Disappearance of isocapnic buffering period during increasing work rate exercise at high altitude

BackgroundAt sea level, ventilation kinetics are characterized during a ramp exercise by three progressively steeper slopes, the first from the beginning of exercise to anaerobic threshold, the second from anaerobic threshold to respiratory compensation point, and the third from respiratory compensation point to peak exercise. In the second ventilation phase, body CO2 stores are used to buffer acidosis owing to lactate production; it has been suggested that this extra CO2 production drives the ventilation increase. At high altitude, ventilation increases owing to hypoxia. We hypothesize that ventilation increase reduces body CO2 stores affecting ventilation kinetics during exercise.DesignIn eight healthy participants, we studied the ventilation kinetics during an exercise performed at sea level and at high altitude (4559 m).MethodsWe used 30 W/2 min step incremental protocol both at sea level and high altitude. Tests were done on a cycloergometer with breath-by-breath ventilation and inspiratory and expir...