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Query: UMLS:C0022116 (ischemia)
 91,303 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We measured cerebral oxygen extraction, cerebral blood flow(CBF), and cerebral metabolic rate (CMRO2) in comatose patients during the first 60 hours after resuscitation from cardiac arrest. Each patient was studied 2 or 3 times. CBF was determined by a modification of the Kety-Schmidt method using inhaled Xenon133. Over the study period jugular venous oxygen tension and saturation rose, while the oxygen content difference between arterial and jugular venous blood fell, indicating a progressive increase in the ratio of CBF to metabolism CBF and CMRO2 measurements confirmed this. Between 2 and 6 hours after resuscitation both measurements were severely but proportionately depressed to less than 50% of normal. After 6 hours CBF was increased disproportionately to CMRO2 so that a relative hyperemia developed and persisted for the duration of the study. Although regional inhomogeneity of flow and regional ischemia cannot be ruled out, we have found no evidence for global cerebral ischemia between 2 and 60 hours post-resuscitation as an explanation for failure of recovery. In man following cardiac arrest restoration of levels of global cerebral blood flow, which can be considered adequate relative to the depressed metabolic state of the tissue, is achieved within 2 hours of resuscitation.
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PMID:Cerebral blood flow and metabolism in man following cardiac arrest. 74 88

The introduction of positron emission tomography (PET) to study the cerebral circulation and metabolism is for the present the last step in the evolution of a technology which started 40 years ago with the gas clearance method developed by Kety and Schmidt. To study cerebral blood flow and metabolism in humans the steady state 15O method (Frackowiak et al., 1980) is widely used in different PET centers. We have used this method in experimental animals. The principles of the method and the mathematical models which are at the basis of the calculation of cerebral blood flow (CBF) and oxygen metabolism (cerebral metabolic rate for oxygen, CMRO2 and oxygen extraction ratio, OER) are relatively simple but during its application in vivo several problems arise as described. The steady state method of Frackowiak et al. allowed in our experiments the accurate measurement of cerebral blood flow and oxygen metabolism in anesthetized dogs. We have investigated the effect of experimental cerebral embolism in different series of experiments. Two different models of cerebral ischemia were assessed. In the first model focal ischemia was produced by infusing Sephadex particles (mean diameter 40 microns) into the left common carotid artery; in the second model an autologous blood clot (100 microliters) was injected into the left internal carotid artery. With both procedures the ischemia was practically limited to the ipsilateral hemisphere. Moreover in the two models the effects of ischemia were very reproducible. This is probably due to the good standardization of the embolization procedures. The results clearly indicate a differential effect of microembolization with particles and blood clot embolization, illustrating the importance of the technique used to produce cerebral embolization in experimental animals. PET offers possibilities for diagnosis of cerebral ischemia. At variance with the classical techniques for studying cerebral blood flow PET also allows simultaneous assessment of cerebral metabolism and to differentiate between brain tissue which is irreversible damaged and tissue which can be potentially salvaged. Therefore PET also offers new possibilities in clinical and experimental research. The reproducible effects obtained with the blood clot model, the metabolic cerebral effects of which are similar to those of clinical stroke, will allow to study the effect of different therapeutic approaches for stroke such as thrombolysis and calcium entry blockade.
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PMID:[The use of radionuclides, specifically positron-emission tomography, in the determination of the blood circulation and metabolism of the brain. Application in experimental cerebral embolism]. 269 May 40

Measurement of regional CBF in transverse section using inert, diffusible tracers can be carried out using a double-integral form of the Kety-Schmidt equation. An implementation of this form proposed by Kanno and Lassen (the K-L estimator) is utilized by the Tomomatic 64, a dynamic single-photon computed tomography system that records washin-washout data during and following inhalation of 133Xe gas. Advantages of the algorithm include noninvasive calibration of the input function and excellent depiction of ischemia: disadvantages are sensitivity to errors in input function delay (delta), the inability to estimate the partition coefficient (lambda) (hence, only the clearance index, k, is estimated), and a noise sensitivity proportional to k. A modification of the method is proposed that not only accounts for delta variations, but also provides an estimate of relative lambda (hence, the perfusion, f, is estimated). The proposed estimator is shown to be robust in the presence of noise with error variances equal to or better than those with the K-L estimator, yet estimates of both relative f and lambda are provided by the modification. New simulation results implicate the Compton scatter fraction as a major contributor in the overestimation of white matter perfusion values using both the K-L and proposed estimators, and illustrate the need for hardware and software scatter fraction reduction and control.
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PMID:Regional multiparameter estimation from tomographic diffusible tracer clearance curves: modification of the double-integral method. 387 81

Cerebral vascular and metabolic effects of lorazepam were evaluated in ten awake monkeys by use of a modification of the Kety-Schmidt technique. Five received ketamine, 10 mg/kg, im, five to eight hours prior to the study, but all animals were otherwise treated identically. Monkeys receiving ketamine had significantly greater (P < 0.05) cerebral blood flow (CBF) values before lorazepam was given (46 +/- 1 ml/100 g/min) than did monkeys not receiving ketamine (41 +/- 1 ml/100 g/min), but in all other respects, premedicated and unpremedicated animals did not differ. Lorazepam administration did not significantly alter systemic arterial blood pressure or blood-gas values. However, it did decrease CBF by 26 per cent and increase cerebral vascular resistance (CVR) by approximately 25 per cent (P < 0.01). The cerebral metabolic rate for glucose (CMRg) decreased 42 per cent (P < 0.05). Following lorazepam administration, the cerebral metabolic rate for oxygen (CMRO2) decreased by 21-30 per cent. When combined CMRO2 data for the two anesthetic groups are pooled, this decrease is significant (P < 0.05). This study indicates that sedative doses of lorazepam decrease cerebral blood flow and metabolism with minimal effects on blood pressure and blood-gas values. Lorazepam administration did not produce any change in cerebral metabolism indicative of brain hypoxia or ischemia.
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PMID:Cerebral circulatory and metabolic responses to intravenously administered lorazepam. 610 64

Multiple approaches are available to measure global and regional cerebral blood flow. The inert gas method of Kety-Schmidt provides the mathematical basis for essentially all of these methods with the exception of microspheres. The preferred method depends largely upon the type of information to be obtained. The preferred method depends largely upon the type of information to be obtained. The three essential problems in cerebral blood flow measurement are establishing reliable cerebral blood flow measurements in pathological processes, the relation of this flow to metabolism, and the clinical application of cerebral blood flow measurements in man for the investigation of a wide variety of significant disease processes including ischemia and intracranial hypertension.
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PMID:Cerebral blood flow determinations by positron emission tomography. 698 50

The immature brain is considered relatively resistant to anoxia and ischemia. Although hypoxia without ischemia has not been considered to produce brain damage in immature rats as well as in adult rats (S. Levine, Anoxic-ischemic encephalopathy in rats, Am. J. Pathol., 36 (1960) 1-17 [8]; D.E. Levy, J.B. Brieley, D.G. Silverman, F. Plum, Brief hypoxia-ischemia initially damages cerebral neurons, Arch. Neurol., 32 (1975) 450-456 [9]; J.E. Rice, R.C. Vannucci, J.B., Brieriey, The influence of immaturity on hypoxic-ischemic brain damage in rat, Ann. Neurol., 9 (1981) 131-141 [14]), hypoxia in postnatal period is possible to cause a functional brain damage (T. Hender, P. Lundborg, Regional changes in monoamine synthesis in the developing rat brain during hypoxia, Acta. Physiol. Scand., 106 (1979) 139-143 [3]; W. Ihle, J. Gross, R. Moller, Effect on chronic postnatal hypoxia on dopamine uptake by synaptosomes from striatum of adult rats, Biomed. Biochem. Acta., 44 (1985) 433-437 [7]; A. Lun, J. Gross, M. Beyer, H.D. Fischer, C. Wustmann, J. Schmidt, K. Hecht, The vulnerable period of perinatal hypoxia with regard to dopamine release and behavior in adult rats, Biomed. Biochem. Acta., 45 (1986) 619-627 [10]). Using microdialysis, we studied the anoxic or hypoxic effect on catecholamine metabolism in immature rat brain by measuring extracellular concentrations of norepinephrine (NE), dopamine (DA), and its metabolites and also 5-hydroxyindole-3-acetic acid (5-HIAA), the serotonin metabolite. DA is a well established excitatory neurotransmitter (R.C. Vannucci, Experimental biology of cerebral hypoxia-ischemia: relation to perinatal brain damage, Pediatr. Res., 27 (1990) 317-326 [16]), and in the previous report using hypoxic 7-day-old rat pups increase of DA was not detected without additional stimulations (K. Gordon, D. Johnston, M.V. Robinson, T.E. Statman, J.B. Becker, F. Silverstein, Transient hypoxia alters striatal catecholamine metabolism in immature brain: An in vivo microdialysis study, J. Neurochem., 54 (1990) 605-611 [2]). Whereas recently in newborn piglets, hypoxic hypoxia produced increase of extracellular DA (C.-C. Huang, N.S. Lajevardi, O. Tammela, A. Pastuszko, Relationship of extracellular dopamine in striatum of newborn piglets to cortical oxygen pressure, Neurochem. Res., 19 (1994) 649-655 [6]; Olano, M., Song, D., Murphy, S., Wilson, D. F. and Pastuszko, A., Relationships of dopamine, cortical oxygen pressure, and hydroxyl radicals in brain of newborn piglets during hypoxia and posthypoxic recovery, J. Neurochem., 65 (1995) 1205-1212 [13]). We consider that hypoxic ischemic brain damage of human newborns that we can treat is a damage, which does not show overt neuropathological changes. We therefore tried to show that transient anoxia and hypoxia caused biochemical alteration if the exposure did not produce marked morphological changes. This rodent model is adequate to study perinatal asphyxia and alteration of monoamine level could be useful for evaluation of brain damage, even if it is not detected histologically.
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PMID:Anoxic and hypoxic immature rat model for measurement of monoamine using in vivo microdialysis. 997 39

The management of critical limb ischemia due to below-the-knee disease remains challenging due to the frequent patient comorbidities, diffuse vascular involvement, and high rates of restenosis and disease progression. The BASIL study has established the substantial equivalence between bypass surgery and percutaneous transluminal angioplasty in this setting, at least at mid-term follow-up, but percutaneous techniques and devices have seen major developments since the publication of this pivotal trial in 2005. A major breakthrough has indeed been the introduction of drug-eluting balloons, which have several theoretical advantages in comparison to standard balloons and metallic stents for infra-popliteal lesions. Two clinical trials have already been reported with favorable results for the In.Pact Amphirion paclitaxel-eluting balloon, when employed for below-the-knee lesions. We hereby discuss the rationale for the use of drug-eluting balloons in this complex setting and the main findings of the study by Schmidt et al. and the DEBATE-BTK trial.
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PMID:Advances in below-the-knee drug-eluting balloons. 2245 43