Enhanced photoacoustic gas analyser (Innocor) for multiple breath washout. Improvements to analyser response time maintains accuracy at fast ventilation rates, and produces a system that meets all washout technology performance targets

Objectives: The Innocor device contains a highly sensitive photoacoustic analyserwhich allows multiple breath washout (MBW) measurements using very lowconcentrations of the tracer gas SF6. Previously, use in smaller subjects has beenrestricted by the need for an analyser response time<100ms to ensure accurateestimation of lung volumes at rapid ventilation rates. Here we report the effect ofresponse time improvements.
Methods: A series of previously reported and novel enhancements were made tothe analyser to produce a clinically practical system with a reduced response time.An enhanced lung model was constructed delivering highly accurate ventilationrates and volumes. This was used to assessin vitroaccuracy of volume calculation,and the effects of flow and gas signal alignment.
Results: 10−90% rise time was reduced from 154 to 88ms. In an adult/child lungmodel, accuracy of volume calculation was −0.9 to 2.9% for all measurements,including at a ventilation rate of 30/min and lung volume 0.5L; for the un-enhancedsystem, accuracy deteriorated at higher ventilation rates and smaller lung volumes.In a separate small volume lung model (ventilation rate 60/min, lung volume 250ml,tidal volume 100ml), mean accuracy of volume calculation for the enhanced systemwas minus 0.95% (range −3.8 to 2.0%).
Conclusion: The Innocor analyser can be enhanced to reliably generate highlyaccurate lung volume measurements down at volumes as low as those simulatinginfant lung settings. Signal alignment is a critical factor. With these enhancements,Innocor achieves all of the recent technical recommendations for MBW apparatus,including those for accuracy in infant settings.