Effects of alveolar dead-space, shunt and V ˙ / Q ˙ distribution on respiratory dead- space measurements Y. Tang, M.J. Turner, A.B. Baker British Journal.

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Effects of alveolar dead-space, shunt and V ˙ / Q ˙ distribution on respiratory dead- space measurements Y. Tang, M.J. Turner, A.B. Baker British Journal of Anaesthesia Volume 95, Issue 4, Pages 538-548 (October 2005) DOI: 10.1093/bja/aei212 Copyright © 2005 British Journal of Anaesthesia Terms and Conditions

Fig 1 Block diagram of the airway and alveolar compartments in the comprehensive cardiorespiratory system model. The respiratory system incorporates a 15-compartment approximation to Weibel's lung model. WG=Weibel generations; Alv=alveolar; DS=dead-space. British Journal of Anaesthesia 2005 95, 538-548DOI: (10.1093/bja/aei212) Copyright © 2005 British Journal of Anaesthesia Terms and Conditions

Fig 2 (a) Carbon dioxide partial pressures and (b) measured ratios of dead-space volumes to tidal volume as functions of Vdphys/Vt (model physiological dead-space to tidal volume ratio). P A CO 2 is arterial Pco2 predicted by the model. P A CO 2 is volume and time-averaged Pco2 in the perfused alveoli of the model. P A XCO 2 is volume and time-averaged Pco2 in all the alveoli of the model. P E ' CO 2 is end-tidal Pco2. P A KCO 2 is alveolar Pco2 calculated by Koulouris' method (Appendix A). VdBE is Bohr–Enghoff dead-space calculated by using Appendix Equation 2. VdBohr is Bohr dead-space calculated by using Equation 1. Vdet: dead-space calculated by using Equation 4. Vdk is dead-space calculated by Koulouris' method (Appendix A). VdFowler is anatomical dead-space calculated by Fowler's graphic method. Dashed straight line in b is the line of identity. British Journal of Anaesthesia 2005 95, 538-548DOI: (10.1093/bja/aei212) Copyright © 2005 British Journal of Anaesthesia Terms and Conditions

Fig 3 (a) Carbon dioxide partial pressures and (b) measured dead-spaces as functions of pulmonary shunt. Abbreviations are the same as in Fig. 2. Vdcorr is the Bohr–Enghoff dead-space corrected by the Kuwabara and Duncalf13 equation in the presence of right-to-left shunt (Appendix Equation 3). British Journal of Anaesthesia 2005 95, 538-548DOI: (10.1093/bja/aei212) Copyright © 2005 British Journal of Anaesthesia Terms and Conditions

Fig 4 (a) Carbon dioxide partial pressures and (b) measured dead-spaces as functions of the combined pulmonary perfusion of the high and low V ˙ / Q ˙ compartments. P a 0 . 1 CO 2 , P a 1 CO 2 and P a 10 CO 2 are Pco2 in the low V ˙ / Q ˙ , middle V ˙ / Q ˙ and high V ˙ / Q ˙ compartments respectively. Other abbreviations as in Fig. 2. British Journal of Anaesthesia 2005 95, 538-548DOI: (10.1093/bja/aei212) Copyright © 2005 British Journal of Anaesthesia Terms and Conditions

Fig A1 Diagrammatic representations of the Fowler method for calculating anatomical dead-space and the method of Koulouris and colleagues11 for the calculation of respiratory dead-space and alveolar partial pressure of carbon dioxide2. (a) Expired carbon dioxide concentration as a function of expired volume. Areas p′ and q′ are equal and the perpendicular line intersects the x-axis at the Fowler dead-space. (b) Expired carbon dioxide volume as a function of expired volume. Areas p and q are equal. According to Koulouris and colleagues,11 the slope of line ca is an estimate of alveolar carbon dioxide concentration and the lengths ia and ae are estimates of Bohr dead-space and alveolar volume respectively. British Journal of Anaesthesia 2005 95, 538-548DOI: (10.1093/bja/aei212) Copyright © 2005 British Journal of Anaesthesia Terms and Conditions

Fig A2 Validation of the computer model. (a) Simulation of airway, arterial, alveolar and mixed venous Pco2 during respiratory cycles. The circles and triangles are mixed venous and arterial Pco2 recorded from in vivo studies.3031 (b) Dynamic P E ' CO 2 changes with different combinations of tidal volume and respiratory rate. The dots are P E ' CO 2 recorded from the patient and the solid line is the model prediction. (c) Effects of tidal volume and respiratory rate on the measured and predicted P a CO 2 and P E ' CO 2 . The carbon dioxide values predicted by the model closely follow those recorded in the patients. RR and Vt are respiratory rate and tidal volume respectively. British Journal of Anaesthesia 2005 95, 538-548DOI: (10.1093/bja/aei212) Copyright © 2005 British Journal of Anaesthesia Terms and Conditions