title: A method for estimating contact time of red blood cells through lung capillary from O2 and CO2 concentrations in rebreathing air in man.
abstract: The gas exchange ratio (R) obtained from O2 and CO2 concentrations measured in rebreathing air usually shows a linear relation to the PCO2. By referring to this relation and the R which equals the Haldane effect coefficient and zero, the true- and oxygenated-venous PCO2 are obtained in addition to the alveolar PCO2. When these PCO2 are evaluated, the R-PCO2 line can also be computed theoretically from a numerical solution on the overall O2 and CO2 diffusions in the red blood cell. By comparing both the experimental and theoretical R-PCO2 lines with each other, we derived a contact time equation. Since the linear approximation of the R-PCO2 relation gave rise to an error in the contact time (tc), first a factor to correct the linearity of the R-PCO2 line was derived. Next, using these parameter values, tc was quantitatively determined from experimental data obtained during rebreathing in 5 normal subjects and it was compared with that estimated from the pulmonary diffusing capacity for CO in the same rebreathing experiment. When the extracellular HCO3- dehydration rate was taken to be 0.1 s in time constant, the tc, being ca. 0.7 and 0.4 s at rest and during exercise, respectively, showed good agreement with those obtained from the diffusing capacity for CO.
mesh_terms: D002196:Capillaries; D002245:Carbon Dioxide / Q000097:blood / Q000378:metabolism*; D002248:Carbon Monoxide / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D008168:Lung / Q000098:blood supply; D008433:Mathematics; D010100:Oxygen / Q000097:blood / Q000378:metabolism*; D011653:Pulmonary Diffusing Capacity; D012044:Regression Analysis; D012119:Respiration; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide; D002248:Carbon Monoxide; D010100:Oxygen