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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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Impact of hardware improvements on SF6 response time (T90).Aligned flow and SF6 signals are shown for a standard Innocor (T90 = 154 ms), and an improved version, labelled “Speeded SF6” (T90 = 88 ms). Double headed arrows indicate the time between 10% and 90% plateau SF6 response.
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pone-0098487-g003: Impact of hardware improvements on SF6 response time (T90).Aligned flow and SF6 signals are shown for a standard Innocor (T90 = 154 ms), and an improved version, labelled “Speeded SF6” (T90 = 88 ms). Double headed arrows indicate the time between 10% and 90% plateau SF6 response.

Mentions: The impact of the response time improvement steps is summarised in Table 2 and illustrated in Figure 3. The intrinsic response time of the PGA was 56 ms. Almost 30 ms of the total 155 ms was caused by the Oxigraf analyser. Shortening the Nafion gas sample line produced small reductions in T90, but had a more significant impact on FGD. In contrast, introduction of an optimised connector design reduced the response time by 25 ms, with relatively trivial impact on FGD. In the final system, the effect of reducing Nafion to 90 cm, removing the Oxigraf, and optimising the connections was a T90 of 88 ms. With a definitive seal to the Nafion gas sample line, this was reduced further to 85 ms. This is illustrated in Figure 3. Gas sample flow of the modified system was measured at 137 ml/min.


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)

Impact of hardware improvements on SF6 response time (T90).Aligned flow and SF6 signals are shown for a standard Innocor (T90 = 154 ms), and an improved version, labelled “Speeded SF6” (T90 = 88 ms). Double headed arrows indicate the time between 10% and 90% plateau SF6 response.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0098487-g003: Impact of hardware improvements on SF6 response time (T90).Aligned flow and SF6 signals are shown for a standard Innocor (T90 = 154 ms), and an improved version, labelled “Speeded SF6” (T90 = 88 ms). Double headed arrows indicate the time between 10% and 90% plateau SF6 response.
Mentions: The impact of the response time improvement steps is summarised in Table 2 and illustrated in Figure 3. The intrinsic response time of the PGA was 56 ms. Almost 30 ms of the total 155 ms was caused by the Oxigraf analyser. Shortening the Nafion gas sample line produced small reductions in T90, but had a more significant impact on FGD. In contrast, introduction of an optimised connector design reduced the response time by 25 ms, with relatively trivial impact on FGD. In the final system, the effect of reducing Nafion to 90 cm, removing the Oxigraf, and optimising the connections was a T90 of 88 ms. With a definitive seal to the Nafion gas sample line, this was reduced further to 85 ms. This is illustrated in Figure 3. Gas sample flow of the modified system was measured at 137 ml/min.

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