Assessment of Dynamic Cerebral Autoregulation During Long-Term Exposure to High Altitude in Normal Subjects by Ultrasonography.

PURPOSE: To evaluate changes in dynamic cerebral autoregulation (CA) during short-term and long-term exposure to high altitude with ultrasonography, and also study the sex differences in the response of CA to altitude. METHODS: We assessed the differences in dynamic CA and measured with Doppler ultrasound of the bilateral internal carotid artery (ICA), vertebral artery (VA), and middle cerebral artery (MCA) and the values of basic information within 48 hours and at 2 years after arrival at Tibet in 65 healthy Han young Chinese volunteers, meanwhile, we compared the resistance index (RI) and pulsatility index (PI) of the right MCA at inhale oxygen 8 minutes when a newcomer with 2 years after arrival at Tibet. RESULTS: With 2 years of altitude exposure, the SaO2 of all subjects was above 90%, the mean PEF, DAP, and HR values decreased, HGB increased compared within 48 hours in same-gender groups. Comparisons of cerebral hemodynamics between before 2 years and after 2 years within male and female groups, the mean RI and PI values of bilateral MCA after 2 years were significantly higher than before 2 years, at the same time, the mean RI and PI values of bilateral ICA were significant differences (P < .05) between male groups, with regard to female groups, showed that the mean RI and PI values of bilateral VA were significant differences (P < .05). Comparisons of Right MCA hemodynamics between after oxygen uptake 8 minutes and 2 years, the mean RI and PI values were no significant difference within male and female groups (P > .05). CONCLUSIONS: Acute mountain sickness could result from an alteration of dynamic autoregulation of cerebral blood flow, but the impaired autoregulation may be corrected with the extension of time, furthermore, the response of CA to altitude in males and females are different.

Assessment of Cerebral Arterial Flow Volume Changes with Carotid Vertebral Artery Duplex Doppler Ultrasound in Young-Middle-aged Subclinical Hashimoto Thyroiditis Patients.

OBJECTIVES: To demonstrate cerebral arterial flow volume changes during the hypothyroid, euthyroid, and hyperthyroid phases and comparing between laboratory findings and cerebral arterial flow changes with carotid-vertebral duplex Doppler ultrasound (CVA-DUSG) in subclinical Hashimoto thyroiditis (HT) patients. METHODS: According to the TSH level, 3 groups were constructed between patient cases. Group 1 (n=29) was the subclinical hyperthyroid group. In this group, the TSH level was between 0.0005 and 0.3 IU/ml. Group 2 (n=175) was the euthyroid group. TSH level in this group was between 0.3 and 4.2 IU/ml. Group 3 (n=76) was the subclinical hypothyroid group. In this group, the TSH level was above 4.2 IU/ml. The control-group (group 4) (n=71) included healthy people. In this group, the TSH level was between 0.3 and 4.2 IU/ml. After obtaining at least three consecutive waves from the bilateral internal cerebral artery and bilateral vertebral artery, volume flows were calculated using CVA-DUSG. Volume flows were calculated as peak systolic velocity + end diastolic velocity/2 × mean arterial diameter. The mean ICA(Internal Carotid Artery) and VA(Vertebral Artery) diameter was measured per ICA and VA. Total cerebral artery flow volume was defined as right ICA + right VA flow volume and left ICA + left VA flow volume. We also demonstrated topographic cerebral artery blood flow changes. Total ICA flow volume was used to assess the anterior part of the brain, total VA flow volume was used to evaluate the posterior part of the brain, right ICA + right VA flow volume was used to assess the right part of the brain, and left ICA + left VA flow volume was used to verify the left part of the brain. RESULTS: There were significant differences between RVA(Right Vertebral Artery) flow volume, LICA (Left Internal Carotid Artery) flow volume, total flow volume, TSH, and T3 and T4 levels in all groups according to the Dunn's multiple comparison test.(p<0.001) Mean TSH level was 0.03 (0.005-0.06) IU/ml in group 1, 2.8 (1.8-3.97) IU/ml in group 2, 7.32 (6.14-9.93) IU/ml in group 3, and 1.76 (1.17-2.49) IU/ml in the control group. The mean T3 level was 4.18 (3.55-5.38) in group 1, 2.88 (2.63-3.16) in group 2, 2.82 (2.49-3.15) in group 3, 3.14 (2.92-3.15) in the control group. The mean T4 level was 1.92 (1.29-2.5) in group 1, 1.16(1.03-1.31) in group 2, 1.01 (0.91-1.16) in group 3, 1.12 (0.97-1.30) in the control group (group 4). Mean total flow volume was 793 (745-898) ml/min in group 1, 742 (684.25-822.5) ml/min in group 2, 747 (692-824) ml/min in group 3, and 700 (673-675) ml/min in the control group. We also demonstrated topographic cerebral arterial volume flow changes with CVA-DUSG. There was a significant difference among all groups in the right and anterior parts of the brain (p < 0.001), and there was a significant difference between groups 1 and 4 in the left part of the brain (p = 0.009). CONCLUSION: This study demonstrated that total cerebral arterial volume flow increased in the hyperthyroid phase of subclinical HT cases without any internal carotid and vertebral artery diameter changes compared with the euthyroid and hypothyroid phases of subclinical HT and healthy cases. We also verified topographic cerebral arterial blood flow changes in subclinical HT cases with a real-time, easily applicable modality (CVA-DUSG) that does not include X-ray or contrast agents. There was a significant difference between all groups in the right and anterior parts of the brain and there was a significant difference between groups 1 and 4 in the left part of the brain.

Technical recommendations for the use of carotid duplex ultrasound for the assessment of extracranial blood flow.

Duplex ultrasound is an evolving technology that allows the assessment of volumetric blood flow in the carotid and vertebral arteries during a range of interventions along the spectrum of health and chronic disease. Duplex ultrasound can provide high-resolution diameter and velocity information in real-time and is noninvasive with minimal risks or contraindications. However, this ultrasound approach is a specialized technique requiring intensive training and stringent control of multiple complex settings; results are highly operator-dependent, and analysis approaches are inconsistent. Importantly, therefore, methodological differences can invalidate comparisons between different imaging modalities and studies; such methodological errors have potential to discredit study findings completely. The task of this review is to provide the first comprehensive, user-friendly technical guideline for the application of duplex ultrasound in measuring extracranial blood flow in human research. An update on recent developments in the use of edge-detection software for offline analysis is highlighted, and suggestions for future directions in this field are provided. These recommendations are presented in an attempt to standardize measurements across research groups and, hence, ultimately to improve the accuracy and reproducibility of measuring extracranial blood flow both within subjects and between groups.

Simulation of cerebral hemodynamics for preoperative risk assessment.

BACKGROUND: An important part of the medical treatment of many cerebrovascular diseases is the occlusion of brain supplying arteries. Until now, the risk of this intervention can only be estimated by invasive diagnostics including the risk of cerebrovascular accidents. METHODS AND RESULTS: As a supporting tool, a computer model of the circle of Willis was designed. The model is based upon linear differential equations describing electrotechnical circuits extended non-linearly. By these means, time continuous simulations of different states and the online observation of all calculated state variables such as blood pressure and blood flow in every modeled vessel became feasible. For individual simulations, model parameters were determined by MR-angiography and boundary values by simultaneous Duplex-measurements in both carotid and vertebral arteries. State variables generated by the model behaved physiologically and the reaction of individual cerebrovascular systems in critical situations could be investigated by special scenarios. Inaccuracies concerning the determination of model parameters and boundary values of the used differential equations are likely to be resolved in the near future through a more careful and technically improved determination of these values. CONCLUSIONS: Computer models of subjects were created taking in account the individual anatomical and non-linear physical properties of real vascular systems supplying the brain. Thereby information could be obtained concerning the hemodynamic effects of an iatrogenic vascular occlusion.

[Assessment of patients with sudden hearing loss by transcranial Doppler ultrasonography]. / Ani isitme kayipli hastalarin transkraniyal Doppler ultrasonografi ile degerlendirilmesi.

OBJECTIVES: We evaluated the utility of transcranial Doppler ultrasonography in determining the vascular pathology in patients with sudden hearing loss. PATIENTS AND METHODS: The study included 13 patients (11 males, 2 females; mean age 46.6+/-17.7 years; range 18 to 66 years) with a diagnosis of sudden hearing loss. Patients having chronic otitis media or other middle ear diseases or a history of surgery in the affected ear were excluded. All the patients were evaluated by pure-tone audiometry, impedance audiometry, transient evoked otoacoustic emissions, auditory brainstem responses, and transcranial Doppler ultrasonography. The results were compared with those of a control group of 19 age- and sex-matched healthy subjects (12 males, 7 females; mean age 46.8+/-6.9 years; range 33 to 58 years) who did not have any ear disease or a history of ototoxic drug intake or working in a noisy environment, and no pathology on otoscopic and audiometric examinations. RESULTS: Compared to the normal ear, the mean blood flow and systolic flow velocities of the vertebral artery were significantly decreased, and the mean pulsatile index was significantly increased on the affected side. The mean flow velocity of the basilar artery in the patient group was lower than that found in the control group. CONCLUSION: Transcranial Doppler ultrasonography can be used for the evaluation of vascular involvement of the vertebral and basilar arteries in patients with sudden sensorineural hearing loss.

Global cerebral blood flow during infusion of adenosine in humans: assessment by magnetic resonance imaging and positron emission tomography.

Adenosine, an endogenous vasodilator, induces a cerebral vasodilation at hypotensive infusion rates in anaesthetized humans. At lower doses (< 100 micrograms kg-1 min-1), adenosine has shown to have an analgesic effect. This study was undertaken to investigate whether a low dose, causing tolerable symptoms of peripheral vasodilation affects the global cerebral blood flow (CBF). In nine healthy volunteers CBF measurements were made using axial magnetic resonance (MR) phase images of the internal carotid and vertebral arteries at the level of C2-3. Quantitative assessment of CBF was also obtained with positron emission tomography (PET) technique, using intravenous bolus [15O]butanol as tracer in four of the subject at another occasion. During normoventilation (5.4 +/- 0.2 kPa, mean +/- s.e.m.), the cerebral blood flow measured by magnetic resonance imaging technique, as the sum of the flows in both carotid and vertebral arteries, was 863 +/- 66 mL min-1, equivalent to about 64 +/- 5 mL 100 g-1 min-1. The cerebral blood flow measured by positron emission tomography technique, was 59 +/- 4 mL 100 g-1 min-1. All subjects had a normal CO2 reactivity. When adenosine was infused (84 +/- 7 micrograms kg-1 min-1.) the cerebral blood flow, measured by magnetic resonance imaging was 60 +/- 5 mL 100 g-1 min-1. The end tidal CO2 level was slightly lower (0.2 +/- 0.1 kPa) during adenosine infusion than during normoventilation. In the subgroup there was no difference in cerebral blood flow as measured by magnetic resonance imaging or positron emission tomography. In conclusion, adenosine infusion at tolerable doses in healthy volunteers does not affect global cerebral blood flow in unanaesthetized humans.

[Control and regulation of the blood circulation in the vertebro-basilar system. Review of the literature]. / Contrôle e regulação da circulação sanguínea no sistema vértebro-basilar. Revisão de literatura.

The author establishes an analogy between the control mechanism and regulation of the cerebral blood flow and of protection of the vascular wall of the internal carotid constituted by the conjunction "internal carotid-cavernous sinus" with the group represented by the system "vertebro basilar-transverse occipital sinus or basilar" (an extension of the cavernous sinus) in the regulation and control of the encephalic circulation carried out through this latter vessels, together with the protection of its vascular walls. The author believes to be very difficult to demonstrate in practice the functioning of these mechanisms, but it is very logical and easy to reason about them, to value them and to give the importance and meaning or motive which forcibly they should have and not simply consider them as freaks of nature and bizarre anatomical features.

[Transoral Doppler ultrasound echography under local anaesthesia for the assessment of vertebral artery blood flow (author's transl)]. / Transorale Doppler-Sonographie unter Schleimhautanästhesie zur Beurteilung der Strömungsverhältnisse in den Aa. vertebrales (Vertebralis-Doppler)

Uncalibrated flow in the vertebral arteries was registered with a bidirectional CW Doppler ultrsound apparatus. It was applied to 20 patients, results being compared with aortic arch angiograms in which the extracranial part of all four cerebral vessels was seen. In 14 the vertebral arteries had a symmetrical flow and lumen, a similar symmetrical result being obtained with the Doppler. Hypoplasia of one vertebral artery was present in two patients the distinct asymmetry being recorded by the ultrasound. Three patients with central stenosis in one subclavian artery and subclavian "steal" were found to have reverse flow by the Doppler method in the vertebral artery on the side of the stenosis. Endarterectomy was performed on the affected subclavian artery in two of these patients: post-operative vertebral ultrasound recordings demonstrated a return to physiological flow direction in both vertebral arteries.