Originally Posted by Internaut
I'm sure I remember reading recently that DVT is more about the quality of air in the aircraft than the air pressure. I've recently heard rumours that some airlines have been reducing the quality of air in cabin to save energy (by reducing the number of times it gets recycled). I can well believe this because recently, I can't do a long haul flight without turning into the "snot monster" (usually corrected with a few Whiskeys)!
I am fairly certain that neither cabin pressure nor air quality have anything to do with thrombosis, not as far as I know. People living at higher altitudes are not at greater risk for thrombosis, and neither are people who live in polluted cities such as Hosuton, Los Angeles or Johannesburg.
It has everything to do with lack of mobility, blood clotting and some other predisposing factors such as use of oral contraceptives, obescity and smoking.
One has to remember that simply developing a pathologic blood clot (thrombis) will not in itself lead to death or severe morbidity. It also will not happen in a healthy person within the span of one long-haul flight. There are predisposing factors (see above), and the formation of a clot severe enough to cause complications will develop over time. The complications only occur when the thrombis blocks a blood vessel or, more seriously, leads to pulmonary embolism. It is certainly is possible that an embolism can form during flight or periods of inactivity, but people should not overexaggerate the connection between flying and thrombosis/embolism.
Smokers and overweight people should think about those issues before whether choosing between first or economy class.