SMALL-AMPLITUDE PRESSURE OSCILLATIONS DO NOT MODIFY RESPIRATORY MECHANICS IN RABBITS

Small-amplitude pressure oscillations do not modify respiratory mechan ics in rabbits. J. Appl. Physiol. 76(3): 1011-1013, 1994. - Changes in respiratory mechanics have occasionally been observed during high-fre quency ventilation. In this study we investigated whether small pressu re oscillations such as those used for respiratory impedance measureme nts modified total respiratory resistance (Rrs) and total respiratory elastance (Ers). The latter were measured in six paralyzed artificiall y ventilated rabbits with and without superimposed pressure oscillatio ns at the airway opening. Rrs and Ers were obtained by least square fi tting of low-pass filtered tracheal pressure and flow to the usual fir st-order model. Pressure oscillations of 2-4 hPa peak-to-peak at 10, 2 0, and 30 Hz applied for periods of 10 min had virtually no effect on Ers (changes ranging from -2.5 to 2.6%) and Rrs (0-8.2%). Analysis of variance did not show a significant difference on the pooled data. Pre ssure oscillations were also applied every other minute after a histam ine aerosol. Ers and Rrs were similarly unchanged. We conclude that th e small pressure oscillations used in respiratory impedance measuremen ts do not modify lung mechanical properties and lung response to bronc homotor agents.