Transcranial Doppler sonographic measurements of middle cerebral artery flow velocity during hyperbaric oxygen exposures

In the present study, experimental exposures to hyperbaric oxygen (HBO2) were performed (30-min exposure to 2.8 bar (280 kPa) pure oxygen). During all phases of the experiment, blood flow velocity in the right middle cerebral artery was monitored with transcranial Doppler (TCD) sonography. Time courses of heart rate, blood pressure, respiratory rate, end-tidal CO2, and TCD mean velocity (Vmean) are described for a group of 23 subjects during uncomplicated exposure to HBO2 and for three subjects who showed signs of central nervous system (CNS) O2 toxicity, including one subject with a HBO2-induced generalized tonic-clonic seizure. Hyperbaric oxygen decreased Vmean an effect that could not completely be explained by changes in end-tidal CO2. The findings of the present study are in agreement with the concept that an increase in partial oxygen pressure is the primary factor underlying CNS O2 toxicity. Of the variables analyzed, the TCD Vmean is the most valuable variable for monitoring a HBO2 exposure. The Vmean showed the most pronounced change during HBO2 application, and in one subject a sudden increase in Vmean during HBO2 exposure heralded toxicity before clinical signs. It should be realized, however, that the small series of subjects with toxicity in this study does not allow us to draw definite conclusions.     

Effect of dehydroepiandrosterone sulfate on fetal middle cerebral artery flow velocity waveforms in term pregnancy

OBJECTIVE: To investigate whether bolus injection of dehydroepiandrosterone sulfate (DHAS) is associated with changes in fetal middle cerebral artery flow velocity waveforms in term pregnancy. METHODS: Ten normal full-term pregnant women received the administration of a 200-mg intravenous dose of DHAS in 20 ml of 5% dextrose. Ten normal full term pregnant women received 20 ml 5% dextrose as controls. Color Doppler flow imaging and pulsed Doppler ultrasonographic assessments were made on fetuses in each group before and 10 min, 30 min, 60 min, 90 min. and 120 min after DHAS or dextrose administration. The pulsatility index (PI) values for the middle cerebral artery, and umbilical artery, and fetal heart rate were recorded. RESULTS: In the DHAS group, middle cerebral artery PI decreased from baseline by 24% (p<.05) after 10 min, and the mean reduction was 22% (p<.05) after 30 min. The PI returned to the baseline value 60 min later. In the control group, there was no change in middle cerebral artery PI. No change was found in umbilical artery PI or fetal heart rate in the control or DHAS group. CONCLUSION: DHAS induces a significant decrease in the fetal middle cerebral artery PI, which suggests a possible decrease in fetal cerebral vascular impedance in term pregnancy.     

Changes in maternal middle cerebral artery blood flow velocity associated with general anesthesia in severe preeclampsia

In women with severe preeclampsia, significant increases in mean arterial pressures (MAP) are common after rapid induction of general anesthesia (GA) and tracheal intubation. The objectives of this prospective study were to assess the effects of the rapid induction-intubation technique on middle cerebral artery (MCA) flow velocity in severe preeclampsia and to examine the correlation between mean MCA flow velocity (Vm) and MAP. Eight women with severe preeclampsia (study group) and six normotensive women at term (control group) scheduled to undergo cesarean section under GA were studied. Before induction, patients in the study group received i.v. labetalol in divided doses to lower diastolic pressures to <100 mm Hg. Anesthesia was induced with pentothal 4-5 mg/kg, followed by succinylcholine 1.5 mg/kg to facilitate tracheal intubation. A transcranial Doppler was used to measure Vm. Both Vm and MAP were recorded before induction and every minute for 6 min after intubation. In the study group, after the administration of labetalol, MAP decreased from 129 +/- 9 to 113 +/- 9 mm Hg (P < 0.05), and Vm decreased from 59 +/- 11 to 54 +/- 10 cm/s (P < 0.05). After intubation, MAP increased from 113 +/- 9 to 134 +/- 5 mm Hg (P < 0.001), and Vm increased from 54 +/- 10 to 70 +/- 10 cm/s (P < 0.001). In the control group, while MAP increased significantly from 89 +/- 6 to 96 +/- 4 mm Hg (P < 0.05) after intubation, the concurrent increase in Vm from 49 +/- 5 to 54 +/- 7 cm/s was not significant. There was a significant positive pooled correlation between Vm and MAP (r = 0.5, P < 0.0006) in the study group but not in the control group (r = 0.24). After induction and intubation, both Vm and MAP values were significantly increased in the study group patients at all observation points compared with the control group patients. The findings indicate that Vm increases significantly after rapid-sequence induction of GA and tracheal intubation in women with severe preeclampsia, and there seems to be a direct relationship between MAP and Vm. Implications: In women with severe preeclampsia, rapid-sequence induction of general anesthesia and tracheal intubation can cause severe hypertension. Our results indicate that the increase in blood pressure is associated with a significant increase in maternal cerebral blood flow velocity and that there is a significant correlation between these two variables.     

Stability of thrombosis induced by electrocoagulation of rat middle cerebral artery

BACKGROUND AND PURPOSE: Although it is often assumed in experimental stroke studies that cautery-induced occlusion is permanent, surgeons commonly expect cauterized vessels to recanalize spontaneously. We used the rat middle cerebral artery to determine if electrocoagulation would produce a permanent occlusion in this preparation. METHODS AND RESULTS: A standard bipolar coagulator, calibrated to determine actual power output, was adjusted to induce platelet aggregation in the middle cerebral artery of anesthetized Sprague-Dawley rats without inducing bleeding through the arterial wall. A reliable temporary thrombosis was induced by a Malis Bipolar Coagulator set to deliver 10 bursts of 1.5 seconds each at a rate of 24 min-1 and a power setting of 3 W. This thrombus was responsive to the antithrombotic agent flunarizine. An apparently permanent occlusion was produced by 30 bursts at 3 W followed by 20 bursts at 5 W. To our surprise, seven of seven such occlusions recanalized spontaneously within 4 hours. CONCLUSIONS: The electrocoagulation process commonly used in experimental stroke studies may produce only a temporary occlusion of the rat middle cerebral artery.     

Changes in local cerebral blood flow, local EEG, and flow in the distal stump of the middle cerebral artery in cats with occlusion of the middle cerebral artery

The local EEG, the local cerebral blood flow (lCBF), and the flow in the distal stump of the occluded middle cerebral artery was simultaneously recorded in 28 acute experiments in cats. Nembutal anaesthesia was used eleven times, and Halothane anaesthesia 17 times. The recordings were made via platinum electrodes: 12 in the ischaemic hemisphere, and 2-3 in the opposite non-ischaemic hemisphere. The flow in the occluded middle cerebral artery was recorded via a platinum electrode introduced into this artery via the transorbital approach. The changes in lEEG, lCBF, and middle cerebral artery flow were studied during normotension, hypertension, and hypotension. A beneficial effect of hypertension was noted in the acute phase of brain ischaemia. Hypertension counteracted also the "diaschisis" in the non-ischaemic part of the ischaemic hemisphere and in the opposite non-ischaemic hemisphere. A correlation between lEEG changes and lCBF changes was noted. In addition, an interesting discrepancy was observed between the rapid H2 clearance in the middle cerebral artery stump and the much slower H2 clearance in the ischaemic brain area. Significant differences between experiments under Halothane and experiments under Nembutal anaesthesia were noted. In the acute phase those changes are probably the result of the different levels of blood pressure in those two groups.     

Lack of asymmetry of middle cerebral artery blood velocity in unilateral migraine

BACKGROUND AND PURPOSE: A recent transcranial Doppler study found reduced blood velocity in seven patients during migraine attacks in the middle cerebral artery at the headache side. This would implicate vasodilation of the middle cerebral artery in the pathogenesis of headache in migraine. We attempted to confirm this finding. METHODS: We determined blood velocity with transcranial Doppler ultrasonography in the middle cerebral arteries of 51 migraine patients with unilateral headache (5 with aura, 46 without aura) and of 14 patients with bilateral headache, during and outside attacks. During attacks, median time from onset of attack to transcranial Doppler examination was 6 hours (range, 1 to 35 hours). RESULTS: We found no difference between blood velocity at the headache and nonheadache sides nor between blood velocity during and outside attacks. Similar results were obtained in a subgroup of 11 patients who were investigated in the first 4 hours of an attack. There were also no differences between attacks with unilateral or bilateral headache. CONCLUSIONS: We cannot support the hypothesis that migraine is associated with vasodilation of the middle cerebral artery ipsilateral to the headache.     

Dynamic exercise enhances regional cerebral artery mean flow velocity

In recent years hyperbaric oxygen has gained an important role in the treatment of osteoradionecrosis of the mandible. In the treatment of 29 patients with osteoradionecrosis of the mandible, a combination of surgical debridement, antibiotics, and hyperbaric oxygen was used in 27 cases. In 20 of the 29 patients the osteoradionecrosis was considered to be resolved after treatment. In 31% of the patients, the continuity of the mandible was lost. It was concluded that combined treatment of surgical debridement, antibiotics, and hyperbaric oxygen gives acceptable results and may, when used in an early phase of the disease, limit the number of patients who lose continuity of the mandible.     

Global and local processing of hierarchical visual stimuli in tufted capuchin monkeys (Cebus apella).

Capuchin monkeys' (Cebus apella) relative accuracy in the processing of the global shape or the local features of hierarchical visual stimuli was assessed. Three experiments are presented featuring manipulations of the arrangement and the density of the local elements of the stimuli. The results showed a clear advantage for local level processing in this species, which is robust under manipulations of the density of the local elements of the stimuli. By contrast, the density of the component elements linearly affected accuracy in global processing. These findings, which support those from other studies in which a local superiority emerged in animals, challenge the generality of early claims concerning the adaptive value of global advantage in the processing of hierarchical visual patterns. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cholinergic modulation of cerebral cortical blood flow changes induced by trauma

These experiments tested the role of cholinergic mechanisms in the changes of cerebral cortical blood flow (CBF) induced by brain trauma. CBF was measured with Iodo-14C-antipyrine autoradiography, in 128 cerebral cortex regions of both hemispheres, distributed in eight coronal slices. The effects of a 6.3-mm diameter craniotomy over the left motor-sensory cortex with no weight drop, and of trauma (drop weight of 20 g from 30 cm height on left motor-sensory cortex through a 6.3 mm circular craniotomy) on CBF were studied at 2 and 24 h after the interventions. A group of control animals that received no intervention was also set up. Animals were treated with the cholinesterase inhibitor physostigmine salicylate (3.3 microg/kg/min i.v. infusion started 60 min before CBF measurements), the cholinergic blocker scopolamine hydrobromide (1 mg/kg i.v. pulse, 18 min before CBF measurements), or with the drugs vehicle (saline). A focus of decreased CBF at the site of impact was observed 2 h after trauma, extending caudally as far as the occipital cortex. CBF on the contralateral cerebral cortex was also decreased. Both phenomena reversed partially at 24 h. This spontaneous recovery of CBF was blocked by scopolamine. Physostigmine reversed the decrease in CBF of the traumatized cortex, partially around the contused area and completely in more distant regions. The cerebral cortex contralateral to the trauma showed significantly higher CBF 24 h after trauma when compared to intact controls or craniotomy that peaked at the area symmetrical to the center of trauma. This phenomenon was also enhanced by physostigmine and completely blocked by scopolamine. These results suggest a prominent role of cholinergic mechanisms in the vascular adjustments that accompany cerebral trauma.     

Changes in blood flow velocity and diameter of the middle cerebral artery during hyperventilation: assessment with MR and transcranial Doppler sonography

PURPOSE: To compare blood flow velocity changes within the middle cerebral artery (MCA) during hyperventilation, as measured with by both transcranial Doppler sonography and MR imaging, with the diameter of the MCA as measured with MR imaging alone. METHODS: The studies were performed in six healthy volunteers ranging in age from 22 to 31 years (mean, 27 years). Transcranial Doppler sonography was carried out with a range-gated 2-MHz transducer. MR examinations were done on a 1.5-T imaging unit. MR angiography was performed using the time-of-flight technique. MR flow measurements were carried out by using the phase-mapping technique with an ECG-triggered phase-contrast sequence. RESULTS: During hyperventilation, the mean blood flow velocity of the proximal MCA declined by 49.6% +/- 5.7 (mean +/- standard deviation) as measured with Doppler sonography, and by 47% +/- 4.6 as measured with MR flow calculation. The diameter of the MCA (3.4 +/- 0.3 mm) remained unchanged on MR imaging studies (3.3 +/- 0.3 mm). CONCLUSION: We found a good correlation between relative flow velocity changes measured by transcranial Doppler sonography and MR techniques. MR imaging revealed no significant changes in the diameter of the proximal MCA during normal versus hyperventilation. Relative changes in flow velocity in the MCA would thereby reflect relative changes in cerebral blood flow, at least during hyperventilation.     

Regional cerebral blood flow during and after 2 hours of middle cerebral artery occlusion in the rat

In this study we explored if the secondary bioenergetic failure, which occurs a few hours after recirculation, following transient middle cerebral artery occlusion (MCAO) in rats, is caused by a compromised reflow. We induced 2 hours of MCAO and measured CBF at the end of the ischemia, as well as 15 minutes, 1, 2, and 4 hours after the start of recirculation, using autoradiographic or tissue sampling 14C-iodoantipyrine techniques. After 2 hours of MCAO, the autoradiographically measured CBF in the ischemic core areas was reduced to 3 to 5% of contralateral values. The reduction in CBF was less in neighboring, penumbral areas. After recirculation, flow already normalized in core tissues after 15 minutes, and remained close to normal for the 4 hours recirculation period studied. However, in penumbral tissues, recovery CBF values were usually below normal. The results show that tissues that are heavily compromised by the 2-hour period of ischemia and are destined to incur infarction, show a "relative hyperemia" during recirculation. In fact, some areas of the previously densely ischemic tissue showed overt hyperperfusion. This finding raises the question whether the relative or absolute hyperemia reflects events that are pathogenetically important. Because drugs that clearly ameliorate the final damage incurred fail to alter the relative hyperperfusion of previously ischemic tissues, it is concluded that vascular events in the reperfusion period do not play a major role in causing the final damage.     

Simultaneous recording of cerebrospinal fluid pressure and middle cerebral artery blood flow velocity in patients with suspected symptomatic normal pressure hydrocephalus

Whether anaphylactic histamine release from rat peritoneal mast cells is influenced by betahistine, a histamine H1-receptor agonist/H3-antagonist, and dimaprit, an H2-agonist, was examined. Treatment with dimaprit at 6 and 60 microM for 20 min significantly inhibited the anaphylactic histamine release, whereas betahistine at up to 80 microM under the same conditions did not affect it. Treatment with dimaprit at 6 and 60 microM for 1 to 20 min and for 5 to 20 min, respectively, caused a time-dependent inhibition of the release, but up to 30 min treatment with 8 and 80 microM betahistine had no effect. The decreased histamine release induced by dimaprit was recovered by neither mepyramine nor cimetidine. However, thioperamide, an H3-selective antagonist, dose-dependently restored the diminished release. From these results, the inhibition of anaphylactic histamine release by dimaprit is not produced by the stimulation of H2-receptors, but involves the stimulation of H3-like receptors or H3-subtype receptors, which are distinct from the H3-receptors located in brain, and suggests that the receptor plays an important role in the negative feedback regulation of histamine release.     

Regional cerebral blood flow increases during preparation for and processing of sensory stimuli

The transferrin receptor (TFR) has been detected in tissues characterised by a high degree of proliferation. We have developed a procedure for isolating TFR from human placental tissues by affinity chromatography on transferrin-Sepharose. Using gel filtration and electrophoresis in 7% PAAG, it has been shown that the molecular mass of the protein is 180 kDa. The protein has a subunit structure and is made up of two identical subunits, 90 kDa each. The constant for the protein binding to transferrin is equal to 5 x 10(-9) M. The yield of the protein isolated by the novel procedure exceeds 5-fold that obtained by previously described methods.     

An analysis of hierarchical processing in visual perception.

Perception is viewed as a process in which attributes of a stimulus are analyzed in step-wise fashion. 2 experiments with 19 undergraduates, were carried out in which the attributes of spatial location and identity were examined for 2 types of materials. Results indicate that identification of letters requires more stimulus energy than identification of lines. There were no differences between identification of lines, localization of lines, or localization of letters. In general, results support a hierarchical processing hypothesis. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of acute hypocapnia on middle cerebral artery transcranial Doppler velocity during orthotopic liver transplantation: changes at reperfusion

This study examines the effects of acute hypocapnia, instituted prior to reperfusion of the graft liver, on the middle cerebral artery (MCA) Doppler blood flow velocity response to reperfusion during orthotopic liver transplantation in humans. Seventeen patients with chronic liver disease underwent continuous, noninvasive Doppler imaging of the MCA. Hyperventilation to an end-tidal Pco2 of 25 +/- 1 mm Hg was associated with a decrease in mean MCA flow velocity (FVm) from 51.6 +/- 5.7 to 37.0 +/- 3.3 cm/s (P < 0.05). After reperfusion, the Paco2 increased from 32 +/- 1 to 40 +/- 1 mm Hg (P < 0.05), mean arterial pressure (MAP) decreased from 76 +/- 3 to 60 +/- 2 mm Hg, and the FVm increased from 37.0 +/- 3.3 to 54.0 +/- 4.7 cm/s (P < 0.05). FVm increased postreperfusion despite prior hyperventilation, decreased MAP, and abrupt increases in central venous and pulmonary artery pressure, but FVm did not exceed the prereperfusion level. In 10 of the 17 patients, the baseline FVm versus Paco2 response slopes and Paco2 measured postreperfusion were used to predict the FVm response to Paco2 after reperfusion. The slopes were similar to those reported for anesthetized patients without liver disease. Predicted FVm exceeded measured FVm in 9 of the 10 patients. We conclude that mild hyperventilation prior to reperfusion of the graft liver prevents FVm increases above prereperfusion baseline level.     

Giant aneurysm of the middle cerebral artery

A case of a giant aneurysm of the middle cerebral artery, (4.5 X 4.5 X 9.5 CM) presenting as a mass lesion, which was successfully excised is described. This case is compared to the few previous accounts of giant aneurysms of the middle cerebral artery larger than 3 cm in diameter.     

Significance of a diastolic notch in the uterine artery flow velocity waveform induced by uterine embolisation in the pregnant ewe

OBJECTIVE: To determine whether water exposure causes middle ear contamination in patients with collar button tympanostomy tubes (TTs). METHOD AND DESIGN: An in vitro model of a human head that contained an auricle, external auditory canal, tympanic membrane with TT, middle ear, eustachian tube, and mastoid cavity was developed. Two electrodes connected to an external ohmmeter resided in the middle ear to detect water entry. The model was tested with 4 types of water exposure: showering, bathing, hair rinsing, and swimming. Statistical analysis was performed by the Fisher exact test. MAIN OUTCOME MEASURES: A positive test result corresponded to water entering the middle ear via the TT, confirmed by a resistance reading of zero on the ohmmeter. A negative test result indicated no change in the initial high resistance reading. RESULTS: No positive test results were obtained for showering (0 of 60 tests), hair rinsing (0 of 60 tests), or head submersion (12.7 cm) in clean tap water (0 of 60 tests). Ten positive test results were obtained for head submersion in soapy water (10 of 97 tests), which was statistically different from clean water (P< or =.007). Swimming pool depths of 30, 45, 60, and 75 cm elicited positive test results in 2 of 16, 3 of 18, 2 of 20, and 11 of 20 tests, respectively. A higher incidence of water entry into the middle ear occurred at depths of more than 60 cm (P< or =.001). No statistical difference between depths of 60 cm or less occurred (P= .88). CONCLUSIONS: Showering, hair rinsing, and head submersion in clean tap water do not promote water entry into the middle ear. Submersion in soapy water increases the probability of water contamination. Pool water infrequently enters the middle ear with head submersion, but the incidence increases with deeper swimming (>60 cm). These data provide further evidence that many water precautions frequently advised in patients with TTs are unnecessary.     

An integrated analysis of the progression of cell responses induced by permanent focal middle cerebral artery occlusion in the rat

Defining the chronology and severity of cell damage in an evolving lesion after ischemia is important for understanding the underlying mechanisms in the development of therapeutic intervention. In the present study, we used a combination of histological and immunocytochemical methods to evaluate cell responses from 30 min to 48 h after permanent occlusion of the middle cerebral artery (MCAO) in the rat. Specific immunocytochemical markers clearly revealed acute early responses in neurons (neurofilament protein 200), astrocytes (glial fibrillary acidic protein), and microglia/macrophages (OX-42 and ED-1) such as enlarged, convoluted neuronal processes, and disintegration of glia. Progressive topographic changes in the developing lesion, pinpointed by immunolabeling, indicated the severity and extension of the cell damage. Proliferation and hypertrophy of astrocytes and microglia around the infarct, and contralaterally, occurred 24-48 h after MCAO and coincided with mass necrosis and infiltration of neutrophils and macrophages into the core. These observations corroborate the suggestion that the inflammatory process is involved in the progression of the infarct.