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KMID : 0377519810060010019
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Chung-Ang Journal of Medicine
1981 Volume.6 No. 1 p.19 ~ p.27
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The Effect of Acute Metabolic Alkalosis on Cerebrospinal fluid pH in Dogs
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Seung Ik-Sang
Cho Hyung-Sang
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Abstract
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It has long been recognized that the pH of cerebrospinal fluid (CSF) is subject to some degree of homeostatic control. As a result of this control CSF pH is controlled within narrower limits than that of the blood, but the factors which affect this control are not fully understood. The purpose of this study was to determine whether the distribution of hydrogen ion(H^+) and bicarbonate ion(HCO_3^-) between CSF and blood was regulated by a process of active ion transport or by passive distribution. In anesthetized and paralyzed dogs ventilated to maintain a normal PaCO_2, acute metabolic alkalosis was induced and held constant over 5 hours by infusion of sodium bicarbonate. Measurement of pH, Pco_2 in CSF and arterial blood were made prior to induction of metabolic alkalosis at pHa of 7.40, as soon after induction as stable arterial values were achieved 1.5, 3, 4 and 5 hours thereafter. ［HCO_3^-］ in CSF and arterial blood were calculated from Henderson-Hasselbalch equation. These changes in pH, Pco_2 and ［HCO_3^-］ during acute metabolic alkalosis were compared with those of control group. The electrical potential differences(E) between CSF and arterial blood were not measured but the electrochemical potential differences(μ) for H^+ and HCO_3^- were calculated assuming E=4 mV at pHa of 7.40 and assuming that E increases 30.5 mV per pH unit fall in pHa. The results were as follows: 1) In normal state, ［H^+］ and Pco_2 in CSF were significantly higher than those of arterial blood. 2) Under normal circumstances the electrochemical potential differences for H^+ and HCO_3^- between CSF and blood were 8.2~8.9 mV and -0.5 ~ +0.5 mV respectively. 3) During acute metabolic alkalosis the change of CSF pH was within narrower range than that of blood in spite of wide change of arterial blool pH. 4) The rate of rise of ［HCO_3^-］ in CSF was 15-40% of that in arterial blood during acute metabolic alkalosis. 5) Return of μHCO_3^- close to control in the steady state was found and this was compatible with passive distribution of this ion between CSF and blood but it is uncertain about the distribution of H^+.
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