CHAPTER 27 - The effects of changes in the carbon dioxide tension

Abstract

A number of special difficulties hinder an understanding of the effects of changes in PCO2. Firstly, there is the problem of species difference, which is a formidable obstacle to the interpretation of animal studies in this as in other fields. The second difficulty arises from the fact that carbon dioxide can exert its effect in a number of ways. For example, the so-called ‘inert gas’ narcotic effect would presumably be produced by carbon dioxide in accord with its physical properties, although it is more likely to exert its effects upon the central nervous system by means of its unique ability to alter the intracellular pH (page 219). This is quite apart from the fact that a change in PCO2 usually alters the pH of the circulating blood. In addition, it remains possible that carbon dioxide can exert specific effects unrelated to the mechanisms listed above, although this would be difficult to prove. The third difficulty in the understanding of the effects of carbon dioxide arises from the fact that the gas seems to act at many different sites in the body. Sometimes the action of carbon dioxide at different sites produces opposite effects upon a particular function, and the action of carbon dioxide upon blood pressure (Figure 27.1) is an example of the complexity of the manner in which its effects may be produced. The subject has been reviewed by Foëx (1980), Prys-Roberts (1980) and Utting (1980).