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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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Accuracy of Innocor gas analyser at calculating lung volumes at different ventilation rates and volumes.Effect of increasing lung model ventilation rate on accuracy of FRC calculation from multiple breath washout for different FRC's. Effect of analyser performance is shown by comparing the speeded system (T90 88 ms) to that of the standard system (T90 154 ms). Data are shown as mean and 95% confidence interval, horizontal lines denote the 5% limits of acceptable error in FRC determination [4]. The “infant” settings at 60minute−1 refer to the smaller lung model, run on the speeded system only.
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pone-0098487-g005: Accuracy of Innocor gas analyser at calculating lung volumes at different ventilation rates and volumes.Effect of increasing lung model ventilation rate on accuracy of FRC calculation from multiple breath washout for different FRC's. Effect of analyser performance is shown by comparing the speeded system (T90 88 ms) to that of the standard system (T90 154 ms). Data are shown as mean and 95% confidence interval, horizontal lines denote the 5% limits of acceptable error in FRC determination [4]. The “infant” settings at 60minute−1 refer to the smaller lung model, run on the speeded system only.

Mentions: A minimum of 5 washouts were performed at each of three lung model ventilation rates (10–32 min−1) and three FRCs (0.5, 1 and 2 L). These were performed using the ‘speeded’ system (with a T90 of 88 ms) and repeated using the same system but with the T90 increased by addition of an extra filter (Camlab, Cambridge, UK) to the gas sample line in order to slow the rise time to 154 ms (i.e. the same as the standard Innocor setup). Since FGD was also increased by addition of the extra filter, the system-specific FGD was used for each analysis. Results are presented in Table 3. FRC accuracy is quoted as percentage of the lung tank volume, excluding the apparatus deadspace. Accuracy was good at slow ventilation rates across all three FRC volumes and in both the fast and slow T90 systems. 100% of all repeats at this rate produced an error of less than 5%. This accuracy was maintained at faster rates for the fast T90 system, where 100% of all washouts at all speeds (n = 49) generated an error in FRC of under 5% (range −0.9 to 2.9% error). For the slow T90 system however, error was greater at ventilation rate>20 min−1, and all washouts at rates >30 min−1 showed error in FRC of >5%. These data are also presented in Figure 5.


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)

Accuracy of Innocor gas analyser at calculating lung volumes at different ventilation rates and volumes.Effect of increasing lung model ventilation rate on accuracy of FRC calculation from multiple breath washout for different FRC's. Effect of analyser performance is shown by comparing the speeded system (T90 88 ms) to that of the standard system (T90 154 ms). Data are shown as mean and 95% confidence interval, horizontal lines denote the 5% limits of acceptable error in FRC determination [4]. The “infant” settings at 60minute−1 refer to the smaller lung model, run on the speeded system only.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0098487-g005: Accuracy of Innocor gas analyser at calculating lung volumes at different ventilation rates and volumes.Effect of increasing lung model ventilation rate on accuracy of FRC calculation from multiple breath washout for different FRC's. Effect of analyser performance is shown by comparing the speeded system (T90 88 ms) to that of the standard system (T90 154 ms). Data are shown as mean and 95% confidence interval, horizontal lines denote the 5% limits of acceptable error in FRC determination [4]. The “infant” settings at 60minute−1 refer to the smaller lung model, run on the speeded system only.
Mentions: A minimum of 5 washouts were performed at each of three lung model ventilation rates (10–32 min−1) and three FRCs (0.5, 1 and 2 L). These were performed using the ‘speeded’ system (with a T90 of 88 ms) and repeated using the same system but with the T90 increased by addition of an extra filter (Camlab, Cambridge, UK) to the gas sample line in order to slow the rise time to 154 ms (i.e. the same as the standard Innocor setup). Since FGD was also increased by addition of the extra filter, the system-specific FGD was used for each analysis. Results are presented in Table 3. FRC accuracy is quoted as percentage of the lung tank volume, excluding the apparatus deadspace. Accuracy was good at slow ventilation rates across all three FRC volumes and in both the fast and slow T90 systems. 100% of all repeats at this rate produced an error of less than 5%. This accuracy was maintained at faster rates for the fast T90 system, where 100% of all washouts at all speeds (n = 49) generated an error in FRC of under 5% (range −0.9 to 2.9% error). For the slow T90 system however, error was greater at ventilation rate>20 min−1, and all washouts at rates >30 min−1 showed error in FRC of >5%. These data are also presented in Figure 5.

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