Elicitation of theoretically predicted feedback oscillation in arterial pressure

1962 ◽  
Vol 203 (1) ◽  
pp. 141-146 ◽  
Author(s):  
Kiichi Sagawa ◽  
Oliver Carrier ◽  
Arthur C. Guyton
Keyword(s):  
Arterial Pressure ◽  
Cerebral Perfusion Pressure ◽  
Cerebral Perfusion ◽  
Perfusion Pressure ◽  
Pressor Response ◽  
Systemic Arterial Pressure ◽  
Time Dependent ◽  
Response Mechanism ◽  
Cerebral Ischemic ◽  
Pressure Changes

In a preceding servoanalytic study of the cerebral ischemic pressor response, the authors predicted that, under certain conditions, this emergency mechanism would go into a feedback oscillation and vasomotor waves would appear. The predicted conditions were a) that the cerebral perfusion pressure be as low as 30–10 mm Hg and b) that the time-dependent variable components of the systemic arterial pressure be transferred to the perfusion pressure with the same magnitude. The present experiment was conducted for the purpose of confirming such a theoretical prediction. The transfer of the systemic arterial pressure changes to the cerebral perfusion pressure was accomplished by a special coupling apparatus, and in all of the 11 experiments the cerebral ischemic response mechanism lapsed into feedback oscillation, and intense vasomotor waves were brought about. The period of these waves coincided almost exactly with those predicted by the servoanalysis of the cerebral ischemic response in individual dogs.

Dynamic performance and stability of cerebral ischemic pressor response

1961 ◽  
Vol 201 (6) ◽  
pp. 1164-1172 ◽  
Author(s):  
Kiichi Sagawa ◽  
Aubrey E. Taylor ◽  
Arthur C. Guyton
Keyword(s):  
Cerebral Perfusion Pressure ◽  
Cerebral Perfusion ◽  
Perfusion Pressure ◽  
Pressor Response ◽  
Dynamic Performance ◽  
Polar Coordinates ◽  
Pressure Waves ◽  
Phase Lag ◽  
Cerebral Ischemic ◽  
Dynamic Performance Analysis

A servoanalytic dynamic performance analysis of the cerebral ischemic pressor response has been made by the frequency response method applied to a linearized ischemic response system. Using an isolated perfused head preparation, the cerebral perfusion pressure was changed sinusoidally with a fixed amplitude of 5 mm Hg, but with varied periods ranging from 320 to 20 sec. The systemic arterial pressure waves caused by these input sinusoidal pressure waves were compared with the latter in terms of amplitude ratio and phase shift relationships. As the mean cerebral perfusion pressure was lowered toward zero, the response increased both in gain and phase lag. When these data were plotted as a vector locus on polar coordinates, the locus encircled the –1 point at 180° clockwise in 10 of 16 dogs. In two others, the locus approached very close to the –1 point. Thus, the nature of the cerebral ischemic pressor response was found to be unstable enough to go into self-oscillation under proper closed-loop conditions.

Effect of hypoxemia on the cardiovascular response to intracranial hypertension in postnatal lambs

1993 ◽  
Vol 265 (5) ◽  
pp. H1557-H1563 ◽  
Author(s):  
M. L. Kearney ◽  
J. E. Backofen ◽  
R. C. Koehler ◽  
M. D. Jones ◽  
R. J. Traystman
Keyword(s):  
Blood Flow ◽  
Intracranial Pressure ◽  
Arterial Pressure ◽  
Cerebral Perfusion Pressure ◽  
Cerebral Perfusion ◽  
Perfusion Pressure ◽  
Cardiovascular Response ◽  
Fetal Sheep ◽  
Peripheral Vasoconstriction ◽  
Significant Difference

Large increases in intracranial pressure in fetal sheep result in more potent peripheral vasoconstriction and better maintenance of cerebral O2 consumption (CMRO2) than in postnatal sheep. The fetus is exposed to a lower PO2. We tested the hypothesis that low PO2 in postnatal lambs potentiates peripheral vasoconstriction and better maintains cerebral perfusion pressure and CMRO2. Pentobarbital-anesthetized lambs, 2-7 days old, were ventilated with either room air (n = 7) or a low O2 mixture to reduce arterial O2 saturation to 50% (n = 7). Elevation of intracranial pressure to within 3-5 mmHg of baseline mean arterial pressure for 30 min by ventricular fluid infusion initially caused a similar increase in arterial pressure in the normoxic [11 +/- 3 (SE) mmHg] and hypoxic (14 +/- 2 mmHg) groups. Plasma catecholamines increased more rapidly in the hypoxic group. However, plasma vasopressin levels were substantially elevated by hypoxia alone and failed to increase further with elevated intracranial pressure. Moreover, there was no significant difference between groups in the steady-state increase in arterial pressure, and microsphere-determined blood flow to intestines, kidney, skin, and muscle did not decrease in either group. Consequently, cerebral perfusion pressure, regional cerebral blood flow, and CMRO2 were reduced similarly in both groups. Therefore, hypoxemia failed to potentiate the postnatal pressor response. Low PO2 is unlikely to be the major mechanism for the potent Cushing response in the fetus.

scholarly journals Left or right, up or down: A case for positioning of unconcious head-injured patients

Curationis ◽  
1992 ◽  
Vol 15 (1) ◽  
Author(s):  
M. Hugo
Keyword(s):  
Intracranial Pressure ◽  
Cerebral Perfusion Pressure ◽  
Nursing Care ◽  
Cerebral Perfusion ◽  
Perfusion Pressure ◽  
Negative Influence ◽  
Head Injured ◽  
Pressure Changes ◽  
Injured Patients ◽  
Increased Icp

Nursing care activities have been proved to cause increases in intracranial pressure (ICP) which could be detrimental to the patient’s health. Because positioning is one of the activities that causes the greatest pressure changes it was evaluated in this study. Cumulative increases also occur when nursing care activities are carried out in quick succession. The analysis of the data and literature suggest that the backrest position with the head of the bed elevated 30 to 45 degrees is the best position for a patient with increased ICP. If further research should prove that this position has a negative influence on the cerebral perfusion pressure, these recommendations will have to be revised.

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