Errors in Pneumotachography with Intermittent Positive Pressure Ventilation

Abstract

Instrument errors that can occur when pneumotachography is used during Intermittent Positive Pressure Ventilation (IPPV) have been described previously (Kafer 1973). Our efforts to eliminate these errors led to the discovery of further inaccuracies, which appear to be due to the design of the differential pressure transducers used with the pneumotachograph head. A system was used in which a sine-wave pump delivered a constant tidal volume to a dummy lung, the tidal volume being measured by means of a pneumotachograph. Using Grass, Statham and Devices differential pressure transducers, the volume recorded as leaving the dummy lung was consistently greater than that recorded as entering, and changing the pneumatic polarity of the differential pressure transducer produced large differences in the recorded volume. In some cases the error was greater than the volume being measured. There would seem to be several causes of such errors. The Sanborn 270 differential pressure transducer and the Greer micro manometer appeared to be free of these artifacts. The results of this study throw into doubt much previously published work using pneumotachography during I P PV.

Measurement Errors in Pneumotachography Due to Pressure Transducer Design

“…* The volume of the model lung (800 ml) was chosen so that the linear range of the pneumotachograph was not exceeded during the tests. The Greer Micromanometer Model M3t has been shown (Abrahams et al 1975) for the conditions encountered during IPPV.…”

“…We have previously shown (Abrahams et al 1975) that many differential pressure transducers cause serious flow measuring error when used under the conditions of pneumotachography with IPPV. 'Ve have now carried out extensive testing on one of these transducers-the Devices UPl.…”

“…In a more recent paper (Abrahams et al 1975), we investigated the magnitude of the instrument errors which may occur when pneumotachography is used in conjunction with IPPV. Using a model lung, Fleisch pneumotachographs and various differential pressure transducers, we tabulated the instrument errors for a range of positive pressures over a wide range of respiratory frequencies.…”

Ambulatory monitoring promises equitable personalized healthcare delivery in underrepresented patients

“…Traditional TV estimation methods incorporate a spirometer or pneumotachometer that is physically attached to the mouth or nose of the patient, making it highly inconvenient for ambulatory measurement. While newer techniques for TV measurement including pitot tubes, 39 ultrasonic airflow meters, 38 respiratory inductance plethysmography, 39 electrical impedance tomography, 40 differential pressure pneumatachographs, 41 and impedance pneumography 42 have been suggested, these techniques require specialized hardware and have restricted telehealth application. Furthermore, the accuracy of pneumotachographs in TV estimation is limited 43 and most of these techniques are inadequate in detecting dynamic respiratory events such as apnoeas.…”