The influence of the angle of confluence on the flow in a vertebro-basilar junction model

In earlier work, it was demonstrated that the flow in models of the vertebro-basilar junction is highly three-dimensional and the geometry exerts a strong influence on the hemodynamics. The morphology of the vertebro-basilar junction is very variable amongst individuals. In a study of 85 human vertebro-basilar junctions, the angle between the vertebral arteries varied between 10 and 160 degrees. To determine how the flow is influenced by this geometrical parameter, the flow is studied both experimentally, with laser Doppler velocimetry, and numerically, with a finite element package. A series of junction models is used with a range of confluence angles (45, 85 and 125 degrees). It appears that the angle of confluence has a strong influence on the structure and strength of the secondary flow field. The secondary velocities persist far downstream. Furthermore, near the apex, a region with low velocities is present. The larger the confluence angle is, the larger this region is, and even backflow may occur. In addition, the occurrence of atherosclerotic plaques in 85 human vertebro-basilar junctions is studied. Only one preferential location was found: the apex, the other plaques seem to be randomly distributed. The magnitude of the confluence angle of junctions with sharp-edged apices has a significant influence (p = 0.006) on the occurrence of a plaque at the apex. Apparently, a large confluence angle is a geometrical risk factor for atherosclerosis.

Distribution and physiological roles of ATP-sensitive K+ channels in the vertebrobasilar system of the rabbit

The effect of an opener (levcromakalim) and a blocker (glibenclamide) of ATP-sensitive K+ (KATP) channels was investigated in the vertebrobasilar system of the rabbit. Arterial tension and membrane potential were measured by the isometric tension recording method and the microelectrode technique, respectively. Glibenclamide (10(-6) mol/L) depolarized the membrane and potentiated the contraction to histamine in vertebral arteries. The sensitivity to the relaxant effects of levcromakalim was in the following descending order: vertebral > proximal basilar > distal basilar > superior cerebellar arteries. Vertebral arteries were approximately 50 times more sensitive to levcromakalim than were superior cerebellar arteries. The relaxation to levcromakalim was abolished by glibenclamide (10(-6) mol/L). Glibenclamide attenuated vasorelaxation to adenosine in proximal arteries (vertebral and proximal basilar) but not in superior cerebellar arteries. Levcromakalim (7 x 10(-8) mol/L) and adenosine (10(-5) mol/L) induced glibenclamide-sensitive membrane hyperpolarization in vertebral arteries but not in distal basilar arteries. These results suggest that KATP channels contribute to the determination of resting membrane potential and resting tone in vertebral arteries. Furthermore, there is a marked heterogeneity in the sensitivity to an opener of KATP channels, and the heterogeneity has a functional link to the mechanism underlying vasorelaxation to adenosine in the vertebrobasilar system of the rabbit.

Are the effects of local joint movement on blood flow limited to the vertebral and internal carotid arteries? Doppler studies of the ulnar artery

OBJECTIVE

To determine what effect wrist extension has on ulnar artery blood flow.

DESIGN AND SETTING

This is a descriptive study performed at a private chiropractic clinic. SUBJECT SELECTION: Sixty-three ulnar arteries were examined from thirty-two volunteers, 15 men and 17 women, whose ages ranged from 21-75 yr. Only wrists that were asymptomatic and freely mobile were candidates for ulnar artery examination.

INTERVENTION

The arteries were insonated approximately 2 cm proximal to the pisiform bone using a continuous-wave Doppler flow meter in the neutral position and during passive wrist extension to the limit with the fingers straightened.

MAIN OUTCOME MEASURES

The persistence or loss of Doppler signals.

RESULTS

Doppler signals from 83% (0.99 confidence interval: 68% < p < 93%) of arteries stopped. In 4% of vessels, the signals were markedly reduced; in 13%, they remained apparently unchanged.

CONCLUSION

Blood flow in ulnar arteries can be severely restricted during wrist extension. By using Doppler ultrasound, the ulnar artery may provide a good model of local joint movement effects on arterial blood flow.

Effects of adrenomedullin, calcitonin gene-related peptide, and amylin on cerebral circulation in dogs

The effect of human adrenomedullin on cerebral circulation was investigated in dogs in vivo and in vitro. Bolus administration of adrenomedullin or its homologous peptides, calcitonin gene-related peptide (CGRP) and amylin, into the vertebral artery induced a dose-dependent increase in vertebral blood flow. The potencies of adrenomedullin and CGRP were similar and approximately 100 times more than that of amylin. The effects of adrenomedullin and CGRP were inhibited by CGRP8-37, an antagonist of CGRP. In contrast to substance P, adrenomedullin did not induce an increase in blood flow after prior administration of CGRP. Pretreatment with either NG-nitro-L-arginine methyl ester or indomethacin did not affect the adrenomedullin-induced increase in blood flow. Intracisternal administration of adrenomedullin induced dilation of the basilar and other major cerebral arteries in a dose-dependent manner, accompanied by an increase in the concentration of cyclic AMP in the cerebrospinal fluid. Adrenomedullin also induced relaxation of isolated basilar and middle cerebral arterial rings. These data suggest that adrenomedullin induces vasodilation of cerebral arteries and an increase in vertebral blood by acting at CGRP receptors positively coupled to adenylate cyclase, and that these effects are not dependent on nitric oxide or prostaglandin formation.

Cardiac arrest after traffic accident induced through vagal reflex in a case with bilateral stenosis of vertebral arteries

An 84-year-old driver suffered cardiac arrest after a traffic accident. He was quickly resuscitated and transferred to a hospital where he was treated in a state of unconsciousness and respiratory failure for 20 days until his death. The brain stem was rendered anoxic during cardiac arrest, which caused the respiratory failure. Artificial ventilation and catecholamine infusion were carried out, resulting in myocardial degeneration. Bilateral stenosis of the vertebral arteries was disclosed, but no injuries or hemorrhage of the brain and spinal cord were detected. On days 3 and 4 after admission, immediately after the head of the victim was flexed forward for examinations, cardiac arrest was induced twice, but was controlled either by administering atropine or by restoring the original posture. Positional change is known to induce vagal reflex that results in bradycardia, hypotension or cardiac arrest in sensitive persons. The victim might have undergone the reflex-mediated cardiac arrest after the accident, to which the stenosis of the vertebral arteries may have contributed.

The effects of pituitary adenylate cyclase-activating polypeptide on cerebral arteries and vertebral artery blood flow in anesthetized dogs

We investigated and compared the effects of pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) on cerebral circulation in anesthetized dogs. The intracisternal administration of PACAP-27, PACAP-38, and VIP dilated canine cerebral arteries in a dose-dependent manner. A 10 nmol dose of PACAP-27, PACAP-38, and VIP dilated the basilar artery by 23 +/- 3, 27 +/- 3 and 30 +/- 3%, respectively. Rostrally located arteries tended to be more responsive to PACAP-27. Pretreatment with NG-monomethyl-L-arginine did not affect PACAP-27-induced vasodilation. Vertebral artery blood flow was also affected by intra-arterial injection of these peptides in a dose-dependent manner. A 100 pmol dose of PACAP-27, PACAP-38, and VIP increased the vertebral artery blood flow by 42 +/- 10, 29 +/- 4, and 62 +/- 11%, respectively. The VIP receptor antagonist, [Lys1,Pro2,5,Arg3,4,Tyr6]VIP, inhibited both the VIP- and PACAP-38-induced increase in vertebral artery blood flow. These findings suggest that PACAP plays a role in the regulation of cerebral circulation.

Doppler sonography of vertebral arteries and audiovestibular system investigation in leprosy

Thirty-six patients with leprosy and 12 sex- and age-matched controls were investigated for disorders of the audiovestibular system, and vertebral artery measurements were calculated using a color Doppler ultrasound technique. Sensorineural hearing loss found to be of cochlear origin was detected in 8 of the leprosy patients. Maximal flow velocity and mean flow velocity were measured, and the total vertebral artery flow was calculated by adding flows from the right and left sides. There was a significant reduction in the total maximal peak flow velocity of the vertebral artery of the lepromatous patients compared to the controls. Doppler sonography of the vertebral artery gave useful information about some pathology seen in lepromatous patients.

Changes of blood flow velocity indicating mechanical compression of the vertebral arteries during rotation of the head in the normal human measured with transcranial Doppler sonography

The dynamical changes of blood flow velocity of the intracranial vertebral arteries (VA's) and proximal basilar artery (BA) provoked by rotation of the head in normal volunteers were measured using pulsed-wave transcranial Doppler sonography (TCD). In another group both VA's were examined simultaneously with 2-channel TCD. Blood flow velocities diminished compared to the neutral position in all vessels, independently of the side. Total obstruction of the flow was not observed. Our findings reveal a definitive decrease of blood flow velocity at the vertebrobasilar artery system provoked by rotation of the head in normal humans. This physiological phenomenon is suggested to have an impact on the cerebral blood flow in patients with impaired autoregulation of the cerebral vessels, low volume flow reserve in the contralateral VA or insufficient collateral channels because of normal anatomical variation, especially those patients under general anesthesia or comatose.

Measurement of anterior and posterior circulation flow contributions to cerebral blood flow. An ultrasound-derived volumetric flow analysis

Ultrasound-derived volumetric flow analysis may be useful in answering questions of basic physiological interest in the cerebrovascular circulation. Using this technique, the authors have sought to describe quantitatively the complete concurrent flow relations among all four arteries supplying the brain. The aim of this study of normal subjects was to determine the relative flow contributions of the anterior (internal carotid arteries) and posterior (vertebral arteries) cerebral circulation. Comparisons between the observed and theoretically expected anterior and posterior flow distribution would provide an opportunity to assess traditional rheological conceptions in vivo. Pulsed color Doppler ultrasonography was used to measure mean flow rates in the internal carotid and vertebral arteries in 21 normal adults. The anterior circulation (internal carotid arteries bilaterally) carried 82% of the brain's blood supply and comprised 67% of the total vascular cross-sectional area. These values demonstrate precise concordance between observations in vivo and the theoretically derived (Hagen-Poiseuille) expected flow distribution. These cerebrovascular findings support the traditional conception of macroscopic blood flow. Further studies using ultrasound-derived volumetric analysis of the brain's arterial flow relations may illuminate the vascular pathophysiology underlying aging, cerebral ischemia, and dementias.

[Measurement of cerebral blood flow in normal subjects by phase contrast MR imaging]

Global cerebral blood flow (CBF) was quantitatively measured with a two-dimensional phase contrast cine magnetic resonance (MR) imaging technique in 24 normal subjects (mean age, 38.6 years; range, 12-70 years). Cine transverse images of the upper cervical region (32 phases/cardiac cycle) were acquired with a 1.5 Tesla MR imaging unit. In five subjects, measurement of CBF was performed before and after intravenous administration of acetazolamide (DIAMOX, 15 mg/kg). Inter- and intraobserver variations in flow volume measurement were small (r = 0.970, standard error of the estimate (SEE) = 2.9 ml/min, n = 80; r = 0.963, SEE = 4.6 ml/min, n = 40, respectively). In measuring flow velocity, they were inferior to those of flow volume measurement. On a visually determined setting of region of interest (ROI), reproducibly of the measurement of flow velocity was not satisfactory in this study. Thus only the results of flow volume measurement are presented. Mean summed vertebral flow volume (171 ml/min, SD = 40.6) was significantly less than mean summed internal carotid flow volume (523 ml/min, SD = 111). Total blood flow volume showed a significant decline with age (r = 0.45, p < 0.05). The mean proportions of carotid and vertebral flow volume to total flow volume were 75.3% and 24.7%, respectively, and showed no significant change with age. The left-to-right ratio of vertebral flow volume (1.39) was significantly higher than that of internal carotid flow volume (0.99, r = 0.05). After DIAMOX i.v., the mean rate of increase in total flow volume was 157%. Mean rates of increase in carotid and vertebral flow volume were 154% and 166%, respectively, which were not significantly different. In conclusion, this method is useful for estimating carotid and vertebral flow volume.

[Effect of sevoflurane on blood flow velocity in the vertebral artery]

Blood flow velocity in the vertebral artery was measured using transcranial Doppler sonography during sevoflurane anesthesia in 12 patients in the knee-chest position. The correlation between mean arterial blood pressure (MBP) and mean blood flow velocity in the vertebral artery (Vmean) was significant in each patient. Normalized data expressed as a percentage of the individual arithmetic means permitted a composite analysis of data from all patients. Linear regression of normalized MBP (%MBP) on normalized Vmean (%Vmean) showed %Vmean = 24.8 +/- 0.75 %MBP (r = 0.78, P < 0.01). The results of the present study suggest that fluctuations in systemic blood pressure may lead to fluctuations in cerebral blood flow. Therefore, the use of sevoflurane anesthesia must be accompanied by careful management of blood pressure during surgery.

Comparison of measurement of stump pressure and transcranial measurement of flow velocity in the middle cerebral artery in carotid surgery

Transcranial Doppler ultrasound measurement of the velocity of blood flow in the middle cerebral artery (MCA) was performed in 24 consecutive patients undergoing carotid endarterectomy. Measurements were performed preoperatively at rest, following common carotid artery compression, and continuously during surgery. In addition, internal carotid artery stump pressures were measured and a subjective assessment of back flow was made. No relationship between MCA flow velocity and stump pressure following carotid clamping was demonstrated. Peak and mean MCA flow velocity was significantly lower in patients with stump pressures < 30 mm Hg (p < 0.03) and those with poor back flow (p < 0.02).

Blood flow dynamics in the vertebrobasilar system: correlation of a transparent elastic model and MR angiography

PURPOSE

To describe the flow patterns in a model of the vertebrobasilar artery and use these observations to explain the appearance of the flow on the MR images.

METHODS

We created an anatomically precise, transparent elastic model of the human vertebrobasilar artery containing a basilar tip aneurysm and perfused the model with non-Newtonian fluid which has similar rheologic properties to blood. Flow patterns in the vessels were directly observed. MR angiogram images were obtained with commercially available two-dimensional time-of-flight, three-dimensional time-of-flight, and 3-D phase-contrast MR angiographic pulse sequences, and they were correlated with the directly seen flow patterns. Quantitative flow velocity measurements were performed with 2-D cine phase-contrast MR angiography and correlated with the flow measured with an electromagnetic flow meter.

RESULTS

Visualization studies showed the dye stream patterns in the vertebrobasilar arteries to be extremely complex and variable. During the MR experiments we found that often the same segment of a vessel could appear very different depending on the pulse sequence. In some instances, the model experiments helped to explain the MR appearance of the vessels. Flow profiles measured with 2-D cine phase contrast were found to be consistent with those measured directly with an electromagnetic flow meter.

CONCLUSION

Clear elastic models can be used to duplicate the flow in human cranial vessels and thus provide a unique means to observe these flow patterns directly. The flow patterns helped to explain the variation in appearance of the vessels and the artifacts with different MR angiography pulse sequences. The artifacts depend on both the geometry of the vessel and the flow pattern within it. Two-dimensional cine phase-contrast MR provides temporal flow field information that is directly related to physiological information about flow volumes and velocity patterns.

Blood flow measurements in the aorta and major arteries with MR velocity mapping

The purpose of this study was to measure antegrade and retrograde flow in the aorta and the major arterial pathways in the body noninvasively with cine magnetic resonance (MR) velocity mapping, to determine the hemodynamic significance of retrograde flow in arteries. Two hundred forty cine velocity maps for blood flow measurements were obtained at 29 sites in the aorta and the major arteries in 31 healthy human subjects of varying age at rest. Synchronous or isolated antegrade and retrograde flow was found in the entire aorta and in arteries supplying muscles. No retrograde flow was found in arteries supplying internal organs, such as the internal carotid or splanchnic arteries. The retrograde flow in the aorta and the extremity arteries contributes substantially to supplying diastolic perfusion of internal organs such as the heart, brain, and kidneys. Antegrade flow tends to be helical in the thoracic aorta.

Endothelium dependency of contractile activity differs in infant and adult vertebral arteries

Contractions to serotonin (5-HT) and endothelin-1 (ET-1) in infant (0-2 yr) and adult (38-71 yr) vertebral arteries were examined in the presence of either the cyclooxygenase inhibitor indomethacin or NG-monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide production. In addition, endothelium-dependent relaxations to acetylcholine were characterized in arteries contracted with agonist. The results showed that: (a) Contractions of infant arteries to 5-HT or ET-1 decreased to 44 +/- 8% and 27 +/- 13%, respectively, within 10 min. Indomethacin or removal of endothelium abolished this decreased response, whereas L-NMMA had no effect. (b) Adult arteries produced sustained contractions to 5-HT or ET-1 that were unaffected by indomethacin, endothelium denudation, or L-NMMA. (c) Endothelium-dependent relaxations to acetylcholine were greater in infant than adult arteries and were abolished by indomethacin (but not L-NMMA) in infants and L-NMMA (but not indomethacin) in adults. Thus, endothelium-dependent responses in infant arteries are attenuated because of increased prostaglandin activity not observed in adult tissues. Additionally, there is an age-dependent change in the primary mechanism responsible for acetylcholine-induced vasodilation. Apparently, endothelium dependency of acetylcholine-induced relaxation is highly dependent on cyclooxygenase activity in the infant vertebral artery, but in the adult artery, nitric oxide is linked to the vasodilator response.

A validation study on the intraobserver reproducibility of transcranial color-coded duplex sonography velocity measurements

Transcranial color-coded duplex sonography (TCCD) is a new method for the measurement of angle-corrected intracranial blood velocities. The insonation angle represents the most important technical variable affecting Doppler velocimetry. The present study was designed to evaluate the intraobserver reproducibility of TCCD for repeated examinations of blood velocity in the anterior, middle and posterior cerebral, basilar and vertebral arteries. Three examinations were performed by the same examiner in each of 20 healthy volunteers within 10 days, with a minimal interval of 2 days between two subsequent examinations. The observer was blinded to previous results. The reproducibility was evaluated by calculating the correlation coefficient (r) and the coefficient of variance (CV) of the difference between the values obtained from the second and the third examination vs. the first examination. The results showed good reproducibility of TCCD velocity measurements in all examined arteries: for maximal systolic velocity r was 0.80-0.94 (p < 0.001), and CV was 5.5-9.4%; for maximal end-diastolic velocities r was 0.89-0.94 (p < 0.001), and CV was 6.6-12.2%.

Carotid and vertebral artery blood flow in left- and right-handed healthy subjects measured with MR velocity mapping

The goal of the study was to establish normal carotid artery flow rates in left-handed and right-handed individuals as a standard against which patients with carotid artery disease could be compared. Antegrade and retrograde flow were measured in the ascending aorta, in the right and left common, internal, and external carotid arteries, and in the vertebral arteries of 12 healthy subjects. Five subjects were right-handed, five left-handed, and two ambidextrous. Measured flow rates were as follows: common carotid arteries, 360-557 mL/min (mean [+/- standard deviation], 465 mL/min +/- 52); internal carotid arteries, 132-367 mL/min (mean, 265 mL/min +/- 60); external carotid arteries, 113-309 mL/min (mean, 186 mL/min +/- 51); vertebral arteries from 133-308 mL/min (mean, 244 mL/min +/- 43); and cerebral circulation, 546-931 mL/min (mean, 774 mL/min +/- 134). All right-handed subjects had higher flow rates in the left internal carotid artery than in the right, and all left-handed subjects had higher flow rates in the right internal carotid artery (P = .007). There were no significant differences in left and right common carotid artery flow rates between left- and right-handed subjects. The standard deviation of a single measurement was 5%. The flow rates were similar to those obtained previously with other techniques and could be used as a normal standard.

[The relation of vertebral artery blood flow velocity to mean arterial pressure during anesthesia with enflurane or isoflurane]

The relation of vertebral artery blood flow velocity (VABFV) to mean arterial pressure (MAP) during anesthesia with enflurane or isoflurane was examined. The subjects were 17 patients on the knee-chest position. Anesthesia was induced with thiamylal and fentanyl. The patients were placed on the knee-chest position after tracheal intubation. Ventilation was adjusted to maintain a constant level of PaCO2 (30-40 mmHg). The patients were divided into two groups. Anesthesia was maintained with enflurane and 67% N2O in group E (8 patients), or with isoflurane and 67% N2O in group I (9 patients). VABFV was measured with a transcranial Doppler sonography (TCD), and MAP was measured through a radial artery catheter. The mean VABFV and MAP were recorded at five-minute intervals. VABFV was found to change with the change in the MAP for the same degree in both groups. The results suggest that cerebral autoregulation is disturbed during either isoflurane-N2O or enflurane-N2O anesthesia.

[Changes of blood flow velocity in the extracranial and basilar arteries in physiological aging]

The maximal blood flow velocity was assessed in extracranial and cephalad arteries: ophthalmic, supratrochlear, common carotid, superficial temporal, subclavian and vertebral in 150 clinically healthy subjects aged 18 to 80 years using continuous ultrasound 5 MHz wave. In all the arteries the flow velocity was decreasing with age. The degree of velocity decrease varied between various arteries, especially in the common carotid and subclavian arteries, less so in the ophthalmic and vertebral arteries, and least in the supratrochlear and superficial temporal arteries. In a small number of cases the maximal systolic velocity was very low in the supratrochlear and ophthalmic arteries although this velocity and the neurological status were normal in these subjects.

Computation of steady three-dimensional flow in a model of the basilar artery

The flow in the basilar artery arises from the merging of the flows from the two vertebral arteries. To study the flow phenomena in the basilar artery, computations have been performed using a finite element (FE) method. We consider steady flow in a geometrically symmetric confluence. For simplicity, channels with a rectangular cross-section have been used. Both symmetric and asymmetric flow cases have been considered. The results show that for the Reynolds number of interest the flow downstream of the junction is highly three-dimensional, and that the flow at the end of the basilar artery, where it splits again, will not be fully developed. The computed phenomena have been confirmed by laser Doppler velocity measurements.

Evaluation of the vertebrobasilar-posterior system by transcranial color duplex sonography in adults

BACKGROUND AND PURPOSE

The transcranial color duplex sonography technique was applied to the vertebrobasilar-posterior system to provide normal data for clinical application.

METHODS

The intracranial posterior circulation was studied in 49 healthy volunteers (mean +/- SD age, 35 +/- 12 years) by a transcranial and suboccipital approach with a 2.0-MHz sector transducer of a computed sonography system.

RESULTS

The posterior cerebral artery and the vertebrobasilar system were depicted clearly in the color Doppler mode. Pulsed Doppler signals could be recorded in the posterior cerebral (100%), basilar (92%), and vertebral arteries (89%). The following normal values were provided for all vessels: systolic peak, end-diastolic maximum, time-averaged, and time-averaged maximum velocities; resistance and pulsatility indexes; and a spectral broadening index. Mean +/- SD values were 45.9 +/- 9.6, 45.5 +/- 10.8, and 39.2 +/- 10.6 cm/sec for time-averaged maximum velocity, and 28.3 +/- 6.5, 30.6 +/- 7.2, and 24.7 +/- 8.4 cm/sec for time-averaged velocity in the posterior cerebral, basilar, and vertebral arteries, respectively. In a reproducibility study, duplex measurements of the posterior cerebral arteries were repeated in 27 subjects. The correlation between the two examiners was high (r = 0.56, p less than or equal to 0.0001 for time-averaged maximum velocity).

CONCLUSIONS

Color duplex sonography of the vertebrobasilar-posterior system is a new, noninvasive, bedside investigative technique. It permits visualization of artery flow in real time, relating these to adjacent brain and cranial structures, as well as angle-corrected duplex measurement of "true" flow velocities at defined sites of the vessels. Thus, it will open new diagnostic possibilities in disorders of the posterior circulation.

[Differences of regional blood flow after stellate ganglion block with local anesthetic and that after stellate ganglion resection using ultrasonic Doppler flowmeter]

Ten mongrel dogs were divided into two groups; stellate ganglion block (SGB, n = 5) group and stellate ganglion resection (SGR, n = 5) group. Anesthesia was induced with pentobarbital 25 mg.kg-1. The animals were mechanically ventilated to maintain a constant PaCO2 (35-40 mmHg). Left common carotid arterial flow (CCAF), left external carotid arterial flow (ECAF), left vertebral arterial flow (VAF) and left brachial arterial flow (BAF) were measured using an ultrasonic transit time flowmeter. Internal carotid arterial flow (ICAF) was calculated by subtracting ECAF from CCAF. After thoracotomy, the first SGB with 0.5% mepivacaine 1.5 ml or SGR was performed. Ninety minutes after the first SGB, the second SGB was performed. The data were taken for 180 minutes after the first SGB or SGR. In SGB, CCAF and BAF increased significantly for the duration of action of local anesthetic. But VAF and ICAF increased significantly for a short time after the block. In SGR, CCAF, BAF and ICAF increased significantly during the experiment. But VAF showed a transitory increase immediately after the resection. The authors conclude that sympathetic ganglion block with local anesthetic should be performed repeatedly when increase of blood flow in blood vessels with strong autoregulation from the brain is anticipated.

Effects of M6434, an orally active .ALPHA.1-adrenoceptor agonist, on experimental postural hypotension in rabbits and dogs

We examined the effects of M6434 on mean blood pressure and heart rate in conscious rabbits and dogs and on experimental models of postural hypotension in conscious rabbits and anesthetized dogs. M6434, given orally, elevated the mean blood pressure in conscious rabbits and dogs. The pressor effect of M6434 was more potent than that of midodrine, but the bradycardiac action of M6434 was weaker than that of midodrine. M6434 (1.0 and 3.0 mg/kg, p.o.) prevented the head-up tilt-induced reductions of mean blood pressure and cerebral tissue blood flow in conscious rabbits, and these effects of M6434 were about 3 times more potent than those of midodrine. In the postural hypotension of anesthetized dogs, M6434 at the doses more than 10 micrograms/kg, i.v. also produced the preventive effects on mean blood pressure and cerebral tissue blood flow. These effects of M6434 were about 10-30 times more potent than those of midodrine. These results show that M6434 possesses a potent hypertensive effect with a weaker bradycardiac action and suggest that M6434 may be a potential candidate for an anti-hypotensive agent that can prevent the deterioration of hemodynamics in postural hypotension.

A new model of global postischemic reperfusion in rabbit

An ideal model of global ischemia in rabbits has not yet been developed. The present study describes a new model of global postischemic reperfusion (GPIR) in the rabbit, characterized by lack of systemic hypotension. The experimental procedure involves reversible occlusion of the bilateral internal carotid arteries (ICA) and bilateral external carotid arteries (ECA) for 60 min combined with permanent ligation of bilateral vertebral arteries (VA). This grouping is called 6-artery occlusion (6AO). Sixty minutes after the occlusion, bilateral ICA and bilateral ECA were released for 120 min at which time the experiment was terminated. The results revealed severely depressed EEG activity; Water content of brain tissue increased to 80.33 +/- 1.20% (control 78.28 +/- 0.59%, p less than 0.01); K, Mg, and Zn decreased (p less than 0.05 or p less than 0.01), and were negatively correlated with tissue water content. Na increased (p less than 0.05) and correlated with water content of brain. No significant changes were observed in lipid peroxide (LPO) levels, but the activity of superoxide dismutase (SOD) of brain tissue decreased (p less than 0.01), and was negatively correlated with water content (r = -0.5808, p less than 0.05). These results were compared with those obtained with the model of 4-artery (bilateral common carotid arteries (CCA) and VA) occlusion (4AO) and suggested that the brain damage be more severe with 6AO than with 4AO.

Color-coded Doppler imaging of normal vertebral arteries

Using color-coded Doppler sonography, we studied the vertebral arteries of 42 persons without history or physical signs of vertebrobasilar disease. The intertransverse portion of the vertebral artery was visualized in all persons on both sides. Its origin was visualized in 37 persons (88.1%) on the right side and in 28 (66.7%) on the left; the atlas loop was visualized in 32 persons (76.2%) on the right side and in 36 (85.7%) on the left. Four vertebral arteries were hypoplastic. Peak systolic blood velocity ranged from 19 to 98 (mean 56) cm/sec and peak diastolic blood velocity ranged from 6 to 30 (mean 17) cm/sec. Resistive indices ranged from 0.62 to 0.75 (mean 0.69). Thus, color-coded Doppler sonography seems to be a promising noninvasive method for the evaluation of hemodynamics in the extracranial portion of the vertebral arteries.

Cochlear blood flow following temporary occlusion of the cerebellar arteries

In order to induce acute transient local blood flow impairment in the guinea pig cochlea, terminal vessels arising from the proximal and middle third of the basilar artery and from the rostral part of the collateral vertebral artery near their junction were occluded by temporary (1-2 min) compression. Clear identification of the anterior inferior cerebellar artery was impeded due to great variation in branching of the cerebellar arteries. To quantify the effect of the vascular occlusion on the cochlear microcirculation, laser Doppler flowmetry was used. Successive compression of the cerebellar arteries resulted in individually differentiated effects on the Doppler signal from the cochlea. In about half of the experiments there was a decrease in the laser signal to 25-55% of the initial level, while in the other cases no clear decrease occurred. Proximal obstruction of the basilar artery was found to reduce the cochlear blood flow up to 10-25% of its initial level, indicating that the Doppler signal primarily reflects microcirculation within the membranous cochlea. The findings are discussed with regard to their significance as an animal model for acute transient cochlear hypoxia.

Endothelin causes contraction of canine and bovine arterial smooth muscle in vitro and in vivo

We have studied the effect of endothelin, an endothelium-derived peptide, on isolated canine and bovine cerebral arteries in vitro and on canine vertebral blood flow (VBF) in vivo. Endothelin produced a dose-dependent contraction of canine and bovine arterial smooth muscle with ED50 values ranging from 4 to 8 nM. The response to endothelin developed slowly and persisted as a sustained contraction. Maximal contraction by endothelin required the presence of extracellular calcium and was independent of the presence of endothelium. The maximal contraction produced by endothelin was approximately 2-3 times greater than that produced by neuropeptide Y or angiotensin II. The injection of endothelin into the vertebral artery decreased vertebral blood flow (VBF) dose-dependently without affecting systemic blood pressure or heart rate. The decrease in VBF produced by endothelin was long-lasting, like that produced by neuropeptide Y, but more potent. The present data, together with our previous study demonstrating that the intracisternal injection of endothelin induces an unusually long-lasting decrease in the basilar artery diameter angiographically, suggests that endothelin may act as a long-lasting vasoconstrictor in cerebral vascular disease.

Effect of subclavian flap angioplasty on growth and circulation of the left front leg in pigs

The effect of subclavian flap angioplasty on the growth of the left front limb and on its collateral circulation was studied in 11 pigs. The left subclavian artery and its first branch, the costocervical trunk, were divided while the remaining three branches--the deep cervical, the vertebral and the internal thoracic artery--were preserved. Postoperative angiographies (5 pigs) showed that the blood supply to the left front limb was maintained through these three branches, which acted as collaterals, supplying blood in retrograde fashion. The left vertebral artery was seen to be the predominant collateral already on postoperative day 1. Four months later the diameter of the left vertebral artery had increased more than that of the contralateral (right) vertebral artery. Eight months postoperatively the size of both front legs (6 pigs) was the same. No signs of cerebral disturbance were seen. The clinical implications of the findings are discussed.

[Pharmacological study of TJ-8007 (tsumura-zokumeito) (II): Protective effect of TJ-8007 against cerebral ischemia]

It has been demonstrated that TJ-8007 (Tsumura-Zokumeito, A traditional Chinese medicine) has a protective effect against cerebral anoxia. This study was done to elucidate the protective mechanism of TJ-8007 against cerebral ischemia and anoxia. TJ-8007 (0.3 approximately 3.0 g/kg, p.o.) inhibited the rise in the cumulative mortality rate after ligation of the bilateral carotid artery (BCA) in mice. TJ-8007 also significantly prolonged the survival time at the dose of 3.0 g/kg, p.o. However, TJ-8007 (1.0 or 3.0 g/kg, p.o.) did not affect the mean survival time after ligation of BCA in Mongolian gerbils and the gasping movement in a decapitated mouse head that served as a complete ischemic model. Ifenprodil (30 mg/kg, p.o.) also showed the protective effect only against ischemic death after ligation of BCA in mice. TJ-8007 (1.0 or 3.0 g/kg, p.o.) increased the vertebral blood flow, but showed no effect on the internal carotid blood flow in anesthetized dogs. These results suggest that the mechanism for the cerebral protective effect of TJ-8007 may be due to its ameliorating action on the cerebral circulation.

Mathematical models of the flow in the basilar artery

The flow in the basilar artery arises from the merging of the flows from the two vertebral arteries. This study deals with the question whether a parabolic (Poiseuille) profile will have been established before the basilar artery divides into both posterior cerebral arteries. The inlet length (that is, the downstream distance needed for the flow to become approximately equal to the limiting Poiseuille flow) and velocity profiles have been computed from two- and three-dimensional mathematical models in which flow pulsatility and vessel wall distensibility have been neglected and the complex geometry of the junction has been taken into account in a simplified form. The results show that the flow at the end of the basilar artery is far from being parabolic and that an asymmetry in the entrance flow will be carried along towards the end of the basilar artery, thus affecting flows in the circle of Willis.

Effects of pentobarbital and cyproheptadine on brain ischemia induced by bilateral occlusions of carotid arteries and vertebral arteries of second cervical vertebra in rats

The bilateral hemispheric ischemia in rats was induced by the occlusion of bilateral common carotid arteries after permanent electrocauterization of bilateral vertebral arteries at the level of the second cervical vertebra. In ischemic rats, (a) electroencephalograms became flat immediately after occlusion of carotid arteries, and (b) mortalities reached maximum levels at day 3 after recirculation. These results suggested that a constant level of cerebral ischemia was produced in this rat model. Pentobarbital markedly inhibited the mortality in these ischemic rats, whereas cyproheptadine did not.

Heterogeneous vasomotor responses of anatomically distinct feline cerebral arteries

1. The vasomotor reactivity to a number of neurotransmitters and blood-borne substances was evaluated in several anatomically distinct arteries of the cat cerebral circulation. Few regional differences were observed in their vasoconstrictor responses to noradrenaline, dopamine, 5-hydroxytryptamine and prostaglandin F2 alpha. Only the anterior cerebral artery reacted strongly to all vasoconstrictor agents. 2. Adenosine, acetylcholine and histamine induced pronounced relaxation in the vast majority of the major cerebral arteries. The relaxation elicited by adenosine showed a slight degree of heterogeneity between the arteries and the overall response accounted for 81 +/- 6% of the pharmacologically-induced tone. On the other hand, the dilatation induced by acetylcholine and histamine varied as a function of the anatomical localization of the cerebral arteries. The acetylcholine-induced vasodilatation was significantly more pronounced in the middle cerebral, anterior communicating and anterior cerebellar arteries, with respective responses of 72, 66 and 83% of the induced tone as compared to 43% in the other vessels. However, all arteries were equally sensitive to acetylcholine with an overall mean pD2 value of 7.47 +/- 0.06. The most heterogeneous results were obtained with histamine and applied both to the magnitude of the maximal response and the sensitivity of the various arteries to this amine. The intensity of the relaxation varied from 20% (anterior communicating artery) to 118% (posterior cerebellar artery). 3. Among the neuropeptides studied, substance P and bradykinin were considerably less potent than vasoactive intestinal peptide on all the cerebral arteries. The least responsive vessel to bradykinin was the anterior cerebral artery with a maximal response of 22 +/- 5% of the induced-tone and a pD2 value of 7.56 +/- 0.24. All vessels responded weakly to substance P and those from the vertebrobasilar circulation were significantly less sensitive to this neuropeptide with pD2 values around 8.07 as compared to 9.82 in the more rostral arteries. Although all vessels were equally sensitive to vasoactive intestinal peptide, the dilator responses were significantly less pronounced in the middle cerebral and basilar arteries (maximal response of 86 +/- 5% and 69 +/- 6% of the induced-tone, respectively, as compared to 110 +/- 9% in the other vessels). 4. The vertebrobasilar arteries were as reactive, if not more reactive, to vasoconstrictors than the vessels originating from the carotid circulation. In contrast, the dilator responses were less marked in most caudal arteries. Such dichotomies may be important in the regulation of local cerebral blood flow. 5. The results emphasize the considerable heterogeneity in the vasomotor responses to a given substance among the various cerebral arteries. Further, they suggest the presence of multiple receptor populations which mediate opposite effects and which are distributed in different proportions among the cephalic arteries.

Input impedance of the canine vertebral artery

In experiments on six anaesthetized dogs it was found that the vertebral artery contributed 69.2 +/- 1.7% of cerebral and 41.5 +/- 2.5% of cephalic flow. The input characteristics were that the vertebral artery had a flow of 0.71 +/- 0.05 ml X s-1 into an input impedance of 23.7 +/- 1.9 GN X m-5 X s. This compared to external and internal carotid flows of 0.69 +/- 0.05 and 0.31 +/- 0.02 ml X s-1 into input impedances of 23.9 +/- 2.1 and 52.1 +/- 2.7 GN X m-5 X s respectively. Standardized per 100 g of tissue the impedances of the vertebral and internal carotid arteries were similar at 18.6 +/- 2.0 and 19.1 +/- 1.5 GN X m-5 X s X 100 g-1 respectively, while that for the external carotid was higher at 129.9 +/- 10.2 GN X m-5 X s X 100 g-1. The impedance spectrum for the vertebral artery was of low impedance type, settling about a characteristic impedance of 2.01 +/- 0.28 GN X m-5 X s without significant oscillation, associated with the phase only becoming slightly positive above 10 Hz and reflexion coefficients of less than 0.25 by a frequency of 6 Hz. This was similar to the spectrum for the internal carotid artery and contrasted with the high impedance spectrum with major reflexion found for the external carotid artery.

Cerebrospinal fluid pulse pressure and the pulsatile variation in cerebral blood volume: an experimental study in dogs

The cerebrospinal fluid pulse pressure (CSFPP) has found application as a measure of intracranial elastance. However, CSFPP is also dependent on the magnitude of the pulsatile variation in cerebral blood volume (delta Vb). The purpose of the present study was to assess the effect on delta Vb of changes in systemic arterial pressure (SAP) and arterial carbon dioxide tension (PaCO2) as well as elevation of intracranial pressure (ICP). Therefore, delta Vb was computed from the electromagnetically measured flow profile in the vertebral artery of the dog on the assumption of a nonpulsatile cerebral venous outflow. During arterial hypotension, delta Vb was increased due to a shift of flow from diastole to systole, whereas mean flow was not affected. The reverse phenomenon was observed when SAP was raised. Changes in PaCO2 had little effect on pulsatile blood flow. The changes in total blood flow that occurred were evenly distributed over the cardiac cycle. Consequently, delta Vb was not significantly affected, although CSFPP was considerably changed. When ICP was raised, a breakpoint pressure was observed above which cerebral blood flow (CBF) decreased and CSFPP and delta Vb increased. This contradiction was explained by the finding of a decrease in diastolic flow, causing the fall in CBF, whereas systolic flow relative to mean flow was increased, resulting in an increased delta Vb. The underlying mechanisms of the pulsatile flow changes are extensively discussed. It is argued that the arterial inflow profile is largely determined by the compliance of the inflow section of the cerebral vascular bed. Vascular compliance is significantly altered by changes in SAP and ICP because they affect the transmural pressure of the vessels, whereas this is not the case during changes in PaCO2.

Delayed reversal of vertebral artery blood flow following percutaneous transluminal angioplasty for subclavian steal syndrome

Twelve patients suffering from subclavian steal syndrome of various severity due to either proximal subclavian stenoses (10 cases) or subclavian occlusion (2 cases) were treated with percutaneous transluminal angioplasty (PTA). Olbert's dilatation catheters were used. The occlusions could neither be recanalized by the transfemoral nor transaxillary approach. In one right-sided subclavian stenosis an additional distal subclavian occlusion prevented proper placement of the catheter. All the other patients were treated successfully with no re-occlusion during a follow-up period of 1 to 7 months. In one patient, a transient embolic occlusion of the finger arteries was seen following post-interventional repeat angiography. Before, during and after PTA, continuous ultrasound monitoring of the homolateral vertebral flow patterns revealed an unexpected "delay" phenomenon. Despite sufficient recanalization of the proximal subclavian artery, the flow direction within the vertebral artery did not immediately change to antegrade but rather did so gradually within 20 s up to several minutes. This delay of flow-reversal is thought to serve as a protective mechanism against cerebral embolism during, and shortly after PTA of the subclavian artery. Relying on Doppler ultrasound findings, a staging of the subclavian steal is proposed in order to allow adequate selection of patients for PTA.

[Condition of the internal arterial and microcirculatory bed of the neck muscles of the dog after simultaneous ligation of the common carotid and vertebral arteries]

In 21 mongrel dogs changes in the intraorganic arterial and microcirculatory bed of the cervical muscles have been studied after a simultaneous ligation of the common carotid and vertebral arteries. The most pronounced changes of rearrangement are observed during early periods after the operation (up to two months). The form, size of the arterial loops and direction of the blood stream change in them. On the base of the arterio-arterial anastomoses collateralies are formed, their degree of development is progressing with the increase of the postoperative time. The arteriolo-arteriolar anastomoses in small loops convert into microvascular collateralies that are of importance only during early postoperative stages. The new conditions of hemodynamics at the arteriolar level result in a dependent rearrangement in other links of the microcirculatory bed, where a number of compensatory-adaptive mechanisms are revealed. After the magistral by-pass ways are completely formed, the changes observed disappear and the microcirculatory network acquires the features specific for intact animals.

Distribution of the blood flow supplied by the vertebral artery in humans as assessed by emission CT

Though unilateral blood distribution of the vertebral artery has not been studied in humans, it is significant when considering the ischemic events especially embolic occlusion in vertebrobasilar system. To clarify the blood distribution, Krypton-81m was continuously infused into the vertebral arteries of 10 patients. Radioactivity was recorded by a rotating gamma camera. The perfusion images, reconstructed by computer in the transaxial plane, were classified according to whether the distribution was equal, or predominantly unilateral. Overlapping of blood supply from each vertebral artery was studied. In addition, the perfusion from one of the vertebral arteries revealed four distribution patterns with respect to laterality. A) ipsilateral; B) contralateral; C) bilateral; D) mosaic. Images obtained following perfusion of the vertebral artery show less uniformity compared to that of the internal carotid artery, suggesting a complicated vascular supply of the vertebral basilar territory. This complex distribution can be classified by the use of continuous infusion of Krypton-81m.

Non-invasive and quantitative measurement of volume flow-rate at internal and external carotid and vertebral arteries

A non-invasive and quantitative system to measure the volume flow-rate, velocity and diameter in the internal and external carotid arteries and vertebral artery was developed. It was verified from the model experiment and clinical applications that this system could provide quite useful flow informations in small and sinuous artery within 8% error.

[Control and regulation of the blood circulation in the vertebro-basilar system. Review of the literature]

The author establishes an analogy between the control mechanism and regulation of the cerebral blood flow and of protection of the vascular wall of the internal carotid constituted by the conjunction "internal carotid-cavernous sinus" with the group represented by the system "vertebro basilar-transverse occipital sinus or basilar" (an extension of the cavernous sinus) in the regulation and control of the encephalic circulation carried out through this latter vessels, together with the protection of its vascular walls. The author believes to be very difficult to demonstrate in practice the functioning of these mechanisms, but it is very logical and easy to reason about them, to value them and to give the importance and meaning or motive which forcibly they should have and not simply consider them as freaks of nature and bizarre anatomical features.

Biomechanical study on aging changes and vasospasm of human cerebral arteries

Mechanical properties of human intracranial arteries were studied with regard to their aging changes as well as cerebral vasospasm. There exists a considerable difference in the development of sclerosis between the intracranial and the extracranial arteries. Intracranial arteries are already stiff at birth and become stiffer with age. Their increase in stiffness is attributable to the marked thickening of their walls, which compensates for the decrease of their elastic modulus with age. The pressure-diameter curve of the intracranial vertebral arteries subjected to subarachnoid hemorrhage is biphasic and has a sharp flexion at the pressure of 180 mmHg when their smooth muscle is activated. Pressure elevation yields little change of diameter in the strongly constricted vessel up to the pressure level at the flexion point, above which the constriction is released abruptly. The existence of flexion point at a high pressure level is an important mechanical feature in considering the development of cerebral ischemia produced by the vasospasm.

Numerical analysis of blood flow in the vertebral artery

Abnormal hemodynamic forces associated with distortions of blood vessel lumen have been thought to play an important role in the pathogenesis of focal vascular lesions. In the vertebral artery, segments located between osseous rings are ectatic compared with those surrounded by the rings. Based on the assumption that arterial blood flow was quasi-steady, this work was undertaken to investigate the structure of flow through arterial models with one or two sinusoidal stenoses. Numerical analysis was performed by an integral-momentum method. The validity of the method was examined by comparison of experimental data so far reported with theoretical results. Velocity and wall shear stress distributions were explored in a model with two stenoses simulating a part of the vertebral artery. The ectatic segments of the vertebral artery have been known as predilection sites for atherosclerotic lesions. The present study suggested that the ectatic wall was under unstable shear stresses, the direction of which was dependent upon the magnitude of the Reynolds number.

Cerebral blood flow changes in orthostatic dysregulation fainters

The changes in blood flow of both the internal carotid and the vertebral artery during orthostatic test with or without fainting attack were studied in 25 healthy children and 30 patients with orthostatic dysregulation (OD). In healthy children and non-fainted OD patients, no change in blood flow occurred in either the internal carotid artery or the vertebral artery during orthostatic test. On the other hand, a significant decrease in blood flow of the internal carotid artery and/or the vertebral artery occurred during fainting of OD patients. These data suggest that three mechanisms might be involved in fainting of OD patients; a decrease in blood flow of the internal carotid artery, the vertebral artery and a decrease in blood flow of both these arteries.

A mathematical model of the flow in the posterior communicating arteries

This paper reports on a mathematical model designed to study the hemodynamics of one posterior communicating artery and its afferent and efferent vessels. The variables in the model are the diameter of the posterior communicating artery, the resistance in the vertebral artery and the ratio of the two peripheral resistances. In the model, the "posterior communicating artery" exhibits a compensatory capacity, as defined in the introduction, which appears to be independent of its diameter. The fluxes in the efferent vessels are dominated by the peripheral resistances.

Central cardiovascular effects of physostigmine in the cat; possible cholinergic aspects of blood pressure regulation

The cental actions of the lipophilic cholinesterase inhibitor physostigmine were investigated by infusing very low doses (0.8 micrograms up to 18 micrograms per kg) into the left vertebral artery of the anaesthetized cat. A dose as low as 2.7 micrograms per kg reduced blood pressure by about 35%. High doses caused bradycardia. Occlusion of the right vertebral artery shifted the dose-response curve to the left. It seems likely that the hypotension was due to stimulation of muscarinic receptors in the pontomedullary region, since pretreatment with dexetimide administered via the vertebral artery strongly reduced the effect. Mecamylamine and the adrenergic blocking agents metoprolol and piperoxan, infused into the vertebral artery, could not reduce the depressor response and the bradycardic action. Both bilateral cervical vagatomy and peripherally applied N-methylatropine did not change the hypotensive action of physostigmine. This observation points towards a reduction of sympathetic outflow as the possible cause of the depressor effect. Atenolol, given intravenously, diminished the bradycardia to a great extent, whereas N-methylatropine did not significantly alter the negative chronotropic action of physostigmine. These results suggest a dominant role for the sympathetic system in reducing cardiac frequency. After intravenous administration, only doses higher than 28 micrograms per kg evoked hypotension, which could not be blocked by intravenously administered N-methylatropine. However, centrally infused dexetimide considerably antagonized this effect, indicating that the hypotension was brought about by a central action and not evoked peripherally. Application of the drug via the external carotid arteries resulted in hypotension after considerably higher doses than those following administration via the vertebral artery, indicating the pontomedullary region as the main site of action. It is concluded that the present experimental data obtained with physostigmine support the hypothesis that ACh might have a transmitter role in the central haemodynamic control.

[Age characteristics of the regional hemodynamic state of cosmonauts]

Hemodynamics of the large hemispheres of the brain, vertebral-basilar system, lungs and legs of 60 cosmonauts, aged 30-37 and 38-47, was investigated rheographically. Measurements were made in the morning, under conditions of basal metabolism and in the daytime, before orthostatic tests. Comparison of the hemodynamic parameters recorded in the morning and at the daytime and in the two age groups showed significant differences revealing the effects of different factors, first of all psychoemotional tension, on the vasomotor regulation, and greater resistance of cerebral and pulmonary vascular systems of older cosmonauts to those effects. These investigations emphasize great importance of studies of regional hemodynamics, especially rheoencephalography, not only before provocative tests but also under conditions of basal metabolism.