Cerebral critical closing pressure and resistance-area product: the influence of dynamic cerebral autoregulation,age and sex

Instantaneous arterial pressure-flow (or velocity) relationships indicate the existence of a cerebral critical closing pressure (CrCP), with the slope of the relationship expressed by the resistance-area product (RAP). In 194 healthy subjects (20–82 years, 90 female), cerebral blood flow velocity (CBFV, transcranial Doppler), arterial blood pressure (BP, Finapres) and end-tidal CO₂ (EtCO₂, capnography) were measured continuously for five minutes during spontaneous fluctuations of BP at rest. The dynamic cerebral autoregulation (CA) index (ARI) was extracted with transfer function analysis from the CBFV step response to the BP input and step responses were also obtained for the BP-CrCP and BP-RAP relationships. ARI was shown to decrease with age at a rate of −0.025 units/year in men (p = 0.022), but not in women (p = 0.40). The temporal patterns of the BP-CBFV, BP-CrCP and BP-RAP step responses were strongly influenced by the ARI (p < 0.0001), but not by sex. Age was also a significant determinant of the peak of the CBFV step response and the tail of the RAP response. Whilst the RAP step response pattern is consistent with a myogenic mechanism controlling dynamic CA, further work is needed to explore the potential association of the CrCP step response with the flow-mediated component of autoregulation.     

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.     

Changes of cerebral blood flow velocities during enhanced external counterpulsation

OBJECTIVES: Intra-aortic counterpulsation is the most frequently used cardiac assist device. However, there are only few studies of the effects of counterpulsation on cerebral blood flow and these report conflicting outcomes. The new enhanced external counterpulsation (EECP) technique reproduces non-invasively the effects of intra-aortic counterpulsation. In this study, we evaluated effects of EECP on blood pressure (BP) and on cerebral flow velocity (CBFV). SUBJECTS AND METHODS: Twenty-three healthy controls and 15 atherosclerotic patients each underwent a 5-min session of EECP. Before, during and after EECP we monitored heart rate, beat-to-beat radial artery BP and CBFV. RESULTS: EECP induced a second increase in BP and CBFV during diastole with a significant increase of mean BP and a decrease of systolic BP in patients and controls. Mean CBFV increased in both groups during the first 5 s of EECP. After 3 min of EECP, diastolic CBFV was still higher than at baseline, but systolic CBVF was lower than at baseline; mean CBFV was as low as before EECP in the patients and lower than the baseline values in the controls. Three minutes after ending EECP, mean and systolic BP were lower in the patients than the corresponding baseline values. Otherwise, CBFV and BP values did not differ from baseline in patients and controls. CONCLUSION: Cerebral autoregulation ensures the constancy of cerebral blood flow even though EECP creates marked systemic changes. In the patients, the decrease of BP after EECP with maintained CBFV indicates an improved BPCBFV relation and a more economic autoregulation.     

Detection of impaired cerebral autoregulation improves by increasing arterial blood pressure variability

Although the assessment of dynamic cerebral autoregulation (CA) based on measurements of spontaneous fluctuations in arterial blood pressure (ABP) and cerebral blood flow (CBF) is a convenient and much used method, there remains uncertainty about its reliability. We tested the effects of increasing ABP variability, provoked by a modification of the thigh cuff method, on the ability of the autoregulation index to discriminate between normal and impaired CA, using hypercapnia as a surrogate for dynamic CA impairment. In 30 healthy volunteers, ABP (Finapres) and CBF velocity (CBFV, transcranial Doppler) were recorded at rest and during 5% CO₂ breathing, with and without pseudo-random sequence inflation and deflation of bilateral thigh cuffs. The application of thigh cuffs increased ABP and CBFV variabilities and was not associated with a distortion of the CBFV step response estimates for both normocapnic and hypercapnic conditions (P=0.59 and P=0.96, respectively). Sensitivity and specificity of CA impairment detection were improved with the thigh cuff method, with the area under the receiver–operator curve increasing from 0.746 to 0.859 (P=0.031). We conclude that the new method is a safe, efficient, and appealing alternative to currently existing assessment methods for the investigation of the status of CA.     

Dynamic cerebral autoregulation: A marker of post-operative delirium?

ObjectiveWe investigated the potential association of cerebral autoregulation (CA) with postoperative delirium (PD), a common complication of cardiac surgery with cardiopulmonary bypass (CPB).MethodsIn patients undergoing coronary artery bypass graft (CABG) surgery with CPB, cerebral blood flow velocity (CBFV) and blood pressure (BP) were continuously recorded during 5-min preoperatively (T1), after 24 h (T2), and 7 days after procedure (T3). Prospective multivariate logistic regression analysis was performed to determine the independent risk factors of PD. Autoregulation index (ARI) was calculated from the CBFV response to a step change in BP derived by transfer function analysis.ResultsIn 67 patients, mean age 64.3 ± 9.5 years, CA was depressed at T2 as shown by values of ARI (3.9 ± 1.7), compared to T1 (5.6 ± 1.7) and T3 (5.5 ± 1.8) (p < 0.001). Impaired CA was found in 37 (55%) patients at T2 and in 7 patients (20%) at T3. Lower ARI at T1 and T2 were predictors of PD (p = 0.003).ConclusionDynamic CA was impaired after CABG surgery with CPB and was a significant independent risk factor of PD.SignificanceAssessment of CA before and after surgery could have considerable potential for early identification of patients at risk of PD, thus reducing poor outcomes and length of stay.Clinical trials registration: www.clinicaltrials.gov (NCT02143544, April 30, 2014).     

Cerebral autoregulation is temporarily disturbed in the early recovery phase after dynamic resistance exercise

Abstract Aim To determine cerebral blood-flow velocity (CBFV) and parameters of dynamic cerebral autoregulation (CA) during and after exhausting resistance exercise. Methods Strength endurance (23 repetitions) and maximal strength training (8 repetitions) in 16 female and 16 male athletes on a leg curler (m. quadriceps training; approx. 2 s contraction) in the upright position. Registration of ECG, blood pressure by Finapres^®, CBFV by transcranial Doppler (TCD), and breathing by a Zak^® breathing-belt. Additional repetitive ergospirometry (O₂-uptake, CO₂-elimination, ventilation) and blood gas analyses were performed in a subgroup of seven athletes. From BP and CBFV cerebrovascular resistance (CVR), pulsatility index (PI) as well as LF-power, gain and phase-angle (frequency analysis) were derived. Results All athletes showed significant (p<0.01) 15 % to 30 % increases in CBFV during both training sets without signs of flow depression due to Valsalva maneuvers. In the early recovery, when blood pressure rapidly decreased, CBFV amplitude significantly (p<0.01) increased for 60–80 seconds with mean flow (Vm) at the exercise level, while CVR and PI showed conflicting results, similar to a presyncopal reaction. Ergospirometry and blood gas analyses revealed no evidence of major changes in pCO₂, but phase angle was reduced (p<0.001) after exercise, together with an LF power increase (p<0.001). Conclusion An unexpected increase in CBFV amplitude and in Vm occurs directly after dynamic resistance exercise without increased pCO₂, which is comparable to a maximum leg press with hypercapnia. CVR and PI results as well as data from frequency analysis show similarities to presyncopal reactions, on the one hand, and point towards a temporarily disturbed cerebral autoregulation, on the other.     

Antibodies in sera from patients with inflammatory demyelinating polyradiculoneuropathy react with ganglioside LM1 and sulphatide of peripheral nerve myelin

Summary Sera from 23 patients with acute Guillain Barré syndrome (GBS), 15 patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and from 40 age-matched blood donors were analysed for antibodies to acidic glycosphingolipids from human brain and peripheral nerve. Antibodies to ganglioside LM1, the major ganglioside of peripheral nerve myelin, were found in 43% of GBS and in 67% of CIDP patients' sera, and in 20% of the blood donors. However, anti-sulphatide antibodies were detected in 65% and 87% of the sera from GBS and CIDP patients, respectively, but only in 15% of the control sera. Sulphatide is the major acidic glycosphingolipid in myelin and its concentration in peripheral nerve myelin is 100 times higher than that of LM1. The high frequency of LM1 and, in particular of sulphatide antibodies, might thus be relevant to the pathogenesis of the GBS and CIDP. Abbreviations: The ganglioside nomenclature used according to Svennerholm [24]. LM1, IV³NeuAc-nLcOse₄Cer, GM1, II³NeuAcGgOse₄Cer; GD1a, IV³NeAc,II³NeuAc-GgOse₄Cer; GD1b, II³(NeuAc)₂-GgOse₄Cer; GT1b, IV³NeuAc,II³(NeuAc)₂-GgOs₄Cer; LU1, sulphate-3-glucuronyl paragloboside; sulphatide, 3-sulphogalacto-sylceramide     

Impaired respiratory sinus arrhythmia with paradoxically normal Valsalva ratio indicates combined cardiovagal and peripheral adrenergic failure

Combined reductions of the heart rate responses to deep breathing (HR_DB) and the Valsalva ratio (VR) are used as a standard test of cardiovagal function. We observed that some patients had marked reduction of HR_DB with a paradoxically normal VR. The mechanism of this paradox was evaluated. We found that these patients had evidence of peripheral adrenergic and postganglionic sudomotor impairment, including an excessive fall in blood pressure on upright tilt. Since VR depends on heart rate responses to blood pressure excursions, we evaluated the phases of the Valsalva manoeuvre and the ensuing heart rate responses in these patients and compared the responses to patients with generalized autonomic failure (Group II) and controls (Group III). Group I patients when compared with controls, had a larger phase II fall in blood pressure and normal phase IV resulting in a significantly enhanced baroreflex stimulus. These patients had a normal heart rate increment but 75% failed to develop reflex bradycardia. We conclude that the paradoxical VR is due to the exaggerated blood pressure swing due in turn to adrenergic failure. When both HR_DB and VR are reduced as in Group II, there may be the additional impairment of cardiac adrenergic failure.     

Ictal cerebral haemodynamic characteristics during typical absence seizures,compared to focal seizures with brief alteration of awareness

Aims. To investigate ictal cerebral haemodynamic characteristics during spontaneous typical absence seizures (TAS) and hyperventilation‐evoked absence seizures in paediatric patients, relative to brief complex partial seizures (BCPS). Methods. All children diagnosed with seizures using real‐time transcranial doppler ultrasonography (TCD) and sleep‐deprived video‐EEG (vEEG) from 2015 to 2017 in our hospital were included. The seizures were diagnosed based on the video and EEG findings. Mean cerebral blood flow velocity (CBFV_m) of the unilateral middle cerebral artery was measured using TCD. TCD and vEEG data were integrated for a synchronous assessment of CBFV_m changes and epileptic status. Baseline and peak CBFV_m for TAS and BCPS were compared by T‐test. Results. Six children (two boys and four girls) with TAS and two girls with BCPS were enrolled. A total of 15 spontaneous TAS, 14 hyperventilation‐evoked absence seizures, and six BCPS were recorded using real‐time TCD‐vEEG monitoring. During spontaneous TAS, whether awake or asleep, the CBFV_m decreased by 20–40% compared to baseline. During hyperventilation‐evoked absence seizures and BCPS, the CBFV_m increased by 50–150% and 20–30% over baseline levels, respectively. Conclusions. The haemodynamic characteristics during TAS and BCPS are distinct, and thus our results may provide a new method to diagnose typical absence seizures using dynamic CBFV_m curves. Ictal cerebral haemodynamic characteristics during spontaneous typical absence seizures and hyperventilation‐evoked absence seizures may reflect different pathophysiological mechanisms and networks compared with BCPS.     

Increasing pressure of external counterpulsation augments blood pressure but not cerebral blood flow velocity in ischemic stroke

External counterpulsation (ECP) is a noninvasive method used to augment cerebral perfusion but the optimal use of ECP in ischemic stroke has not been well documented. We aimed to investigate the effects of ECP treatment pressure on cerebral blood flow and blood pressure (BP). We recruited 38 ischemic stroke patients with large artery occlusive disease and 20 elderly controls. We commenced ECP treatment pressure at 150 mmHg and gradually increased to 187.5, 225 and 262.5 mmHg. Mean cerebral blood flow velocities (CBFV) of bilateral middle cerebral arteries and continuous beat-to-beat BP were recorded before ECP and during each pressure increment for 3 minutes. Patient CBFV data was analyzed based on whether it was ipsilateral or contralateral to the infarct. Mean BP significantly increased from baseline in both stroke and control groups after ECP commenced. BP increased in both groups following raised ECP pressure and reached maximum at 262.5 mmHg (patients 16.9% increase versus controls 16.52%). The ipsilateral CBFV of patients increased 5.15%, 4.35%, 4.55% and 3.52% from baseline under the four pressures, respectively. All were significantly higher than baseline but did not differ among different ECP pressures; contralateral CBFV changed likewise. Control CBFV did not increase under variable pressures of ECP. ECP did increase CBFV of our patients to a roughly equal degree regardless of ECP pressure. Among the four ECP pressures tested, we recommend 150 mmHg as the optimal treatment pressure for ischemic stroke due to higher risks of hypertension-related complications with higher pressures.     

Cerebral syncope: insights from Valsalva maneuver

BACKGROUND AND PURPOSE: Cerebral syncope refers to a loss of consciousness associated with cerebral vasoconstriction in the absence of systemic hypotension. The diagnosis of cerebral syncope could be established by the head-up tilt test (HUT) and transcranial Doppler ultrasonography. Valsalva maneuver (VM) permitted assessment of cerebral autoregulatory function by provoking blood pressure (BP) changes. To develop a path-physiological approach for vasomotor reactivity of cerebral syncope, the authors combined these maneuvers (HUT/transcranial Doppler/VM). METHODS: Using transcranial Doppler ultrasonography, we simultaneously recorded systemic arterial BP in the radial artery and flow velocities in both middle cerebral arteries (MCAFV) in 10 cerebral syncope patients (4 males and 6 females, 35.24 +/- 4.5 years old) during the Valsalva maneuver. RESULTS: The characteristic changes in BP (phases I-IV) were seen in all subjects, accompanying distinct changes in cerebral blood flow velocity. The BP/heart rate responding to VM was within normal limit in all subjects. There was no orthostatic hypotension. Instead, BP increased during the tilting test in 2 subjects (20.00%). The MCAFV dropped 25.4 +/- 2.3% from baseline. Abnormal flattening of MCAFV during late phase II (IIb), the paradoxical drop of flow velocity despite restoration of BP, was noted in 9 subjects (90.00%). CONCLUSION: During VM there are complex changes in relevant cardiovascular and cerebrovascular variables within a short time span. The paradoxical drop of MCAFV during phase IIb was the result of complex parameters. Among them, a failure in cerebrovascular resistance reduction and even paradoxical vasoconstriction might further compromise cerebral perfusion pressure and lead to syncope.     

Cardiovascular and respiratory consequences of bilateral involvement of the medullary intermediate reticular formation in syringobulbia

We studied five patients with clinical and radiological evidence of syringobulbia (SB) to determine whether the distribution of lesions in relationship to the cardiorespiratory control networks in the medullary intermediate reticular zone (IRt) correlates with the presence of abnormalities in autonomic cardiovascular and respiratory control in these patients. All patients underwent high resolution MRI to characterize the size, volume and distribution of the SB lesions, cardiovascular autonomic function testing and polysomnography. One patient with bilateral IRt involvement at both the rostral and caudal medulla had orthostatic hypotension (OH), absent HR_DB, abnormal Valsalva ratio, exaggerated fall of BP during phase II and absent phase IV during VM, and a dramatic fall of BP during head up tilt; this patient also had severe obstructive sleep apnea (OSA) and exhibited BP drops during each respiratory effort. A second patient, with bilateral IRt involvement restricted to the caudal medulla, had less severe cardiovascular autonomic dysfunction but also exhibited severe OSA. The other three patients had small SB cavities sparing the IRt and had sleep apnea but no autonomic dysfunction. Autonomic dysfunction could not be related to the size of the syrinx or the degree of atrophy in the cervical spinal cord in any of the five patients. Bilateral involvement of the IRt by SB produces cardiovascular autonomic failure and sleep apnea. In patients with more restricted lesions, autonomic and respiratory dysfunction may be dissociated. Clinico-radiological correlations using high resolution MRI assessment of medullary lesions can provide insight into the central organization of cardiovascular and respiratory control in humans. Received: 6 August 2002, Accepted: 26 September 2002 Correspondence to Dr. Martín Nogués     

Stimulation of sympathetic activity by carbon dioxide in patients with autonomic failure compared to normal subjects

In vivo studies selectively assessing preganglionic and central autonomic nervous system activity in patients with autonomic failure have so far been limited to testing pituitary function. In animal experiments carbon dioxide (CO₂) selectively stimulates central sympathetic nuclei in the ventrolateral medulla and preganglionic sympathetic neurons in the cervical trunk. This central stimulation seems to overrule less pronounced peripheral vasodilatatory effects. This study addressed the question of whether hypercapnea is a suitable challenge procedure to test preganglionic and central autonomic activity in healthy subjects and in patients with autonomic failure of preganglionic and central origin. Seven patients with multiple system atrophy (MSA) and 30 age-matched healthy volunteers underwent a protocol including a Valsalva manoeuvre (VM) under normo- and hypercapnic conditions and exposure to hypercapnea under supine resting conditions. Blood pressure (BP), heart rate (HR) and end-tidal CO₂ partial pressure were measured continuously and non-invasively. In normal controls hypercapnea induced significantly higher BP values in phases II, IIe, III and IV of the VM compared to the normocapnic VM and a significant increase in BP during steady-state supine exposure compared to normocapnic baseline. HR increased significantly only after 40 s of steady-state hypercapnea during the latter challenge. In patients with MSA and autonomic failure, in whom a predominantly preganglionic lesion of the autonomic nervous system is established, no significant effects of hypercapnea on the cardiovascular parameters were found. Although this non-invasive challenge procedure cannot differentiate between pre- and postganglionic autonomic failure, exposure to hypercapnea enables the investigation of efferent autonomic activity to vasoconstrictors generated from autonomic centres in the brainstem and cervical trunk.     

Dynamic cerebral autoregulation is compromised in ischaemic stroke of undetermined aetiology only in the non-affected hemisphere

Background and purposeTo assess dynamic cerebral autoregulation (CA) in patients with acute ischaemic stroke of undetermined aetiology, within 72 h of stroke onset.Materials and methodsIn 6 patients with ischaemic stroke of undetermined aetiology (aged 66 ± 9 years, National Institutes of Health Stroke Scale [NIHSS] score on admission: 4.0, range: 4–11), selected based on screening of 118 consecutive ischaemic stroke patients and in 14 volunteers (aged 62 ± 10 years), we continuously monitored RR intervals (RRI), mean arterial pressure (MAP) by means of photoplethysmography, mean cerebral blood flow velocity (CBFV) using transcranial Doppler ultrasonography, end-tidal CO₂ (ETCO₂) and respiration during 2-min deep breathing paced at 6 min⁻¹ (0.1 Hz). To assess CA, we evaluated the impact of breathing-induced MAP oscillations on fluctuations of CBFV in the hemispheres with stroke, the non-involved hemispheres and randomly selected hemispheres of controls by applying cross-spectral analysis and calculating coherence, transfer function gain (CBFV–MAP gain) and phase shift angle between the two oscillating signals.ResultsPhase shift angle between MAP and CBFV oscillations showed values >0 and was significantly reduced in the hemispheres without stroke as compared to controls (0.39 ± 0.95 vs. −1.59 ± 0.33 rad, p = 0.015), whereas in the hemispheres with stroke, phase shift angle did not differ significantly from that observed in the control hemispheres. Clinical status of stroke patients significantly improved at discharge from the hospital (NIHSS: 2.0, range: 1–8, p = 0.028).ConclusionsDuring the first days of ischaemic stroke of undetermined aetiology, dynamic cerebral autoregulation is compromised in the non-affected hemisphere, but not in the hemisphere with ischaemic lesion.     

Ganglioside–basic protein interaction: Protection of gangliosides against neuraminidase action

The ability of acidic phospho- and sphingolipids to interact with basic proteins was studied by double diffusion analysis. The phospholipids, tri- and diphosphoinositide, and the sphingolipid, sulfatide, interacted with myelin basic protein as evidenced by precipitin line formation. Of the sialoglycosphingolipids (gangliosides) tested, only the myelin-specific monosialoganglioside, G_M4

1 The ganglioside nomenclature used here is according to the system of Svennerholm [1963]. The gangliosides are designated as follows: G_M4 = I³NeuAc? GalCer; G_M3 = II³NeuAc? LacCer; G_M1 = II³NeuAc? GgOse₄Cer; G_D1a = IV³ NeuAc, II³NeuAc? GgOse₄Cer; G_D1b = II³(NeuAc)₂? GgOse₄Cer; and G_T1b = IV³NeuAc, II³(NeuAc)₂? GgOse₄Cer.

, formed a precipitin line with myelin basic protein. In addition, myelin basic protein retarded the activity of Clostridium perfringens neuraminidase against G_M4 and the disialoganglioside, G_D1b. Examination of purified rat brain myelin suggested the presence of a neuraminidase activity intrinsic to myelin. This finding, in concert with ganglioside-myelin basic protein complexes which selectively protect against neuraminidase, may provide a physiological explanation for the simplified ganglioside pattern found in myelin.     

Dynamic cerebral autoregulation in stroke patients with a central sympathetic deficit

Gierthmühlen J, Allardt A, Sawade M, Baron R, Wasner G. Dynamic cerebral autoregulation in stroke patients with a central sympathetic deficit.
Acta Neurol Scand: 2011: 123: 332–338.
© 2010 John Wiley & Sons A/S. Objective – To investigate the functional role of the sympathetic innervation on cerebral autoregulation. Materials and methods – Seventeen patients with infarction of the dorsolateral medulla oblongata affecting central sympathetic pathways (Wallenberg′s syndrome) and 21 healthy controls were included in the study. Cerebral blood flow velocity (CBFV) in the medial cerebral artery was investigated using transcranial Doppler ultrasound during decrease in cerebral perfusion pressure induced by leg‐cuff test and tilt table. Results – Upon leg‐cuff test, changes of cerebral blood flow and mean arterial blood pressure as well as autoregulatory index did not differ between patients or controls. No differences were found in changes of CBFV, mean arterial blood pressure and heart rate between patients or controls during the tilt table test. Conclusions – We suggest that the sympathetic nervous system does not have an influence on cerebral autoregulation after decrease in perfusion pressure under normotonous conditions.     

Hemispheric asymmetry and temporal profiles of cerebral pressure autoregulation in head injury

A moving correlation index (Mx-ABP) between arterial blood pressure (ABP) and mean middle cerebral artery blood flow velocity (CBFV) can be used to monitor dynamic cerebrovascular autoregulation (CA) after traumatic brain injury (TBI). In this study we examined hemispheric CA asymmetry and temporal CA profiles, their relationship with ABP and CBFV, and their prognostic relevance. Mx-ABP was calculated for each hemisphere in 25 TBI patients second-daily for as long as they were receiving sedation and analgesia. Forty-nine recordings were obtained, between one and six per patient. Four time periods were defined: immediate - postinjury days (PID) 0 and 1; early - PID 2 and 3; intermediate - PID 4 and 5, and late - PID 6 and later. GOS was estimated at discharge, GOS 4 and 5 were considered favorable (15 patients) and GOS 1-3 unfavorable outcome (10 patients). A Mx difference >0.2 was classified as hemispheric asymmetry (HA). HA was observed at least once in 12 of the 25 patients (48%) and in 18 of 49 recordings (37%). It was observed during all time periods: 35%, 43%, 25%, 43%, respectively, and was not related to outcome. There was no difference in mean CBFV or ABP between patients with and without HA. HA was not related to interhemispheric CBFV differences. A significant improvement in Mx was seen over time. Hemispheric CA asymmetry is common after traumatic brain injury. It does not bear significant clinical or predictive relevance, and it is unrelated to CBFV or ABP. CA is most profoundly disturbed during the immediate postinjury phase and improves gradually during the ICU course. Further studies are needed to investigate CA during post ICU recovery and rehabilitation.     

Reduced cerebral blood flow velocity and impaired cerebral autoregulation in patients with Fabry disease

Abstract. In Fabry disease, there is glycosphingolipid storage in vascular endothelial and smooth muscle cells and neurons of the autonomic nervous system. Vascular or autonomic dysfunction is likely to compromise cerebral blood flow velocities and cerebral autoregulation. This study was performed to evaluate cerebral blood flow velocities and cerebral autoregulation in Fabry patients. In 22 Fabry patients and 24 controls, we monitored resting respiratory frequency, electrocardiographic RR-intervals, blood pressure, and cerebral blood flow velocities (CBFV) in the middle cerebral artery using transcranial Doppler sonography. We assessed the Resistance Index, Pulsatility Index, Cerebrovascular Resistance, and spectral powers of oscillations in RR-intervals, mean blood pressure and mean CBFV in the high (0.15–0.5 Hz) and sympathetically mediated low frequency (0.04–0.15 Hz) ranges using autoregressive analysis. Cerebral autoregulation was determined from the transfer function gain between the low frequency oscillations in mean blood pressure and mean CBFV. Mean CBFV (P < 0.05) and the powers of mean blood pressure (P < 0.01) and mean CBFV oscillations (P < 0.05) in the low frequency range were lower,while RR-intervals, Resistance Index (P < 0.01), Pulsatility Index, Cerebrovascular Resistance (P < 0.05), and the transfer function gain between low frequency oscillations in mean blood pressure and mean CBFV (P < 0.01) were higher in patients than in controls. Mean blood pressure, respiratory frequency and spectral powers of RR-intervals did not differ between the two groups (P > 0.05). The decrease of CBFV might result from downstream stenoses of resistance vessels and dilatation of the insonated segment of the middle cerebral artery due to reduced sympathetic tone and vessel wall pathology with decreased elasticity. The augmented gain between blood pressure and CBFV oscillations indicates inability to dampen blood pressure fluctuations by cerebral autoregulation. Both, reduced CBFV and impaired cerebral autoregulation, are likely to be involved in the increased risk of stroke in patients with Fabry disease.     

Compromised cerebrovascular modulation in chronic anxiety: evidence from cerebral blood flow velocity measured by transcranial Doppler sonography

Objective Cerebral autoregulation(CA) is the mechanism by which constant cerebral blood flow is maintained despite changes in cerebral perfusion pressure.CA can be evaluated by dynamic monitoring of cerebral blood flow velocity(CBFV) with transcranial Doppler sonography(TCD).The present study aimed to explore CA in chronic anxiety.Methods Subjects with Hamilton anxiety scale scores≥14 were enrolled and the dynamic changes of CBFV in response to an orthostatic challenge were investigated using TCD.Results In both the anxious and the healthy subjects,the mean CBFV was significantly lower in the upright position than when supine.However,the CBFV changes from supine to upright differed between the anxious and the healthy groups.Anxious subjects showed more pronounced decreases in CBFV with abrupt standing.Conclusion Our results indicate that cerebrovascular modulation is compromised in chronic anxiety;anxious subjects have some insufficiency in maintaining cerebral perfusion after postural change.Given the fact that anxiety and impaired CA are associated with cardiovascular disease,early ascertainment of compromised cerebrovascular modulation using TCD might suggest interventional therapies in the anxious population, and improve the primary prevention of cardiovascular disease.     

EEG,evoked potentials and pulsed Doppler in asphyxiated term infants

ObjectiveTo evaluate electroencephalograms (EEG), evoked potentials (EPs) and Doppler findings in the cerebral arteries as predictors of a 1-year outcome in asphyxiated newborn infants.MethodsEEG and EPs (brain stem auditory (BAEP), somatosensory (SEP), visual (VEP) evoked potentials) were assessed in 30 asphyxiated and 30 healthy term infants during the first days (range 1–8). Cerebral blood flow velocities (CBFV) were measured from the cerebral arteries using pulsed Doppler at ∼24 h of age. EEG, EPs, Doppler findings, symptoms of hypoxic ischemic encephalopathy (HIE) and their combination were evaluated in predicting a 1-year outcome.ResultsAn abnormal EEG background predicted poor outcome in the asphyxia group with a sensitivity of 67% and 81% specificity, and an abnormal SEP with 75% and 79%, respectively. Combining increased systolic CBFV (mean + 3SD) with abnormal EEG or SEP improved the specificity, but not the sensitivity. The predictive values of abnormal BAEP and VEP were poor. Normal EEG and SEP predicted good outcome in the asphyxia group with sensitivities from 79% to 81%. The combination of normal EEG, normal SEP and systolic CBFV < 3SD predicted good outcome with a sensitivity of 74% and 100% specificity.ConclusionsCombining abnormal EEG or EPs findings with increased systolic CBFV did not improve prediction of a poor 1-year outcome of asphyxiated infants. Normal EEG and normal SEP combined with systolic CBFV < 3SD at about 24 h can be valuable in the prediction of normal 1-year outcome.SignificanceCombining systolic CBFV at 24 h with EEG and SEP examinations can be of use in the prediction of normal 1-year outcome among asphyxiated infants.