CENTRAL XI'.RA'Ol'S SYSTEM— ROSOMOFF 255 



the cerebral IjUjckI flow fell at a constant rate, whereas the mean blood pressure 

 fluctuated through wide extremes. Therefore, the cereliral vascular resistance was 

 actively and rapidly varyin*^ in maintaining a constant cerebral blood flow in the 

 face of a fluctuating blood pressure. This led to the conclusion that there must be 

 a mechanism, mediated through the brain, by which this occurred and is most likely 

 some function of the respiratory gas tensions in the blood. 



It was noticed during the first set of experiments that the brain appeared smaller 

 at 25° C. than at ?)7° C We attempted to confirm this observation and to quanti- 

 tate the degree of change. Using a modification of the method of White for deter- 

 mining brain volume, the following results were obtained (table I). Attention is 

 called to the last two coluiuns. At 25° C. there is a decrease in brain volume of 4.1 



TABLE I 



DU'^FEKENTIAL INDICES OF BrAIN VoLUME, CHANGES IN EXTRACEREBRAL SpACE, AND 



Changes in Brain Volume of Nine Hypothermic Dogs (25° C.) 



Differential 



index of Change in Change in 



hrain extracerebral brain 



Oog volume space volume 



no. ' ; % % 



102 18.6 +68.9 —8.5 



104 13.9 +26.3 —?>.2> 



lOfi 14.6 +32.2 —40 



108 13.6 +23.8 —2.9 



112 15.0 +36.2 —4.8 



113 14.2 +28.6 —3.5 



115 15.7 +42.4 —5.3 



116 14.0 +27.0 —iZ 



117 12.1 + 9.9 —1.3 



Means 14.4 +31.8 —4.1 



per cent ; whereas the extracerebral s])ace, meaning that intracranial space not oc- 

 cupied by the brain, increases 31.8 per cent. The lajtter figure has a very important 

 clinical significance since it represents the amount of sp?ce available for expansion 

 of intracranial mass lesions. 



Figure 3 shows an example of the cerebrospinal fluid pressure curves of nine 

 animals during hypothermia. Note the elevation of pressure in one-half of the 

 animals. This always occurred in the presence of shivering. \\'hen shivering was 

 eliminated or was not present, there was a decline in the cerebrospinal fluid 

 pressure. 



\^enous pressure and cerebrospinal fluid pressure were measured simultaner)uslv 

 (fig. 4). Both functions decreased at ai)i)roximateh- the same rate, 5.5 per cent ])er 

 degree Centigrade in this temperature range. 



This has been a rather (|uick review of some of the effects of hvjjothermia on 

 the normal physiology of the nervous system. Now to review the abnormal. 



It has been well established that occlusion of the middle cerebral arterv in the 

 dog produces an infarct of significant magnitude. If the metabolism could be suffi- 

 ciently reduced at the time of occlusion long enough for collateral circulation to 

 establish itself, infarction might be minimized or prevented. It was proposed that 

 hypothermia could achieve these conditions. Two series of experiments were con- 



