This study investigated the persistence of adaptation to intermittent normobaric hypoxic exposures (IHE) of three hours each day for three consecutive days to a sea-level barometric pressure atmosphere with an oxygen fraction simulating the partial pressure of oxygen found at 4,300 m altitude. End-tidal CO2 (PEtCO2), Acute Mountain Sickness scores (AMS-C), Heart Rate (HR), Blood Oxygen Saturation (SaO2) and Mood State were measured before and after all exposures to this simulated 4,300 m altitude. PEtCO2, the hallmark of adaptation to high altitude, was reduced after the three days of acclimation and remained reduced after 24 hours but returned to control values by 48 hours post IHE. The results of this study suggest that decay of IHE acclimation to a simulated altitude of 4,300 m is substantially complete between 24 and 48 hours after the last three hour exposure to a simulated altitude of 4,300 m
