In most planes, there isn't exactly a "recycled air" problem. Planes leak like sieves. The cabin pressure is maintained by bleed air or, in the case of piston engines, turbocharger air, which is brought in from the outside world and compressed/conditioned. The actual number of air changes per hour in an aircraft is substantially higher than in an operating room. (of course, there are more people in an aircraft, and no amount of air changes will keep some shmo from sneezing on you)