i 7 8 4 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY' III 



CSF PULSE 



G,V) 



62 mm H 2 



49m* H 2 



19mm 



30mmH 2 



ECG 



'J 



U% 



e i sec 

 I 1 



fig. 12. Simultaneous ECG and pulse records from the 

 cerebral ventricle, cisterna magna and lumbar subarachnoid 

 space of an I [-year-old boy. The pulses, in millimeters of water, 

 arc: ventricular, b.>; cisternal, 49; lumbar, 29. [From Bering 

 (34-)] 



1 In- diir.il sinuses must increase, an unlikely event with 

 a raised venous pressure. Presumably some dislocation 

 of fluid takes place, i.e., some of the cranial fluid 

 passes into regions where the venous pressure has not 

 been raised, namely into the spinal subarachnoid, 

 room being made for it by an appropriate constriction 

 oi the veins in this region. That such readjustments are 

 constantly being made during change in posture is 

 very likely. Space does not permit a full discussion of 

 the many interesting phenomena described and dis- 

 cussed by Weed & Flexner, Carmichael, Masserman 

 and others on this particular aspect. 3 '-' Suffice it to say 

 thai when the fluid pressure in man is recorded firsl in 



B The interested reader maj be referred u> the following 

 papers Weed el at. (240), Flexner et al. (84), Weed S Flexner 

 Flexnei & Weed (85), Masserman (154 and von 

 Storch el al (228) The simple physical treatment of the prob- 

 lem, so enthusiastically pursued by Weed 8 Flexnei who com- 

 puted coefficients ol meningeal elasticity, must be taken with a 

 grain of salt. Pollock & Boshes (175) have blown a refrr ihing, il 

 copious, blast ol common sense on the purely me< li.mu .rl 

 aspei ts "i the Quid pressure, 



the lateral recumbent and then in the sitting posi- 

 tions, the pressure in the first posture is about 150 mm 

 saline, while in the sitting position it is some 400 mm 

 saline. The column of fluid that comes into play on 

 sitting is some 675 mm saline, so that only about 40 

 per cent of the theoretically possible increase takes 

 place. The system is, however, a closed one in the sense 

 that an actual movement of fluid down the spinal 

 subarachnoid space will be resisted by the fall in 

 pressure that must occur if the space occupied by the 

 fluid is not immediately filled. Thus, if a water-filled 

 tube, sealed at the top, is raised to the vertical posi- 

 tion, the fluid will not flow out because the atmos- 

 pheric pressure will balance the height of the column. If 

 the tube is open at the top the fluid will flow out of 

 the tube because now the atmospheric pressure acts 

 on the fluid in the tube. The state of affairs in the 

 cerebrospinal system is something between these ex- 

 tremes, the system behaving as though the top of the 

 tube were closed by an elastic cap; now the column of 

 fluid becomes effective, but only partially, because the 

 elastic tension in the cap resists the downward pull. If 

 we transpose this picture to the cerebrospinal system, 

 the elastic component becomes the extent to which 

 the cranial vessels can expand to make room for the 

 dislocation of cerebrospinal fluid from the ventricles 

 and the cranial subarachnoid space. Similarly, when 

 an animal is placed vertically, in the head-down posi- 

 tion, the elastic component will be governed by the 

 extent to which the spinal vessels can dilate. It is es- 

 sentially the interplay between the distcnsibilities of 

 the veins in the different regions of the central nervous 

 system that determines the magnitude of the changes 

 in cerebrospinal fluid pressure that result from changes 

 in posture. In general, this interplay is such as to 

 reduce very considerably the effects that might other- 

 wise be expected when large columns of fluid suddenly 

 are brought to bear. 



That the vascular system reacts immediately to 

 changes in the cerebrospinal fluid pressure is made 

 very clear by the study of the effects of withdrawal or 

 addition of fluid from or to the cerebrospinal system. 

 Withdrawal of, say , 30 ml from man causes a rapid fall 

 in fluid pressure followed by a fairly rapid return to 

 normal, withdrawal of a further 30 ml has now a much 

 more marked effect on the fluid pressure ( 1 ",-', 1 , 

 Evidendy, tin- fust loss was mainly compensated by an 

 expansion of the blood vessels, such .1 process of com- 

 pensation is, however, limited in extent so that a 

 subsequent withdrawal produces a higher elastic reac- 

 tion in the walls of the veins, and the compensatory 



