Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0917798 (cerebral ischemia)
 17,036 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.
 ...
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.
 ...
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

Cerebral blood flow and metabolism were measured repeatedly during surgery for cerebral tumours by a modification of the classical Kety & Schmidt method using 133Xe infusion intravenously. Our standard procedure for neuroanaesthesia (pentobarbitone-fentanyl induction, halothane-nitrous oxide maintenance) reduced blood flow from 47.1 to 24.2 ml X 100 g X ml-1 and metabolism from 3.30 to 1.83 ml O2 X 100 g-1 X ml-1. PaCO2 was reduced by hyperventilation from 5.3 to 3.6 kPa. Additional thiopental loading and maintenance using 4 + 4 mg X kg-1 (n = 5) or 8 + 8 mg X kg-1 (n = 5) reduced cerebral metabolism by an additional 15% (P less than 0.01) and blood flow by 16.5% (P less than 0.01), while mean arterial blood pressure fell from 11.0 to 9.9 kPa (P less than 0.05). PaCO2 remained unchanged. This additional reduction in cerebral metabolism and blood flow is small, but we nevertheless conclude that it may well be of clinical interest to the problem of protecting the brain in case of episodes of focal cerebral ischaemia which may arise peroperatively during intracranial surgery.
 ...
PMID:Minimum cerebral blood flow and metabolism during craniotomy. Effect of thiopental loading. 649 4

A noninvasive, simple, and continuous method to assess cerebral perfusion during cardiopulmonary bypass (CPB) could help prevent cerebral ischemia. Transcranial Doppler sonography (TCD) allows a noninvasive, on-line measurement of blood flow velocity in cerebral arteries. The correlation of TCD-estimated and actual cerebral blood flow (CBF) has not been well studied during CPB. We determined the correlation of middle cerebral artery (MCA) mean velocity and CBF determined by the Kety-Schmidt method during nonbypass and two hypothermic bypass flow conditions. Sixteen patients undergoing hypothermic (27 degrees C) CPB for coronary artery bypass grafting and/or valve replacement surgery were enrolled in the study. We were able to determine MCA velocity in only 12 patients. We determined CBF and MCA velocity in each patient during four 15-min study periods: 1) prebypass after sternotomy before aortic cannulation; 2) hypothermic (27 degrees C) CPB with 1.2 L.min-1.m-2 pump flow; 3) hypothermic CPB with 2.4 L.min-1.m-2 pump flow, and 4) 30 min after weaning from CPB. There was no difference in the mean arterial pressure between the two CPB pump blood flows. The pooled change in MCA velocity and CBF as percentage of baseline (prebypass) for all patients and at all time points had a correlation of 0.33 (r). A decrease or increase in MCA velocity did not necessarily indicate a corresponding decrease or increase in CBF. This technology may be of limited usefulness during the circulatory condition of hypothermic, nonpulsatile CPB.
 ...
PMID:The relationship between cerebral blood flow and transcranial Doppler blood flow velocity during hypothermic cardiopulmonary bypass in adults. 894 25

Gaining insights into brain oxygen metabolism has been one of the key areas of research in neurosciences. Extensive efforts have been devoted to developing approaches capable of providing measures of brain oxygen metabolism not only under normal physiological conditions but, more importantly, in various pathophysiological conditions such as cerebral ischemia. In particular, quantitative measures of cerebral metabolic rate of oxygen using positron emission tomography (PET) have been shown to be capable of discerning brain tissue viability during ischemic insults. However, the complex logistics associated with oxygen-15 PET have substantially hampered its wide clinical applicability. In contrast, magnetic resonance imaging (MRI)-based approaches have provided quantitative measures of cerebral oxygen metabolism similar to that obtained using PET. Given the wide availability, MRI-based approaches may have broader clinical impacts, particularly in cerebral ischemia, when time is a critical factor in deciding treatment selection. In this article, we review the pathophysiological basis of altered cerebral hemodynamics and oxygen metabolism in cerebral ischemia, how quantitative measures of cerebral metabolism were obtained using the Kety-Schmidt approach, the physical concepts of non-invasive oxygen metabolism imaging approaches, and, finally, clinical applications of the discussed imaging approaches.
 ...
PMID:Oxygen metabolism in acute ischemic stroke. 2879 76