Respiration and the cerebrospinal fluid.

INTRODUCTION It has long been known that changes in the hydrogen ion concentration ([H+]) and carbon dioxide tension (Pco2) of the blood affect respiration. These alterations in ventilation are probably produced by a chemical stimulus at more than one site (Lambertsen et al., 1961). The presence of arterial chemoreceptors in relation to the carotid sinus and aortic arch is well known. Recently, Mitchell et al. (1963) have demonstrated another chemosensitive region in the anterolateral surface of the medulla which responds rapidly to changes in [H+] and Pco2 in the cerebrospinal fluid (c.s.f.). Because of the blood-brain and blood-c.s.f. barriers, changes in the [H+] of the c.s.f. are not necessarily the same, nor do •they occur at the same rate, as in the blood. This is important in understanding the consequences of ventilatory disturbances produced by anaesthesia, artificial respiration and disease. This article reviews the following: (i) The evidence that acid-base changes in the c.s.f. affect pulmonary ventilation. (ii) The possible mechanisms whereby these effects are produced. (iii) The c.s.f. changes which follow respiratory and metabolic acid-base disturbances. (iv) The mechanisms whereby the [H+] of the c.s.f. is maintained constant in a variety of acidbase disturbances of the body. Finally, the possible clinical and physiological applications of these findings are discussed.