Journal of Applied Physiology, Vol 70, Issue 4 1686-1699, Copyright © 1991 by American Physiological Society

ARTICLES

Analysis of abnormalities of capillary CO2 exchange in vivo

A. Bidani
Department of Medicine, University of Texas Medical Branch, Galveston 77550.

Capillary CO2 exchange in vivo is affected by several interdependent reactions and transport processes. A mathematical model that includes all the significant chemical and transport events that are presumed to occur during capillary gas exchange has been used to investigate the effect of inhibition of 1) erythrocyte HCO(3-)-Cl- exchange, 2) lung carbonic anhydrase (CA) activity with access to plasma, and 3) erythrocyte CA activity on overall pulmonary CO2 excretion (VCO2) during rest and moderate exercise. Any decrement in VCO2 due to inhibition of HCO(3-)-Cl- exchange and/or CA activity, should result in compensatory alterations in cardiac output and/or an increase in the mixed venous blood-to-alveolar PCO2 gradient [(delta PCO2)V-A] to restore steady-state VCO2. Our computations show that complete inhibition of erythrocyte anion exchange would require a compensatory increment in cardiac output of approximately 30-40% or an increase in (delta PCO2)V-A from 6 to 8.3 Torr at rest and from 12 to 15.6 Torr during moderate exercise, if lung CA activity is intact. In the absence of availability of lung CA activity to plasma, the necessary (delta PCO2)V-A is 10.5 Torr at rest and 19.5 Torr during moderate exercise. Complete inhibition of lung and erythrocyte CA activity is predicted to require (delta PCO2)V-A of 39.1 Torr at rest and 74.2 Torr during moderate exercise. These results suggest that HCO(3-)-Cl- exchange might not be vital to maintenance of CO2 transfer and perhaps has a more important role in minimizing the changes in plasma pH associated with microvascular gas exchange in vivo.

This article has been cited by other articles:

				K. M. Gilmour, M. Bayaa, L. Kenney, B. McNeill, and S. F. Perry Type IV carbonic anhydrase is present in the gills of spiny dogfish (Squalus acanthias) Am J Physiol Regulatory Integrative Comp Physiol, January 1, 2007; 292(1): R556 - R567. [Abstract] [Full Text] [PDF]

				S. F. Perry1, K. M. Gilmour, E. R. Swenson, B. Vulesevic, S. F. Chew, and Y. K. Ip An investigation of the role of carbonic anhydrase in aquatic and aerial gas transfer in the African lungfish Protopterus dolloi J. Exp. Biol., October 1, 2005; 208(19): 3805 - 3815. [Abstract] [Full Text] [PDF]

				S. Chakraborty, V. Balakotaiah, and A. Bidani Diffusing capacity reexamined: relative roles of diffusion and chemical reaction in red cell uptake of O2, CO, CO2, and NO J Appl Physiol, December 1, 2004; 97(6): 2284 - 2302. [Abstract] [Full Text] [PDF]

				K. M. Gilmour and S. F. Perry Branchial membrane-associated carbonic anhydrase activity maintains CO2 excretion in severely anemic dogfish Am J Physiol Regulatory Integrative Comp Physiol, June 1, 2004; 286(6): R1138 - R1148. [Abstract] [Full Text] [PDF]

				O. Rosen, C. Suarez, V. L. Schuster, and L. P. Brion Expression of carbonic anhydrase IV in mouse placenta Am J Physiol Regulatory Integrative Comp Physiol, February 1, 2001; 280(2): R365 - R375. [Abstract] [Full Text] [PDF]

				B. W. Scheuermann, J. M. Kowalchuk, D. H. Paterson, and D. A. Cunningham VCO2 and VE kinetics during moderate- and heavyintensity exercise after acetazolamide administration J Appl Physiol, May 1, 1999; 86(5): 1534 - 1543. [Abstract] [Full Text] [PDF]

				V. Cardenas Jr., T. A. Heming, and A. Bidani Kinetics of CO2 excretion and intravascular pH disequilibria during carbonic anhydrase inhibition J Appl Physiol, February 1, 1998; 84(2): 683 - 694. [Abstract] [Full Text] [PDF]

				Y.-H. H. Lien and L.-W. Lai Respiratory acidosis in carbonic anhydrase II-deficient mice Am J Physiol Lung Cell Mol Physiol, February 1, 1998; 274(2): L301 - L304. [Abstract] [Full Text] [PDF]

				S. Deem, M. K. Alberts, M. J. Bishop, A. Bidani, and E. R. Swenson CO2 transport in normovolemic anemia: complete compensation and stability of blood CO2 tensions J Appl Physiol, July 1, 1997; 83(1): 240 - 246. [Abstract] [Full Text] [PDF]