Cerebral blood flow and oxygenation during head-up tilt in patients with multiple system atrophy and healthy control subjects

To assess cerebral hemodynamics in patients with multiple system atrophy (MSA), cerebral blood flow and oxygenation were evaluated in 7 MSA patients and 9 healthy controls during a head-up tilt test (HUT) by means of transcranial Doppler ultrasonography and near-infrared spectrophotometry. In the MSA patients examined, the perfusion pressure reduction during HUT was marked, but severe reduction in blood flow velocity was prevented because of a decrease in cerebrovascular resistance. The MSA patients showed no severe reduction in cerebral oxygenation during HUT. These findings indicate that our MSA patients exhibited a compensatory cerebral vasodilatation response to orthostatic hypotension.     

Cerebrovascular reactivity during the Valsalva maneuver in migraine, tension-type headache and medication overuse headache

The aim of this study was to investigate, by means of transcranial Doppler ultrasound (TCD), cerebrovascular reactivity during the Valsalva maneuver (VM) during the headache-free interval in patients with migraine (M), migraine plus tension-type headache (M+TTH), and migraine plus medication overuse headache (M+MOH). A total of 114 patients (n=60 M, n=38 M+TTH, n=16 M+MOH) and n=60 controls were investigated; diagnoses were made according to the International Headache Society criteria. All subjects underwent TCD monitoring and, simultaneously, non-invasive assessment of arterial blood pressure and end-tidal CO2. Two indices were determined: the cerebrovascular Valsalva ratio (CVR) was calculated as the maximum end-diastolic flow velocity acceleration during the late straining phase of the VM [cm/s2] and the centroperipheral Valsalva ratio (CPVR) was defined as the quotient of CVR to the concomitant arterial blood pressure acceleration [cm/mmHg x s]. The dynamic cerebrovascular autoregulatory response to the VM, measured as CVR, was increased in patients with M and M+TTH compared to age-matched healthy subjects. By contrast, CPVR (i.e. the quotient of the cerebrovascular to the peripheral autonomic response), was increased in M patients compared to healthy subjects and all other headache conditions tested. Cerebrovascular autoregulatory response during the VM was increased in M patients compared to age-matched normal healthy subjects, indicating a disturbed autonomic control of cerebral vasoreactivity. The CPVR seems to be a sensitive parameter for distinguishing between M patients and M+TTH or M+MOH patients.     

Multimodality monitoring during passive tilt and Valsalva maneuver under hypercapnia.

In occlusive cerebrovascular disease cerebral blood flow (CBF) autoregulation can be impaired and constant CBF during fluctuations in blood pressure (BP) cannot be guaranteed. Therefore, an assessment of cerebral autoregulation should consider not only responsiveness to CO2 or Diamox. Passive tilting (PT) and Valsalva maneuver (VM) are established tests for cardiovascular autoregulatory function by provoking BP changes. To develop a comprehensive test for vasomotor reactivity with a potential increase of sensitivity and specificity, the authors combined these maneuvers. Blood pressure, corrected to represent arterial pressure at the level of the circle of Willis, middle cerebral artery Doppler frequencies (DF), heart rate (HR) and endtidal partial pressure of CO2 (PtCO2) were measured continuously and noninvasively in 81 healthy subjects (19-74 years). Passive tilt and Valsalva maneuver were performed under normocapnia (mean, 39 + 4 mmHg CO2) and under hypercapnia (mean, 51 + 5 mm Hg CO2). Resting BP, HR, and DF increased significantly under hypercapnia. Under normocapnia and hypercapnia, PT induced only minor, nonsignificant changes in mean BP at the level of the circle of Willis compared to baseline (normocapnia: + 2 + 15 mm Hg; hypercapnia: -3 +/- 13 mm Hg). This corresponded with a nonsignificant decrease of the mean of DF (normocapnia: -4 +/- 11%; hypercapnia -6 +/- 12%). Orthostasis reduced pulsatility of BP by a predominantly diastolic increase of BP without significant changes in pulsatility of DF. Valsalva maneuver, with its characteristic rapid changes of BP due to elevated intrathoracic pressure, showed no significant BP differences in changes to baseline between normocapnic and hypercapnic conditions. Under both conditions the decrease in BP in phase II was accompanied by significantly increased pulsatility index ratio (PIDF/PIBP). Valsalva maneuver and PT as established tests in autonomic control of circulation provoked not only changes in time-mean of BP but also in pulsatility of BP. The significant increase in pulsatility ratio and decrease of the DF/BP ratio during normocapnia and hypercapnia indicated preserved CBF autoregulation within a wide range of CO2 partial pressures. Hypercapnia did not significantly influence the autoregulatory indices during VM and PT. Physiologically submaximally dilated cerebral arterioles can guarantee unchanged dynamics of cerebral autoregulation. Combined BP and MCA-DF assessment under hypercapnia enables investigating the effect of rapid changes of blood pressure on CO2-induced predilated cerebral arterioles. Assuming no interference of hypercapnia-induced vasodilation, VM, with its rapid, distinct changes in BP, seems especially to be adequate provocation for CBF autoregulation. This combined vasomotor reactivity might provide a more sensitive diagnostic tool to detect impaired cerebral autoregulation very early.     

Right-to-left-shunts detected by transesophageal echocardiography and transcranial Doppler sonography

BACKGROUND: Transesophageal echocardiography (TEE) and transcranial Doppler sonography (TCD) can identify right-to-left-shunts that predispose to paradoxical embolism. In a large cohort we compared the results of both techniques. METHODS: 222 patients were investigated by both techniques using the contrast agent Echovist-300 and performing each test once without and once with the Valsalva maneuver (VM). RESULTS: TEE-proven right-to-left-shunts were detected by TCD with a high sensitivity of 94%. In addition, TCD revealed shunts not noted during TEE in about 20% of all patients studied. These shunts are in general smaller than those concordantly identified; however, 9% of the patients without a TEE-proven shunt presented with a shunt that allows a considerable amount of contrast medium to pass. There were 12% more microbubbles detected in the right middle cerebral artery than in the left middle cerebral artery during the TCD test performed with VM, but not during the TCD test performed without VM. CONCLUSIONS: Contrast-enhanced TEE and TCD are complementary methods in the assessment of stroke and stroke-prone patients. The side difference of microbubbles may indicate a selective streaming of cardiac emboli during VM.     

Cerebral vasoconstriction precedes orthostatic intolerance after parabolic flight

The effects of brief but repeated bouts of micro- and hypergravity on cerebrovascular responses to head-up tilt (HUT) were examined in 13 individuals after (compared to before) parabolic flight. Middle cerebral artery mean flow velocity (MCA MFV; transcranial Doppler ultrasound), eye level blood pressure (BP) and end tidal CO(2) (P(ET)CO(2)) were measured while supine and during 80 degrees HUT for 30 min or until presyncope. In the postflight tests subjects were classified as being orthostatically tolerant (OT) (n = 7) or intolerant (OI) (n = 6). BP was diminished with HUT in the OT group in both tests (p < 0.05) whereas postflight BP was not different from supine in the OI group. Postflight compared to preflight, the reduction in P(ET)CO(2) with HUT (p < 0.05) increased in both groups, although significantly so only in the OI group (p < 0.05). The OI group also had a significant decrease in supine MCA MFV postflight (p < 0.05) that was unaccompanied by a change in supine P(ET)CO(2). The decrease in MCA MFV that occurred during HUT in both groups preflight (p < 0.05) was accentuated only in the OI group postflight, particularly during the final 30 s of HUT (p < 0.05). However, this accentuated decrease in MCA MFV was not correlated to the greater decrease in P(ET)CO(2) during the same period (R = 0.20, p = 0.42). Although cerebral vascular resistance (CVR) also increased in the OI group during the last 30 s of HUT postflight (p < 0.05), the dynamic autoregulatory gain was not simultaneously changed. Therefore, we conclude that in the OI individuals, parabolic flight was associated with cerebral hypoperfusion following a paradoxical augmentation of CVR by a mechanism that was not related to changes in autoregulation nor strictly to changes in P(ET)CO(2).     

脑血流自动调节监测在脑血管疾病中的临床应用

脑血流自动调节（cerebral autoregulation,CA）是指脑血流在动脉血压（arterial blood pressure,ABP）和脑灌注压（cerebral perfusion pressure,CPP）发生改变时保持相对稳定的能力。临床主要通过改变血压后测量脑血流的变化以反映CA的方式很多,常用的有：下肢负压、冷加压试验、Valsalva动作等。通过改变脑灌注压来评估CA能力主要由经颅多普勒超声（transcranial Doppler,TCD）来实现,它是在生理和病理情况下测定脑血流速度和CA的有效工具,它结合体位改变对脑血流进行测量是一种更方便、更易接受的方法,对缺血性脑血管病的预后评估起到重要作用。本文就CA监测在脑血管疾病中的临床应用做一综述。     

Valsalva maneuver suggests increased rigidity of cerebral resistance vessels in familial dysautonomia

In familial dysautonomia (FD), cerebral autoregulation (CA) must adjust cerebral blood flow to extreme and rapid fluctuations in systemic blood pressure. Compromised CA during systemic blood pressure (BP) fluctuations might contribute to central autonomic dysfunction in FD. To evaluate CA during rapid BP changes, we monitored heart rate (HR), radial artery BP and middle cerebral artery blood flow velocity (CBFV), using transcranial Doppler sonography, in eight FD patients and twelve age-matched controls in supine position at baseline and during a Valsalva maneuver (VM, 40 mmHg expiratory pressure for 15 seconds). The best of four VM recordings was analyzed. We calculated two autoregulation parameters. CA_II reflects BP related autoregulatory CBFV increase in late phase II of VM. CA_II = [(CBFV_{II late}-CBFV_{II early})/CBFV_{II early}]/[(BP_{II late}-BP_{II early})/BP_{II early}]. CA_IV reflects BP and HR related autoregulatory CBFV increase in phase IV of VM. CA_IV = (CBFV_IV/CBFV_I)/(BP_IV/BP_I)/(HR_IV/HR_I). Baseline systemic BP, but not CBFV, was higher in the patients than the controls. During VM, both groups had similar CBFV and BP values, but CAIV and especially CA_II were significantly lower in the patients than the controls. We have documented that FD patients maintain stable CBFV during rapid BP fluctuations associated with early and late phase II and phase IV of VM suggesting that small intracerebral vessels of FD patients are less responsive to rapid systemic blood pressure fluctuations. To compensate for decreased sympathetic vascular innervation, we propose that FD patients may alter the myogenic component of CA by vessel wall thickening resulting in increased rigidity of intracerebral resistance vessels. The resulting vasoconstriction would allow maintenance of normal baseline CBFV in spite of chronic recumbent hypertension. Received: 31 August 2001, Accepted: 24 April 2002 Correspondence to M. J. Hilz, M. D., Ph. D.     

Cerebrovascular mechanisms in neurocardiogenic syncope with and without postural tachycardia syndrome.

BACKGROUND AND PURPOSE: Recent transcranial Doppler studies in patients with neurocardiogenic syncopes (NCS) have demonstrated that the cerebrovascular response to sudden systemic hypotension is vasoconstriction instead of compensatory vasodilation (autoregulation). We tried to characterize the conditions leading to this unexpected response in NCS patients further by continuously monitoring autoregulation and autonomic parameters during a standardized tilt-table test (TTT). METHODS: Sixteen patients below the age of 50 years with a history of at least three syncopes of undetermined cause and tilt-table verified NCS and 20 normal controls were studied. Arterial blood pressure (ABP) and heart rate (HR) were monitored by Finapres and cerebral blood flow velocity (CBFV) of the left middle cerebral artery by transcranial Doppler. Baroreflex sensitivity and autoregulation parameters were measured continuously, using cross-spectral analysis of Mayer waves (3-9 cycles per minute oscillations) in ABP, HR and CBFV, respectively. Pulsatility indices (PI) of CBFV and ABP were determined continuously. Measurements were taken during 5 min in supine and during 5 min in tilted position. In patients, tilting was continued for a maximum of 45 min until the onset of syncope or presyncope. RESULTS: According to the maximum increase in heart rate (deltaHR) during the first 5 min of standing, heart rate responses were classified as postural tachycardia syndrome (POTS) (deltaHR > 35/min) or as normal. Only one out of 20 control subjects showed a POTS (5%) in contrast to seven patients (44%). Patients with a POTS had significantly lower PI values in ABP and higher ratios between the PI of CBFV and the PI of ABP both in supine and in tilted positions. Baroreflex sensitivity during standing decreased significantly in POTS patients when compared to controls. Although autoregulation remained intact during standing, mean CBFV decreased significantly and continuously. The nine patients without a POTS showed almost the same cardiovascular and cerebrovascular responses as the control subjects. All 16 patients showed similar circulatory responses during syncope (sudden hypotension, relative or absolute bradycardia, reduced CBFV and increased PI in CBFV). CONCLUSIONS: The development of a POTS during tilting indicates a high risk for fainting. The characteristic hemodynamic features in the initial phase of standing in these patients can be interpreted in terms of central hypovolemia (low PI of ABP) with sufficient ABP regulation and increased cerebrovascular resistance (defined as the ratio between PI of CBFV and ABP). Cerebral autoregulation seems not to be affected in patients suffering from NCS.     

Supine-to-standing transcranial Doppler test in patients with multiple system atrophy

BackgroundSupine-to-standing test, a transcranial Doppler (TCD) based technique, has been recently developed to evaluate cardiovascular dysautonomia. We explored the value of supine-to-standing TCD test in predicting the course of multiple system atrophy (MSA) with orthostatic hypotension (OH).MethodsBy monitoring the signals of middle cerebral artery during supine-to-standing posture changes, the trend curves of cerebral blood flow velocities, pulsatility index and resistance index were obtained from 38 MSA patients with OH and 31 healthy subjects. The correlation between TCD findings and the clinical outcome of the patients, which was determined by follow-up structured phone interview, was analyzed. Adverse outcome was defined if a patient died, was in bed-ridden state or had recurrent syncope (>1 per month).ResultsTwo characteristic TCD findings were revealed in the MSA patients but not in the controls, i.e. a blunted cerebral blood flow velocity rebound after standing and/or sustained higher pulsatility index upon standing than supine baseline. Structured phone interview was completed in 31 of the 38 patients (mean follow-up time, 20 ± 11 months). While no subject had recurrent syncope before enrollment, 12 patients developed an adverse outcome during follow-up. The coexistence of two characteristic TCD findings predicted adverse outcomes with positive predictive value 66.7% and negative predictive value 87.5%.ConclusionsSupine-to-standing TCD test is valuable in predicting the course of MSA with OH at early stage. We hypothesize baroreflex failure effects and paradoxical cerebral vasoconstriction in response to OH may account for the TCD findings in MSA patients.     

Electrodermal activity in patients with neurally mediated syncope

Abstract. Electrodermal activity (EDA) increases during arousal, emotional stimuli or thermoregulatory sweating and is sometimes apparent in unfiltered ECG recordings. We hypothesized that changes in EDA precede any change in blood pressure (BP) or cerebral blood velocity (CBV) observed at syncope. Data from 70 patients referred for recurrent syncope were retrospectively analyzed. 400Hz continuous waveforms were recorded of BP (Finapres), CBV (transcranial Doppler), expired CO₂ (PCO₂) and ECG at rest and during 80° head-up tilt (HUT). Two independent investigators determined the onset and termination of EDA in relation to syncope using the raw and a low pass filtered ECG trace. Of the 53 patients who experienced syncope during HUT, 33 (62 %) increased EDA 257 ± 357s prior to syncope that continued for 75 ± 73s following syncope. Seven patients (13%) had EDA only after syncope for 208 ± 213s. In 13 patients (25 %), EDA was not detectable. In most cases, EDA preceded any change in BP, PCO₂ or CBV and persisted past the hemodynamic recovery following syncope. Although variable, EDA may be an objective correlate to the clinical observation that patients symptoms precede any measurable change in cerebral perfusion. The actual relationship between EDA and symptoms of presyncope requires further investigation.     

Exaggerated Valsalva maneuver may explain stretch syncope in an adolescent

We describe cardiovascular responses during the Valsalva maneuver and syncope in the youngest reported patient with stretch syncope, which was induced by neck stretching and back hyperextension. The pattern of cardiovascular responses during stretch syncope was similar to that during a pathologic Valsalva maneuver, indicating adrenergic dysfunction in this patient. These findings indicate that the underlying mechanisms of these two processes are not fundamentally different, and that adrenergic dysfunction observed during the Valsalva maneuver may have resulted in stretch syncope in this patient. However, a simple Valsalva maneuver should not have sufficed to precipitate these episodes, because no syncope or significant hypotension occurred during the Valsalva maneuver. Thus, we suggest that additional factors, such as mechanical compression of vessels or physiologic responses to orthostasis, were aggravated during pathologic Valsalva maneuver responses, which were responsible for the stretch syncope observed.     

Detection of paradoxical cerebral echo contrast embolization by transcranial Doppler ultrasound

Contrast echocardiography has been shown to be a sensitive method for detecting patent foramen ovale in embolic stroke, implying paradoxical embolization. However, not all two-dimensional echocardiographic studies are of diagnostic quality, and direct evidence for paradoxical cerebral embolization remains lacking. We addressed these problems by simultaneously using transcranial Doppler ultrasound and contrast echocardiography to compare relative sensitivity and concordance in the detection of right-to-left vascular shunting. Forty-six patients with stroke, transient neurologic defect, or question of atrial septal defect underwent study at rest and during Valsalva strain. Two-dimensional echocardiography detected shunting in 26% at rest and 15% during Valsalva strain, whereas transcranial Doppler study returned rates of 41% and 41%, respectively. Concordance was 82% and 75%, respectively. Discordant studies almost always had evidence of paradoxical contrast embolization by transcranial Doppler and intermediate findings by two-dimensional echocardiography. Transcranial Doppler is a sensitive, unambiguous technique for the detection of anatomic substrates and target organ involvement in patients suspected to have paradoxical cerebral embolization.     

A new sign of sympathetic neurocirculatory failure: premature ventricular contraction as a “one-beat Valsalva maneuver”

Sympathetic neurocirculatory failure (SNF) features orthostatic hypotension and abnormal beat-to-beat blood pressure (BP) responses to the Valsalva maneuver. This article describes a new sign of SNF, based on changes in BP after premature ventricular contractions (PVCs). Records of supine beat-to-beat BP at rest were reviewed from 22 patients with SNF and 52 control subjects. Records were also taken during intravenous infusion of the ganglion blocker trimethaphan from 38 control subjects. In all 10 control subjects who had PVCs, after the postextrasystolic beat, mean arterial pressure increased progressively to levels higher than before the PVC, peaking at about the eighth beat. In contrast, in all 13 patients with SNF who had PVCs, after the postextrasystolic beat, BP decreased to less than baseline and then increased gradually back to baseline. In all 3 control subjects who had at least one PVC before trimethaphan infusion and another during trimethaphan infusion, the post-PVC pressure pattern during trimethaphan infusion resembled that in SNF patients. Because of a brief increase in sympathetic cardiovascular outflows, after a PVC, BP increases progressively to greater than pre-PVC values, mimicking the pressure overshoot after release of the Valsalva maneuver. Just as the absence of the overshoot of BP after release of the Valsalva maneuver supports a diagnosis of SNF, so does the absence of the overshoot after a PVC.     

Challenging cerebral autoregulation in patients with preganglionic autonomic failure

Intact cerebral autoregulation is essential to prevent cerebral hypoperfusion during pronounced changes in arterial blood pressure (ABP) in patients with autonomic failure (AF). It is still a matter of debate whether and to what extent cerebral autoregulation is disturbed in these patients. This study evaluates the interaction between cerebral blood flow velocity (CBFV) and ABP during Valsalva maneuver (VM) and tilt-table testing in nine patients with multiple system atrophy including AF and in 14 age-matched controls. CBFV and ABP were recorded noninvasively using transcranial Doppler sonography and the Finapres device. Responses to VM were graded by the autoregulation slope index (ASI). Cerebrovascular resistance changes were estimated by the conventional ratio ABP/CBFV and by the dynamic pressure-velocity relationship. To challenge cerebral autoregulation further, tests were repeated under hypercapnic predilation of cerebral arterioles. During VM, CBFV reincreased in patients despite a pronounced ABP drop and showed an overshoot after the strain, thus, being similar to controls. The ASI was higher in patients than in controls ( p < 0.05). During 70 degrees head-up tilt, ABP dropped markedly, but the decrease in CBFV was small and did not differ significantly from controls. In patients, both tests were associated with a substantial decrease of the dynamic but not of the conventional pressure-velocity relationship. Under hypercapnia, the CBFV response in patients remained unchanged. We conclude that 1). cerebral arterioles have the capacity for adequate vasodilation during ABP drops in patients with AF and that this ability is still present under hypercapnic predilation. 2). The mechanism of cerebral autoregulation in itself does not seem to be affected by the AF but is rather well exercised. 3) The VM presents, in addition to tilt-table testing, a simple test for clinical evaluation of cerebral autoregulation in patients with AF.     

Wave reflection analysis of the human cerebral circulation during syncope

Up till now, the presence of wave reflection of pressure and flow waves was not considered in studies on the cerebral circulation. This study tested the hypothesis whether the typical changes in cerebral blood flow velocity (CBFV) seen in patients during vasovagal syncope can be explained by the emergence of a wave reflection site in the cerebrovascular vessels. Continuous recordings of peripheral blood pressure (ABP, by Finapres) and CBFV (by transcranial Doppler) of 20 control subjects and 10 patients with syncope during tilt table testing were analyzed. Wave reflection analysis (WRA) consisted of a multivariate regression analysis with CBFV as dependent variable and simultaneous ABP as well as delayed ABP (by systematically varied time lags) as independent variables. The time delay yielding the best prediction of CBFV was interpreted as the reflection time. A univariate regression analysis with only simultaneous ABP as independent variable served as control method. In patients and controls CBFV during supine position could be explained sufficiently (explained variance=88-90%) by univariate regression without improvement by WRA. During syncope, multivariate regression improved the prediction of CBFV (explained variance=58% with univariate and 77% with multivariate regression) in 9 of 10 patients. The mean reflection time was 160 ms. The results can be explained by a collapse of the distal bridging veins during systemic hypotension giving rise to a pressure wave moving backward with a resulting distortion of the flow wave. In particular, the WRA model could account for the characteristic changes in the diastolic flow shape during syncope.     

Scalp-recorded slow EEG responses generated in response to hemodynamic changes in the human brain.

OBJECTIVE: To study whether hemodynamic changes in human brain generate scalp-EEG responses. METHODS: Direct current EEG (DC-EEG) was recorded from 12 subjects during 5 non-invasive manipulations that affect intracranial hemodynamics by different mechanisms: bilateral jugular vein compression (JVC), head-up tilt (HUT), head-down tilt (HDT), Valsalva maneuver (VM), and Mueller maneuver (MM). DC shifts were compared to changes in cerebral blood volume (CBV) measured by near-infrared spectroscopy (NIRS). RESULTS: DC shifts were observed during all manipulations with highest amplitudes (up to 250 microV) at the midline electrodes, and the most pronounced changes (up to 15 microV/cm) in the DC voltage gradient around vertex. In spite of inter-individual variation in both amplitude and polarity, the DC shifts were consistent and reproducible for each subject and they showed a clear temporal correlation with changes in CBV. CONCLUSIONS: Our results indicate that hemodynamic changes in human brain are associated with marked DC shifts that cannot be accounted for by intracortical neuronal or glial currents. Instead, the data are consistent with a non-neuronal generator mechanism that is associated with the blood-brain barrier. SIGNIFICANCE: These findings have direct implications for mechanistic interpretation of slow EEG responses in various experimental paradigms.     

Methodological parameters influence the detection of right-to-left shunts by contrast transcranial Doppler ultrasonography.

BACKGROUND AND PURPOSE: Contrast transcranial Doppler ultrasonography is a new method to detect intracardiac right-to-left shunts, such as the patent foramen ovale. However, the methodology of the procedure varies considerably among investigators. This study was undertaken to assess the influence of methodological parameters on the results of the contrast transcranial Doppler examination in the detection of right-to-left shunts. METHODS: A total of 72 patients (mean age, 58.2+/-14.7 years) had a contrast transcranial Doppler ultrasonography examination. To study the influence of methodological factors, patients with evidence of a right-to-left shunt underwent repeated examinations with modified procedures. Parameters under investigation were the timing of the Valsalva maneuver, the dose of the contrast medium, and the patient's posture during the examination. RESULTS: The median contrast signal count was 58.5 and 48.0 (P<0.001) and the median latency of the first intracranially detected contrast signal was 12.5 and 8.5 seconds (P=0.05) when the Valsalva maneuver was performed 5 and 0 seconds after the start of the injection, respectively. Reducing the contrast medium dose from 10 to 5, 2.5, and 1.2 mL resulted in a decline of the median signal count from 54.5 to 28.5, 20.5, and 12.0 (P<0.01), respectively, while the latency of the first contrast signal increased from 13.3 to 14.0, 14.6, and 15.0 seconds (P<0.05). The sitting position also produced a lower signal count than the supine position (P<0.02). CONCLUSIONS: This study demonstrates that several essential methodological parameters influence the results of the contrast transcranial Doppler ultrasonography examination. Therefore, it is necessary to standardize the procedure to permit comparable quantitative assessments of the shunt volume. The findings of the present study suggest that 10 mL of contrast medium be injected with the patient in the supine position and that the Valsalva maneuver be performed 5 seconds after the start of the injection.     

Dynamic cerebral autoregulation testing as a diagnostic tool in patients with carotid artery stenosis

Evaluation of dynamic cerebral autoregulation might yield a physiologically more adequate measure of cerebral hemodynamic impairment in carotid artery stenosis than CO2-reactivity. This study re-evaluates and compares the Valsalva maneuver (VM) and phase shift during deep breathing. Nineteen patients with severe carotid artery stenosis and 17 age-matched controls were examined using transcranial Doppler sonography and non-invasive blood pressure recordings (Finapres). Phase shift was determined by cross-spectral analysis, responses to VM were graded by the formerly-introduced autoregulation slope index (ASI) and the new Valsalva time index (VTI). Phase shift and autoregulatory indices were significantly reduced on the affected side (p < 0.001). Correlations with CO2-reactivity were significant when pooling values of controls and patients (r from 0.54 to 0.78; p < 0.001). Correlations except for the VTI (r = -0.65; p = 0.002) were not significant considering only the affected side in patients. Correlations of pooled values between phase shift and VM-derived indices were significant (VTI r = -0.62; p < 0.001; ASI r = 0.49; p < 0.001), within patients only when comparing side-to-side differences (VTI r = -0.58; p = 0.009; ASI r = 0.52; p = 0.023). In conclusion, detection of impaired cerebral autoregulation is possible both by deep breathing and VM. The new VTI seems to be more suitable than the conventional ASI. Inter-method agreement concerning the extent of impairment is only acceptable for intra-individual side-to-side differences. Since absolute values of one autoregulation testing method or CO2-reactivity alone might fail, various tests should be combined for comprehensive assessment of cerebral hemodynamic impairment.     

Autoregulatory cerebral vasodilation occurs during orthostatic hypotension in patients with primary autonomic failure

It is unclear whether patients with autonomic failure autoregulate cerebral blood flow during hypotension. The objective in this study was to examine cerebral autoregulatory capacity in patients with autonomic failure by studying changes in middle cerebral artery blood flow velocity using transcranial Doppler ultrasonography before, during, and after tilt-induced hypotension. Nine patients with primary autonomic failure were evaluated. Mean arterial pressure and middle cerebral artery blood flow velocity were simultaneously recorded while the patients were in the supine position, during 60^o head-up tilt, and after they were returned to the horizontal position. The results were as follows: during tilt-induced hypotension, mean arterial pressure decreased significantly more than middle cerebral artery mean blood flow velocity (58% versus 36%, p<0.0002). After return to the horizontal position, mean arterial pressure returned to baseline, and middle cerebral artery blood flow velocity transiently increased above pretilt value (p<0.02). It is concluded that cerebral autoregulatory vasodilation occurs in patients with autonomic failure. This was demonstrated by a more pronounced decline in mean arterial pressure than in middle cerebral artery blood flow velocity during hypotension and by a transient increase in middle cerebral artery blood flow velocity (ie, hyperemic response) after blood pressure was restored.     

Balloon test occlusion with the Doppler velocity guidewire

Transcranial Doppler ultrasonography is the most commonly used method of cerebrovascular blood flow velocity measurement, but it is subject to certain technical and anatomic limitations. The Doppler velocity guidewire measures blood flow velocity within any vessel during cerebral angiography, overcoming these limitations. We report the first use of this guidewire in the measurement of blood flow velocity during balloon test occlusion, with results similar to simultaneously measured transcranial Doppler ultrasonography. Velocity measurement by Doppler guidewire could be useful in balloon test occlusion for vertebrobasilar circulation, where transcranial Doppler ultrasonography is limited, and provide anatomically specific blood flow velocity measurements in the diagnosis and treatment of stroke and other cerebrovascular diseases.