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Poster asa-2012-evol vca-pmeas-final

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Michael B. Jaffe
Michael B. Jaffe

This document discusses the evolution of volumetric CO2 measurements from manual methods in the 19th century to computer-based techniques today. Early physiologists in the 1900s collected expired air into bags and analyzed the CO2-volume curve to determine respiratory dead space. In the 1950s, fast CO2 analyzers allowed recording of real-time CO2 and flow profiles. Fletcher introduced the single breath test in 1980 using phase terminology to analyze the expiratory CO2 curve. Current analysis methods fit models to phases of the volumetric capnogram curve to estimate clinically useful metrics like dead space.

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Evolution of volumetric CO2 measurements Michael B. Jaffe PhD Philips-Respironics, Wallingford, CT As the technology for CO2 and volume/flow measurements in respired gases evolved from the manual time-consuming methods of the mid-19th century to the real-time electronic methods of the mid-20th century, the analysis of the CO2 and flow waveforms have evolved from paper based research methods to computer-based optimization techniques for robust determinations of volumetric CO2 measurements such as CO2 elimination (VCO2) and dead space. Physiologists of the early 20th century did not have fast responding infrared gas analyzers available and as such employed clever approaches to analyze the composition of alveolar air throughout the respiratory cycle. While methods were known to estimate VCO2 as early as the late 19th century, little was published about the shape of the expiratory volumetric CO2 curve. Aitken & Clark-Kennedy (1928) (1) collected expired air from exercising subjects into "separate successive portions (e.g. rubber bags) suitable for measurement and analysis (upper figure below). The resulting data points were represented by a smooth curve from which they determined the size and nature of respiratory dead space using an area based method under the expired CO2-volume curve (similar to the later method of Fowler (2) for N2) (lower figure below). Volumetric capnographic measurements and analysis method continue to evolve with increased robustness, and reliability with improvements in technology and algorithms. Conclusions DiscussionDiscussionIntroductionIntroduction It was Fletcher who, in his doctoral thesis (1980) (5) and in later publications (6) first presented the concepts of dead space, effective and ineffective ventilation and VCO2 in a unified framework using phase terminology of Fowler (2). His presentation became widely known as the single breath test (SBT) or single breath CO2 (SBCO2) curve (i.e. the expiratory portion of the volumetric capnogram). ReferencesReferences 1.Aiken, R.S. & Clark-Kennedy, A.E. J. Physiol. (1928). 65, 389-411. 2.Fowler, W.S. Am. J. Physiol. (1948). 154, 405. 3.Elam, J.A., Brown, E.L., Ten Pas R.H. Anesthesiology (1955). 16, 876-885 4.Berengo, A. & Cutillo, A. , J. Appl. Physiol. (1961) 16, 522- 530. 5.Fletcher, R. (1980). The single breath test for carbon dioxide (Thesis). Lund, Sweden. 6.Fletcher, R. & Jonson, B. Br. J. Anaesth. (1984), 56, 109- 119. 7.Ream RS, et al. Anesthesiology. (1995);82(1):64-73. 8.Breen PH, Jacobsen BP. Anesth Analg. (1997);85(6):1372-6. While this framework remains in wide use, the terms SBT and SBCO2 are being replaced with a more descriptive term, volumetric capnogram. The term Capnograph now synonymous with a carbon dioxide analyzer was originally a trademark (1st use in commerce in 1959 and registered in 1965) before becoming genericized. The term volumetric capnography started to become widely used in the mid 1990s (7) and promulgated as a more appropriate term. Other terminology such as carbon dioxide spirogram(8) have been suggested as well. Analysis methods in use include minimization techniques such as least-squares for fitting the central portions of phase II and III as well as the entire expiratory curve to allow for robust and reliable estimates of clinically useful diagnostic measures of the slopes of phase II and III. Elam (3) (1955), using a fast responding breathe-through (i.e. mainstream) CO2 gas analyzer (Liston-Becker Model 16) and screen pneumotachograph for flow, published time-based CO2 and flow profiles of human respiration. The flow profile was used in order to determine an alveolar value of CO2 by comparison of the time records (see figure below). Their work on CO2 homeostasis included both normal and abnormal characteristics of the CO2 profiles and measurements of dead space and alveolar ventilation. DiscussionDiscussion Single breath volumetric curves for CO2 using fast responding analyzers appeared as early as 1961 in the literature. Berengo and Cutillo (1961) noted that other workers focused on the last portion of the capnogram but had not reported any detailed study of the capnogram as a whole including analysis of its different phases. With data from a CO2 gas analyzer and a spirometer, the experimental CO2 and expired air volume data was fitted to a 4th degree polynomial to find the "flexion" points.

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Poster asa-2012-evol vca-pmeas-final

  • 1. Evolution of volumetric CO2 measurements Michael B. Jaffe PhD Philips-Respironics, Wallingford, CT As the technology for CO2 and volume/flow measurements in respired gases evolved from the manual time-consuming methods of the mid-19th century to the real-time electronic methods of the mid-20th century, the analysis of the CO2 and flow waveforms have evolved from paper based research methods to computer-based optimization techniques for robust determinations of volumetric CO2 measurements such as CO2 elimination (VCO2) and dead space. Physiologists of the early 20th century did not have fast responding infrared gas analyzers available and as such employed clever approaches to analyze the composition of alveolar air throughout the respiratory cycle. While methods were known to estimate VCO2 as early as the late 19th century, little was published about the shape of the expiratory volumetric CO2 curve. Aitken & Clark-Kennedy (1928) (1) collected expired air from exercising subjects into "separate successive portions (e.g. rubber bags) suitable for measurement and analysis (upper figure below). The resulting data points were represented by a smooth curve from which they determined the size and nature of respiratory dead space using an area based method under the expired CO2-volume curve (similar to the later method of Fowler (2) for N2) (lower figure below). Volumetric capnographic measurements and analysis method continue to evolve with increased robustness, and reliability with improvements in technology and algorithms. Conclusions DiscussionDiscussionIntroductionIntroduction It was Fletcher who, in his doctoral thesis (1980) (5) and in later publications (6) first presented the concepts of dead space, effective and ineffective ventilation and VCO2 in a unified framework using phase terminology of Fowler (2). His presentation became widely known as the single breath test (SBT) or single breath CO2 (SBCO2) curve (i.e. the expiratory portion of the volumetric capnogram). ReferencesReferences 1.Aiken, R.S. & Clark-Kennedy, A.E. J. Physiol. (1928). 65, 389-411. 2.Fowler, W.S. Am. J. Physiol. (1948). 154, 405. 3.Elam, J.A., Brown, E.L., Ten Pas R.H. Anesthesiology (1955). 16, 876-885 4.Berengo, A. & Cutillo, A. , J. Appl. Physiol. (1961) 16, 522- 530. 5.Fletcher, R. (1980). The single breath test for carbon dioxide (Thesis). Lund, Sweden. 6.Fletcher, R. & Jonson, B. Br. J. Anaesth. (1984), 56, 109- 119. 7.Ream RS, et al. Anesthesiology. (1995);82(1):64-73. 8.Breen PH, Jacobsen BP. Anesth Analg. (1997);85(6):1372-6. While this framework remains in wide use, the terms SBT and SBCO2 are being replaced with a more descriptive term, volumetric capnogram. The term Capnograph now synonymous with a carbon dioxide analyzer was originally a trademark (1st use in commerce in 1959 and registered in 1965) before becoming genericized. The term volumetric capnography started to become widely used in the mid 1990s (7) and promulgated as a more appropriate term. Other terminology such as carbon dioxide spirogram(8) have been suggested as well. Analysis methods in use include minimization techniques such as least-squares for fitting the central portions of phase II and III as well as the entire expiratory curve to allow for robust and reliable estimates of clinically useful diagnostic measures of the slopes of phase II and III. Elam (3) (1955), using a fast responding breathe-through (i.e. mainstream) CO2 gas analyzer (Liston-Becker Model 16) and screen pneumotachograph for flow, published time-based CO2 and flow profiles of human respiration. The flow profile was used in order to determine an alveolar value of CO2 by comparison of the time records (see figure below). Their work on CO2 homeostasis included both normal and abnormal characteristics of the CO2 profiles and measurements of dead space and alveolar ventilation. DiscussionDiscussion Single breath volumetric curves for CO2 using fast responding analyzers appeared as early as 1961 in the literature. Berengo and Cutillo (1961) noted that other workers focused on the last portion of the capnogram but had not reported any detailed study of the capnogram as a whole including analysis of its different phases. With data from a CO2 gas analyzer and a spirometer, the experimental CO2 and expired air volume data was fitted to a 4th degree polynomial to find the "flexion" points.