An example of data obtained using the flow resistance method for determining inhaled helium concentrations, taken for the Hi-Ox mask supplied with 10 l/min of 78/22% helium/oxygen (He/O
), while ventilating at 30 breaths/min with a tidal volume of 500 ml and a ratio t
of 1/2. Each curve is an average of data obtained over seven consecutive breaths. Also shown is a representative trace showing the inspiratory flow pattern.