Pulsed Electromagnetic Field (PEMF) Mitigates High Intracranial Pressure (ICP) Induced Microvascular Shunting (MVS) in Rats

OBJECTIVE

High-frequency pulsed electromagnetic field (PEMF) stimulation is an emerging noninvasive therapy that we have shown increases cerebral blood flow (CBF) and tissue oxygenation in the healthy rat brain. In this work, we tested the effect of PEMF on the brain at high intracranial pressure (ICP). We previously showed that high ICP in rats caused a transition from capillary (CAP) to non-nutritive microvascular shunt (MVS) flow, tissue hypoxia and increased blood brain barrier (BBB) permeability.

METHODS

Using in vivo two-photon laser scanning microscopy (2PLSM) over the rat parietal cortex, and studied the effects of PEMF on microvascular blood flow velocity, tissue oxygenation (NADH autofluorescence), BBB permeability and neuronal necrosis during 4 h of elevated ICP to 30 mmHg.

RESULTS

PEMF significantly dilated arterioles, increased capillary blood flow velocity and reduced MVS/capillary ratio compared to sham-treated animals. These effects led to a significant decrease in tissue hypoxia, BBB degradation and neuronal necrosis.

CONCLUSIONS

PEMF attenuates high ICP-induced pathological microcirculatory changes, tissue hypoxia, BBB degradation and neuronal necrosis.

Induced Dynamic Intracranial Pressure and Cerebrovascular Reactivity Assessment of Cerebrovascular Autoregulation After Traumatic Brain Injury with High Intracranial Pressure in Rats

OBJECTIVE

In previous work we showed that high intracranial pressure (ICP) in the rat brain induces a transition from capillary (CAP) to pathological microvascular shunt (MVS) flow, resulting in brain hypoxia, edema, and blood-brain barrier (BBB) damage. This transition was correlated with a loss of cerebral blood flow (CBF) autoregulation undetected by static autoregulatory curves but identified by induced dynamic ICP (iPRx) and cerebrovascular (iCVRx) reactivity. We hypothesized that loss of CBF autoregulation as correlated with MVS flow would be identified by iPRx and iCVRx in traumatic brain injury (TBI) with elevated ICP.

METHODS

TBI was induced by lateral fluid percussion (LFP) using a gas-driven device in rats. Using in vivo two-photon laser scanning microscopy, cortical microcirculation, tissue oxygenation (NADH autofluoresence), and BBB permeability (fluorescein dye extravasation) were measured before and for 4 h after TBI. Laser Doppler cortical flux, rectal and brain temperature, ICP and mean arterial pressure (MAP), blood gases, and electrolytes were monitored. Every 30 min, a transient 10 mmHg rise in MAP was induced by i.v. bolus of dopamine. iPRx = ΔICP/ΔMAP and iCVRx = ΔCBF/ΔMAP.

RESULTS

We demonstrated that iPRx and iCVRx correctly identified more severe loss of CBF autoregulation correlated with a transition of blood flow to MVS after TBI with high ICP compared to TBI without an increase in ICP.

CONCLUSIONS

In TBI with high ICP, high-velocity MVS flow is responsible for the loss of CBF autoregulation identified by iPRx and iCVRx.

Drag-Reducing Polymer Enhances Microvascular Perfusion in the Traumatized Brain with Intracranial Hypertension

Current treatments for traumatic brain injury (TBI) have not focused on improving microvascular perfusion. Drag-reducing polymers (DRP), linear, long-chain, blood-soluble, nontoxic macromolecules, may offer a new approach to improving cerebral perfusion by primary alteration of the fluid dynamic properties of blood. Nanomolar concentrations of DRP have been shown to improve hemodynamics in animal models of ischemic myocardium and ischemic limb, but have not yet been studied in the brain. We recently demonstrated that DRP improved microvascular perfusion and tissue oxygenation in a normal rat brain. We hypothesized that DRP could restore microvascular perfusion in hypertensive brain after TBI. Using in vivo two-photon laser scanning microscopy we examined the effect of DRP on microvascular blood flow and tissue oxygenation in hypertensive rat brains with and without TBI. DRP enhanced and restored capillary flow, decreased microvascular shunt flow, and, as a result, reduced tissue hypoxia in both nontraumatized and traumatized rat brains at high intracranial pressure. Our study suggests that DRP could constitute an effective treatment for improving microvascular flow in brain ischemia caused by high intracranial pressure after TBI.