INFLUENCE OF WAVE-FORM AND ANALYSIS TECHNIQUE ON LUNG AND CHEST-WALL PROPERTIES

To test an approach for measuring respiratory system resistance (R) an d elastance (E) during non-sinusoidal forcing, we measured airway and esophageal pressures and flow at the trachea of 9 anesthetized-paralyz ed dogs during sinusoidal forcing (SF) and 4 types of non-sinusoidal f orcings at 0.15 and 0.6 Hz and 300 ml tidal volume. During SF, calcula tions of E and of R of the lungs, chest wall or total system from disc rete Fourier transform (DFT) and two other widely used methods (multip le regression and volume-pressure loop analysis) did not differ from e ach other (P>0.05). During forcing with sinusoidal or step inspiration with passive expiration (inspiratory to expiratory ratio, I/E, = 1:1) , Es from any analysis method were within 10% of values during SF. Alt hough Rs of the lungs, chest wall or total system were not affected by waveform shape with DFT (P>0.05), the other analysis methods gave val ues for R during non-SF that differed (P<0.05) from those during SF by up to 77%. If I/E was changed to 1:2, with or without an added 10% in spiratory pause, values for E and R differed least from values during SF if DFT was used. During severe pulmonary edema induced by infusion of oleic acid in the right atrium, results for lung properties were si milar to controls, despite large increases in E and R of the lungs. We conclude that E and R of the lungs and chest wall can be measured by DFT using nonsinusoidal forcing waveforms available on most clinical v entilators, incurring only modest error.