Changes in vertebral artery blood flow following normal rotation of the cervical spine

BACKGROUND

Extreme rotation of the cervical spine may cause compromised vertebral artery (VA) blood flow. This is of particular interest to manual therapists because of the potential risks associated with these movements. The question is whether the decreased blood flow is significant and therefore likely to cause vertebrobasilar insufficiency/ischemia (VBI) and whether contralateral and ipsilateral rotations are equally affected. Several studies measuring VA blood flow have been reported. However, different parts of the VA were studied, in small samples of normal subjects and patients over a wide range of ages. Hence, the results are controversial.

OBJECTIVE

To investigate intracranial VA blood flow in normal male subjects and female subjects, aged 20 to 30 years, in neutral and maximally rotated cervical spinal positions.

METHODS

Transcranial Doppler sonography was used to measure intracranial VA blood flow, with the cervical spine in neutral and then rotated maximally to the left and later to the right. The sample consisted of 60 male subjects and 60 female subjects (240 VAs). Comparisons between the neutral and rotated head positions were made within and between the groups.

RESULTS

There was a significant decrease (P =.001) in intracranial VA blood flow following cervical spine rotation, irrespective of side but greater on the contralateral side, in the total sample and in male subjects. Female subjects had a significantly higher blood flow than male subjects, and although they showed a significant decrease with contralateral rotation, there was no significant difference in blood flow on the ipsilateral side.

CONCLUSION

Maximal rotation of the cervical spine may significantly affect vertebral artery blood flow, particularly when used in the treatment of patients with underlying vascular pathology.

The effect of cervical rotation on blood flow in the contralateral vertebral artery

Twenty asymptomatic volunteers (mean age 33 years, range 26 - 54 years) underwent investigation using duplex Doppler ultrasound with real-time imaging and colour flow enhancement. With the subjects seated, peak velocity at C1-2 and volume flow rate at C5-6 were measured in the artery contralateral to the direction of rotation, in the four positions of neutral, 45 degrees and end range rotation, plus a subsequent neutral position. No change in peak velocity at C1-2 between the initial neutral measurement and the measurements at 45 degrees and end range rotation was found (P>0.05). Peak velocity was less in both vertebral arteries on return to the neutral position as compared with end range rotation, however the difference was significant for the left vertebral artery only (P=0.005). This lends support for the rest period, which is taken between cervical movement tests when conducting pre-manipulative testing, to allow for any latent effect on blood flow of the tests themselves. There was no change in volume flow rate between any of the test positions (P=0.349). There was no indication of a cumulative effect of the test procedure (P>0.05).

[The effect of gravity on blood volumes in the main cervical arteries in healthy humans]

The study of the effect of gravity on blood volumes in the main cervical arteries was conducted with voluntary participation of 50 normal men and women. Blood volumes were determined with the ultrasound technique. The circulatory effect of gravity was simulated by administration of the active standing test. Circulating volumes in the common carotid, internal carotid and vertebral arteries in the supine position were 464, 342 and 110 ml/min, respectively and decreased significantly up to 352, 262 and 84 ml/min, respectively in the standing position. The orthostatic reduction in the volume of blood circulating along the vertebral artery was proportional to that in the internal carotid artery. Specific contribution of changes in vascular capacity to the blood volume reduction was shown to be predominant.

Mechanism of the antihypertensive effect of stevioside in anesthetized dogs

Stevioside is a sweet-tasting glycoside isolated from the leaves of Stevia rebaudiana. It has been used as a noncaloric sugar substitute in Japan and Brazil for decades. Previous studies have shown that it lowered blood pressure in spontaneously hypertensive rats by intravenous injection. This study was designed to evaluate the hypotensive effect of stevioside in dogs and to define the underlying mechanism. After nasogastric administration of stevioside powder (200 mg/kg), the blood pressure of healthy mongrel dogs began to significantly decrease at 60 min and returned to baseline level at 180 min. The reduction of blood pressure was more rapid (at 5-10 min) and effective after intravenous injection. However, no significant change of blood pressure was noted after injection through left vertebral artery, implicating that the hypotensive effect is not related to the central nervous system. Stevioside also showed significant hypotensive effects in renal hypertensive dogs, in a dose-dependent manner. In cultured rat aortic smooth muscle cells (A7r5 cell line), stevioside can dose-dependently inhibit the stimulatory effects of vasopressin and phenylephrine on intracellular Ca(2+) in a calcium-containing medium. However, no intracellular Ca(2+) inhibitory effect was observed in calcium-free medium, implicating that stevioside may inhibit the Ca(2+) influx from extracellular fluid. Our present data show that stevioside did not influence the calcium ionophore (A23187) induced Ca(2+) influx, indicating that the antagonistic effect was through Ca(2+) channels. This study confirmed that stevioside is an effective antihypertensive natural product, and its hypotensive mechanism may be probably due to inhibition of the Ca(2+) influx.

Cerebral autoregulation in middle cerebral artery territory precedes that of posterior cerebral artery in human cortex

OBJECTIVE

Cerebral autoregulation tends to compensate changes in arterial blood pressure. This mechanism of cerebral blood flow regulation appears to be insufficient in orthostatic dysregulation in which mainly vertebrobasilar symptoms occur. To investigate this hypothesis, we compared cerebral autoregulation in the vascular territory of the carotic and vertebrobasilar vessel system using a leg cuff test to induce a drop in cerebral perfusion pressure.

METHODS

We measured blood flow velocity in 10 healthy young volunteers (aged 26.7 +/- 0.3 years, 7 male) simultaneously in the middle and posterior cerebral artery with transcranial Doppler sonography. A leg cuff test was used to induce a sudden decrease in arterial blood pressure. Arterial blood pressure was measured with a non-invasive photoplethysmographic method. The averaged relative blood flow velocity changes due to the pressure step were compared between both vessel territories.

RESULTS

After cuff release systolic (diastolic) blood flow velocity increased with a latency of 1.1 +/- 0.3 s (1.8 +/- 0.4 s). Due to a smaller decrease and identical time courses cerebral blood flow velocity recovery in the posterior cerebral artery precedes blood flow recovery in the middle cerebral artery by 0.9 +/- 0.3 s.

DISCUSSION

Cerebral autoregulation in the carotid and vertebrobasilar system does not differ in the time course of the blood flow velocity recovery. Due to a smaller decrease in blood flow velocity recovery in the posterior cerebral artery precedes recovery in the middle cerebral artery by nearly 1 s.

[Blood flow of the vertebral artery in cases of pontine high intensity area identified by T2-weighted MRI--a study with ultrasonography of vertebral arteries]

Ultrasonography of vertebral arteries (Duplex method) was conducted in cases of pontine high intensity area identified by T2-weighted MRI. Patients complaining headache, vertigo and dizziness were classified into two groups: 19 cases with pontine high intensity area; and 58 cases of control without abnormality in the pons. In comparison with the control, the cases with pontine high intensity area had lower minimum diastolic flow velocity and stroke volume in the dominant vertebral artery, suggesting the presence of basilar artery insufficiency. These findings may support previous data that pontine high intensity area represents diffuse ischemia in the brainstem.

[Ischemia of the brain stem caused by compression of the vertebral arteries by head rotation--an etiology for SIDS?]

Hypoperfusion of the brainstem during head rotation may be a risk factor for the development of SIDS. On this background we established a Doppler sonographic screening programme of the basilar cerebral arteries to evaluate the dependency of blood flow on head and body position.

PATIENTS AND METHOD

We investigated 3840 newborns (1872 girls and 1968 boys) with a birth weight of 3399 +/- 497 g and a gestational age of 39.2 +/- 1.4 weeks. The investigations were performed in the neonatal period with an average age of 4.7 +/- 3 days. In all infants blood flow was measured in the basilar artery (BA) in supine position with the head in the midline. From the flow profile peak systolic flow velocity Vs and time average flow velocity TAV were measured. Additionally flow measurements were performed in supine and prone position with rotation of the head to the right and left side. A decrease of blood flow velocities below 50% of the value in neutral position was considered to be abnormal. Retrograde or biophasic flow profiles during rotation were considered to be pathologic. In infants with abnormal or pathologic flow during rotation of the head flow measurements in the vertebral arteries (VA) were additionally performed. Blood flow velocities in the VA were measured in supine and prone position with the head in the midline position and after rotation to the right and to the left. In neutral position unilateral vertebral hypoplasia, aplasia and normal VA were differentiated. The judgement after rotation was performed such as in the BA.

RESULTS

In 3807 infants (99.14%) blood flow velocities during head rotation did not decrease below 50% of the value measured in neutral position. In 33 infants (0.86%) a decrease of blood flow velocities below 50% could be found during rotation. In 7 infants (0.18%) a pathologic flow could be found during head rotation. 27 of the 33 infants with abnormal and pathologic blood flow in the BA during rotation showed anatomic abnormalities of the VA. 20 of these infants (61%) had unilateral vertebral hypoplasia (11 right, 9 left side), 7 (21%) had unilateral vertebral aplasia (4 right, 3 left side). 32 of the 33 infants with abnormal flow in the BA showed a decrease of blood flow in the contralateral VA during head rotation. 9 infants had an abnormal, 19 a pathologic flow within the contralateral VA. In 4 infants the corresponding VA could not be measured during head rotation. The decrease of blood flow velocities in the BA during head rotation was caused by compression of the contralateral VA at the craniocervical junction.

CONCLUSION

Blood flow within the basilar artery of healthy infants is independent of body position and rotation of the head. A decrease of the flow velocities below 50% during rotation has to be considered as an abnormality. The incidence of pathologic blood flow during head rotation with 1.8@1000 approximates the incidence of SIDS. Hypoperfusion of the brainstem during head rotation may be a risk factor of SIDS.

Effect of internal carotid artery occlusion on vertebral artery blood flow: a duplex ultrasonographic evaluation

The aim of this study was to evaluate the effect of unilateral internal carotid artery occlusion on blood flow volume and blood flow velocities in both vertebral arteries using duplex Doppler ultrasonography in the cervical segment. Forty patients with unilateral extracranial internal carotid artery occlusion confirmed by angiography were studied, and the results were compared with those obtained in 57 age-matched patients in whom cervical duplex ultrasonography showed no abnormalities. We measured the diameter, flow velocities, and blood flow volume in both vertebral arteries, and the side-to-side differences were also calculated. Eleven patients (27.5%) with an occluded internal carotid artery had increased peak systolic velocity in the ipsilateral vertebral artery, and 6 (15%) had increased peak systolic velocity in the contralateral vertebral artery. The mean peak systolic velocity and the mean blood flow volume were statistically greater in the ipsilateral vertebral arteries than in the same-side vertebral arteries of the control group (P < .05). We also detected a mean increase of 14.29% of the net blood flow volume in the vertebral arteries compared with the control group. Patients with extracranial unilateral internal carotid artery occlusion may have a compensatory increase in both the peak systolic velocity and the blood flow volume in both vertebral arteries.

Color duplex sonographic findings in human vertebral arteries during cervical rotation

PURPOSE

The aims of this study were to determine whether vertebral artery blood flow velocity changes during contralateral cervical rotation, to determine the extent of rotation necessary to affect the velocity, and to find direct evidence of stretching or compression of the vertebral arteries during cervical rotation.

METHODS

Color duplex sonography was used to measure the blood flow velocities and diameters of the vertebral arteries in 20 patients. Measurements were taken with the patients' heads in the neutral position and at 10 degrees increments of contralateral neck rotation (determined using a cervical range of motion goniometer) to the end-range.

RESULTS

The data showed no significant change in the mean blood flow velocity for the entire study population during cervical rotation. However, there were marked changes in the blood flow velocities in 7 vertebral arteries toward the end-range of rotation. No arteries displayed any evidence of major stretching of the arterial walls, although localized compression of 2 arteries was observed.

CONCLUSIONS

The results of this study suggest that vertebral arteries are usually unaffected by contralateral cervical rotation and that Doppler sonography may provide an indirect assessment of mechanical stresses to the arterial wall.

Vertebral arteries and neck rotation: Doppler velocimeter interexaminer reliability

The purpose of this study was to test the interexaminer reliability of Doppler ultrasound (US) velocimeter examination of vertebral arteries during contralateral cervical rotation. Vertebral arteries from 20 adults were insonated using a bidirectional Doppler velocimeter at the suboccipital portal (standard technique) and C2 transverse process level (new technique) during contralateral cervical rotation. The data obtained by two examiners, regarding persistence or major reduction in Doppler signals, were compared. There was 93% agreement between the data from the two examiners, and the kappa score was 0.78 at p = 0.05. These results provide evidence to support the interexaminer reliability of bidirectional Doppler velocimeter examination for the purpose of assessing the effects of contralateral rotation on vertebral artery blood flow.

Flow velocity and flow volume measurements in the extracranial carotid and vertebral arteries in healthy adults: reference data and the effects of age

To establish reference data and to investigate the development of haemodynamics in the extracranial carotid and vertebral arteries, we performed a prospective study in 78 age- and gender-matched healthy adults from 20 to 85 y old. Angle-corrected flow velocities and luminal diameters were measured and waveform parameters and flow volumes calculated in all the arteries. Side-to-side differences and the influence of age on these parameters were also investigated. In the common carotid arteries, the internal carotid arteries and the vertebral arteries (CCA, ICA and VA, respectively) all flow velocities decreased significantly during ageing. The luminal diameter remained constant in all the carotid arteries, but increased slightly with age in the VA. An age-related decline of intravascular flow volume was observed in the ICA. Due to a pronounced decrease in end-diastolic flow velocity, the resistance index decreased in ICA and VA during ageing. There were no significant side-to-side differences in flow velocities and flow volumes in any of the extracranial arteries. The luminal diameters of the CCA, ICA and ECA were significantly smaller in women than in men. No relevant gender-related differences in flow velocities or waveform parameters were found in the extracranial arteries. There was no gender-linked difference in the flow volumes of the brain-feeding arteries and, in the ECA, flow volumes were significantly higher in men. Reference data on all flow velocities and waveform parameters, luminal diameters and flow volumes were established for different age groups between 20 and 85 y old. These data allow us to outline the development of cerebral haemodynamics during "benign ageing" and to utilise flow volume measurements in clinical practice, especially in patients with cerebrovascular diseases.

Color-SieScape imaging of carotid and vertebral arteries

OBJECTIVE

The aim of this study was to estimate the feasibility and limitations of Color-SieScape imaging of carotid and vertebral arteries in healthy subjects.

METHODS

extended field of view procedure was applied during the examination of 80 carotid and 80 vertebral arteries in 40 healthy volunteers.

RESULTS

visualisation of a common carotid artery together with a proximal segment of both an internal (ICA) and external carotid artery (ECA) in one Color-SieScape image was possible in nine cases. Clear presentation of a common carotid artery in one Color-SieScape image with a segment of an ICA or ECA of varying length was possible in 49 cases. In 22 cases, visualisation of an ICA was possible only on a minimal length, with major artefacts or completely impossible. Color-SieScape images of vertebral arteries were good or very good in 34 cases and poor or very poor in 46 cases. Artefacts arose due to the pulsatile movements of the arterial wall, especially in vessels lying close to the skin and in the proximal part of a common carotid artery. Tracing a tortuous vessel and ICA coming from common carotid artery at an angle close to 90 degrees produced significant artefacts.

CONCLUSIONS

Color-SieScape images of carotid and vertebral arteries of good quality are usually possible to obtain.

A biomechanical study of the human vertebral artery with implications for fatal arterial injury

We studied the biomechanical behaviour of ring and strip specimens from along the length of 18 vertebral arteries taken from 16 subjects aged 28-90 years, in order to consider some of the factors which may play a role in vertebral artery rupture. The method was chosen to allow a comparison between circumferential distension (ring samples) and longitudinal extension, (strip samples). The samples were extended between the jaws of a tensile testing apparatus until the specimen broke and a number of biomechanical parameters were derived. These were the percentage extension to break, the tensile strength, Young's modulus and the peak load. There were a number of important findings. The vertebral artery was shown to be susceptible to longitudinal stretching with a number of strip samples breaking when extended by as little as 16-20%. The tensile strength and load at peak of the strip specimens were correspondingly lower than for the ring samples. Marked intersubject variations were shown for all these parameters and prominent changes in behaviour occurred along the vertebral artery. This study indicates that the artery may be susceptible to head and neck movements which cause the vessel to stretch, and intersubject variations in behaviour may be one important explanation for the marked differences in outcome which appear to exist in subjects who suffer broadly similar head and neck insults.

Color-coded duplex ultrasonography of the origin of the vertebral artery: normal values of flow velocities

The introduction of color-coded duplex ultrasonography has improved the ease of performing ultrasound investigations of the vertebral arteries. So far, normal values of flow velocities have been reported only for the intertransverse region of the vertebral artery (V2 segments). Atherosclerotic disease at the origin of the vertebral arteries (V0 segment) is frequent and is one of the risk factors for vertebrobasilar ischemic disease. Normal values of flow velocities of the vertebral artery origin are needed to assess pathologic findings, such as vertebral artery origin stenosis or dissection. The aim of this study was to describe the normal flow velocities of vertebral artery origin (V0 segment) and the pre- (V1 segment) and intertransverse (V2 segment) part in 50 age-matched neurologic patients (mean age 54) without ischemic cerebral disease. The V0 segment could be visualized in 46 persons (92%) on the right side and in 43 (86%) on the left. The peak systolic blood velocity ranged from 30 to 100 cm/s (mean 63.6 +/- 17.5 cm/s), and end-diastolic blood velocity ranged from 10 to 35 cm/s (mean 16.1 +/- 5.1 cm/s). Analysis of side-to-side differences showed no significant differences of flow velocities in all subjects. It is concluded that color duplex ultrasonography is a feasible method to insonate the origin of the vertebral artery, and that nomogram data could be established. It is suggested that color-coded duplex ultrasonography of the vertebral artery origin should be performed in all patients with clinical symptoms or signs of vertebrobasilar ischemic disease. Nevertheless, further studies are needed to determine the normal and pathologic values of flow velocities of the vertebral artery origin and their reproducibility.

Vertebral arteries and neck rotation: Doppler velocimeter and duplex results compared

The purpose of this study was to test the validity of Doppler ultrasound (US) velocimeter examination of vertebral arteries during contralateral (to the opposite side) cervical rotation. Vertebral arteries from 20 subjects were insonated using a bidirectional Doppler velocimeter at the suboccipital portal (standard technique) and C2 transverse process level (new technique) during contralateral cervical rotation. The results, regarding persistence or major reduction in Doppler signals, were then compared with those from a colour-flow duplex US scanner using the same procedure. There was complete agreement between the combined suboccipital and C2 velocimeter results and those from the duplex scanner (k = 1.00 at p = 0.01): both sensitivity (n = 5) and specificity (n = 34) were 100%. This study provides evidence to support the validity of bidirectional Doppler velocimeter examination, by an experienced examiner, for the purpose of assessing the effects of contralateral rotation on vertebral artery blood flow.

Reference values for vertebral artery flow volume by duplex sonography in young and elderly adults

BACKGROUND AND PURPOSE

Vertebrobasilar ischemia has been attributed to a reduction of net vertebral artery flow volume, the product of mean flow velocity and the cross-sectional area of the vessel. It can be determined by duplex sonography. There are no reference values for vertebral artery flow volume in an age group representative of patients with cerebrovascular disease.

METHODS

We examined 50 nonvascular neurological patients (age 55.8+/-14.0 years). Flow velocities and vessel diameters were recorded in the intertransverse (V2) segments bilaterally, and the flow volume was calculated according to the following equations: (1) Q1=time-averaged mean velocity times area and (2) Q2=(time-averaged maximum velocity/2)times area.

RESULTS

Flow velocities and vessel diameters tended to be lower on the right side, resulting in a lower flow volume. Flow volumes (according to Equation 1) were 77.2+/-29.8 mL/min on the right side, 105.3+/-46.4 mL/min on the left side, and 182.0+/-56.0 mL/min net. Side-to-side differences were not significant. Flow volumes calculated with the 2 equations did not differ significantly. An age dependence could not be shown, but vessel diameters and net vertebral artery flow volumes were significantly lower in women than in men. The normal range for net vertebral artery flow volume defined by the 5th to 95th percentiles is between 102.4 and 301.0 mL/min. This wide range is due to the high interindividual variability of the parameters.

CONCLUSIONS

On the basis of the reference values presented here, the association of decreased vertebral artery flow volume and vertebrobasilar ischemia should be reevaluated. Additional areas for investigation include the quantification of collateral flow in the vertebral arteries in carotid artery occlusive disease and their contribution to overall cerebral blood flow volume.

Vertebral artery flow and cervical manipulation: an experimental study

BACKGROUND

Spinal manipulation therapy is used by millions of patients each year to relieve symptoms caused by biomechanical dysfunction of the spine. Cerebrovascular accidents in the posterior cerebral circulation are a feared complication, but little research has been done on vertebral artery hemodynamics during cervical manipulation.

OBJECTIVE

The purpose of this study was to develop an experimental model for investigations of volume blood flow changes in the vertebral arteries during premanipulative testing of these vessels and during spinal manipulation therapy of the cervical spine.

DESIGN AND SETTING

An experimental study in a university biomedical laboratory.

MATERIAL AND METHODS

The vertebral arteries were exposed in 8 adult pigs after extensive mediastinal dissection. Volume blood flow was measured on both sides simultaneously by advanced transit-time flowmetry.

RESULTS

After cervical manipulation, the vertebral artery volume blood flow increased significantly for 40 seconds before returning to baseline values in less than 3 minutes. We found no significant changes in volume flow during premanipulative testing of the vertebral arteries (DeKleyn's test).

CONCLUSION

We present an experimental model for investigations of vertebral artery hemodynamics during biomechanical interventions. We found a modest and transient effect of cervical manipulation on vertebral artery volume flow. The model may have further applications in future biomechanical research, for example, to determine whether any of several spinal manipulative techniques imposes less strain on the vertebral artery, thereby reducing possible future cerebrovascular accidents after such treatment.

Vertebral artery volume flow in human beings

BACKGROUND

A number of studies have investigated vertebral artery flow velocity. Because perfusion relates to the volume of blood flowing through the vessel, this parameter is of great importance when vertebral artery hemodynamics are investigated. We could not find any such Doppler studies in the literature, possibly because of known errors with previous techniques. New advanced color-coded duplex sonography has since been validated and may be used with confidence for volume flow investigations.

OBJECTIVE

To use advanced color-coded duplex sonography to investigate volume flow through the vertebral arteries during cervical rotation, as well as before and after spinal manipulation therapy.

DESIGN AND SETTING

A randomized controlled study at a university hospital vascular laboratory.

PARTICIPANTS

Twenty university students.

RESULTS

Volume blood flow through the vertebral arteries does not change with cervical rotation or after spinal manipulation therapy.

CONCLUSION

This appears to be the first in vivo Doppler study on human vertebral artery volume blood flow. Our results indicate that in symptom-free subjects there is no change in vertebral artery perfusion during rotation in spite of significant changes in flow velocity. This finding, as well as the observed changes in flow velocity reported by others, may be explained by a positional change in the vertebral artery diameter. In addition, we have investigated volume blood flow in the vertebral arteries before or after spinal manipulation therapy but found no significant changes.

Different responses of cerebral vessels to -30 degrees head-down tilt in humans

This study explored changes of the cerebral circulation and evaluated the responses to weightlessness in 12 volunteers (18-22 yr of age). The velocities, diameters and blood flow volume of the common carotid artery (CCA), internal carotid artery (ICA), vertebral artery (VA) and internal jugular vein (IJV) were measured with color Doppler echogram before and during simulated weightlessness. -30 degrees head-down tilt (HDT) for 45 min was used as a weightlessness simulation model. When the subjects' positions were changed from the supine to -30 degrees HDT, blood flow velocities along the CCA, ICA and IJV decreased significantly (p< 0.05), and their diameters were increased. The subjects were divided into two groups according to measured changes in flow volume of the ICA and IJV: group I with a net in-flow of cerebral blood flow (CBF) and group II with a net out-flow of CBF during HDT. Symptoms were recorded in the two groups during HDT (nasal congestion, sensation of head fullness, headache, and others) and graded on a four-point scale, from absent to serious. Results showed that group I had a higher symptoms score while group II had a lower symptoms score. Although this difference did not reach statistical significance, it suggests that cerebral blood flow changes may be partly responsible for the symptoms observed in subjects during HDT.

Effect of premanipulative tests on vertebral artery and internal carotid artery blood flow: a pilot study

BACKGROUND

Neck manipulation occasionally causes stroke after trauma to the vertebral or internal carotid artery. Premanipulativ e tests involving cervical spine rotation or extension have been recommended to detect patients at risk of neurovascular ischemia. However, the effect of these procedures on extracranial blood flow is not well established, and their validity is thus controversial.

OBJECTIVE

To determine the effect of premanipulative tests involving cervical spine rotation or extension on vertebral artery and internal carotid artery blood flow parameters.

DESIGN

Two-group experimental study.

SUBJECTS

Twenty subjects consisting of 16 patients treated with physiotherapy and four volunteers.

METHODS

Subjects were tested with a recommended premanipulative protocol by both an independent physiotherapist and an investigator. One group consisted of 10 subjects with signs or symptoms indicative of neurovascular ischemia on premanipulative testing, with 10 subjects with no signs or symptoms indicative of neurovascular ischemia on premanipulative testing comprising the second group. Hemodynamic measurements for both vertebral and both internal carotid arteries were taken by use of duplex Doppler ultrasonography with color-flow imaging with the subjects in the following positions: neutral, end-range extension, 45 degrees contralateral rotation, end-range contralateral rotation, and combined end-range contralateral rotation/extension.

RESULTS

The reliability of premanipulative testing was supported. Significant changes in flow velocity of the vertebral artery (and to a lesser extent of the internal carotid artery) were shown in end-range positions involving rotation and extension. No meaningful significant differences were found between the two groups.

CONCLUSIONS

Screening procedures that use rotation and extension may be useful tests of the adequacy of collateral circulation. A larger study is needed to determine whether subjects testing positive significantly differ from those testing negative.

Color Doppler flow imaging (CDFI) of the vertebral arteries--the normal appearance, normal values and the proposal for the standards

In order to assess mean diameters and blood flow velocities (BFV), Color Doppler Flow Imaging (CDFI) of vertebral arteries (VA) was performed. Five hundred and ninety six persons without carotid disease or symptoms related to vertebrobasilar system were analyzed by CDFI of VA. Mean right VA diameter was 3.37 +/- 0.6 mm and left 3.55 +/- 0.61 mm. Women had thinner VA (p < 0.05). Left VA was wider (p < 0.05). Mean right BFV was 48.31 +/- 14.09 cm/s and left 48.93 +/- 13.94 cm/s. Females had higher BFV (p < 0.05). BFV didn't very with age (p > 0.05). The VA hypoplasia was present in 2.34%, asymmetry in 15% (left VA dominant in 64%). Visualisation of V1 and V2 segment was possible in 100% and of the origin in 81.7% on the right, and 80.7% on the left side. CDFI is a reliable method for evaluation of VA. Left VA was wider. Women had thinner VA. Hypoplasia was present in 2.34% and asymmetry in 15%.

MR phase-contrast flow measurement with limited spatial resolution in small vessels: value of model-based image analysis

Magnetic resonance phase-contrast volume flow rate (VFR) measurement with limited resolution in small vessels is subject to two major sources of error: a) partial volume artifacts, causing systematic overestimation of the VFR, and b) errors related to the selection of vessel pixels [region of interest (ROI)], causing large inter-observer and intra-observer variability. Additionally, limited resolution results in Gibbs-ringing around vessels, which adversely affects VFR determination. In this paper, a semi-automatic model-based method is presented that effectively eliminates errors due to both partial volume effect and Gibbs-ringing and also minimizes errors from variability in the ROI selection. The model assumes a parabolic flow profile and cylindrical vessel geometry, incorporates inflow effects, and takes into account the point-spread function of the acquisition. The method automatically estimates maximum velocity, vessel radius, and VFR. The method is validated in phantoms under various conditions and evaluated in vivo. For small vessels with moderately pulsatile flow, it is demonstrated that accurate VFRs and diameter estimates are obtained, virtually independent of the ROI selection, even in vessels covered by just a few pixels. Compared with conventional VFR analysis, both accuracy and reproducibility improve significantly.

Changes and implications of blood flow velocity of the vertebral artery during rotation and extension of the head

OBJECTIVE

To study the effects of extension and extension-rotation of the head on the blood flow velocity of the vertebral artery experimentally and clinically.

DESIGN

Randomized experimental clinical study.

SETTING

Institute of Clinical Anatomy and Biomechanics and the Department of Ultrasound, NanFang Hospital of the First Military Medical University, Guangzhou, China.

SUBJECTS

The fresh spines from T1-2 to the occipital bone were obtained from persons who died of acute brain death (n = 10). For the transcranial Doppler measurement, 27 asymptomatic subjects with routine physical examination results and 23 students from the above-mentioned university took part in the test.

INTERVENTIONS

The instillation experiment in the cadavers was made. Clinical measurements of blood flow velocity in the vertebral artery in the subjects and students were taken and recorded.

MAIN OUTCOME MEASURES

Changes in the drop of the vertebral artery were measured by the instillation test in the experimental sample. The blood flow velocity was measured with transcranial Doppler sonography during extension and extension-rotation of the head.

RESULTS

During one-sided rotation of the head with extension of the head, measurements in the contralateral vertebral artery and the bilateral vertebral arteries were both reduced in the instillation experiment. The blood flow velocity in the bilateral vertebral arteries decreased during extension and extension-rotation of the head in the subjects and the students. The pulsatility index in the right vertebral arteries increased more than that in the left in extreme extension and that in the bilateral vertebral arteries in neutral position.

CONCLUSIONS

Extreme rotation and extension are dangerous to patients who have abnormal vertebral arteries when extreme rotatory and extension manipulations are applied. Doctors should be very careful when rotating the patient's head to the right side.

Vertebral artery compression resulting from head movement: a possible cause of the sudden infant death syndrome

OBJECTIVE

Vertebral artery compression causing brainstem ischemia has been suggested to underlie the sudden infant death syndrome. Vertebral artery distortion from neck movements has been demonstrated by angiography in infants, but direct evidence for arterial compression is lacking. In an attempt to demonstrate vertebral artery compression from head movement, we examined at postmortem the vertebral arteries of infants after neck extension or rotation.

METHODS

The C1-C7 spinal column, together with a 2-cm rim of skull base, was removed from 20 infants dying from sudden infant death syndrome or other causes. In 5 cases the neck was extended, in 9 cases it was rotated 90 degrees to the right, and in 6 cases the neck was held in the neutral position. The neck was maintained in these positions during formalin fixation, and serial sections of selected blocks were examined microscopically.

RESULTS

In 3 of 5 extended cases, bilateral vertebral artery compression was seen between the occipital bone and C1. In 3 of 9 rotated cases, the left vertebral artery was compressed adjacent to C1 before the artery entered the transverse foramen. No vertebral artery compression was seen in the necks held in the neutral position.

CONCLUSIONS

The vertebral arteries of some infants can be compressed by neck movement. This could induce lethal brainstem ischemia in infants with inadequate collateral blood flow or with poor compensatory arterial dilatation, and may underlie some cases of sudden infant death syndrome.

Internal auditory artery infarction: clinicopathologic correlation

OBJECTIVE

To study the pathophysiology of labyrinthine infarction.

BACKGROUND

The syndrome of sudden onset vertigo or hearing loss is commonly attributed to inner ear vascular disease, yet histologic studies of isolated labyrinthine infarction in humans have been rare and have not included a complete examination of the vertebrobasilar vascular system.

METHODS

Temporal bones, brainstem, cerebellum, and the supplying blood vessels were subjected to gross and microscopic postmortem examinations in a 92-year-old woman who had a sudden onset of vertigo and hearing loss in the right ear 7 years before death.

RESULTS

There were prominent atherosclerotic changes at the vertebrobasilar junction, but the internal auditory artery and its branches were patent on both sides. Histologic studies showed degenerative changes in the cochlea and vestibular labyrinth on the right. The posterior canal ampulla and saccular macule were relatively preserved showing partial areas of intact sensory epithelium with underlying nerve fibers. The right vestibulocochlear nerve showed a fibrotic scar and multiple patchy areas of degeneration. These findings are most consistent with a transient period of reduced perfusion of the internal auditory artery.

CONCLUSION

The partial sparing of the inferior vestibular labyrinth may indicate a decreased vulnerability to ischemia because of its better collateral blood supply.

Spinal cord protection by papaverine and intrathecal cooling during aortic crossclamping

AIM

To extend the safe period of aortic crossclamping in the porcine model by intrathecally dilating the spinal arteries, with cooling of the spinal cord, or using selfoteL METHODS: Experimental design and setting: prospective domestic laboratory pig study.

INTERVENTIONS

fifteen animals were assigned to a control group (C, N=5), intrathecal papaverine plus spinal cord cooling group (IP+C, N=5), or selfotel group (S, N=5). In the IP+C group, a lumbar laminectomy was performed and an intrathecal catheter placed for intrathecal injection of papaverine and perfusion with cold Ringer's solution (4 degrees C) prior to aortic crossclamping. In the selfotel group, 20 mg/kg of selfotel was administered 30 minutes before aortic crossclamping. In all 15 animals, the aorta was crossclamped for 60 minutes at normothermia.

MEASURES

immediately after the operation and 24 hours later, lower limb function was evaluated.

RESULTS

All five control animals were paralyzed; all 5 IP+C animals could stand or walk (p=0.004 versus control); and in the selfotel group, one had paraparesis, three had paraplegia and one died before evaluation (p=n.s.)

CONCLUSIONS

The combination of intrathecal papaverine to dilate spinal arteries and prevent spasm from the cold solution plus intrathecally cooling the spinal cord appears to extend the period of safe aortic crossclamping. Selfotel, in this model of extended, severe, spinal cord ischemia, was ineffective.

[The correlation of Doppler's blood flow distempers in vertebral arteries with degenerative cervical spine changes of patients undergoing treatment for tinnitus]

120 patients aged 20-81 years were treated at the Otolaryngology Clinic of the CM UJ in years 1994-1996 for tinnitus. The radiological method showed degenerative changes of the cervical spine in 100 of them. The otolaryngological and neurological methods excluded any reason of tinnitus other than distempers of vertebrobasilar arterial system. The ACUSON 128 XP/10 (Duplex Scan + Color Doppler) was used during examination of blood flows in vertebrobasilar arterial system. The correlation index was calculated as a proportion between the number of patients with pathological vertebral artery blood flow and the total number of patients. For all patients aged 20-81 it was 45.0%. The correlation index for the subsequent age groups grew proportionally to the age of patients, reaching values from 0% to 73.7%.

Blood flow velocity changes in carotid and vertebral arteries with stellate ganglion block: measurement by magnetic resonance imaging using a direct bolus tracking method

BACKGROUND AND OBJECTIVES

Stellate ganglion block (SGB) leads to vasodilation of the head and neck, as a result of a regional sympathetic blockade. However, in such cases, controversy remains concerning changes in cerebral and extracerebral blood flow in the head. We estimated the effect of SGB on blood flow in the head by measuring the blood flow velocity in cervical vessels, using magnetic resonance imaging and the direct bolus tracking method. This noninvasive method is free from potential artifacts of bones and other connective tissues.

METHODS

Seven adult patients with acute or chronic pain in the head or neck underwent SGBs, using an anterior paratracheal approach with 6-8 mL of 1% mepivacaine (3 right and 4 left SGBs). Blood flow velocity in common carotid and vertebral arteries (CCA and VA) was measured simultaneously before and after SGB, using the direct bolus tracking method.

RESULTS

On the side of SGB, blood flow velocity in CCA significantly increased (P < .002), whereas velocity in VA was unchanged after SGB. On the side contralateral to the SGB, significant changes in blood flow velocity in CCA and VA were never observed.

CONCLUSIONS

Blood from the VA flows primarily to cerebral vessels, whereas that from CCA goes to both cerebral and extracerebral vessels. Given the presumed differences in blood flow distribution through the VA and CCA, we assume that the observed CCA blood flow increases, ipsilateral to the SGB, primarily as a result of vasodilation of extracerebral vessels and independent of changes in brain blood flow.

Contribution of the vertebral artery to cerebral circulation in the rat snake Elaphe obsoleta

Blood supplying the brain in vertebrates is carried primarily by the carotid vasculature. In most mammals, cerebral blood flow is supplemented by the vertebral arteries, which anastomose with the carotids at the base of the brain. In other tetrapods, cerebral blood is generally believed to be supplied exclusively by the carotid vasculature, and the vertebral arteries are usually described as disappearing into the dorsal musculature between the heart and head. There have been several reports of a vertebral artery connection with the cephalic vasculature in snakes. We measured regional blood flows using fluorescently labeled microspheres and demonstrated that the vertebral artery contributes a small but significant fraction of cerebral blood flow (approximately 13% of total) in the rat snake Elaphe obsoleta. Vascular casts of the anterior vessels revealed that the vertebral artery connection is indirect, through multiple anastomoses with the inferior spinal artery, which connects with the carotid vasculature near the base of the skull. Using digital subtraction angiography, fluoroscopy, and direct observations of flow in isolated vessels, we confirmed that blood in the inferior spinal artery flows craniad from a point anterior to the vertebral artery connections. Such collateral blood supply could potentially contribute to the maintenance of cerebral circulation during circumstances when craniad blood flow is compromised, e.g., during the gravitational stress of climbing.

Cerebral hemodynamic changes induced by simulated tracheal intubation: a possible role in perioperative stroke? Magnetic resonance angiography and flow analysis in 160 cases

BACKGROUND AND PURPOSE

Perioperative stroke is a rare complication of generalized surgery (1% to 6%). Unexpected difficulties with tracheal intubation (TI), as well as the hyperextended position, may predispose a patient to or play a role in stroke. We sought to identify blood flow changes in carotid and vertebral arterial circulation during simulated TI and develop profile models for stroke risk before possible generalized surgery.

METHODS

One hundred sixty consecutive patients with suspected cerebral vascular disease or pending surgery underwent MR angiography with flow analysis. Simulated TI position was maintained for 3 to 4 minutes per acquisition.

RESULTS

The cohort consisted of 89 females (56%) and 71 males (44%) with a mean age of 66 years (range, 17 to 89 years). Hypoplastic vertebral arteries with flow less than 50 mL/s were present in 40 patients (25%). Profound alteration in basilar artery flow was noted in this group with increased frequency of microinfarctions on MRI (77% versus 38%). Unsuspected carotid occlusion (n=6) and vertebral artery occlusion (n=2) were associated with significant basilar artery flow changes. Flow reversal was present in five cases. Carotid arterial changes were not significant with simulated TI. No overt ischemic symptoms developed during these maneuvers.

CONCLUSIONS

Simulated TI is safe yet induces distinct and potentially detrimental flow abnormalities. Individuals identified with the biological markers of hypoplasia, carotid and vertebral occlusion, severe stenosis, or prior ischemic vascular disease should receive special attention to neck position not only during surgery but also in the postoperative period. Sustained neck hyperextension greater than 12 minutes appears to be a neglected potential hemodynamic factor that may play a pivotal role in the pathogenesis of perioperative stroke.

Inner ear blood flow in the rat after unilateral arterial occlusion in the vertebrobasilar arterial system

It is generally accepted that certain kinds of vertigo and hearing disturbances are caused by blood flow insufficiency in the vertebrobasilar arterial system. Using the microsphere method we investigated whether unilateral vertebral artery or unilateral posterior inferior cerebellar artery occlusion could cause an imbalance between right and left inner ear blood flow in rats. We also studied the differential vulnerability between blood flow in the cochlea and in the ampullae of the three semicircular canals. We counted the numbers of microspheres distributed to the cochlea (CO) and microspheres distributed to three ampullae of semicircular canals (SC) under a microscope with the surface preparation method. The results were as follows: i) no imbalances were observed between bilateral CO or SC even in animals with arterial occlusion, and ii) the CO/SCs of animals with arterial occlusion were not significantly different from that of the control animals. These findings suggest that total inner ear blood flow over a certain period of time was even between the ears bilaterally even in animals with arterial occlusion. The blood flow in the ampullae of the three semicircular canals was not more or less affected by arterial occlusion than the blood flow in the cochlea.

Hemodynamics of a simulation of the vertebrobasilar system using silicone tube

We investigated the hemodynamics of the vertebrobasilar system (VBS) using a simulation model tube made of silicone which had different diameters between the bilateral vertebral artery (VA) ducts (stenotic and normal VA ducts). Using the ultrasonic Doppler method. the laterality index (L.I.) of the flow velocity in the VA duct was 32.88%. The flow volume of the anterior inferior cerebellar artery duct and the posterior inferior cerebellar artery duct also had significant laterality. By investigating the effects of the rotatory pulse rate and fluid viscosity, a maximal decrease to below 40-50% of the flow volume of the branches, and to below 71.93% in the mean flow velocity of the basilar artery (BA) duct (BA duct) were observed. and the maximum L.I. increased to 43.15%. When the unilateral stenotic VA duct was occluded by clamping (clamping occlusion), the flow volume profiles of the branches were the same as without clamping occlusion. The L.I. showed no significant changes and the maximal decrease in the mean flow velocity of the BA duct was 68.61%. Using the laser Doppler method, the flow velocity distribution of the BA duct was shifted towards the side of the stenotic VA duct. These results suggest that the rheological dynamics in the main vessels can certainly reflect the posterior circulatory dynamics, and that modulating factors also aggravate the hemodynamics of the VBS with this disorder.

The development of hemodynamics in the extracranial carotid and vertebral arteries

To investigate the development of hemodynamics in the extracranial carotid and vertebral artery system, a prospective color duplex sonography study was performed in 94 healthy children and adolescents between 3 and 18 y old. Angle-corrected flow velocities and luminal diameters were measured; waveform parameters and flow volumes were calculated. Side-to-side differences of volumetric data were analyzed. In 53 children, an intrasession test-retest flowmetry of the internal carotid and vertebral arteries was performed. From 3 to 18 y old, flow volumes decreased significantly in the vertebral arteries (p < or = 0.01) and increased in the external carotid artery (p < or = 0.0001); the luminal diameter increased in all the carotid arteries (p < or = 0.0001) and remained constant in the vertebral arteries; mean flow velocities declined in the common and internal carotid arteries and in the vertebral arteries (p < or = 0.0001), but increased in the external carotid arteries (p < or = 0.01). Flow volume rate was lower in the right than the left vertebral artery (p < or = 0.0001), and there was no side difference in any of the carotid arteries. The test-retest correlation of volumetric data was high (0.81 < or = r < or = 0.97; p < or = 0.0001). By comparing the reference data presented here with analogous adult data, we were able to delineate the physiologic development of extracranial and cerebral hemodynamics from childhood to adulthood. These data make possible the clinical application of quantitative flowmetry in extracranial cerebral arteries of children and adolescents.

Triplex ultrasound of vertebral artery flow during cervical rotation

BACKGROUND

Reviewing the literature on vertebral artery flow during cervical rotation shows various results. Furthermore, most studies have investigated exclusively the effects of contralateral rotation employing less-than-optimal Doppler ultrasound technique.

OBJECTIVE

The aim of this study was to use the latest advancement in Doppler ultrasound technology to investigate flow velocity in the vertebral artery during both ipsilateral and contralateral cervical rotation in normal subjects.

DESIGN AND SETTING

A prospective, controlled study in a university hospital vascular laboratory.

PARTICIPANTS

Twenty healthy university students.

RESULTS

Peak flow velocity decreased significantly during contralateral rotation and increased significantly during ipsilateral rotation. The differences, however, were modest. We found no correlation between peak flow velocity and systolic blood pressure.

CONCLUSION

With modern Doppler ultrasound technique, preventing some sources of error in measuring, our finding during contralateral rotation were in accordance with most previous studies showing a decrease in peak flow velocity. For the first time, however, we report an increased flow velocity in the vertebral artery during ipsilateral rotation.

Changes in cerebral blood flow and vasoreactivity in response to acetazolamide in patients with transient global amnesia

OBJECTIVE

Previous reports about changes in cerebral blood flow (CBF) in transient global amnesia disclosed decreased flow in some parts of the brain. However, CBF analyses in most reports were qualitative but not quantitative. The purpose of this study was to determine changes in CBF in transient global amnesia.

METHODS

The CBF was measured and the vasoreactive response to acetazolamide was evaluated in six patients with transient global amnesia using technetium-99m hexamethylpropylene amine oxime single-photon emission computed tomography (SPECT). The CBF was measured during an attack in two patients and soon after an attack in the other four. About one month later, CBF was re-evaluated in each patient.

RESULTS

Two patients examined during an attack and one patient examined five hours after an attack had increased blood flow in the occipital cortex and cerebellum. Three patients examined at six to 10 hours after an attack had decreased blood flow in the thalamus, cerebellum, or putamen. These abnormalities of blood flow almost disappeared in all patients one month after onset. The vasodilatory response to acetazolamide, which was evaluated initially using SPECT, was poor in areas of increased blood flow. By the second evaluation of CBF with acetazolamide, the vasodilatory response had returned to normal.

CONCLUSIONS

In a patient with transient global amnesia, CBF increased in the vertebrobasilar territory during the attack and decreased afterwards. The vasodilatory response to acetazolamide may be impaired in the parts of the brain with increased blood flow. It is suggested that transient global amnesia is distinct from migraine but may share the same underlying mechanism.

Harmonic imaging of the vertebrobasilar system

BACKGROUND AND PURPOSE

Gas bubbles of ultrasound contrast agents resonate at frequencies used for diagnostic ultrasound and produce harmonics or multiples of the transmitted frequency. Processing of the second harmonic frequency results in a reduction of the signal-to-noise ratio and the signal-to-tissue artifacts. This study is the first to evaluate second harmonic imaging in the cerebral circulation.

METHODS

We used a duplex system (HP SONOS 2500) in connection with a 1.8/3.6-MHz (second harmonic) and a 2.5-MHz (conventional) sector transducer. Levovist (6.5 mL; 400 mg/mL) was injected intravenously for second harmonic and conventional color duplex imaging in 13 healthy volunteers (age range, 23 to 34 [median, 29] years).

RESULTS

When second harmonic imaging was compared with conventional color duplex imaging, more cerebellar arteries were detected (35 versus 31), the duration of blooming artifact was significantly reduced (7.9 versus 29.9 seconds; P = .03), and the duration of diagnostically useful signal enhancement was increased (248.5 versus 117.4 seconds; P = .0003), but the maximal investigation depth was reduced (8.4 versus 9.3 cm; P = .001). When conventional and second harmonic duplex were compared, there was a significant (P < .04) difference in the systolic blood flow velocity in the vertebral and basilar arteries.

CONCLUSIONS

Second harmonic color duplex imaging in the vertebrobasilar system increases the time of diagnostic useful signal enhancement and produces a better spatial resolution compared with conventional color duplex imaging.

Global cerebral blood flow during infusion of adenosine in humans: assessment by magnetic resonance imaging and positron emission tomography

Adenosine, an endogenous vasodilator, induces a cerebral vasodilation at hypotensive infusion rates in anaesthetized humans. At lower doses (< 100 micrograms kg-1 min-1), adenosine has shown to have an analgesic effect. This study was undertaken to investigate whether a low dose, causing tolerable symptoms of peripheral vasodilation affects the global cerebral blood flow (CBF). In nine healthy volunteers CBF measurements were made using axial magnetic resonance (MR) phase images of the internal carotid and vertebral arteries at the level of C2-3. Quantitative assessment of CBF was also obtained with positron emission tomography (PET) technique, using intravenous bolus [15O]butanol as tracer in four of the subject at another occasion. During normoventilation (5.4 +/- 0.2 kPa, mean +/- s.e.m.), the cerebral blood flow measured by magnetic resonance imaging technique, as the sum of the flows in both carotid and vertebral arteries, was 863 +/- 66 mL min-1, equivalent to about 64 +/- 5 mL 100 g-1 min-1. The cerebral blood flow measured by positron emission tomography technique, was 59 +/- 4 mL 100 g-1 min-1. All subjects had a normal CO2 reactivity. When adenosine was infused (84 +/- 7 micrograms kg-1 min-1.) the cerebral blood flow, measured by magnetic resonance imaging was 60 +/- 5 mL 100 g-1 min-1. The end tidal CO2 level was slightly lower (0.2 +/- 0.1 kPa) during adenosine infusion than during normoventilation. In the subgroup there was no difference in cerebral blood flow as measured by magnetic resonance imaging or positron emission tomography. In conclusion, adenosine infusion at tolerable doses in healthy volunteers does not affect global cerebral blood flow in unanaesthetized humans.

The influence of the blunting of the apex on the flow in a vertebro-basilar junction model

The apex of human vertebro-basilar junctions can be sharp-edged or blunted. In the present study, the effect of blunted apex on the flow in vertebro-basilar junction models is investigated. We compared the flow phenomena in a series of junction models with blunted apices and confluence angles 45, 85, and 125 deg with the flow phenomena in a series of junction models with sharp-edged apices and the same range of confluence angles, studied in a previous paper (Ravensbergen et al., 1996b). The blunting of the apex appears to have an effect on the size of the local recirculation area near the apex and the prevailing low velocities. Large recirculation areas are found in the models with blunted apices, especially in those with small confluence angles. In addition, the blunting of the apex has no influence on the flow further downstream, nor on the structure and strength of the secondary flow field. Furthermore, a blunted apex appears to be a geometric risk factor for atherosclerosis. This supports the hypotheses that recirculation areas and low wall shear stress influence the development of atherosclerotic plaques.

Repositioning of the vertebral artery as treatment for neurovascular compression syndromes. Technical note

Neurovascular compression syndromes are usually treated by interposing Teflon felt or padding or some other implant between the offending vessel and the nerves. However, this cannot be done in some cases in which ectatic vertebrobasilar arteries are involved. In these instances, alternative techniques must be used. The authors report the use of a sling made of Prolene to reposition the vertebral artery in two patients with neurovascular compression disorder. The clinical results were gratifying, with complete resolution of the patients' symptoms. Compression by large vessels is an uncommon but important source of neurovascular compression in patients with trigeminal neuralgia, hemifacial spasm, disabling positional vertigo, and, possibly, hypertension. The technique described may be useful to surgeons treating these problems.

Extended Willis circle model to explain clinical observations in periorbital arterial flow

A fluid-dynamic model of the circle of Willis and its periorbital links with the external carotid arteries has been established and tested. It is based on anatomic data and takes Doppler measurements as flow input conditions. The model explains, on fluid-dynamic grounds, the clinical observations of periorbital reverse flow and arrival pulse time delay. It also obtains the velocity and pressure pulse at any point of the studied area. This allows the comparison between the normal or healthy condition and the flow distribution when an internal carotid is externally or pathologically occluded. Several combinations of the communicating artery sizes are explored to obtain the reduced cerebral flow. The combination of the communicating diameters can lead to insufficient irrigation which can be hydrodynamically assessed. No other physiological response is included, and the results must be considered as a minimum assured. These results show the need for a common evaluation of the alternative paths and explain some paradoxes found in literature.

The cervical subluxation and regional cerebral blood flow

OBJECTIVE

This article specifically addresses the question of whether the manipulable cervical lesion is likely to cause extrinsic compression of the vertebral arteries sufficient to cause such symptoms of reduced regional cerebral blood flow as might be relieved by spinal manipulation.

DATA SOURCES

Literature on normal and abnormal cerebral circulation, including vertebrobasilar insufficiency.

DATA SYNTHESIS

Signs and symptoms produced by extrinsic compression of the vertebrobasilar system have been compared with those attributed elsewhere to the manipulable cervical lesion (cervical subluxation).

RESULTS

Extrinsic compression of the vertebrobasilar system generally does not produce signs and symptoms consistent with those attributed to the manipulable cervical lesion.

CONCLUSION

It has been hypothesized elsewhere that the manipulable cervical lesion may induce localized decreases in regional cerebral blood flow, and so signs and symptoms attributable to "cerebral hibernation." If a causal relationship does exist between the cervical subluxation and reduced regional cerebral blood flow, it is not likely to be caused by mechanical compression of the vertebral arteries.

[Unusual subclavian steal syndrome]

A case of unusual subclavian steal syndrome in a 50-years-old man without vertebro-basilar deficiency symptoms is reported. The lack of typical symptoms was caused by an uncommon collateral between the left vertebral and the left external carotid artery. The subclavian steal syndrome was revealed while diagnosing right hemiparesis which was the main cause of hospitalization.

Continuous measurement of changes in internal carotid and vertebral arterial blood flow with chronically implanted ultrasonic Doppler probes in anesthetized and conscious rabbits

Chronically implanted ultrasonic Doppler flowmeters were used to obtain simultaneously recorded flow velocity signals from internal carotid and vertebral arteries, and the sagittal sinus, in rabbits. All three signals increased to 144 +/- 7-215 +/- 35% of baseline during hypercapnia (arterial Pco2 55 mmHg) in both anesthetized and conscious animals. During the period of change in inspired CO2, the relationship between simultaneously recorded mean internal carotid and mean sagittal sinus signals was linear, with the correlation ranging from 0.83 to 0.96. Since forebrain arterial inflow must approximate forebrain venous outflow, the high correlation between internal carotid and sagittal sinus signals indicates that these measures provide reliable and valid indices of cerebral blood flow (CBF). Vertebral and internal carotid angiography confirmed the location of Doppler probe. Chronically implanted ultrasonic Doppler flowmeters can, thus, provide continuous noninvasive measurements of cerebral arterial flow in both anesthetized and conscious rabbits.

Age dependence of total cerebral blood flow volume from childhood to adulthood

In a prospective study of the natural development of total cerebral blood flow volume (CBFV), the common, external and internal carotid and vertebral arteries were examined in 94 healthy children and adolescents between 3 and 18 years of age (sex and age evenly distributed) using a 7.0-MHz transducer of a computed sonography system. Intravascular flow volumes were calculated with the product of angle-corrected time-averaged flow velocity and the cross-sectional area of the vessel. CBFV was determined as the sum of flow volumes in the internal carotid and vertebral arteries of both sides. CBFV increased significantly between 3 and 6.5 years of age (from 687 +/- 85 to 896 +/- 110 ml/min; age correlation, p < or = 0.01) and declined thereafter (p < or = 0.001) to a constant level of approximately 700 ml/min at 15 years of age. There was no difference in CBFV between sexes. The proportion of bilateral vertebral artery flow volume in total CBFV decreased significantly between the ages of 3 and 18 years (p < or = 0.001). As the flow volumes of the external carotid arteries increased markedly from childhood to adulthood, flow volumes of the common carotid arteries were not representative of CBFV. Intrasession test-retest correlation of CBFV was high (r = 0.89, p < or = 0.0001). Reference data for the childhood years presented here and previously described results from healthy adults allow us to outline the natural evolution of CBFV in humans. The reliability of the method has already been demonstrated. Thus, it may now be introduced into clinical application.

Doppler studies comparing the effects of cervical rotation and lateral flexion on vertebral artery blood flow

OBJECTIVE

To determine the effects of cervical contralateral rotation and cervical contralateral lateral flexion on vertebral artery blood flow velocity.

DESIGN AND SETTING

A prospective study was performed at a private chiropractic clinic.

PATIENTS

One hundred forty-eight patients had their vertebral arteries insonated as part of the premanipulative screening procedure.

INTERVENTION

The vertebral arteries were insonated using a Doppler ultrasound velocimeter in the neutral position, during cervical contralateral rotation to the end range and during contralateral lateral flexion to the end range.

MAIN OUTCOME MEASURES

Persistence or loss of Doppler signals from the vertebral arteries during neck movement was recorded.

RESULTS

Of 280 vertebral arteries able to be insonated, 5% (0 < 5% < 9% at p = .99 confidence interval) had Doppler signals that stopped during contralateral rotation. Doppler signals from all 187 vertebral arteries tested during lateral flexion persisted, whereas 6 (3.2%) of this group of arteries had signals that ceased during contralateral rotation.

CONCLUSION

Vertebral artery Doppler signals from patients can be greatly reduced or extinguished during contralateral cervical rotation. However, this is an unusual finding. The same phenomenon was not observed during contralateral cervical lateral flexion, which suggests that there may be less mechanical stress placed on the vertebral artery during lateral flexion.