derivation of physiologic dead space bohr

Later, Krogh and Lindhard showed that alveolar CO 2 reaches a plateau by the end of expiration once the volume of gas in the anatomical dead space has been washed out. Haldane and Priestley believed that representative alveolar CO 2 samples could only be obtained at the end of a forced expiration. The measurement of PACO 2 is technically difficult and has caused hot debates in the past. assuming that CO 2 in the inspired gases is zero. VD Bohr can be calculated with accuracy using volumetric capnography. Mean VD Bohr from VC was close to the value obtained by MIGET with a mean bias of 0.010 ml and limits of agreement between −0.044 and 0.064 ml. Mean PACO 2 from VC was very similar to the one obtained by MIGET with a mean bias of −0.10 mmHg and limits of agreement between −2.18 and 1.98 mmHg. We found close linear correlations between the two methods for calculating both PACO 2 ( r = 0.99) and VD Bohr ( r = 0.96), respectively (both p < 0.0001). Then, PACO 2 was obtained applying the alveolar air formula ( PACO 2 = VCO 2/alveolar ventilation). MIGET estimated expired CO 2 output ( VCO 2) and PeCO 2 by its V/Q algorithms. PACO 2 was determined by VC as the midpoint of the slope of phase III of the capnogram, while mean expired partial pressure of CO 2 ( PeCO 2) was calculated as the mean expired fraction of CO 2 times the barometric minus the water vapor pressure. MethodsĮxpired gases of seven lung-lavaged pigs were analyzed at different lung conditions using main-stream VC and multiple inert gas elimination technique (MIGET). The aim of this work was to validate VD Bohr using PACO 2 derived from volumetric capnography (VC) against VD Bohr with PACO 2 values obtained from the standard alveolar air formula. Bohr’s dead space (VD Bohr) is commonly calculated using end-tidal CO 2 instead of the true alveolar partial pressure of CO 2 ( PACO 2).

Derivation of physiologic dead space bohr