There are plenty of effects on the body of chronic exposure to high altitude, but I don't think they are relevant here.
Firstly, altitude effects in the normal individual are not generally thought to occur until above 2,600m or roughly your 8,000ft cabin altitude, so forget blood changes or anything like that for this reason alone. Secondly, the exposure is not 'long-term', it's just a few hours at a time. To get deleterious altitude effects you need to go up and stay up. This is why acclimatising climbers sleep lower than they climb during the day.
The level of oxygen in your blood changes continually from breath to breath and, unless you were being monitored at the time, the level at say 1000 hrs yesterday cannot be determined at 1000 hrs today.
True in only a limited sense and not really relevant. The changes are tiny and if you had a normal arterial oxygen tension at rest at sea level in a healthy state yesterday you will have one today too, assuming nothing has changed.
Overall, exposure to 8,000ft cabin altitudes, per se, is highly unlikely to be a cause of occupational illness.
QDM