Cerebral venous blood oxygen content and brain blood flow
In both groups of patients the internal jugular blood oxygen concentration was reduced significantly from the recumbent value (p < 0.01). Comparable increases in the cerebral arteriovenous oxygen differences were observed. The increase in this oxygen difference after three minutes of tilt was significant in the patients studied after sympathectomy (p < 0.02), but was not in the pa- tients with essential hypertension. The decreases in the -oxygen content of cerebral venous blood after 20 minutes of tilt cannot be attributed to significant reductions in cerebral blood flow in either
group.
Cerebral oxygen consumption
Although the cerebral arteriovenous oxygen difference increased only 10% in the hypertensives, the 9% increase in cerebral oxygen consumption after 20 minutes of tilt proved to be highly significant (p < 0.01). Cerebral oxygen con- sumption was not increased in the postsympathetomy group.
Cerebrovascular resistance
The cerebral blood flow of the patients after sympathectomy was decreased 1 1% with a 26% reduction in "effective" mean cerebral pressure.
This can be explained by the fact that the cerebrovascular resistance decreased 17%o from 2.3 to 1.9 units, indicating a highly significant relaxation of cerebral vessels during the tilt period. A comparable reduction in cerebrovascular resistatice
was found both in the hypertensive patients and in the normotensive subjects.
By JOSEPH H. HAFKENSCHIEL, CHARLES W. CRUMPTON,2 HENRY A.
SHENKIN, JOHN H. MOYER,3 HAROLD A. ZINTEL, HERBERT
WENDEL,4 AND WILLIAM A. JEFFERS, WITH THE TECHNICAL
ASSISTANCE OF SALLY CONLIN HARNED, NELLYJ. KEFFER, AND GERALDINE CROFT