You have to be prepared to take risks in order to fulfil your potential, and fins out where your limits really are. Once you start entering the harder ultras, it is only a matter of time before you get a DNF, and with the very hardest races, you might make a calculation to try them knowing that the odds are against you.
Here is some information on a mountaineering website about altitude coughs:
Many people who travel to high altitude complain of cough. It is a dry debilitating cough and its consequences, aside from interfering with climbing and sleeping can be severe. On the 1971 International Himalayan Expedition no less than four members suffered rib fractures because of their cough.
Altitude cough may be due to bronchoconstriction (the narrowing of the airways that commonly occurs in asthma) or infections, but research has shown that the cough can occur without any evidence of infection or airway narrowing.
Cough could be caused by breathing cold dry air on the mountains, but studies of cough in hypobaric chambers that controlled the ambient temperature and humidity suggest that the receptors in the airways that provoke cough are actually more sensitive at altitude.
What might make cough receptors more sensitive? Three possible theories exist. Firstly, inflammation in the airways at high altitude may increase the receptor sensitivity. Secondly, changes in the brain caused by acclimatisation could sensitise the receptors that cause cough or thirdly, there could be a build up of fluid in the lungs. Some scientists think that a small amount fluid leaks out into the air spaces in many people who go to high altitude without actually causing the symptoms and signs of HAPE. Nevertheless, a severe cough and breathlessness could represent high altitude pulmonary oedema and if suspected, urgent descent is necessary. Preventative measures include:
Wear a mask which heats and moisturizes the air.
Wear a balaclava at night.
Wear a mask with a metallic net inserted into a lightweight shell.
Avoid over exertion (Not exactly an option for us).
Regulate your breathing when necessary (Some European runners chew gum).
Drinking plenty of water, especially hot water. This gives added moisture from the steam.
Taking plenty of throat lozenges.
Wearing a balaclava at night.
If you plan on quickly climbing to a high altitude, ask your doctor about a medication called acetazolamide (Diamox). This drug helps your body get used to higher altitudes more quickly, and reduces minor symptoms. It should be taken the day before you climb, and then for the next 1 to 2 days.