Regional Oxygen Utilization Research Articles

Regional Metabolic Supply Dependency in Chronic Congestive Heart Failure

We present a 64-year-old man with New York Heart Association (NYHA) Class III chronic congestive heart failure (CHF) who was examined for an alteration in cerebral cortex regional oxygen utilization as reflected by changes in local cerebral metabolic rates for glucose (LCMRglu). LCMRglu was determined by positron emission tomography at baseline and while oxygen delivery (DO2) was optimized during dobutamine infusion. Baseline DO2 was 8.31 mL/min/kg and cardiac output (CO) was 3.4 L/min, whereas oxygen consumption (VO2) measured by respired gas analysis was 3.64 mL/min/kg. At optimal dobutamine effect (7.5 μg/kg/min), DO2 increased to 16.8 mL/min/kg, CO to 7.2 L/min, and VO2MEAS was 3.67 mL/min/kg. Mean percentage Increase in cortical gray matter LCMRglu was 99.4 ± 11.7% (mean ± SD) and was statistically significant ( p < 0.001; Student's paired t-test). Our results demonstrate that the cerebral glucose utilization and therefore oxygen consumption increased parallel with Increases in DO2. This phenomenon is contrary to the conventional concept that cerebral perfusion is strictly autoregulated and that substrate utilization is independent of oxygen delivery.

Generalized decrease in brain glucose metabolism during fasting in humans studied by PET.

In prolonged fasting, the brain derives a large portion of its oxidative energy from the ketone bodies, beta-hydroxybutyrate and acetoacetate, thereby reducing whole body glucose consumption. Energy substrate utilization differs regionally in the brain of fasting rat, but comparable information has hitherto been unavailable in humans. We used positron emission tomography (PET) to study regional brain glucose and oxygen metabolism, blood flow, and blood volume in four obese subjects before and after a 3-wk total fast. Whole brain glucose utilization fell to 54% of control (postabsorptive) values (P less than 0.002). The whole brain rate constant for glucose tracer phosphorylation fell to 51% of control values (P less than 0.002). Both parameters decreased uniformly throughout the brain. The 2-fluoro-2-deoxy-D-glucose lumped constant decreased from a control value of 0.57 to 0.43 (P less than 0.01). Regional blood-brain barrier transfer coefficients for glucose tracer, regional oxygen utilization, blood flow, and blood volume were unchanged.

Comparative measurement of regional blood flow, oxygen and glucose utilisation in soft tissue tumour of rabbit with positron imaging.

The C15O2 and 15O2 steady state techniques have been used to quantitatively measure regional blood flow (RBF) and regional oxygen utilisation (ROU) in a rabbit tumour model. RBF values of 4.6 +/- 0.6 ml min/100 cc were measured for normal muscle tissue and 11.0 +/- 3.0 ml/min/100 cc for tumour surface. Corresponding values for ROU were 18.3 +/- 3.5 mumol/min/100 cc for normal tissue and 39.7 +/- 20.1 mumol/min/100 cc for tumour surface. 18F-2-fluoro-2-deoxy-D-glucose (2FDG) was used in the same tumour model to measure glucose metabolic rate. The values obtained were 4.3 +/- 2.1 mumol/min/100 cc for normal muscle tissue and 53.8 +/- 18.3 mumol/min/100 cc for tumour tissue. Tumour growth was followed with a series of measurements of blood flow, oxygen, and glucose metabolism at intervals of 1 week. Tumour-to-muscle ratios increased more rapidly with time for 2FDG than for oxygen utilisation and blood flow. The effect of radiation on tumour and normal tissue was followed by measurements of RBF and ROU. RBF values increased both in tumour and normal muscle tissue during radiation and decreased during one week after radiation. ROU-values decreased (30%) in tumour and increased (45%) in normal muscle tissue during radiation. Even at one week after radiation, ROU-values were 30% lower in tumour and 45% higher in normal muscle tissue than before radiation.

The effects of L-DOPA on regional cerebral blood flow and oxygen metabolism in patients with Parkinson's disease.

Studies performed on 18 patients with Parkinson's disease and 6 control subjects have shown that acute administration of L-DOPA in clinically effective doses gives rise to a diffuse increase in regional cerebral blood flow without accompanying stimulation of regional oxygen utilization. The data suggest that this rise in rCBF is caused by vasodilatation due to a direct action of the drug on the cerebral blood vessels. The effect of L-DOPA on rCBF did not correlate with the degree of clinical improvement seen in each patient after treatment. The therapeutic effect of L-DOPA in the brain was not reflected in any change of regional cerebral oxygen utilization as measured by our technique. We suggest that the pharmacological actions of L-DOPA in the brain take place on at least two different levels.

EVALUATION OF CEREBRAL PERFUSION RESERVE IN PATIENTS WITH CAROTID-ARTERY OCCLUSION

Regional cerebral blood flow, oxygen utilisation, fractional oxygen extraction, and cerebral blood volume were measured by positron emission tomography in thirty-two patients with internal-carotidartery occlusion. In most cases, any reduction in cerebral blood flow in the territory distal to an occluded carotid artery was matched to diminished cerebral metabolic demands. Cerebral blood flow was inappropriately low in only six patients, in whom regional oxygen utilisation was maintained by a compensatory rise in oxygen extraction ratio. The frequent finding of high cerebral blood volume distal to occluded vessels was consistent with a state of focal vasodilatation in response to diminished cerebral perfusion pressure. Analysis of the relation between cerebral blood flow, blood volume, and oxygen extraction ratio suggested that the reduction in cerebral perfusion pressure, and hence circulatory reserve; could be most reliably predicted by the ratio of cerebral blood flow to blood volume. By identifying those patients with carotid occlusion who are most compromised on haemodynamic grounds, combined measurement of cerebral blood flow and blood volume should be valuable in selection of candidates for extracranial-intracranial bypass surgery.

EVALUATION OF CEREBRAL PERFUSION RESERVE IN PATIENTS WITH CAROTID-ARTERY OCCLUSION

Regional cerebral blood flow, oxygen utilisation, fractional oxygen extraction, and cerebral blood volume were measured by positron emission tomography in thirty-two patients with internal-carotidartery occlusion. In most cases, any reduction in cerebral blood flow in the territory distal to an occluded carotid artery was matched to diminished cerebral metabolic demands. Cerebral blood flow was inappropriately low in only six patients, in whom regional oxygen utilisation was maintained by a compensatory rise in oxygen extraction ratio. The frequent finding of high cerebral blood volume distal to occluded vessels was consistent with a state of focal vasodilatation in response to diminished cerebral perfusion pressure. Analysis of the relation between cerebral blood flow, blood volume, and oxygen extraction ratio suggested that the reduction in cerebral perfusion pressure, and hence circulatory reserve, could be most reliably predicted by the ratio of cerebral blood flow to blood volume. By identifying those patients with carotid occlusion who are most compromised on haemodynamic grounds, combined measurement of cerebral blood flow and blood volume should be valuable in selection of candidates for extracranial-intracranial bypass surgery.

Circulatory and metabolic aspects of cerebral ischemia in experimental animals and in men.

In normal conditions, there is a precise link between regional metabolism and blood flow in the brain. In pathological states there may be an uncoupling between CBF and metabolism, due to many mechanisms. In particular, anaerobic glycolisis, membrane depolarization, and altered neurotransmitter release are relevant for the final damage of the tissue. Postischemic recovery was analyzed in experiments with 14C-deoxyglucose. In men, the noninvasive approach with 15O by inhalation allowed the determination of regional oxygen utilization. In TIAs, there is a chronic ischemic condition, while in strokes there is often a relative luxury perfusion.

A Study of the Regional Oxygen Utilization: Blood Flow Relationships within the Brain of Controls and Neurological Patients by Non-Invasive Monitoring with Oxygen-15

A Study of the Regional Oxygen Utilization: Blood Flow Relationships within the Brain of Controls and Neurological Patients by Non-Invasive Monitoring with Oxygen-15