Influence of waveform and analysis technique on lung and chest wall properties

Abstract

To test an approach for measuring respiratory system resistance (R) and elastance (E) during non-sidusoidal forcing, we measured airway and esophageal pressures and flow at the trachea of 9 anesthetized-paralyzed dogs during sinusoidal forcing (SF) and 4 types of non-sinusoidal forcings at 0.15 and 0.6 Hz and 300 ml tidal volume. During SF, calculations of E and of R of the lungs, chest wall or total system from discrete Fourier transform (DFT) and two other widely used methods (multiple regression and volume-pressure loop analysis) did not differ from each other (P>0.05). During forcing with sinusoidal or step inspiration with passive expiration (inspiratory to expiratory ration, I E, = 1:1), Es from any analysis method were within 10% of values during SP. Although 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 values of R during non-SF that differed (P<0.05) from those during SF by up to 77%, If I/E was change to 1:2, with or without an added 10% inspiratory 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 similar to controls, despite large increases in E and R of the lungs. We conlude that E and R of the lungs and chest wall can be measured by DFT using non-sinusoidal forcing waveforms available on most clinical ventilators, incurring only modest error. © 1994.