Effects of the nasal passage on forced oscillation lung function measurements

The forced oscillation technique (FOT) is a non-invasive pulmonary function test which is based on the measurement of respiratory impedance. Recently, promising results were obtained by the application of FOT on patients with respiratory failure and obstructive sleep apnea (OSA). By using a nasal mask instead of a mouthpiece, the influences of the nasal passage and upper shunt alter the measured mechanical impedance. In this paper, we investigated the effects of the nasal passage and mask on FOT measurements from eight healthy subjects. A method for flow correction has been developed, which contains a pressure-flow characteristics compensation of the undetermined flow leakage at the face-mask interface. Impedance calculation and parameter estimation were performed in the frequency domain using fast Fourier transform (FFT). Average nasal parameters were Rnaw=4.07 cmH2O/l/s for resistance and Lnaw=0.0183 cmH2O/l/s2 for inertance. On average, the nasal resistance corresponds to 65.85% of the total resistance.