放射性微球技术检测激素性骨组织血流量的研究

目的：应用放射性微球技术检测激素性兔骨组织血流量。方法：20只成年兔分为2组，一组为对照组，另一组给予地塞米松注射8周，采用放射性微球技术测量两组兔骨组织血流量。结果：对照组骨组织血流量，在长骨干、皮质骨和骨髓中，以肱骨血流量最高；在不规则骨中，以颈椎血流量最高。激素组骨组织血流量较对照组低，降低幅度最明显的为长骨骨髓、椎骨和股骨颈。结论：长程使用糖皮质激素可降低兔骨组织血流量。     

Radioactive microsphere measurement of cardiac output and regional tissue blood flow in the sheep

Summary Previous reports have shown that radioactive microspheres may be used to obtain quantiative measurements of regional tissue blood flow in a number of species. The present work has shown that this also applies to the conscious sheep, and further, that microspheres provide a simple, accurate and reliable method for the routine measurement of cardiac output. Assessment of blood flow through arteriovenous anastomoses is also described. Duplicate measurements of blood flow to the tissues listed below, had a mean difference of 7.2%. Normal values for blood flow to the following tissues were determined for thirteen adult and three 8-week old Merino sheep under resting conditions in a thermoneutral environment: skin of the body and extremities, panniculus muscle, maxillo turbinals, nasal mucosa, tongue, skeletal muscle, lymph nodes, thyroids, heart, adrenals, kidneys, spleen, rumen, small and large intestine, liver (arterial), pituitary (arterial), brain and spinal cord.     

A model of cerebral blood flow control in hypercapnia

A mathematical model of cerebral blood flow control to increases inP _aCO₂ is developed. The controlled system of the model (the brain) is composed of three well-mixed lumped parameter compartments: blood, cerebral extracellular fluid (ECF), and cerebral intracellular fluid (ICF). The conservation of mass equations are written for three chemical species: molecular carbon dioxide, bicarbonate ion, and hydrogen ion in each compartment, yielding nine first-order nonlinear differential equations. For the controller, cerebral blood flow is assumed a function of the chemical species in the compartments; in particular the hypotheses that blood flow is a function of interstitial fluid pH, or a function of interstitial fluid carbon dioxide tension operating through a proportional controller are investigated in detail. The parameters for these controllers were obtained from data in the physiologic literature as well as experiments performed as part of this study. This model is the first attempt to describe the transient behavior of the cerebral circulatory system to acid base disturbances. When the predictions of the model are compared with experimental data it is found that the model predicts a cerebral blood flow change to hypercapnia consistently slower than that found experimentally. This suggests that the cerebral circulatory response to CO₂ inhalation is not exclusively a function of ECF or CO₂ and that therefore other controls and/or mechanisms play a role as well.     

Effect of anesthesia and cerebral blood flow on neuronal injury in a rat middle cerebral artery occlusion (MCAO) model

Middle cerebral artery occlusion (MCAO) models have become well established as the most suitable way to simulate stroke in experimental studies. The high variability in the size of the resulting infarct due to filament composition, rodent strain and vessel anatomy makes the setup of such models very complex. Beside controllable variables of homeostasis, the choice of anesthetics and the grade of ischemia and reperfusion played a major role for extent of neurological injury. Transient MCAO was induced during either isoflurane or ketamine/xylazine (ket/xyl) anesthesia with simultaneously measurement of cerebral blood flow (CBF) in 60 male Wistar rats (380–420 g). Neurological injury was quantified after 24 h. Isoflurane compared with ket/xyl improved mortality 24 h after MCAO (10 vs. 50 %, p = 0.037) and predominantly led to striatal infarcts (78 vs. 18 %, p = 0.009) without involvement of the neocortex and medial caudoputamen. Independent of anesthesia type, cortical infarcts could be predicted with a sensitivity of 67 % and a specificity of 100 % if CBF did not exceed 35 % of the baseline value during ischemia. In all other cases, cortical infarcts developed if the reperfusion values remained below 50 %. Hyperemia during reperfusion significantly increased infarct and edema volumes. The cause of frequent striatal infarcts after isoflurane anesthesia might be attributed to an improved CBF during ischemia (46 ± 15 % vs. 35 ± 19 %, p = 0.04). S-100β release, edema volume and upregulation of IL-6 and IL-1β expression were impeded by isoflurane. Thus, anesthetic management as well as the grade of ischemia and reperfusion after transient MCAO demonstrated important effects on neurological injury.     

Post traumatic brain perfusion SPECT analysis using reconstructed ROI maps of radioactive microsphere derived cerebral blood flow and statistical parametric mapping

Background  

Assessment of cerebral blood flow (CBF) by SPECT could be important in the management of patients with severe traumatic brain injury (TBI) because changes in regional CBF can affect outcome by promoting edema formation and intracranial pressure elevation (with cerebral hyperemia), or by causing secondary ischemic injury including post-traumatic stroke. The purpose of this study was to establish an improved method for evaluating regional CBF changes after TBI in piglets.     

Fetal lamb cerebral blood flow (CBF) and oxygen tensions during hypoxia: a comparison of laser Doppler and microsphere measurements of CBF

This study was undertaken to compare microsphere and laser Doppler flowmetry techniques for the measurement of cerebral blood flow, to assess the effect of probe implantation at the tip of the sensing probe and to measure brain tissue P _O2 (t P _O2) in response to acute hypoxia. Fetal sheep of ≈131 days gestation (   n = 8  ) were chronically instrumented with bilateral laser Doppler probes in the parietal cortices and catheters for injection of fluorescent microspheres. Five days after surgery fetuses were subjected to 1 h periods of baseline control breathing, hypoxia and recovery. Microspheres were injected 10 min prior to and 10, 30, 50 and 120 min after initiation of hypoxia. Microspheres were counted in four 12 mm³ tissue samples from each hemisphere, the tip of the laser Doppler probe being positioned in the centre of one of the cubes. The cube containing the probe tip was also subdivided into 4 mm³ pieces of tissue. In response to hypoxia, fetal arterial P _O2 declined from 21 ± 2 to 12 ± 1 Torr and brain tissue P _O2 fell from 10 ± 1 to a nadir of 1 ± 1 Torr. Each method detected a significant increase in CBF that reached a maximum after 30-45 min, although the increase of flow measured by laser Doppler flowmetry was less than that measured by spheres after 10 and 30 min (   P < 0.05  ). Microspheres did not detect altered flow at the probe tip or heterogeneity of flow in surrounding volumes of cortical tissue. In summary, laser Doppler flowmetry is a useful measure of continuous relative changes of CBF in the chronically instrumented fetal sheep. Flow compensations in acute hypoxia are not adequate to sustain O₂ delivery, and other compensations, including reduced metabolic rate, are possible.     

The role of noise in the measurement of cerebral blood flow and partition coefficient using xenon-enhanced computed tomography

Monte Carlo simulations have been used to study the accuracy which can be expected in the quantification of blood flow and the partition coefficient using xenon-enhanced computed tomography in the presence of noise. We have demonstrated that the markedly asymmetric frequency distribution of estimates increases in size rapidly with an increase in the standard error of the input CT data. On the basis of our results, we recommend that controllable sources of noise (eg. CT number drift) be corrected and that estimates be obtained by averaging CT data and then fitting, rather than averaging blood flow and partition coefficients derived from individual pixels, as the latter procedure results in the introduction of considerable bias.     

Validation of diffuse correlation spectroscopic measurement of cerebral blood flow using phase-encoded velocity mapping magnetic resonance imaging

Diffuse correlation spectroscopy (DCS) is a novel optical technique that appears to be an excellent tool for assessing cerebral blood flow in a continuous and non-invasive manner at the bedside. We present new clinical validation of the DCS methodology by demonstrating strong agreement between DCS indices of relative cerebral blood flow and indices based on phase-encoded velocity mapping magnetic resonance imaging (VENC MRI) of relative blood flow in the jugular veins and superior vena cava. Data were acquired from 46 children with single ventricle cardiac lesions during a hypercapnia intervention. Significant increases in cerebral blood flow, measured both by DCS and by VENC MRI, as well as significant increases in oxyhemoglobin concentration, and total hemoglobin concentration, were observed during hypercapnia. Comparison of blood flow changes measured by VENC MRI in the jugular veins and by DCS revealed a strong linear relationship, R=0.88, p<0.001, slope=0.91±0.07. Similar correlations were observed between DCS and VENC MRI in the superior vena cava, R=0.77, slope=0.99±0.12, p<0.001. The relationship between VENC MRI in the aorta and DCS, a negative control, was weakly correlated, R=0.46, slope=1.77±0.45, p<0.001.     

Reduced cerebral blood flow and N-acetyl aspartate in a murine model of cerebral malaria

Cerebral malaria is an important cause of morbidity and mortality in many parts of the world. It has been suggested that cerebral malaria is associated with reduced perfusion due to the blockage of blood vessels by parasitized erythrocytes; although, no quantitative validation of this has been done. We infected C57BL/6 mice with the ANKA strain of Plasmodium berghei and on day 6 of infection we investigated alterations in brain function using arterial spin labeling MRI and proton MRS. MR images did not demonstrate signs of damage. However, there was a significant reduction in cerebral blood flow (P<0.012) and the ratio of N-acetyl-aspartate (NAA) to creatine (Cr) (P<0.01) relative to non-infected mice. The NAA/Cr ratios were significantly correlated with cerebral perfusion (r=0.87) suggesting a relationship between impaired oxygen delivery and neuronal dysfunction. Pathological examination revealed accumulations of damaged axons providing a correlate for the decreased NAA/Cr ratio in infected mice. This murine model will permit non-invasive studies of neurologic function during malarial infection.     

Validity and reproducibility of electrical impedance tomography for measurement of calf blood flow in healthy subjects

The Sheffield electrical impedance tomography; (EIT) system produces images of changes in the distribution of resistivity within tissue. The paper reports on the application of electrical impedance tomography in monitoring volume changes in the limb during venous occlusion. The aim of the study is to assess the feasibility, reproducibility and validity of calf blood flow measurements by EIT. In 14 healthy volunteers calf blood flow is compared, as determined in a calf segment by strain-gauge plethysmography (SGP), with the impedence changes measured by EIT during rest and post-ischaemic hyperaemia. The measurements are repeated to assess reproducibility. The reproducibility for the EIT, assessed from the repeated measurements and expressed as a reproducibility coefficient, is 0.88 during rest and 0.89 during hyperaemia. The reproducibility coefficient for SGP data is 0.83 at rest and 0.67 during hyperaemia. Flow measurements, assessed by means of two methods, correlate well at rest (r=0.89), but only moderately during hyperaemia (r=0.51). The correlation coefficient for the pooled flow measurements is 0.98. It is concluded that EIT is a valid and reliable method for assessing blood flow in the limb. Possible applications of EIT in localising fluid changes are discussed.     

脑血流自动调节功能的三单元模型

目的建立一个三单元集中参数模型来模拟脑血流的自动调节功能。方法根据Bloor的实验数据拟合了一条在脑血流自动调节功能中,反映脑血流量和平均动脉压之间关系的三次曲线,然后利用这一拟合曲线来确定模型中的不定常电阻元件。结果利用这一模型,对不同压力变化情况下的脑血流量变化进行了数值模拟。通过与实验数据进行了对比,发现这一不定常三单元模型能够较为简单地模拟脑血流自动调节功能。结论经过改造的这一三单元集中参数模型可以为脑血流自动调节功能及脑血管疾病的研究提供帮助。     

Rapid measurement of regional cerebral blood flow in the baboon using15O-labelled water and dynamic positron emission tomography

The sensitivity and reproducibility of rapid measurements of regional cerebral flow (rCBF) using a bolus injection of H₂ ¹⁵O and dynamic positron emission tomography (PET) were investigated in anaesthetised baboons. The cerebrovascular reactivity to changes in arterial pCO₂ was used as an experimental support. PET data were acquired over 4 min following a single bolus intravenous injection of H₂ ¹⁵O, while arterial blood was withdrawn for continuous activity counting. Images were reconstructed with a dynamic sequence of 45×2s+15×10s, including a correction for decay. Regional values of CBF were derived from non-linear least-squares fits of the time activity curves using a four-parameter two-compartment model. The results obtained with a four-parameter fitting method were compared with those obtained with two other rapid estimation methods, first fitting two parameters only, CBF and partition coefficient (p), and secondly autoradiography (with p fixed at 0·95 ml brain ml blood⁻¹). Twelve regions of interest were analysed. The values for the basal CBF obtained from 13 measurements in two baboons were close to published values obtained with other techniques. Reproducibility checks showed a mean variation of 9·7 per cent. The CBF measurements performed in hypercapnic conditions gave results similar to published data in other animal species, showing a 4·5±0·9 per cent increase in CBF per mm Hg p_aCO₂. The results obtained with the three estimation techniques were closely correlated. The dynamic bolus H₂ ¹⁵O method appeared to be suitable for high blood flow measurements.     

Locally applied 133Xenon for the measurement of regional cerebral blood flow (rCBF): an experimental study in the pig

A method for measuring regional cerebral blood flow has been developed. On pig brain cortex a 1 cm2 size polyester film was placed, under which 0.6-1.3 mCi of 133Xenon in 2-4 microliter of saline was applied atraumatically. The wash-out process was registered with an external detector, and can be described as a sum of monoexponential functions. The first component of the curve, obtained by curve resolution, indicates blood flow in grey matter and the second slow component indicates blood flow in white matter. When total ischaemia was induced, there was no wash-out of the isotope. Freezing the brain after isotope application at different stages during the wash-out showed isotope in both grey and white matter. The isotope did not diffuse into the polyester film. This technique was also used in studies on the spinal medulla where white matter is outermost and grey innermost. The wash-out curve obtained consisted of only one monoexponential function; blood flow from grey matter was not present in the wash-out curve. For calculation of cerebral blood flow a modified two-compartment model was used. It is concluded that this method measures local cerebral blood flow in both grey and white matter. The method can be used clinically to measure the local cerebral blood flow during neurosurgical operations.     

A PC-based neural network for on-line measurement of regional cerebral blood flow.

The measurement of regional cerebral blood flow has been used in diagnoses for many cerebral disorders. However, the complexity of data processing makes the technique only possible for off-line study. This paper explores a PC-based neural net technique for on-line determination of the blood flow rate. Experimental results justify the efficiency of the proposed methodology and raise the possibility of designing a portable system for time-critical applications.