Systematic errors and susceptibility to noise of four methods for calculating anatomical dead space from the CO2 expirogram Y. Tang, M.J. Turner, A.B.

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Presentation transcript:

Systematic errors and susceptibility to noise of four methods for calculating anatomical dead space from the CO2 expirogram Y. Tang, M.J. Turner, A.B. Baker British Journal of Anaesthesia Volume 98, Issue 6, Pages 828-834 (June 2007) DOI: 10.1093/bja/aem090 Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

Fig 1 CO2 expirogram and corresponding expired CO2 volume vs expired volume curve. (a) Solid line: simulated CO2 expirogram. Dotted lines: idealized expirogram (no airway asymmetry and no mixing) and construction lines for the calculation of anatomical dead space by the Fowler method. Areas p and q are equal and are bounded by the CO2 expirogram curve, the x-axis, and the extrapolated regression line of phase III of the CO2 expirogram. (b) Solid line: simulated expired CO2 volume as a function of expired volume. Dotted line: second order polynomial which is the cumulative area under the dotted line in (a). British Journal of Anaesthesia 2007 98, 828-834DOI: (10.1093/bja/aem090) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

Fig 2 (a) Simulated CO2 expirograms with normalized phase III slopes of 0.4 (dotted line) and 1.2 litre−1 (solid line). The expirogram represented by the solid line includes Gaussian noise with a standard deviation of 0.0026 vol/vol (5% of indicated Feco2 at Feco2 = 0.05). (b) The areas under the corresponding expirograms in (a). Integration reduces the noise substantially (solid curve). The integral of the expirogram with the larger phase III slope exhibits greater curvature (dotted line) at volumes greater than the anatomical dead space. British Journal of Anaesthesia 2007 98, 828-834DOI: (10.1093/bja/aem090) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

Fig 3 Bias in anatomical dead space calculated by the four methods as a function of the normalized slopes of phase III. Dead space calculated by: the Fowler equal area method (VdF), the Hatch linear regression method (VdH1), the modified Cumming second order polynomial regression method (VdC2), and the modified Bowes third order polynomial regression method (VdB3). British Journal of Anaesthesia 2007 98, 828-834DOI: (10.1093/bja/aem090) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

Fig 4 Bias and standard deviation in anatomical dead space as a function of noise. Dead space calculated by: the Fowler equal area method (VdF), the Hatch linear regression method (VdH1), the modified Cumming second order polynomial regression method (VdC2), and the modified Bowes third order polynomial regression method (VdB3). Small horizontal offsets are added to each data point for clarity. *Standard deviations of VdF are significantly larger than corresponding standard deviations of VdH1, VdC2, and VdB3. †Means of VdF are significantly smaller than mean of VdF at zero noise. British Journal of Anaesthesia 2007 98, 828-834DOI: (10.1093/bja/aem090) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

Fig 5 Intra-individual standard deviations of anatomical dead space under constant baseline ventilatory conditions in 10 patients. Dead space calculated by: the Fowler equal area method (VdF), the Hatch linear regression method (VdH1), the modified Cumming second order polynomial regression method (VdC2), and the modified Bowes third order polynomial regression method (VdB3).*Mean variance significantly smaller than variance of VdF. †Mean variance significantly smaller than variance of VdB3. All other symbols represent individual subjects studied. British Journal of Anaesthesia 2007 98, 828-834DOI: (10.1093/bja/aem090) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

Fig 6 The effect of phase III slope on the difference between VdH1 and VdC2 in the clinical study. The solid line is the regression line. Broken lines are the 95% confidence intervals of the regression. Dead space calculated by: the Hatch linear regression method (VdH1), the modified Cumming second order polynomial regression method (VdC2). British Journal of Anaesthesia 2007 98, 828-834DOI: (10.1093/bja/aem090) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions

British Journal of Anaesthesia 2007 98, 828-834DOI: (10 British Journal of Anaesthesia 2007 98, 828-834DOI: (10.1093/bja/aem090) Copyright © 2007 British Journal of Anaesthesia Terms and Conditions