A comparison of response characteristics of airflow and pressure transducers commonly used in rhinomanometry.

Abstract

Although the ranges in which pneumotachographs evidence linear output to static flows are documented in the literature, measures of output reliability or the stability of calibration functions resulting from the input of dynamic nonsinusoidal flows (such as those which occur during nasal breathing) have not been investigated. Furthermore, it is not known whether the type of requisite pressure transducer used in conjunction with the pneumotachograph influences the pneumotachograph's linearity, output reliability, or dynamic response. To provide information on these points, we determined the dynamic and static responsiveness of three pneumotachographs commonly used in rhinomanometry, in combination with three requisite pressure transducers. In general, a) output reliability depended on the pneumotachograph/pressure transducer combination and was not readily predictable from the reliabilities of the individual components, b) heating increased pneumotachograph reliability, and c) differences in accuracy existed among transducer combinations at high, but not low, flow frequencies. In addition, results from the calibration syringe study (in which the pneumotachograph is calibrated with dynamic non-sinusoidal flows) suggested that: a) a single calibration factor, as supplied by most pneumotachograph manufacturers, is inadequate for accurately measuring the full range of flows produced in sniffing and breathing tasks; b) the measurement of complex waveforms, even when the dominate frequencies of such waveforms are low, requires pneumotachographs that accurately respond to relatively high frequencies; and c) the use of dynamic nonsinusoidal flows (as opposed to static flows) to calibrate pneumotachographs results in a calibration function with higher reliability.