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Fig. 21 | Fluids and Barriers of the CNS

Fig. 21

From: Fluid and ion transfer across the blood–brain and blood–cerebrospinal fluid barriers; a comparative account of mechanisms and roles

Fig. 21

Classic studies on the regulation of CSF pH. pH (a, b) and [HCO3 ] (c, d) in CSF are plotted against values of the same parameters in arterial blood plasma. a, c are for humans with acid–base disorders as indicated (taken from the compilation in Table 2 of [52] with all of the data shown). b, d are for goats exposed to different [HCO3 ]arterial over a week by systemic administration of NH4Cl or NaHCO3 (data extracted from Fig. 2 of [352] with pHarterial calculated as in their Fig. 3). pH is regulated by controlling the ratio [HCO3 ]/pCO2 (see Sect. 6.1.1). A metabolic disturbance of pH is one in which the causal event is a change in [HCO3 ] while a respiratory disturbance of pH is one in which the causal event is a change in pCO2. All of the data reported for goats are for metabolic disturbances. As can be seen in both humans and goats, in metabolic acidosis and alkalosis (dashed lines) pHCSF changes by much less than pHarterial, i.e. there is tighter regulation of pHCSF. By contrast in humans in respiratory acidosis (dotted line) the variation in pHCSF is as large or larger than the change in pHarterial. In metabolic acidosis and alkalosis the tighter control of pHCSF is a consequence of the smaller variation in CSF of [HCO3 ] (see c, d) and hence of the [HCO3 ]/pCO2 ratio than in arterial plasma. More recent data confirm the variations shown for metabolic disturbances and the general features of the responses to respiratory disturbances [185]). The relations between changes in [HCO3 ] and changes in pH are considered further in footnote 21

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