Measurement of dead-space in a model lung using an oscillating inspired argon signal

In a model lung, airways dead-space can be accurately measured using a forced inspired oscillating argon signal, which varies sinusoidally about a mean concentration of 6% v/v with an amplitude of +/- 4% v/v. With sinusoid forcing periods longer than 120 seconds, and at a breathing rate of 13.4 breaths minute-1, the mean airways dead-space can be measured with a standard error of less than 5%. Sinusoid forcing periods shorter than 120 s provided inaccurate estimates of dead-space and so should not be used with this technique.