Simulating the Physiological Purpose of Cushing Reflex: An Accessory Cerebral Windkessel in Extremis
Racheed Mani1, Nahid Shirdel Abdolmaleki4, Anand Ravishankar4, Liu Yang5, Yicun Wang2, Jade Basem3, Chiemeka Uwakwe3, Petar Djuric4, Michael Egnor3
1Department of Neurology, 2Department of Radiology, 3Department of Neurological Surgery, Stony Brook University Hospital, 4Department of Electrical and Computer Engineering, Stony Brook University, 5Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University
Objective:
We simulate arterial hypertension and bradycardia in Cushing reflex in severe obstructive hydrocephalus (OH) using an electric circuit model.
Background:
Cushing reflex is the triad of hypertension, bradycardia, and irregular respirations in the setting of acute hydrocephalus and/or markedly elevated intracranial pressure (ICP). Intracranial dynamics can be understood within the framework of the cerebral windkessel. The cerebral windkessel is a buffer that protects the brain capillaries from the arterial blood pressure (ABP) pulse by diverting this pulse from the arteries through the cerebrospinal fluid (CSF) to the veins. This is akin to an electric circuit, in which direct current (DC) power (smooth blood flow) travels in the capillary circulation and alternating current (AC) power (pulsatile CSF flow) travels in the CSF pathways. Severe OH is characterized by high impedance to AC power in the CSF path due to high CSF space resistance which impairs the windkessel and reroutes AC power from the CSF through the capillaries, leading to deleterious capillary disruption, edema, elevated ICP, and herniation.
Design/Methods:
We model OH as windkessel impairment caused by increased resistance to AC power in the CSF pathway simulated in an electric circuit with parallel inductance and capacitance to simulate the pulsatile flow of blood and CSF as AC power, and smooth flow as DC power. We then simulate Cushing reflex by lowering the frequency from the AC voltage source (to stimulate bradycardia) and by increasing the DC voltage (to simulate arterial hypertension).
Results:
In our simulation, Cushing reflex improves windkessel function by reducing AC power in the cranium and augmenting DC power in the capillary circulation.
Conclusions:
Arterial hypertension increases DC power in the cerebral capillaries and bradycardia increases intracranial inertance and decreases total AC power, which varies proportionately with frequency. Cushing reflex ameliorates windkessel impairment and can be understood as an accessory cerebral windkessel in extremis.
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