble those of paraquat
poisoning12. |
I have asthma and dive with extended period of O2 dceo when necessary. I follow unammended protocols on air breaks and have never had a problem.