Respiratory traces of hyperoxic manipulations using the new circuit (right) vs. an oxygen mask (left). In the first row we show tests where 50% O2 and 100% O2 were administered in two different instances and in which flow rate was 15 L/min during the entire manipulation. In the second row we repeated the first experiments but increasing the flow rate to 30 L/min during 1 m:30s after transitions. Fractional concentrations are given as partial pressure with respect to an atmospheric pressure of 760 mmHg. FA = fractional concentration of administered O2; Fi = fractional concentration of inspired O2; ET model = model of the fractional concentration of expired O2; FR = flow rate.