Based upon a quick Google search, I believe the answer is yes, according to this
article in
The Internet Journal of Pulmonary Medicine. 38,000' appears to the maximum altitude allowed for commercial airliners.
..."When one is breathing pure O2 at 33,700 ft, the partial pressure of O2 in the alveoli is the same as the pressure at SL when breathing air. Above 34,000 ft, the partial pressure of O2 in the lungs begins to fall below the pressure at SL, even though 100 % O2 is breathed. At altitudes greater than 40,000 ft, the partial pressure of O2 decreases rapidly and falls below the limit that maintains the body in a physiologically safe condition."
..."Cabin pressurization in modern aircraft ensures that the effective altitude to which occupants are exposed is much lower than that at which the aircraft is flying. Commercial aircraft are not pressurized to sea level but to a relatively modest intermediate cabin altitude. This allows the aircraft to fly at much higher altitudes, which is fuel efficient for jet engines and more comfortable since it avoids much turbulence. Aircraft cabin altitude can thus approach 2438 m (8000 ft) while the aircraft is flying at 11,582 m (38,000 ft). Therefore, a pressure differential exists across the cabin wall, commonly of up to 9 pounds per square inch (psi). International aviation regulations stipulate that, at a plane's maximum cruising altitude, the cabin pressure should not exceed 2438 m (8000 ft). This may be exceeded in emergencies. (5)
In the event of failure of the cabin pressurization system at high altitude, all occupants would require supplemental oxygen to prevent an unacceptable degree of hypoxemia. Commercial aircraft are thus equipped with an emergency oxygen system for passengers, demonstrated before each flight in accordance with civil aviation regulations. However, some passengers with impaired respiratory function may be unusually susceptible to the effects of ascent even to normal cabin altitudes. (6)"By the time normal cabin pressure is restored in 6 hours, I would expect to see many passengers in varying degrees of respiratory distress.
