Voice: Low Atmosphere and Pure Oxygen Effects

[VoiceQ]

What effects would 100% oxygen and low atmospheric pressure (5 psi) have on human vocal cords/speech?

From what I've read, helium produces a high pitch (vibration) effect b/c the mass of helium is much less than nitrogen; however at atmospheric pressures much greater than sea level, speech with helium becomes unintelligible. (Oxygen is slightly greater in mass than nitrogen.)

[canalon]

I have no idea, but I would not recommend it as pure oxygen would probably not do much good to your lungs.