[Fred Brackin]

Questions about the specific mechanism of the atmosphere's problematic nature could come up.

For example, a common effect of a higher than usual CO2 level is stimulating the lungs to take more breaths per minute to compensate. This might mix badly with increased pressure and lead to some sort of repiratory difficulty while still being tolerable at lower pressures.

Without knowing the ipp of oxygen it's really hard to suggest possibilities. If the atmosphere was only 70% nitrogen both the IPPs of CO2 and O2 could be above Earth-normal. Then your lungs trying to clear CO2 and that leading to too much oxygen as just one possibility.

Most of the holdover in the front of my head from doing G:Atlantis, TS:Under Pressure and G:Blue Planet is the insane complexity of the subject of variant breathable atmospheres and the ways in which they can be bad for you.

I probably couldn't answer your question even if I had all the data but we don't even have enough for a good start right now.