3i8 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY' I 



19 20 21 Zl 23 2+ 



Time in Minutes 



FIG. 2. Graph of change in SP during asphyxia which resuhed from clamping airway. /, tracheal 

 airway clamped; i', ECG completely suppressed; 3, heart stops. [From Goldring & O'Leary (11).] 



oscillographic recording upon strips of film, the 

 chopper is temporarily disconnected. By convention, 

 shifts in potential from the base line will be referred 

 to as positive or negative with respect to the surface 

 electrode. 



Under optimal conditions the initial determination 

 of pia-ventricular SP has varied usually between 0.5 

 and 5.0 mv positive (i i). These data include meas- 

 urements upon 20 rabbits which were anesthetized 

 with ether for only the brief tiine required to pro- 

 cainize the skin and paravertebral muscles over the 

 C5 cord segment and divide the cord there. Anesthesia 

 could then be discontinued, and the scalp similarly 

 infiltrated with procaine as a prelude to exposing the 

 brain for recording. With insertion of the deep lead 

 into the subcortical white matter (in the cat), negative 

 injury potential about the deep electrode tip con- 

 tributes to the positivity at the surface, and larger 

 voltage discrepancies may be recorded. In human 

 subjects under nitrous oxide and thiopental anesthesia 

 in whom the pia-ventricular potential has been re- 

 corded, the measurement in the majority of cases has 

 been 0.3 to 0.5 mv positive (17). Here injury potential 

 was not believed to be a significant complicating 

 factor. Returning to the animal experiments, we note 

 that SP may not fluctuate more than 0.5 mv during 

 several hours of continuous recording if no procedure 

 is undertaken after the preparation of the animal. 

 With the high cord section (at Ci), necessitating arti- 

 ficial respiration, systemic failure has often developed 

 in rabbits; under this circumstance SP may show a 

 continuous negative drift terminating with the death 

 of the animal. Clamping the trachea in an animal in 



good condition, in which SP has not undergone sig- 

 nificant alterations during several hours of continuous 

 recording, will result m a significant SP change (11). 

 While \ariaijle and somewhat complex, this consists 

 principally of an initial positive shift (2 mv) followed 

 by an even more prominent negative one (4 mv). 

 The major change which follows clamping of the 

 airway usually ends in 8 min. The heart ceases to 

 beat between the maximum and the end of the nega- 

 tive deflection (fig. 2). 



Leao (26) demonstrated a similar negative shift 

 incident to cortical anemia and van Harreveld el al. 

 have also shown a negative SP shift with asphyxia 

 (41, 43). Other investigators, leading from the cortex 

 and using the sciatic nerve as reference point, have 

 also recorded SP shifts with anoxia and asphyxia 

 (4, 10). 



The injection of malononitrile, which liberates 

 cyanide ions, evokes an analagous picture (18). This 

 has been followed during the intravenous injection 

 of between 10 and 20 ml of a freshly prepared i per 

 cent solution delivered by Murphy drip. As the in- 

 jection proceeds the animal becomes hyperpneic, 

 and at aijout that time the ECG commences to slow, 

 with the appearance of random components showing 

 higher voltage than previously. As the ECG changes, 

 SP commences to shift positively. With further de- 

 terioration in the preparation the ECG becomes 

 isoelectric, and SP continues to shift positively to a 

 total of 2.5 mv. Clonic convulsive movements may 

 appear during the positive phase. These electrical 

 events can be reversed if 5 per cent sodium thiosulfate 

 is injected at the beginning of the positive SP change. 



