In vitro assessment of equipment and software to assess tidal breathing parameters in infants

The aim of this in vitro study was to compare the measurement accuracy of t wo currently available devices for measuring tidal breathing in infants, A mechanical model pump was used to generate flow profiles which simulated th ose observed in infants. A range of flows was applied simultaneously to two different devices, namely the commercially available SensorMedics 2600 (SM 2600) and more recently developed, custom-made equipment based on the flow -through technique (FTT), Automatically derived values from both devices we re compared with one another and with manual calculations of printouts of t he same breaths. There were no differences in the raw flow signal obtained from the two devi ces, nor between values calculated automatically or manually from the FTT, Similarly, the deviations between the FTT and SM 2600,were <3% for tidal vo lume, respiratory frequency and minute ventilation. However, when comparing either with manually calculated values or those derived automatically from the FTT, there was a systematic and highly significant underestimation of shape-dependent parameters, such as the time to peak tidal expiratory from as a proportion of tidal expiratory time (tPTEF/tE), derived by the SM 2600 , The lower the applied flow, the higher the observed deviations, the under estimation being up to 60% when flows simulating those observed in preterm neonates,were applied, These errors appear to result from differences in signal processing such as the algorithms used for breath detection and can only be detected if appro priate nonsinusoidal flow profiles representing those seen in infants are u sed to evaluate equipment.