Anesthetic modulation of cerebral hemodynamic and evoked responses to transient middle cerebral artery occlusion in cats

The Effects of Vaccinium myrtillus Extract on Hamster Pial Microcirculation during Hypoperfusion-Reperfusion Injury

Introduction

The present study was aimed to assess the in vivo hamster pial microvessel alterations due to 30 min transient bilateral common carotid artery occlusion (BCCAO) and reperfusion (60 min); moreover, the neuroprotective effects of Vaccinium myrtillus extract, containing 34.7% of anthocyanins, were investigated.

Materials and Methods

Two groups of male hamsters were used: the first fed with control diet and the other with Vaccinium myrtillus supplemented diet. Hamster pial microcirculation was visualized by fluorescence microscopy through an open cranial window. Pial arterioles were classified according to Strahler’s method.

Results

In age-matched control diet-fed hamsters, BCCAO caused a decrease in diameter of all arterioles. At the end of reperfusion, the reduction of diameter in order 3 arterioles was by 8.4 ± 3.1%, 10.8 ± 2.3% and 12.1 ± 1.1% of baseline in the 2, 4 and 6 month control diet-fed hamsters, respectively. Microvascular permeability and leukocyte adhesion were markedly enhanced, while perfused capillary length (PCL) decreased. The response to acetylcholine and papaverine topical application was impaired; 2’-7’-dichlorofluoresceine-diacetate assay demonstrated a significant ROS production. At the end of BCCAO, in age-matched Vaccinium myrtillussupplemented diet-fed hamsters, the arteriolar diameter did not significantly change compared to baseline. After 60 min reperfusion, order 3 arterioles dilated by 9.3 ± 2.4%, 10.6 ± 3.1% and 11.8 ± 2.7% of baseline in the 2, 4 and 6 month Vaccinium myrtillus supplemented diet-fed hamsters, respectively. Microvascular leakage and leukocyte adhesion were significantly reduced in all groups according to the time-dependent treatment, when compared with the age-matched control diet-fed hamsters. Similarly, the reduction in PCL was progressively prevented. Finally, the response to acetylcholine and papaverine topical application was preserved and there was no significant increase in ROS production in all groups.

Conclusions

In conclusion, Vaccinium myrtillusextract protected pial microcirculation during hypoperfusion-reperfusion, preventing vasoconstriction, microvascular permeability, leukocyte adhesion, reduction in PCL and preserving the endothelium function.

Detection of neurological injury using time-frequency analysis of the somatosensory evoked potential

Somatosensory evoked potentials (SEPs) can be monitored during critical surgery to help detect or possibly prevent post-operative injury to the brain. This paper presents the application of time-frequency analysis to detect both temporal and spectral changes in the SEP waveform that may occur due to injury. Time-frequency distributions, which provide a measure of signal energy at both a specific time and frequency, were computed for averaged SEPs acquired from anesthetized cats during various stages of hypoxic injury and then recovery. Wigner distributions of SEP waveforms were found to contain a peak of signal energy at a specific time and frequency, a peak that is altered during injury. Four characteristics of the distribution peak that demonstrate changes due to injury were computed: peak time, peak frequency, peak power, and peak sharpness. Peak time was found to increase while peak frequency, peak power, and peak sharpness were found to decrease during injury. Furthermore, the total signal power in a time-frequency space around the normal peak location was monitored by developing a time-frequency window filter (TFWF) method. For all cases, onset of hypoxia was detected an average of 2.75 min earlier by the TFWF method than by the conventional amplitude measurement method. Time-frequency analysis of EP signals may therefore be useful as a monitoring tool for early detection of brain injury.

Translational neuroscience and magnetic-resonance microscopy

Magnetic-resonance microscopy is a rapidly growing and a widely applied imaging method in translational neuroscience studies. Emphasis has been placed on anatomical, functional, and metabolic studies of genetically engineered mouse models of human disease and the need for efficient phenotyping at all levels. Magnetic-resonance microscopy is now implemented in many laboratories worldwide due to the availability of commercial high-field magnetic-resonance instruments for use in small animals, the development of accessories (including miniature radio-frequency coils), magnetic-resonance compatible physiological monitoring equipment, and access to adjustable anaesthesia techniques. Two of the major magnetic-resonance microscopy applications in the neurosciences-structural and functional magnetic-resonance microscopy-will be reviewed.

Effects of hypothermia and rewarming on evoked potentials during transient focal cerebral ischemia in cats

We examined the effects of mild to moderate hypothermia and the influence of rewarming on electrophysiological function using somatosensory evoked potentials (SEPs) in transient focal ischemia in the brain. Nineteen cats underwent 60 min of left middle cerebral artery occlusion under normothermic (36 degrees-37 degrees C, n = 6) or hypothermic (30 degrees -31 degrees C, n = 13) conditions followed by 300 min of reperfusion with slow (120 min, n = 6) or rapid (30 min, n = 7) rewarming. Whole-body hypothermia was induced during ischemia and the first 180 min of reperfusion. SEPs and regional cerebral blood flow were measured before and during ischemia and during reperfusion. The specific gravity of gray and white matter was examined as the indicator of edema. During rewarming, SEP amplitudes recovered gradually. After rewarming, SEPs in the normothermic and rapid rewarming groups remained depressed (20%-40% of pre-occlusion values); however, recovery of SEPs was significantly enhanced in the slow rewarming group (p < 0.05). Hypothermia followed by slow rewarming reduced edema in gray and white matter. Rapid rewarming did not reduce edema in the white matter. The recovery of SEPs correlated with the extent of brain edema in transient focal ischemia. Rapid rewarming reduced the protective effect of hypothermia.

Comparison of time-frequency analysis techniques in intraoperative somatosensory evoked potential (SEP) monitoring

Somatosensory evoked potentials (SEPs) can be monitored during spinal surgery to prevent possible spinal cord injury. In order to improve the reliability of SEP monitoring, an investigation of the application of various time-frequency analysis (TFA) techniques to detect both temporal and spectral changes in SEP waveforms was conducted. SEP signals from 15 scoliosis patients were analysed using various methods. The time-frequency distributions (TFDs) computed using these methods were assessed and compared. The most appropriate TFA technique may depend on the type of SEP signal, Short term Fourier transform (STFT) with a 20 point length Hanning window probably provides the best result for SEP signals.

The effects of sevoflurane and halothane anesthesia on cerebral blood flow velocity in children

We compared cerebral blood flow velocity during anesthesia with sevoflurane and halothane in 23 children admitted for elective surgery (age, 0.4-9.7 yr; median age, 1.9 yr; ASA physical status I-II). Inhaled induction was performed in a randomized sequence with sevoflurane or halothane. Under steady-state conditions, cerebral blood flow velocity (systolic [V(s)], mean [V(mn)], and diastolic [VD]) were measured by a blinded investigator using transcranial pulsed Doppler ultrasonography. The anesthetic was then changed. CBFV measurements were repeated after washout of the first anesthetic and after steady-state of the second (equivalent minimal alveolar concentration to first anesthetic). The resistance index was calculated. VD and V(mn) were significantly lower during sevoflurane (V(mn) 1.35 m/s) than during halothane (V(mn) 1.50 m/s; P = 0.001), whereas V(s) was unchanged. The resistance index was lower during halothane (P < 0.001). Our results indicate lower vessel resistance and higher mean velocity during halothane than during sevoflurane.

IMPLICATIONS

The mean cerebral blood flow velocity is significantly decreased in children during inhaled anesthesia with sevoflurane than during halothane. This might be relevant for the choice of anesthetic in children with risk of increased intracranial pressure, neurosurgery, or craniofacial osteotomies.

Pharmacologic reduction of mean arterial pressure does not adversely affect regional cerebral blood flow and intracranial pressure in experimental intracerebral hemorrhage

OBJECTIVE

To determine the effect of mean arterial pressure (MAP) reduction on regional cerebral blood flow and intracranial pressure (ICP) in intracerebral hemorrhage. We tested the hypothesis that there is ischemia in the perihematoma region after intracerebral hemorrhage, which can be exacerbated by a pharmacologic reduction of MAP.

DESIGN

Prospective, controlled, laboratory trial.

SETTING

Animal research laboratory.

SUBJECTS

Eighteen mongrel dogs, weighing 15 to 25 kg.

INTERVENTIONS

We introduced intracerebral hemorrhage in 12 anesthetized dogs by autologous blood injection under arterial pressure in the deep white matter adjacent to the left caudate region. We measured serial regional cerebral blood flow using radiolabeled microspheres in animals with two different volumes of injected blood (2.8 mL [Group A, n = 6] and 4.4 mL [Group B, n = 6]) and compared them with control animals (n = 6). Intravenous labetalol was administered 90 mins after administration of hematoma, while maintaining cerebral perfusion pressure >65 mm Hg. Regional cerebral blood flow measurements were repeated 10 and 30 mins after labetalol administration. MAP and ICP were monitored continuously using intra-arterial and cisterna magna catheters, respectively.

MEASUREMENTS AND MAIN RESULTS

Compared with control animals, significant elevation in ICP was observed in Groups A and B and elevation in MAP was observed in Group B at 45 mins after injection of blood. These hemodynamic alterations were not accompanied by any significant differences in regional cerebral blood flow in any group. Administration of labetalol resulted in a decrease in MAP (mm Hg+/-SEM) in Groups A (119.0+/-9.2 to 103.0+/-9.1) and B (124.5+/-7.4 to 100.5+/-4.8) and controls (103.5+/-4.3 to 85.0+/-8.0). No differences were observed in regional cerebral blood flow after MAP reduction in both Groups A and B compared with controls in regions around or distant to the hematoma. There were no changes in ICP in Groups A and B both at 10 and 30 mins after reduction in MAP compared with pretreatment values.

CONCLUSIONS

In our model, pharmacologic reduction of MAP within the normal autoregulatory limits of cerebral perfusion pressure, 90 mins after onset, had no adverse effect on ICP and regional cerebral blood flow in regions around or distant to the hematoma. These results support the controlled use of antihypertensive treatment in intracerebral hemorrhage in the initial time period.

Reduction of infarct volume by halothane: effect on cerebral blood flow or perifocal spreading depression-like depolarizations

Halothane is a strong inhibitor of potassium evoked spreading depression (SD) in cats. In the current study, we investigate halothane effects on induction of perifocal SD-like depolarizations, CBF, and infarct evolution in focal ischemia. Calomel and platinum electrodes measured cortical direct current potential and CBF in ectosylvian, suprasylvian, and marginal gyri. Left middle cerebral artery occlusion (MCAO) induced permanent focal ischemia for 16 hours in artificially ventilated cats (30% oxygen, 70% nitrous oxide) under halothane (0.75%, n = 8) or alpha-chloralose anesthesia (60 mg/kg intravenously, n = 7). Under alpha-chloralose, MCAO induced severe ischemia in ectosylvian and suprasylvian gyri(mean CBF < 10 mL/100 g/min), and direct current potentials turned immediately into terminal depolarization. In marginal gyri, CBF reduction was mild (more than 20 mL/100 g/min), and in six of seven animals, frequent SD-like depolarizations turned into terminal depolarization at a later stage of the experiments. Under halothane, MCAO induced severe ischemia (less than 10 mL/100 g/min) and immediate terminal depolarization only in ectosylvian gyrus. In suprasylvian gyrus, residual CBF remained significantly higher (more than 10 mL/100 g/min) than under alpha-chloralose, whereas in marginal gyri, CBF did not differ between groups. Compared with chloralose, the number of transient depolarizations was significantly reduced in marginal gyrus, and in suprasylvian gyrus transient but significantly longer depolarizations than in marginal gyrus were recorded. Except for one animal, transient depolarizations did not turn into terminal depolarization under halothane, and infarct volume reduction was particularly seen in suprasylvian gyrus. We conclude that halothane, the most commonly used anesthetic in studies of experimental brain ischemia, has protective properties, which may depend on both cerebrovascular and electrophysiologic influences.

Ligation of lateral carotid artery attenuates disturbance of brain function caused by subsequent cerebral ischemia in rabbits

The effects of right carotid artery ligation on the subsequent cerebral ischemia, induced by iron particle injection, in rabbits, were evaluated by recording somatosensory evoked potentials (SEPs) and cerebral blood flow (CBF) using laser Doppler flowmetry. Iron particle injection decreased CBF over 120 min and delayed SEP onset latency in rabbits with no previous carotid artery ligation (control group). In rabbits with a carotid ligation 3 days before, iron particle injection induced the decrease of CBF, as in the control group, but did not prolong the latency of SEP. Injection of iron particles induced only a transient decrease of CBF (less than 10 min) followed by an abrupt recovery, and no prolongation of SEP latency was observed in rabbits with a carotid ligation 6 days before. These results suggest that carotid artery ligation induces a beneficial effect on cerebral function during the subsequent ischemia, which is independent on the CBF changes.

Somatosensory evoked potentials in cerebral ischemia of rabbits

Twenty-one rabbits were used in the ischemic group and six in the control group. Cerebral ischemia of variable degree was induced by Fe particle injection method. Somatosensory evoked potentials (SEPs) and cerebral blood flow (CBF) were compared when the CBF levels decreased to their minimum. The latency of the SEPs increased along with the decrease of the CBF when it was lower than 20 ml/100 g/min (68% of the pre-ischemic control level). This may be related to the ischemic change of the white matter. The amplitude showed diphasic changes. When the CBF decreased below 20 ml/100 g/min, the amplitude increased; when the CBF was lower than 11 ml/100 g/min (38% of the pre-ischemic level), it decreased. These results indicate that the functions of the cerebral cortex might be excited in mild ischemia, and be suppressed in severe ischemia.

Rapid monitoring of changes in water diffusion coefficients during reversible ischemia in cat and rat brain

Changes in the diffusion constant of water during reversible brain ischemia and cardiac arrest were monitored with a 10-s time resolution. Results (five cats, three rats) indicate that these changes are reversible and that the bulk of the changes are not caused by temperature or motion related to brain pulsations and blood flow. The rapid time course of the changes corresponds to the known time course for changes in energy state, signal transduction, and ionic homeostasis.