Dynamics of cerebral blood flow autoregulation in hypertensive patients

In hypertensive patients, the upper and lower limits of cerebral autoregulation are shifted to higher levels. However, the dynamics of cerebral autoregulation in hypertensive patients are less well known. We compared the dynamics of cerebral autoregulation in 21 treated hypertensive patients (13 men and 8 women; mean age: 48.9+/-13.6 years) and in 21 normotensive subjects (13 men and 8 women; mean age: 51+/-14.5 years) by transcranial Doppler (TCD) of the middle cerebral artery (MCA) during the acute decrease in blood pressure induced by standing up after 2 min in squatting position. MCA maximal outline blood flow velocity (FV), blood pressure (Finapres) and end-tidal PCO2 were continuously monitored and computerised. A cerebral vascular resistance index (CR) was calculated as follows: mean arterial BP/MCA mean FV with normalised changes in CR per second during the blood pressure decrease (CR slope). The CR slope reflecting the rate of cerebral autoregulation did not differ between the two groups and within the hypertensive patients [well controlled (8 patients) and not controlled (13 patients)]. The time to maximum decrease of CR (T1) and the time to full recovery of CR after the initial drop (T2) were also similar in the two groups (controls T1: 11.3+/-3.1 s, T2: 12+/-5.9 s; hypertensive T1: 11.7+/-2.5 s, T2: 10.7+/-4.5 s) and within hypertensive patients. These findings suggest that the dynamics of cerebral autoregulation are well preserved in hypertensive patients, with no difference according to the efficiency of treatment of hypertension.     

Cerebral vasomotor reactivity in Parkinson's disease, multiple system atrophy and pure autonomic failure

Parkinson's disease (PD), multiple system atrophy (MSA) and pure autonomic failure (PAF) are neurodegenerative disorders frequently associated with orthostatic hypotension and syncope, though with different underlying mechanisms. Cerebral hemodynamic responses in these three neurodegenerative diseases are still incompletely studied and it is possible that they would be differentially affected. We measured blood flow velocity (BFV) in the middle cerebral artery (MCA) and vertebral artery (VA) in patients with these disorders and investigated whether cerebral vasomotor reactivity (VMR) differs in these three disorders. Twenty-four patients (9 with PD, 10 with MSA and 5 with PAF) were studied. VMR was assessed in the MCA and VA, using transcranial Doppler (TCD) and Diamox test (injection of 1 g acetazolamide i.v.) with the patients in a recumbent position. The percent difference between BFV before and after acetazolamide injection was defined as VMR% and the results were compared by ANOVA. The mean MCA and VA blood flow velocities were similar in the three disorders and within normal limits for our laboratory. The mean MCA VMR values were 37.5+/-24.0%, 27.9+/-28.0% and 38.0+/-33.9% in PD, MSA and PAF, respectively. The VA VMR values were 22.9+/-23.6%, 32.4+/-38.0% and 18.9+/-18.3%, respectively, with no significant differences between the groups. We conclude that BFV is normal in PD, MSA and PAF and that the VMR, as investigated by TCD and the Diamox test, did not disclose differences in cerebral vasomotor responses between these conditions.     

Impaired dynamic cerebral autoregulation in middle cerebral artery stenosis

BACKGROUND AND PURPOSE: Analysis of dynamic cerebral autoregulation during transient falls in blood pressure is considered a sensitive and convenient method for evaluating patients with carotid artery stenosis. To this point, there have been few reports on the efficacy of using the thigh cuffs technique to analyse middle cerebral artery (MCA) stenosis. If it could be determined whether cerebral blood flow can be maintained (autoregulated) during sudden falls in arterial blood pressure (ABP), then it might be possible to identify patients with MCA stenosis who are at risk of stroke. METHODS: We used the thigh cuff technique to estimate dynamic cerebral autoregulation in 57 patients with MCA stenosis and 72 normal controls. After a stepwise fall in arterial blood pressure, we determined the rate of the rise of MCA blood velocity and compared it with the rate of the rise of arterial blood pressure. In this manner, the dynamic cerebral autoregulation of 11 patients undergoing MCA M1 stent angioplasty was estimated both pre- and post-operation. RESULTS: The autoregulatory index (ARI) was significantly reduced in patients with stenosed/occluded MCA (3.24 +/- 1.52), as compared with normal controls (5.25 +/- 1.39; p<0.001) (results reported as mean +/- SD). Poor ARI values are usually observed in patients with a higher degree of stenosis and particularly in patients with insufficient collateral compensation. ARI was significantly reduced in severe stroke patients (modified ranking scale>or=1), as compared with asymptomatic or TIA patients (p<0.05). After MCA stent angioplasty was performed, there was a significant improvement in ARI in 11 subjects, which caused a mean increase in ARI from 2.08 +/- 1.10 to 3.80 +/- 1.36 (p=0.008). CONCLUSIONS: Dynamic cerebral autoregulation is impaired in patients with middle cerebral artery stenosis. Assessing dynamic cerebral autoregulation may allow a subgroup of patients with MCA stenosis who are at risk of hemodynamic stroke to be identified. Dynamic cerebral disautoregulation in patients with severe MCA stenosis is mostly remedied by stent angioplasty.     

Evaluation of blood flow velocity and cerebrovascular reactivity in patient with posterior circulation stroke

The aim of our study was to determine the type of blood flow disturbances and cerebrovascular reactivity of major anterior and posterior circulation cerebral vessels in patients with posterior stroke (POCI). The examined group consisted of 17 patients, mean age 57 +/- 12 yr, with posterior circulation infarct. Neurological examination, brain CT and Doppler examination including evaluation of BFV and CVR of MCA, PCA and VA was performed in each patient. Doppler examination was done using Pioneer TC 2020 and capnograph Tidal Wave sp Novametrix. RESULTS: BFV of ICA's, MCA's, ACA's and PCA's were diminished while BFV of VA's were significantly diminished in the examined patients compared to healthy controls. CVR of MCA in posterior circulation stroke patients was significantly lower compared to controls. CVR of PCA and VA was significantly lower compared to CVR of MCA in patients with posterior circulation stroke. CONCLUSION: Impairment of CVR, especially in posterior circulation, plays an important role in posterior circulation stroke pathogenesis.     

Orthostatic tolerance, cerebral oxygenation, and blood velocity in humans with sympathetic failure

BACKGROUND AND PURPOSE: Patients with orthostatic hypotension due to sympathetic failure become symptomatic when standing, although their capability to maintain cerebral blood flow is reported to be preserved. We tested the hypothesis that in patients with sympathetic failure, orthostatic symptoms reflect reduced cerebral perfusion with insufficient oxygen supply. METHODS: This study addressed the relationship between orthostatic tolerance, mean cerebral artery blood velocity (V(mean), determined by transcranial Doppler ultrasonography), oxygenation (oxyhemoglobin [O(2)Hb], determined by near-infrared spectroscopy), and mean arterial pressure at brain level (MAP(MCA), determined by finger arterial pressure monitoring [Finapres]) in 9 patients (aged 37 to 70 years; 4 women) and their age- and sex-matched controls during 5 minutes of standing. RESULTS: Supine MAP(MCA) (108+/-14 versus 86+/-14 mm Hg) and V(mean) (84+/-21 versus 62+/-13 cm. s(-1)) were higher in the patients. After 5 minutes of standing, MAP(MCA) was lower in the patients (31+/-14 versus 72+/-14 mm Hg), as was V(mean) (51+/-8 versus 59+/-9 cm. s(-1)), with a larger reduction in O(2)Hb (-11. 6+/-4 versus -6.7+/-4.5 micromol. L(-1)). Four patients terminated standing after 1 to 3.5 minutes. In these symptomatic patients, the orthostatic fall in V(mean) was greater (45+/-6 versus 64+/-10 cm. s(-1)), and the orthostatic decrease in O(2)Hb (-12.0+/-3.3 versus -7.6+/-3.9 micromol. L(-1)) tended to be larger. The reduction in MAP(MCA) was larger after 10 seconds of standing, and MAP(MCA) was lower after 1 minute (25+/-8 versus 40+/-6 mm Hg). CONCLUSIONS: In patients with sympathetic failure, the orthostatic reduction in cerebral blood velocity and oxygenation is larger. Patients who become symptomatic within 5 minutes of standing are characterized by a pronounced orthostatic fall in blood pressure, cerebral blood velocity, and oxygenation manifest within the first 10 seconds of standing.     

Disparate cardio-cerebral vascular modulation during standing in multiple system atrophy and Parkinson disease

PURPOSE: The dynamic variance of cerebral blood flow velocity (CBFV), monitored by transcranial doppler (TCD), can reveal the integrated effects of cardio-cerebral vascular autoregulation. We investigated the characteristics of CBFV curve during active standing in multiple system atrophy (MSA), Parkinson's disease (PD) and healthy volunteers. METHODS: The CBFV curve of middle cerebral arteries was recorded using TCD in 22 patients with probable MSA; 20 PD patients and 20 volunteers matched for age. All individuals started in a supine posture, followed by abrupt standing for 2 min before returning to supine. The features of CBFV curve were compared among the groups. RESULTS: In the healthy volunteers, the CBFV decreased following standing up but quickly rebounded and reached the same or greater level as the supine baseline. Afterwards, the CBFV decreased abruptly to a sustained level, lower than the supine baseline, forming a spike wave that appeared in CBFV curve. This spike wave was present in 5/22 of MSA, significantly less than PD patients (18/20) and volunteers (20/20) (P<0.001). The CBFV decrease after standing showed no significant difference between MSA than PD (9+/-7 vs. 6+/-3 cm/s, P=0.163). CONCLUSIONS: The different pattern of CBFV curves during active standing suggests MSA may possess cardio-cerebral vascular modulation different from PD. The clinical value of the CBFV curve in differentiating MSA from PD needs further investigation.     

Transcranial Doppler for evaluation of idiopathic intracranial hypertension

OBJECTIVES: The value of transcranial Doppler (TCD) ultrasonography in assessing patients with Idiopathic Intracranial Hypertension (IIH) is uncertain. We sought to determine the contribution of TCD to their evaluation. MATERIALS AND METHODS: Twenty-three patients with suspected IIH underwent TCD. Mean blood flow (BFV), peak systolic (PSV) and end-diastolic (EDV) velocities, and pulsatility (PI) and resistance (RI) indexes were obtained in the middle cerebral (MCA) and vertebral (VA) arteries and compared (Student's t-test) between patients with confirmed IIH and controls. IIH patients and controls were comparable in terms of age, gender and weight. RESULTS: The mean +/- SD BFV(MCA), PSV(MCA), EDV(MCA) and PI(VA) in the 13 IIH patients were higher than in the ten controls (59 +/- 6.8, 94 +/- 28.5, 43 +/- 12.4, 0.86 +/- 0.16 and 50 +/- 8.6, 72 +/- 25.8, 32 +/- 11.5, 0.58 +/- 0.45 respectively, P < 0.05) but still within normal values. The mean +/- SD PI(MCA), RI(MCA) and RI(VA) values in the IIH patients and controls were similar. CONCLUSIONS: TCD parameters had no useful unique features for monitoring IIH patients.     

Dynamic regulation of middle cerebral artery blood flow velocity in aging and hypertension

BACKGROUND AND PURPOSE: Although aging and hypertension may predispose hypertensive elderly subjects to cerebral hypoperfusion during orthostatic stress, their effects on the acute cerebral autoregulatory response to hypotension are not known. METHODS: Continuous middle cerebral artery blood flow velocity (BFV) (transcranial Doppler ultrasound) and mean arterial pressure (MAP, Finapres) were measured in response to (1) acute hypotension during standing, (2) steady-state sitting and standing, and (3) hypercarbia during CO(2) rebreathing in 10 healthy young subjects (age 24+/-1 years), 10 healthy elderly subjects (age 72+/-3 years), and 10 previously treated hypertensive elderly (age 72+/-2 years) subjects. CO(2) reactivity was computed as the slope of cerebrovascular conductance (CVC=BFV/MAP) versus end-expiratory CO(2). Coherence, transfer magnitudes, and phases between low-frequency MAP and BFV signals were computed from their autospectra during 5 minutes of sitting and standing. RESULTS: MAP fell to a similar extent in all groups by an average of 21 to 26 mm Hg (22% to 26%) within 30 seconds of standing. Mean BFV also fell in all subjects but significantly less in the older subjects (-4.7+/-0. 7 cm/s in hypertensives and -5.3+/-1.2 cm/s in normotensives, P=NS) compared with younger subjects (-10.1+/-1.1 cm/s, P<0.05). CO(2) reactivity was greater in the young subjects (0.19+/-0.01) compared with normotensive (0.14+/-0.01, P<0.05) and hypertensive elderly subjects (0.11+/-0.02, P<0.05) (P=NS between elderly groups). Fewer hypertensive subjects had coherence between MAP and BFV signals; for subjects with coherence, there were no significant group differences in phase or transfer magnitudes in either sitting or standing positions. CONCLUSIONS: Despite reduced CO(2) reactivity, elderly normotensive and previously treated hypertensive subjects retain cerebral autoregulatory capacity in response to acute orthostatic hypotension.     

Dynamic but not static cerebral autoregulation is impaired in acute ischaemic stroke

It remains unclear as to whether dynamic and static cerebral autoregulation (CA) are impaired in acute ischaemic stroke, and whether these changes are related to stroke subtype. This could have important implications with regard to post-stroke prognosis and the management of blood pressure (BP) in the acute post-ictal period. Using transcranial Doppler ultrasonography and non-invasive manipulation of BP, we compared both mechanisms in 61 patients with ischaemic stroke within 96 h of ictus, and 54 age- and sex-matched controls. There was no difference in static and dynamic CA indices between the various stroke subtypes. Combining all stroke subtypes dynamic autoregulation, as measured using thigh cuff release, was significantly impaired in both the affected and non-affected stroke hemispheres compared to controls (mean autoregulation index 4.1 +/- 3.3, 4.8 +/- 3.1 and 6.2 +/- 2.3, respectively, p < 0.05). By comparison static autoregulation, assessed using isometric hand grip and thigh cuff inflation, was not significantly different. In conclusion, dynamic but not static CA appears to be globally impaired in acute ischaemic stroke. This deserves further study and may identify possibilities for therapeutic intervention.     

Orthostasis as a test for cerebral autoregulation in normal persons and patients with carotid artery disease.

Orthostasis reduces mean flow velocity (FVmean) in cerebral arteries. This might be used as an alternative provocation test for cerebral hemodynamics in patients with carotid artery disease (CAD). In 21 unilateral CAD patients and 21 controls, FVmean in both middle cerebral arteries (MCA) was measured by transcranial Doppler, together with blood pressure (BP) and heart rate (HR) during a tilt table test. Cerebrovascular reserve (CVR) was measured by an acetazolamide test. In all cases, FVmean dropped to a lower level (controls: 81.9 +/- 9.4% of baseline; patients: 84.3 +/- 7.9% symptomatic side, 85.6 +/- 9.0% contralateral). Impaired CVR patients showed a smaller (p < 0.01) decrease (90.6 +/- 3.3%) compared to contralateral (84.9 +/- 6.0%), to normal CVR patients (81.1 +/- 7.8%) and to controls. Heart rate increased in both groups (controls: +16.6 +/- 9.9%, patients +10.3 +/- 9.9%; p < 0.01); BP showed no change. Orthostasis induces a decrease of MCA FVmean as already previously described. This decrease is significantly smaller in patients with impaired CVR. Since BP does not change, some authors explain the lower MCA Fvmean during orthostasis as caused by sympathetic induced vasoconstriction of cerebral resistance vessels. The authors speculate that in impaired CVR-patients autoregulative protection against ischemia might limit vasoconstriction. In combination with standard tests for measurement of CVR, this test might be useful for evaluation of cerebral autoregulation.     

Cerebral oxygenation declines in healthy elderly subjects in response to assuming the upright position

BACKGROUND AND PURPOSE: With increasing age, assuming the upright position is more often accompanied by symptoms such as dizziness and lightheadedness, possibly as a result of a diminished oxygen supply to the brain due to impaired cerebral autoregulation. We aimed to quantify postural changes in cerebral oxygenation and systemic hemodynamics in healthy elderly and young subjects. METHODS: In 18 healthy elderly subjects (aged 70 to 83 years) and 10 healthy young subjects (aged 22 to 45 years), frontal cortical oxygenation and hemodynamic responses were continuously monitored by near infrared spectroscopy and Finapres, respectively, before and during 10 minutes of active standing. RESULTS:-Cortical oxyhemoglobin concentration [O(2)Hb] decreased by -4.6+/-2.2 micromol/L (P<0.001) and cortical deoxyhemoglobin concentration increased by 1.5+/-2.4 micromol/L (P<0.05) in the elderly subjects after posture change, whereas these variables did not change significantly in the young subjects. The postural hemodynamic changes tended to be attenuated in the elderly subjects, except for the increases in systolic blood pressure (BP). Smaller postural increases in diastolic BP were related to larger [O(2)Hb] decreases (r=0.53, P<0.01, corrected for the age effect). CONCLUSIONS: Assuming the upright position evokes an asymptomatic decrease in frontal cortical oxygenation in healthy elderly subjects but not in healthy young subjects. Cortical [O(2)Hb] changes are affected by diastolic BP changes. These findings may indicate that regulation of cerebral oxygenation alters with increasing age.     

Dynamic cerebral autoregulation associates with infarct size and outcome after ischemic stroke

Reinhard M, Rutsch S, Lambeck J, Wihler C, Czosnyka M, Weiller C, Hetzel A. Dynamic cerebral autoregulation associates with infarct size and outcome after ischemic stroke.
Acta Neurol Scand: 2012: 125: 156–162.
© 2011 John Wiley & Sons A/S. Objectives – Cerebral autoregulation is particularly challenged in acute ischemic stroke. We investigated (1) clinical and radiological factors related to dynamic cerebral autoregulation (DCA) in acute stroke and (2) the relationship between DCA and clinical outcome of stroke. Methods – A total of 45 patients with middle cerebral artery (MCA) stroke were analyzed pooling two previous studies. DCA was measured by transcranial Doppler in both MCAs early (within 48 h from onset) and late (day 5–7) using low‐frequency phase and correlation analysis (index Mx). Outcome was assessed by modified Rankin scale after a mean period of 4 months. Results – Mx increased (i.e. autoregulation worsened) between the early and late measurement, more so on affected (P = 0.005) than on unaffected sides (P = 0.014). Poorer autoregulation as indicated by lower ipsilateral phase (early and late) and higher Mx (late measurement) were significantly related to larger infarction. More severe stroke was significantly related to poorer ipsilateral Mx and phase. Ipsilateral phase in the early (P = 0.019) and Mx in the late measurement (P = 0.016) were related to poor clinical outcome according to univariate analysis. Conclusions – Impairment of DCA ipsilateral to acute ischemic stroke is associated with larger infarction. Dysautoregulation tends to worsen and spread to the contralateral side over the first days post‐stroke and is associated with poor clinical outcome.     

Cerebral atrophy in multiple system atrophy by MRI

Cranial magnetic resonance images (MRI) of the cerebral areas of 40 patients with multiple system atrophy (MSA) and of 61 age-matched controls were analyzed. The cerebral area of MSA patients was 131. 95+/-15.89 cm(2) (mean+/-S.D.), which was significantly smaller than that of normal controls at 149.01+/-10.93 cm(2) (P<0.0001). All 23 MSA cases subjected to the MRI study over a 1-year period showed progressive cerebral atrophy, and the atrophy rate was 2.46+/-1. 66%/year. There were no significant differences within the MSA subtypes or between gender. The progression of cerebral atrophy in MSA correlated more with duration (r=-0.634) than age (r=-0.421). We conclude that MRI findings throughout the course of MSA suggest progressive cerebral atrophy, which is common in all subtypes and reflects duration of the disease rather than age.     

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.     

Impaired dynamic cerebral autoregulation in middle cerebral artery stenosis

Abstract

Background and purpose: Analysis of dynamic cerebral autoregulation during transient falls in blood pressure is considered a sensitive and convenient method for evaluating patients with carotid artery stenosis. To this point, there have been few reports on the efficacy of using the thigh cuffs technique to analyse middle cerebral artery (MCA) stenosis. If it could be determined whether cerebral blood flow can be maintained (autoregulated) during sudden falls in arterial blood pressure (ABP), then it might be possible to identify patients with MCA stenosis who are at risk of stroke.

Methods: We used the thigh cuff technique to estimate dynamic cerebral autoregulation in 57 patients with MCA stenosis and 72 normal controls. After a stepwise fall in arterial blood pressure, we determined the rate of the rise of MCA blood velocity and compared it with the rate of the rise of arterial blood pressure. In this manner, the dynamic cerbral autoregulation of 11 patients undergoing MCA M1 stent angioplasty was estimated both pre- and post-operation.

Results: The autoregulatory index (ARI) was significantly reduced in patients with stenosed/occluded MCA (3.24 ± 1.52), as compared with normal controls (5.25 ± 1.39; p<0.001) (results reported as mean ± SD). Poor ARI values are usually observed in patients with a higher degree of stenosis and particularly in patients with insufficient collateral compensation. ARI was significantly reduced in severe stroke patients (modified ranking scale≥1), as compared with asymptomatic or TIA patients (p<0.05). After MCA stent angioplasty was performed, there was a significant improvement in ARI in 11 subjects, which caused a mean increase in ARI from 2.08 ± 1.10 to 3.80 ± 1.36 (p=0.008).

Conclusions: Dynamic cerebral autoregulation is impaired in patients with middle cerebral artery stenosis. Assessing dynamic cerebral autoregulation may allow a subgroup of patients with MCA stenosis who are at risk of hemodynamic stroke to be identified. Dynamic cerebral disautoregulation in patients with severe MCA stenosis is mostly remedied by stent angioplasty.     

Serial changes in static and dynamic cerebral autoregulation after acute ischaemic stroke

BACKGROUND: The longitudinal changes in static and dynamic cerebral autoregulation (CA) following acute ischaemic stroke are unknown and were assessed in this study. METHODS: Fifty-four ischaemic stroke patients were studied within 96 h of ischaemic stroke and again 7-14 days later, using transcranial Doppler techniques to measure CA. Results were compared to an age-, sex- and blood pressure (BP)-matched control group. Static BP pressor stimulus was produced by thigh cuff inflation and dynamic stimulus by rapid thigh cuff release. RESULTS: Dynamic, but not static, CA was globally impaired at initial (mean dynamic CA index 3.9 +/- 3.1 vs. 6.2 +/- 2.3, p < 0.005) and follow-up studies (dynamic CA 3.9 +/- 2.8 vs. 6.2 +/- 2.3, p < 0.01) in stroke patients compared to controls. Static CA was similar in stroke patients and controls and was unchanged during follow-up. CONCLUSIONS: Dynamic, but not static, CA is impaired after acute ischaemic stroke and remains abnormal for at least 1-2 weeks post ictus. These changes are present in both the affected and non-affected hemispheres and are unrelated to previous antihypertensive treatment, baseline BP levels or BP changes after stroke, age or stroke type.     

Is cerebral autoregulation impaired in Parkinson's disease? A transcranial Doppler study

Orthostatic hypotension (OH) is one of the many autonomic disturbances observed in Parkinson's disease (PD). It has been debated whether an additional impairment of cerebral autoregulation (CA) in PD patients may exacerbate the consequences of OH upon brain perfusion. We assessed CA in PD patients and the potential influence of dopaminergic agents. CA was determined by means of transcranial Doppler (TCD) monitoring of the middle cerebral artery (MCA) at rest and during a thigh cuff release test inducing a systemic blood pressure (BP) drop. Fourteen patients were investigated when taking their usual dopaminergic medication and after drug discontinuation for 12 h. A control group was composed of 11 age-matched subjects (CS). In comparison with PD patients, CS presented a significantly higher increase of the mean cerebral blood flow velocities in the MCA after the BP drop. Mean velocities were increased above the initial values in all CS, whereas a flattened curve was observed in PD patients. No significant differences could be further observed between the PD patients regarding the BP, the cerebrovascular resistance, the heart rate and the pulsatility index. These results provide evidence of an impaired cerebral autoregulation in PD patients which appears independent of dopaminergic treatment.     

Comparison of Non-invasive and Invasive Arterial Blood Pressure Measurement for Assessment of Dynamic Cerebral Autoregulation

Background

There is a growing interest in measuring cerebral autoregulation in patients with acute brain injury. Non-invasive finger photo-plethysmography (Finapres) is the method of choice to relate arterial blood pressure to changes in cerebral blood flow. Among acutely ill patients, however, peripheral vasoconstriction often limits the use of Finapres requiring direct intravascular blood pressure measurement. We evaluated how these two different forms of blood pressure monitoring affect the parameters of dynamic cerebral autoregulation (DCA).

Methods

We performed 37 simultaneous recordings of BP and cerebral blood flow velocity in 15 patients with acute brain injury. DCA was estimated in the frequency domain using transfer function analysis to calculate phase shift, gain, and coherence. In addition the mean velocity index (Mx) was calculated for assessment of DCA in the time domain.

Results

The mean patient age was 58.1 ± 15.9 years, 80 % (n = 12) were women. We found good inter-method agreement between Finapres and direct intravascular measurement using Bland–Altman and correlation analyses. Finapres gives higher values for the efficiency of dynamic CA compared with values derived from radial artery catheter, as indicated by biases in the phase (26.3 ± 11.6° vs. 21.7 ± 10.5°, p = 0.001) and Mx (0.571 ± 0.137 vs. 0.649 ± 0.128, p < 0.001). Gain in the low frequency range did not significantly differ between the two arterial blood pressure methods. The average coherence between CBFV and ABP was higher when BP was measured with arterial catheter for frequencies above 0.05 Hz (0.8 vs. 0.73, p < 0.001).

Conclusion

Overall, both methods yield similar results and can be used for the assessment of DCA. However, there was a small but significant difference for both mean Mx and phase shift, which would need to be adjusted for during monitoring of patients when using both methods. When available, invasive arterial blood pressure monitoring may improve accuracy and thus should be the preferred method for DCA assessment in the ICU.     

Transcranial Doppler sonographic studies of cerebral autoregulation in Shy-Drager syndrome

Summary A study is reported of mean arterial blood pressure and heart rate in four patients suffering from Shy-Drager syndrome. Blood flow velocity in the middle cerebral artery (MCA) was recorded by transcranial Doppler sonography. Concomitant changes in cerebral blood flow and the effect of cerebral autoregulation were thus examined. During tilt (60°, head up) mean arterial blood pressure decreased by 40 mm Hg or 35%, while MCA blood flow velocity dropped by 14 cm/s or 28% (mean values). The lower percentage reduction in flow velocity may indicate a preserved cerebral autoregulation in central autonomic insufficiency.     

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.