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Enhanced photoacoustic gas analyser response time and impact on accuracy at fast ventilation rates during multiple breath washout.

Horsley A, Macleod K, Gupta R, Goddard N, Bell N - PLoS ONE (2014)

Bottom Line: A series of previously reported and novel enhancements were made to the gas analyser to produce a clinically practical system with a reduced response time.Signal alignment is a critical factor.With these enhancements, the Innocor analyser exceeds key technical component recommendations for MBW apparatus.

View Article: PubMed Central - PubMed

Affiliation: Institute of Inflammation and Repair, University of Manchester, Manchester, United Kingdom; Manchester Adult Cystic Fibrosis Centre, University Hospital of South Manchester, Manchester, United Kingdom.

ABSTRACT

Background: The Innocor device contains a highly sensitive photoacoustic gas analyser that has been used to perform multiple breath washout (MBW) measurements using very low concentrations of the tracer gas SF6. Use in smaller subjects has been restricted by the requirement for a gas analyser response time of <100 ms, in order to ensure accurate estimation of lung volumes at rapid ventilation rates.

Methods: A series of previously reported and novel enhancements were made to the gas analyser to produce a clinically practical system with a reduced response time. An enhanced lung model system, capable of delivering highly accurate ventilation rates and volumes, was used to assess in vitro accuracy of functional residual capacity (FRC) volume calculation and the effects of flow and gas signal alignment on this.

Results: 10-90% rise time was reduced from 154 to 88 ms. In an adult/child lung model, accuracy of volume calculation was -0.9 to 2.9% for all measurements, including those with ventilation rate of 30/min and FRC of 0.5 L; for the un-enhanced system, accuracy deteriorated at higher ventilation rates and smaller FRC. In a separate smaller lung model (ventilation rate 60/min, FRC 250 ml, tidal volume 100 ml), mean accuracy of FRC measurement for the enhanced system was minus 0.95% (range -3.8 to 2.0%). Error sensitivity to flow and gas signal alignment was increased by ventilation rate, smaller FRC and slower analyser response time.

Conclusion: The Innocor analyser can be enhanced to reliably generate highly accurate FRC measurements down at volumes as low as those simulating infant lung settings. Signal alignment is a critical factor. With these enhancements, the Innocor analyser exceeds key technical component recommendations for MBW apparatus.

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Signal to noise profile of the Innocor gas analyser.Mean SF6 concentration versus signal to noise ratio (defined as standard deviation of the signal as a percentage of mean signal for a minimum of 2000 samples). Horizontal dotted line represents the 5% signal to noise ratio deemed acceptable from a technical point of view.
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pone-0098487-g004: Signal to noise profile of the Innocor gas analyser.Mean SF6 concentration versus signal to noise ratio (defined as standard deviation of the signal as a percentage of mean signal for a minimum of 2000 samples). Horizontal dotted line represents the 5% signal to noise ratio deemed acceptable from a technical point of view.

Mentions: SNR varied from 0.1% at a mean [SF6] of 0.18%, to 10.6% at a mean [SF6] of 0.0009%. Non-linear regression of the graph of SNR vs SF6 concentration (Figure 4) generated the equation SNR = 0.0234.x−0.842 (where x is [SF6]) with an R2 of 0.99. According to this, SNR is below 5% (the level deemed technologically acceptable) for concentrations of SF6 above 0.002% (see Figure 4).


Enhanced photoacoustic gas analyser response time and impact on accuracy at fast ventilation rates during multiple breath washout.

Horsley A, Macleod K, Gupta R, Goddard N, Bell N - PLoS ONE (2014)

Signal to noise profile of the Innocor gas analyser.Mean SF6 concentration versus signal to noise ratio (defined as standard deviation of the signal as a percentage of mean signal for a minimum of 2000 samples). Horizontal dotted line represents the 5% signal to noise ratio deemed acceptable from a technical point of view.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4043749&req=5

pone-0098487-g004: Signal to noise profile of the Innocor gas analyser.Mean SF6 concentration versus signal to noise ratio (defined as standard deviation of the signal as a percentage of mean signal for a minimum of 2000 samples). Horizontal dotted line represents the 5% signal to noise ratio deemed acceptable from a technical point of view.
Mentions: SNR varied from 0.1% at a mean [SF6] of 0.18%, to 10.6% at a mean [SF6] of 0.0009%. Non-linear regression of the graph of SNR vs SF6 concentration (Figure 4) generated the equation SNR = 0.0234.x−0.842 (where x is [SF6]) with an R2 of 0.99. According to this, SNR is below 5% (the level deemed technologically acceptable) for concentrations of SF6 above 0.002% (see Figure 4).

Bottom Line: A series of previously reported and novel enhancements were made to the gas analyser to produce a clinically practical system with a reduced response time.Signal alignment is a critical factor.With these enhancements, the Innocor analyser exceeds key technical component recommendations for MBW apparatus.

View Article: PubMed Central - PubMed

Affiliation: Institute of Inflammation and Repair, University of Manchester, Manchester, United Kingdom; Manchester Adult Cystic Fibrosis Centre, University Hospital of South Manchester, Manchester, United Kingdom.

ABSTRACT

Background: The Innocor device contains a highly sensitive photoacoustic gas analyser that has been used to perform multiple breath washout (MBW) measurements using very low concentrations of the tracer gas SF6. Use in smaller subjects has been restricted by the requirement for a gas analyser response time of <100 ms, in order to ensure accurate estimation of lung volumes at rapid ventilation rates.

Methods: A series of previously reported and novel enhancements were made to the gas analyser to produce a clinically practical system with a reduced response time. An enhanced lung model system, capable of delivering highly accurate ventilation rates and volumes, was used to assess in vitro accuracy of functional residual capacity (FRC) volume calculation and the effects of flow and gas signal alignment on this.

Results: 10-90% rise time was reduced from 154 to 88 ms. In an adult/child lung model, accuracy of volume calculation was -0.9 to 2.9% for all measurements, including those with ventilation rate of 30/min and FRC of 0.5 L; for the un-enhanced system, accuracy deteriorated at higher ventilation rates and smaller FRC. In a separate smaller lung model (ventilation rate 60/min, FRC 250 ml, tidal volume 100 ml), mean accuracy of FRC measurement for the enhanced system was minus 0.95% (range -3.8 to 2.0%). Error sensitivity to flow and gas signal alignment was increased by ventilation rate, smaller FRC and slower analyser response time.

Conclusion: The Innocor analyser can be enhanced to reliably generate highly accurate FRC measurements down at volumes as low as those simulating infant lung settings. Signal alignment is a critical factor. With these enhancements, the Innocor analyser exceeds key technical component recommendations for MBW apparatus.

Show MeSH