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by jwynia 3993 days ago
My ResMed S9 machine detects exhalation (configurable levels) and backs off of the pressure. The mask that I wear (covers mouth and nose) has small holes that vent both exhalation and the pressurized air. The air flow out of those holes is relatively stable during both inhale and exhale, with the machine adjusting pressure to keep fresh air flowing through the mask and maintaining the pressure.