Rolf Nyberg-Hansen

A comparison of transcranial Doppler and cerebral blood flow studies to assess cerebral vasoreactivity.

Background and Purpose The aim of this study was to determine the ability of transcranial Doppler ultrasonography when used to assess cerebral vasoreactivity. The results of this method were compared with regional cerebral blood flow measurements. Methods Forty-three patients with symptoms suggesting cerebrovascular disease took part Transcranial Doppler findings in the middle cerebral arteries were compared with regional cerebral blood flow in the corresponding perfusion territories before and after acetazolamide administration. Results There was a significant positive correlation between the absolute increase in cerebral blood flow in milliliters per 100 g per minute and the percent increase in velocity (r=0.63). The right-left, side-to-side difference of the acetazolamide response obtained by the two methods also showed a positive correlation (r=0.80). Control limits obtained from healthy subjects were used for both the blood flow increase (absolute values and asymmetry in absolute values) and the velocity increase (percent increase and asymmetry in percent increase). The two methods then agreed in their evaluation of vasoreactivity in 74 (86%) of the 86 middle cerebral artery perfusion territories; 20 (23%) were assessed by both methods as having a reduced vasodilatory reserve. Eleven hemispheres with a slightly reduced regional cerebral blood flow response to acetazolamide were not detected by transcranial Doppler, whereas all territories with a marked reduction were identified by Doppler. Only one hemisphere with a normal cerebral blood flow increase after acetazolamide administration was assessed by Doppler as having reduced vasoreactivity. Conclusions Transcranial Doppler and the acetazolamide test may be used in clinical situations to assess cerebral vasoreactivity.

Effect of nitroglycerin on cerebral circulation measured by transcranial Doppler and SPECT.

We used a combination of transcranial Doppler ultrasonography and single-photon emission computed tomography to noninvasively assess changes in the diameter of the middle cerebral artery induced by sublingual nitroglycerin in 10 healthy subjects. Nitroglycerin reduced mean blood flow velocities without concurrently changing regional cerebral blood flow in the perfusion territory of this vessel. Our results strongly suggest that nitroglycerin causes vasodilatation of the basal intracranial arteries.

SOME COMMENTS ON THE PYRAMIDAL TRACT, WITH SPECIAL REFERENCE TO ITS INDIVIDUAL VARIATIONS IN MAN

It has for a long time been generally accepted that a lesion of the pyramidal tract usually results in a spastic hemiplegia, characterized by impairment of skilled voluntary movements, increased myotatic (deep or tendon) rcflcxes, and weakened or abolished cutaneous reflexes with an extensor plantar response. However, after sectioning the middle third of the ccrebral peduncle in man containing the pyramidal tract fibres scvcral authors have reported that there is no, or only a slight and transient, spasticity and that the capacity to perform skilled voluntary moverncnts is only nioderately impaired ( WaIker 1849, W h i f e 1050, Bzicy 1857, Bucy & Keplinger 1961). These observations lctl Rucy to ask “Is there a pyramidal tract?”, and to suggest that cortical impulscs responsible for the production of skilled voluntary movements might take an “extrapyramidal” routc. Although symptomatological variations which may be seen following lesions supposed to involve the pyramidal tract infantile hemiplegia included may be due to concomitant damage to “extrapyramidal” structures, a problem to which we will briefly return in the final section of this paper, the question has often been raised whether such variations are due to a greater or lesser extent to individual morphological variations of the pyramidal tract. The chief purpose of the present paper is to review what is known of individual variations of this fibre system in man with regard to the following items : decussation of fibres, aberrant fibres, number and size of fibres and myelination of fibres. For a proper discussion of this, certain relevant data on the anatomy of the pyramidal tract have to be considered as well. Only few systematical studies on the individual variations of this fibre system in man have, however, been made. The data on which this review is based are, therefore, largely collcctcd from clinical case reports in the literature. Where it is relevant, data from other species will be considered.

Effect of acetazolamide on cerebral artery blood velocity and regional cerebral blood flow in normal subjects.

SummaryThe effect of intravenous acetazolamide L g on cerebral artery blood velocity and regional blood flow (rCBF) was investigated in eight normal subjects. Blood velocity was measured with 2 MHz pulsed Doppler in the proximal segments of the middle, anterior and posterior cerebral artery (MCA, ACA, and PCA) and in the distal extracranial internal carotid artery (ICA). The rCBF in the regions of interest tentatively corresponding to the perfusion territories of these vessels was estimated using133Xe inhalation and a rapidly rotating single photon emission computer tomograph.Both blood velocity and rCBF increased after acetazolamide. There was no significant difference between the percentage ICA blood velocity increase (22 ± 12%) and the percentage rCBF increase in the ICA region of interest (25 ± 9%). In the MCA, ACA, and PCA, however, blood velocity increased more (mean increase 36–42%) than the rCBF in the corresponding regions of interest (mean increase 24–26%). These differences were highly significant suggesting a direct and site specific effect of acetazolamide in narrowing the lumen of the proximal MCA, ACA, and PCA, but not of the extracranial ICA. We also propose that the effect of acetazolamide induces reciprocal changes in the extent of adjacent perfusion territories in individual brain hemispheres.Data compiled from all subjects investigated at two very different perfusion levels (before and after acetazolamide) revealed a significant positive correlation between blood velocity and rCBF.

Blood velocity and regional blood flow in defined cerebral artery systems

SummaryCerebral artery blood velocity and regional blood flow (rCBF) were investigated in 17 normal subjects. Blood velocity was measured with 2 MHz pulsed Doppler ultrasound in the proximal segments of the middle, anterior and posterior cerebral artery (MCA, ACA, and PCA) and in the distal extracranial internal carotid artery (ICA). The rCBF in the regions of interest tentatively corresponding to the perfusion territories of these vessels was estimated using133Xe inhalation and a rapidly rotating single photon emission computer tomograph.Concomitant capnograph recordings showed that the end-expiratory pCO2 was higher during the rCBF than during the blood velocity examinations. This difference was highly significant. While there was no significant correlation between blood velocity and rCBF when these clear differences in pCO2 were disregarded, we did find significant positive correlations when the data were normalized to a standard pCO2 (5.3 kPa) using accepted formulas. The best correlation was found for the MCA (r=0.630, p<0.001) and the PCA (r=0.73, p < 0.001), with a lower correlation in the ACA (r=0.49, p<0.01) and the ICA (r=0.41, p<0.05). The estimated blood velocity (V) given rCBF=0 was not significantly different from 0.The results support the validity of expressing the relationship between blood velocity (V) and rCBF in defined cerebral artery systems as: V=1/60(rCBF) T (A)−1, where A represents the area of the lumen of the vessel segment where the velocity is being measured, and T denotes the size of the brain region being perfused from this artery.

Cerebral Vasoreactivity Assessed With Transcranial Doppler and Regional Cerebral Blood Flow Measurements: Dose, Serum Concentration, and Time Course of the Response to Acetazolamide

BACKGROUND AND PURPOSE To improve the assessment of cerebral vasoreactivity using acetazolamide (ACZ), we studied the time course of the response and the relationship between dose, response, and serum concentration. METHODS Blood flow velocities were measured with the use of transcranial Doppler ultrasonography in one of the middle cerebral arteries of 48 healthy subjects after the intravenous administration of 1 to 1.6 g ACZ. In 34 subjects (group 1), velocities were measured every second minute to detect the maximum middle cerebral artery velocity increase. We also measured regional cerebral blood flow using single-photon emission computed tomography in 27 of the subjects in group 1 before and approximately 15 to 20 minutes after the ACZ injection. The serum concentration of ACZ was measured in 15 subjects. In the remaining 14 subjects (group 2), middle cerebral artery velocity measurements were made 10, 25, 30, and 45 minutes after ACZ administration to obtain information regarding the late time course of the response. RESULTS In group 1 the plateau phase of the velocity response was reached 8 to 15 minutes after ACZ administration. A large range of velocity increase was observed, and a significant correlation was found between the maximum velocity increase and the dose and serum concentration of ACZ. In group 2 subjects, maximum velocities were maintained 30 minutes after the injection, but after 45 minutes velocities had decreased to 68% of their highest level. No significant relationship was found between dose or serum concentration of ACZ and the regional cerebral blood flow increase. The velocity increase after ACZ was similar in both older and younger subjects. CONCLUSIONS This study shows that cerebral vasoreactivity is best assessed 10 to 30 minutes after ACZ administration and that the dose should probably exceed 15 mg/kg if a maximum vasodilatory response in the cerebral circulation is to be obtained.

Cerebral vasoreactivity and blood flow before and 3 months after carotid endarterectomy.

We measured regional cerebral blood flow and cerebral vasoreactivity before and 3 months after carotid endarterectomy using xenon-133 inhalation with single-photon emission computed tomography and the acetazolamide test in 14 selected patients who had suffered cerebral transient ischemic attacks due to an ipsilateral internal carotid artery stenosis. The patients had neither clinical nor cerebral computed tomographic evidence of infarction. Baseline regional cerebral blood flow was symmetrical before and unchanged after endarterectomy. Before endarterectomy, vasoreactivity in the middle and anterior cerebral artery territories of the symptomatic side was significantly reduced (p less than 0.05); however, vasoreactivity was normalized 3 months after surgery. Our findings strongly suggest that the stenoses caused a reduction in perfusion reserve that was improved by carotid endarterectomy.

Simultaneous Assessment of Vasoreactivity Using Transcranial Doppler Ultrasound and Cerebral Blood Flow in Healthy Subjects

Blood flow velocities in both middle cerebral arteries and regional cerebral blood flow in their perfusion territories were measured simultaneously in 36 healthy subjects. In 20 subjects, the measurements were first performed under basal conditions and then repeated 15–20 min after an intravenous injection of 1 g of acetazolamide. Reproducibility of simultaneous blood flow and velocity measurements was tested by examining 16 subjects on two occasions under basal conditions with an interval of 20 min. Relatively good reproducibility was found for repeated measurements of velocity and blood flow, being best when side-to-side asymmetry was assessed. The increase in blood flow velocities after acetazolamide was symmetrical (right side, 34.2%; and left side, 35.5%), and the velocity increase was significantly correlated with basal values. The increase in cerebral blood flow was also symmetrical (right side, 29.8%; left side, 30.1%) but not correlated with basal flow values. No significant relationship was found between velocity increase and increase in regional cerebral blood flow. This finding is probably not only due to methodological inaccuracies but may suggest that acetazolamide has an effect on the diameter of the middle cerebral artery or on the magnitude of this arterys perfusion territory. This study supports the use of acetazolamide for assessing cerebral vasoreactivity following the definition of lower limits for velocity and flow increase and for asymmetry of the response.

Acetazolamide effect on cerebellar blood flow in crossed cerebral-cerebellar diaschisis.

We studied the effect of acetazolamide on cerebellar blood flow in 11 stroke patients with large, unilateral cerebral hemispheric infarcts and no evidence of cerebellar infarction, but with cerebrocerebellar diaschisis of cerebral blood flow. Blood flow was determined with xenon-133 inhalation and dynamic single-photon emission computed tomography at rest and 20 minutes after the intravenous injection of 1.0 g acetazolamide. After acetazolamide, the mean +/- SD increases in blood flow in the affected and contralateral cerebellar hemispheres were 11.1 +/- 3.7 and 12.0 +/- 5.3 ml/100 g/min, respectively; the difference between hemispheres was not significant. The absolute increase in cerebellar flow in these 11 patients was of the same magnitude as that in 12 healthy controls. We conclude that cerebellar vasoreactivity is intact in stroke patients with crossed cerebrocerebellar diaschisis of cerebral blood flow. Our results lend further support to the concept that reduced cerebellar blood flow is secondary to functional deactivation. Our patients were studied 2 weeks to 5 years after their stroke, indicating that this phenomenon may be persistent.

A comparison of regional cerebral blood flow and middle cerebral artery blood flow velocities : simultaneous measurements in healthy subjects

Blood flow velocities were measured in both middle cerebral arteries (MCAs) of 36 healthy subjects using transcranial Doppler ultrasound. Measurements were first made using a hand-held probe. Velocities were then studied bilaterally with fixed probes under resting conditions and during simultaneous regional CBF (rCBF) measurements. A significant (p < 0.05) positive correlation was found between MCA flow velocities and rCBF in the estimated perfusion territory of this artery. The correlation coefficient was highest when the measurements were performed simultaneously (p < 0.001) or when velocities recorded with a hand-held probe were adjusted to take into account the significant velocity increase induced by the CBF study situation. The increased velocities during CBF measurements cannot be fully explained by the moderate but significant Pco2 increase. Other possible mechanisms are increased blood flow due to mental activation or MCA vasoconstriction secondary to stimulation of the sympathetic nervous system. The effect of mental activation and Pco2 differences should therefore be considered when comparing the results of repeated velocity and CBF measurements.