i8 4 6 



HANDBOOK OF 1HYSIOLOGY 



NEUROPHYSIOLOGY III 



cerebral blood How. In general, perfusion methods 

 and flow-meter techniques are limited by their re- 

 quirement of extensive operative procedures, par- 

 ticularly in most laboratory animals in which the 

 anatomy of the cerebral vasculature is unsuitable (71. 

 In man, plethysmography techniques (45) and 

 dilution techniques employing cither T-1824 (Evans 

 blue dye) ( ")8, 91) or thorium B-labelcd red cells 

 (134) have been employed for quantitative measure- 

 ment of human cerebral blood flow, but the nitrous 

 oxide method of K.etv & Schmidt (91, 100) has been 

 most widely used and found to yield the most reliable 

 results. (A description of the details of these methods 

 and their critical evaluation are presented by Kety 

 in Chapter LXXI of this Handbook.) The original 

 nitrous oxide method has been adapted for use in 

 animals (iof>, 137), and several modifications have 

 been employed in man. One simplifies it and reduces 

 the volume of blood sampling required by the pro- 

 cedure (158). Another adapts it to children (87, 88), 

 and a third substitutes the radioactive gas, Kx 86 , 

 lor nitrous oxide as the tracer material with some 

 improvement in the precision of the method (114). 



Polarographic Techniques 



The oxygen electrode has been employed for the 

 ;/; vivo measurement of local cortical oxygen tension 

 and consumption (22, 23). By applying such an 

 electrode to the surface of the exposed cortex, one 



can make continuous measurements of cortical oxygen 



tension before and during occlusion of the circulation 

 to the local area. During occlusion the oxygen tension 

 falls linearly as oxygen is consumed by the tissue, and 

 the rate of fall is a measure of the local cortical oxygen 

 consumption. This technique has also been employed 

 in combination with the artificial perfusion of an 

 isolated section of cerebral cortex (67). 



CHARACTERISTICS OF NORMAL METABOLISM OF 

 THE CENTRAL NERVOUS SYSTEM IN VIVO 



Almost all of our present knowledge concerning the 

 substances normally utilized and produced by the 

 metabolism of the central nervous system is derived 

 from studies of the brain, frequently made in human 

 subjects, both normal and pathological. 



In table 1 are summarized the reported results of 

 such studies in normal adult human subjects The 

 range of the mean values reported by the various 

 investigators is presented; and since the techniques, 

 the degree of precision, and the nature and number of 

 the subject material vary somewhat from one labora- 

 tory to another, the median of the mean values was 

 chosen as most representative of the function studied. 



Normal Substrates ami Producti 



The functions presented in table 1 are the arterial- 

 cerebral venous differences for various metabolites 



table 1. Substances I'tili.yd o> Produced In Normal Young Adult Human Brain 



'Mean alues r< poi ted l>\ \ ai ious .miliors. 



i I wo 1 1 1 1 1 ported means statistically significant \> < 0.05) but of opposite siejis. 



I Not statistical!) significant from zero (p ~. , 



