Abstract
During conventional ventilation, tidal volume (VT) can be measured from variations in the transthoracic impedance (TTI) signal. The purpose of this study was to determine if TTI could be used to measure VT during high frequency ventilation (HFV), thus providing a non-invasive technique which can be applied continuously during HFV of human infants. VT was measured in 2 lambs (3-4 weeks old) placed in a whole-body, pressure-compensated, integrated flow plethysmograph during HFV provided by a flow-interrupter (Bird VDR). The frequency response of the plethysmograph was flat up to 20 Hz. TTI was measured from a tetrapolar disk electrode system (SAAB Respimeter). The impedance signal and the calibrated plethysmograph volume signal were recorded. A computer averaging technique was used to extract the high frequency VT component of each signal from background volume changes associated with spontaneous breathing. Magnitude in ohms of the extracted TTI waveform (VTZ) was compared with the corresponding plethysmographic volume change (VTp1). 54 simultaneous measurements of VTp1 and VTZ were made at frequencies varied between 300-900 breaths per minute and at VT between 2.8 and 90 ml. VTZ had a close linear correlation with VTp1 (r=0.99). These results indicate that the frequency response of VTZ is sufficient to apply the technique to HFV and that measurement of absolute VT at high frequency can be provided by calibrating the impedance signal during low-rate conventional ventilation.
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Sandberg, K., Krueger, E., Lindstrom, D. et al. 1826 TRANSTHORACIC IMPEDANCE AS A METHOD OF MEASURING TIDAL VOLUME DURING HIGH FREQUENCY VENTILATION. Pediatr Res 19, 415 (1985). https://doi.org/10.1203/00006450-198504000-01844
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DOI: https://doi.org/10.1203/00006450-198504000-01844