S. Szabó

Cerebrovascular Reserve Capacity Many Years After Vasospasm Due to Aneurysmal Subarachnoid Hemorrhage: A Transcranial Doppler Study With Acetazolamide Test

BACKGROUND AND PURPOSE Vasospasm in aneurysmal subarachnoid hemorrhage results in proliferative vasculopathy. Systemic hypertension also causes vascular hypertrophy. Both of these histological changes can lead to rigidity of the cerebrovascular system, reducing its autoregulatory capacity. METHODS Blood flow velocity (BFV) in the middle cerebral artery at rest and cerebrovascular reserve capacity (CVRC) (percent rise in BFV after acetazolamide stimulation) measured by means of transcranial Doppler sonography were studied many years after aneurysmal subarachnoid hemorrhage in patients with proven cerebral vasospasm (mean BFV > 160 cm/s). The BFV under resting conditions and the CVRC values of the ipsilateral and the contralateral hemispheres were measured in 29 patients (mean age, 43 years; mean follow-up, 4.6 years) and compared with those of control subjects. RESULTS Persistent high BFV (> 120 cm/s) was found in three patients in the peripheral branch of the ipsilateral middle cerebral artery. In the main trunks of the arteries of the anterior circle of Willis, BFV was normal in all cases. CVRC was normal in all patients (ipsilateral, 52 +/- 21%; contralateral, 56 +/- 17%); values did not differ significantly from each other or from the control value (45 +/- 18%). The higher value of CVRC on the contralateral side was found to be statistically significant in selected groups (hypertensive patients and patients with residual infarct on late CT). CONCLUSIONS Proliferative vasculopathy developed at the time of vasospasm must have resolved and did not reduce late vasoreactivity. Comorbidity with hypertension also did not seem to influence the late vasoreactivity toward normalization.

Harvey Cushing, a pioneer of neuroanesthesia

Harvey Cushing’s name is most frequently mentioned in conjunction with Cushing’s syndrome, and Cushing’s reflex following raised intracranial pressure. The aim of this review is to pay tribute to Cushing’s contribution to anesthesia. Besides his own specialty, he used an anesthesia chart for the first time, he introduced blood pressure measurement and precordial auscultation to anesthesiological practice, he employed the first independent neurosurgical anesthetist, and he described the terminology of regional anesthesia.

Structure and magnetic properties of nanocrystalline soft ferromagnets

The structure and magnetic properties of soft magnetic nanocrystalline composites crystallised from amorphous ribbons are reviewed. The Fe-Early Transition Metal-Boron (Nanoperm-type) nanostructures are discussed in details and compared to the Si containing (Finemet) alloys. The nanocrystallization process was studied by calorimetry; the spatial dimension, the composition and the relative fraction of the bcc and the residual amorphous phases were investigated by X-ray diffraction and Mössbauer spectroscopy. A small fraction of Fe atoms (about 4%) was found which cannot be assigned either to the residual amorphous or to the bcc phase. It is suggested that the magnetic anisotropy of the bcc phase is decreased due to the dissolved Zr and B impurities. The Curie point and Fe atomic moments in the residual amorphous tissue are determined and compared to that of a macrosized amorphous phase of similar composition. The observed deviations do not scale with the average characteristic size of the amorphous phase and thus cannot be explained in the framework of the existing models. Magnetic dipolar coupling and tensile stresses between the grains of the different phases are suggested for explaining the soft magnetic behaviour of the nanostructures.

Effect of sevoflurane on cerebral blood flow and cerebrovascular resistance at surgical level of anaesthesia: a transcranial Doppler study

Background and objective: It is widely accepted that sevoflurane affects cerebral circulation, but there are uncertainities regarding the magnitude of its effect. The aim of the present work was to assess the effect of sevoflurane on the cerebral circulation at surgical levels of anaesthesia. Methods: Twenty patients undergoing elective lumbar discectomies were investigated. Anaesthesia was induced with propofol and maintained with sevoflurane. The level of surgical anaesthesia was determined by bispectral index, the target level was 45–55. Transcranial Doppler (TCD) measurement was performed before induction and after reaching the surgical level of anaesthesia. Besides routine parameters (middle cerebral artery mean blood flow velocity (MCAV) and pulsatility index (PI)) derived parameters (estimated cerebral perfusion pressure (eCPP), cerebral blood flow index (CBFI) and resistance area product (RAP)) were calculated by taking changes of mean arterial pressure also into account. Results: MCAV decreased from 54.1 ± 13.3 to 43.7 ± 18.5 cm s−1, P < 0.01 and PI increased from 0.79 ± 0.2 to 0.92 ± 0.2, P < 0.01 after reaching the surgical level of anaesthesia. As a result eCPP decreased by 18.2%, CBFI by 25.5% and RAP increased by 15% respectively. Conclusions: Our data indicate a vasodilatory effect of sevoflurane at surgical level of anaesthesia on large cerebral vessels or a vasoconstriction of the resistance arterioles likely caused by decreased brain metabolism.

Regional cerebral 18FDG uptake during subarachnoid hemorrhage induced vasospasm

Abstract Objectives: The aim was to elucidate whether aneurysmal subarachnoid hemorrhage (SAH)-induced vasospasm induces changes of regional glucose uptake in surgically treated, asymptomatic cases. Methods: 18FDG uptake (standardized uptake value, SUV) was analysed with PET in eight surgically treated aneurismal patients with a mean middle cerebral artery flow velocity >120 cm/seconds measured with transcranial Doppler ultrasound. Data were compared with a healthy control group using Statistical Parametric Mapping (SPM99b). Results: Six of the eight patients had no focal neurological signs. The inhomogeneous bilateral increase in SUV (p<0.0001) was asymmetrical, with an almost 70% larger volume on the operated side. Reduced glucose uptake was found in the frontal and temporobasal regions of the two patients with neurological deficits (p<0.0001); the affected volume was 40% larger on the operated side. Discussion: SAH-induced vasospasm results in widespread increase of glucose uptake—probably reflecting increased glycolysis. This was earlier than neurological focal signs appear. Decreased glucose uptake can be detected in severe cases of vasospasm reflected by neurological deficit. Although the changes are more prominent where surgery had taken place our results suggest that not only the surgery, but also subarachnoid blood might have resulted in our findings.

Correlation between central somatosensory conduction time, blood flow velocity, and delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage.

In this retrospective study of 67 aneurysmal patients, the predictive role of central conduction time (CCT) on vasospasm occurrence evaluated by means of transcranial Doppler sonography (TCD) and the correlation of CCT to blood flow velocity measured simultaneously in postoperative course were studied.Data about the clinical state of patients at the time of admission (Hunt Hess scale), severity of subarachnoidal hemorrhage on initial CT scan (Fisher grade), timing of surgery (acute or delayed), outcome (Glasgow Outcome Scale), severity of vasospasm graded by highest mean blood flow velocity (BFV) during the entire clinical course, and CCT values measured at admission (preoperatively), then post-operatively (one day after surgery) and simultaneously with later TCD investigations were collected from the files. Interhemispheric difference of CCT was also calculated.The results showed that CCT at admission was not predictive for vasospasm. CCT measured either at admission or on the first postoperative day did not differ significantly in the different grades of vasospasm. Similar results were obtained in the acute and in the late operated group of patients. The results also suggest that increased CCT and interhemispheric difference at the time of admission indicate a worse prognosis, but this can be related to higher surgical risk rather than to a higher incidence of late ischemic deterioration. Simultaneous CCT and TCD examinations demonstrated that coincident and statistically significant (p < 0.01) increase of actual CCT (6.7 msec) was found only in the severe grade of vasospasm (BFV < 200 cm/s). The authors discuss the role of CCT and TCD monitoring in the management of aneurysmal subarachnoid hemorrhage.

Correlation between the grain-shape and magnetic properties in nanocrystalline iron

Abstract Correlation between magnetic properties and time evolution of size (d) and shape of grains of pure nanocrystalline iron produced by ball-milling were investigated by Barkhausen-noise and lowfield magnetization measurements. Strong texture and elongated grain structure were developed after some hours milling time, and the thickness of elongated grains was in accordance with the grain size obtained from X-ray line broadening. After prolonged milling, disruption of the elongated grains and development of equiaxed grain structure was observed. There was a maximum in the Barkhausen-noise when the above lamellar structure was the most typical. It is shown that the coercive force (Hc) is not sensitive to the formation of the grain structure, but the course of the Hc(d) curve strongly depends on the initial and preparation conditions. In accordance with our previous results, the saturation magnetization was independent of the grain size.

Jerky magnetic noises generated by cyclic deformation of martensite in Ni2MnGa single crystalline shape memory alloys

It is shown that during periodic deformation of martensitic Ni2MnGa single crystalline alloy jerky magnetic noises are emitted. Above a threshold limit in the deformation amplitude, the noise energy per deformation cycle showed increasing tendency with increasing deformation. Energy and amplitude probability distributions of the noise were characterized by power law functions. The energy exponents were independent of the deformation amplitude in the investigated range. The decrease of the noise energy as well as power exponents with increasing magnetic field was interpreted by the decrease of the multiplicity of the martensite variants.

Mössbauer effect and magnetic properties of nanocrystalline Fe and Fe(Si) alloys

Abstract Nanocrystalline Fe and Fe-9at%Si alloys were produced by ball milling. The average grain size, determined from X-ray line broadening, decreased to about 6 nm as the milling time increased from 0 to 380 hours in the case of Fe and from 0 to ISO bours in the case of the Fe-9at%Si alloy. The coercitive force (Hc) and the magnetic Barkhausen noise (MBN) were measured by Barkhausen noise technique as a function of the grain size for Fe-9at%Si alloy. The results are in accordance with the random anisotropy model. The Mossbauer spectra as a function of the milling time were also measured at room temperature, and well detectable changes were observed at smaller grain sizes (

Correlation between Barkhausen noise and mechanical sensitivity in FINEMET-type materials

Measuring technique, developed at our Laboratory for the investigation of ferromagnetic industrial materials, experimental results obtained and their analysis are reviewed. The magnetic properties (permeability, mechanical sensitivity) of as received and heat treated Finemet type ribbons (Fe75Si15NbBCu) were measured with common industrial equipments. The above properties were correlated with magnetic Barkhausen noise parameters. The distributions of peak area A and peak noise energy E were analyzed and it was found that distribution of the noise parameters P(x) (where x = A or E), were in good agreement with the theory of self organized criticality (SOC), satisfying power laws in the form P(x) ~x. Useful correlation between the noise parameters and the mechanical sensitivity has been established. The noise did not considerably depend on the other parameters of ribbons.