Years ago I drove up Pike's Peak. Summit elevation is 14,115 feet. I didn't "need" oxygen, but just walking from the car park to the concession building on a cool day resulted in fatigue and sweating.
The car I owned then had vacuum operated windshield wipers. Drove through fog/mist on the way up, and down. The wipers stopped working at around elevation 10,000 or 11,000 feet. Even at the base (which is around 7,000 feet) they were lazy. I thought they were broken -- until I got back to lower elevations and they were miraculously "fixed." I had that car for another ten years, and the wipers never gave me any problems -- as long as I stayed under 6,000 feet.