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Journal of Clinical Monitoring and Computing

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Open Access 01-01-2008

Validation and Clinical Application of a First Order Step Response Equation for Nitrogen Clearance During FRC Measurement

Authors: Gary Choncholas, Soren Sondergaard, MD, PhD, Erkki Heinonen

Published in: Journal of Clinical Monitoring and Computing | Issue 1/2008

Abstract

Objective

To derive a difference equation based on mass conservation and on alveolar tidal volumes for the calculation of Functional Residual Capacity. Derive an equation for the FRC from the difference equation. Furthermore, to derive and validate a step response equation as a solution of the difference equation within the framework of digital signal processing where the FRC is known a priori.

Methods

A difference equation for the calculation of Functional Residual Capacity is derived and solved as step response of a first order system. The step response equation calculates endtidal fractions of nitrogen during multiple breath nitrogen clearance. The step response equation contains the eigenvalue defined as the ratio of FRC to the sum of FRC and alveolar tidal ventilation. Agreement of calculated nitrogen fractions with measured fractions is demonstrated with data from a metabolic lung model, measurements from patients in positive pressure ventilation and volunteers breathing spontaneously. Examples of eigenvalue are given and compared between diseased and healthy lungs and between ventilatory settings.

Results

Comparison of calculated and measured fractions of endtidal nitrogen demonstrates a high degree of agreement in terms of regression and bias and limits of agreement (precision) in Bland & Altman analysis. Examples illustrate the use of the eigenvalue as a possible discriminator between disease states.

Conclusion

The first order step response equation reliably calculates endtidal fractions of nitrogen during washout based on a Functional Residual Capacity. The eigenvalue may be a clinically valuable index alone or in conjunction with other indices in the analysis of respiratory states and may aid in the setting of the ventilator.

Available only for authorised users

Bland & Altman analysis is utilized in spite of the methods, measured and calculated values of F_ETN₂, are not independent but mathematically linked.

The ‘baby lung’ concept requires the strain to be calculated at FRC without PEEP (ZEEP).

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Title: Validation and Clinical Application of a First Order Step Response Equation for Nitrogen Clearance During FRC Measurement
Authors: Gary Choncholas
Soren Sondergaard, MD, PhD
Erkki Heinonen
Publication date: 01-01-2008
Publisher: Springer Netherlands
Published in: Journal of Clinical Monitoring and Computing / Issue 1/2008
Print ISSN: 1387-1307
Electronic ISSN: 1573-2614
DOI: https://doi.org/10.1007/s10877-007-9101-0

At a glance: The STEP trials

Springer Medicine

Validation and Clinical Application of a First Order Step Response Equation for Nitrogen Clearance During FRC Measurement

Abstract

Objective

Methods

Results

Conclusion

At a glance: The STEP trials

Springer Medicine

Abstract

Objective

Methods

Results

Conclusion

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