THE EFFECTS OF ALTERED ARTERIAL TENSIONS OF CARBON DIOXIDE AND OXYGEN ON CEREBRAL BLOOD FLOW AND CEREBRAL OXYGEN CONSUMPTION OF NORMAL YOUNG MEN

The treatment of cerebral ischemia with hyperbaric oxygen (OHP)

The treatment of a patient for three and one-half months, following occlusion of the right middle cerebral artery with the associated neurological sequelae, with hyperbaric oxygen combined with methyldopa and hydrochlorthazide is presented. Treatment scheduled was two and one-half atmospheres absolute. The treatment was interrupted after 15 treatments to rule out spontaneous remission for a period of 30 days, and no further improvement occurred until treatments were reinstituted. The dramatic return to a near normal state during treatment appears to indicate that he did benefit from therapy.

The effect of passive hyperventilation on intraventricular pressure in the dog

✓ The effectiveness of passive hyperventilation in reducing intracranial pressure was studied in mongrel dogs by varying the levels of end-tidal pCO2 and airway pressure, and comparing the positive-negative and positive-atmospheric pressure. It has been shown that there is a point beyond which reduction of pCO2 does not affect cerebral blood flow. The present study demonstrates that another limiting factor is the degree of positive or negative airway pressure. Positive airway pressure impedes venous drainage, thereby increasing intracranial pressure. This increase could only partly be offset by applying negative expiratory airway pressure, since it was found that excessive negative airway pressure (greater than static recoil pressure of the lung) may trap air in alveoli. An optimal range of positive and negative airway pressures is defined.

Cerebrovascular response to acute hypocapnic and eucapnic hypoxia in normal man

Alterations in human cerebral blood flow and related blood constituents were studied during exposure to acute hypoxia. Observations were made during serial inhalation of decreasing O(2) concentrations with and without maintenance of normocarbia, during 8 min inhalation of 10% O(2), and after hyperventilation at an arterial P(O2) of about 40 mm Hg. In the range of hypoxemia studied, from normal down to arterial P(O2) of about 40 mm Hg, the magnitude of the cerebral vasodilator response to hypoxia appeared to be largely dependent upon the coexisting arterial CO(2) tension. The mean slope of the increase in cerebral blood flow with decreasing arterial O(2) tension rose more quickly (P < 0.05) when eucapnia was maintained when compared with the slope derived under similar hypoxic conditions without maintenance of eucapnia. When 12 subjects inhaled 10% oxygen, cerebral blood flow rose to more than 135% of control in four whose mean decrease in arterial CO(2) tension was - 2.0 mm Hg. The remaining eight had flows ranging from 97 to 120% of control, and their mean decrease in CO(2) tension was - 5.1 mm Hg. When mean arterial P(O2) was 37 mm Hg, hyperventilation was carried out in 10 subjects. Arterial P(O2) increased insignificantly, arterial P(CO2) declined from 34 to 27 mm Hg (P < 0.05), and cerebral blood flow which had been 143% of control decreased to 109%, a figure not significantly different from control.These data demonstrate the powerful counterbalancing constrictor effects of modest reductions in CO(2) tension on the vasodilator influence of hypoxia represented by arterial P(O2) reductions to about 40 mm Hg. Indeed, mild hyperventilation completely overcame the vasodilator effect provided by an arterial O(2) tension as low as 40 mm Hg. The effects of hypoxia on the control of the cerebral circulation must be analyzed in terms of the effects of any associated changes in CO(2) tension.

Effects of hyperbaric oxygen on intracranial pressure and cerebral blood flow in experimental cerebral oedema

Increased intracranial pressure was induced in anaesthetized dogs by application of liquid nitrogen to the dura mater. Intracranial pressure and cerebral blood flow were measured, together with arterial blood pressure and arterial and cerebral venous blood gases.Carbon dioxide was administered intermittently to test the responsiveness of the cerebral circulation, and hyperbaric oxygen was delivered at intervals in a walk-in hyperbaric chamber, pressurized to two atmospheres absolute.Hyperbaric oxygen caused a 30% reduction of intracranial pressure and a 19% reduction of cerebral blood flow in the absence of changes in arterial PCO(2) or blood pressure, but only as long as administration of carbon dioxide caused an increase in both intracranial pressure and cerebral blood flow. When carbon dioxide failed to influence intracranial pressure or cerebral blood flow then hyperbaric oxygen had no effect. This unresponsive state was reached at high levels of intracranial pressure.

Effects of inhalation of oxygen on blood flow and microvasculature of ischemic and nonischemic cerebral cortex

The right middle cerebral artery was occluded in cats, and Pa o o2 was increased by increasing the amount of oxygen inhaled by the animals at atmospheric pressure. Cortical blood flow (CBF) was measured with Krypton-85, and observations and photographs of the superficial cortical microvasculature were made bilaterally. In two of five animals, increasing the Pa o o2 caused constriction of surface arterioles of the nonischemic hemispheres, with an associated decrease of CBF; in the three other animals, there were no circulatory responses to the increased Pa o o2 . In seven animals, increasing the Pa o o2 had no apparent effect on CBF or arteriolar caliber of the ischemic cerebral hemispheres. In four animals, at Pa o o2 greater than 400 torr, reactivity to increases of Pa CO CO2 was preserved in nonischemic cortex but impaired in ischemic cortex. Reddening of venous blood of the microvasculature of ischemic cerebral cortex occurred when Pa o o2 was increased, indicating that more oxygen was made available to the ischemic cerebral tissue. However, no beneficial effects could be demonstrated on the changes in the microvasculature produced by ischemia.

Protective effects of acetazolamide and hyperbaric oxygenation on experimentally induced syncope

The protective effects of acetazolamide and hyperbaric oxygenation on experimentally induced syncope were evaluated in seven healthy male subjects. Syncope was induced by vigorous hyperventilation and Valsalva maneuver. Each subject performed these procedures three times in each of the following conditions: (1) breathing room air at normal atmospheric pressure, (2) breathing 100% oxygen at 2.36 atmospheric pressure, (3) breathing 9% oxygen at 2.36 atmospheres and (4) after intravenous injection of 500 mg of acetazolamide while breathing 100% oxygen at 2.36 atmospheres. With comparable changes of arterial pCO 2 and blood pressure during the hyperventilation-Valsalva maneuver, syncope occurred in 19 of 21 (91%) hyperventilation-Valsalva maneuvers performed at ambient environment, in 18 of 21 (86%) when subject was breathing 9% oxygen at 2.36 atmospheres, in 14 of 21 (67%) when 2.36 atmospheres of 100% oxygen was used, and in only 7 of 21 (33%) when acetazolamide was used in conjunction with hyperbaric oxygen. Syncope was completely prevented by hyperbaric oxygenation in one subject and by the combination of acetazolamide and hyperbaric oxygen in four subjects. These studies demonstrate that cerebral vasodilation induced by acetazolamide combined with increased oxygen delivery to the brain resulting from hyperbaric oxygenation may preserve cerebral function during the period of hypotension and hypocapnia produced by hyperventilation and Valsalva maneuver.

The measure in vivo of regional cerebral oxygen utilization by means of oxyhemoglobin labeled with radioactive oxygen-15

Regional cerebral oxygen utilization rate is measured in vivo by the following method:A small volume of blood with radioactive oxygen-15-tagged hemoglobin is rapidly injected into the internal carotid artery of the patient under study. The first injection is followed by the injection carried out under identical circumstances but with blood labeled with water-(15)O. After each injection, the distribution of the radioactive label in the brain is measured and recorded, as a function of time, by six collimated scintillation probes placed over the subject's head. The recording, subsequent to the first injection, reflects (a) the arrival of the labeled oxygen into the tissues, (b) its partial conversion into water of metabolism, and (c) the washout of labeled water from the brain. The ratio of the amount of labeled water formed to the amount of oxygen perfusing the tissues, which can be derived from the recording, is a measure of fractional oxygen utilization. The second injection provides a measure of blood flow by the interpretation of the washout of labeled water from brain tissues. The product, fractional oxygen utilization x blood flow x arterial oxygen content, gives a measure of oxygen utilization rate. Some aspects of the validity of this method are tested by the injection of a nondiffusible indicator, carboxyhemoglobin-(15)O. Regional cerebral oxygen utilization rates for a series of patients with cerebral pathology are reported.

Resection of an internal carotid artery aneurysm under regional anesthesia: posterior cervical block

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Cerebral oxygen, glucose, lactate, and pyruvate metabolism in stroke. Therapeutic considerations

Cerebral blood flow, oxygen, glucose, lactate, and pyruvate metabolism were measured in 13 subjects with completed stroke. Cerebral blood flow and oxygen consumption were reduced, glucose consumption and pyruvate production were normal, and lactate production was increased, suggesting a shift from aerobic to anaerobic cerebral glycolysis.

To test this hypothesis, cerebral blood flow and oxygen delivery were decreased by hyperventilation and increased by inhalation of 5% CO 2 in air. Hyperventilation decreased cerebral oxygen consumption (CMRO 2 ) and increased cerebral lactate production. Inhalation of 5% CO 2 in air increased cerebral blood flow and oxygen delivery and increased both glucose and oxygen consumption. Relationships between reduction in PaCO 2 and cerebral venous PO 2 and increased cerebral lactate production were found.

Increasing cerebral blood flow by 5% CO 2 inhalation improved circulation and oxygen delivery to ischemic cerebral areas and improved oxygen and glucose metabolism in the majority of cases since these procedures do not alter CMRO 2 in normal persons. Intravenous injection of glucose increased cerebral glucose uptake but insulin did not.

Intracellular PO2 and its regulation in resting skeletal muscle of the guinea pig

Intracellular Po 2 in the gracilis muscle of lightly anesthetized guinea pigs was measured by means of an O 2 microelectrode to see (a) whether the Po 2 was low enough that it might limit O 2 consumption, and (b) whether it would increase with high O 2 breathing. The resting cell membrane potential was used to localize the electrode tip. Of 184 cells tested in 26 animals, 70 cells had a Po 2 of less than 1 mm Hg. Mean intracellular Po 2 was about 4 mm Hg. When 100% O 2 or 98% O 2 -2% CO 2 was administered while the electrode was in a cell, 60 of 89 cells tested (20 animals) showed no change in Po 2 . In the other 29 cells, the Po 2 increased by 5% or more. We have concluded that blood flow in resting skeletal muscle in the anesthetized guinea pig is regulated so as to maintain a low Po 2 -low enough that it could limit O 2 consumption.

Monitoring cerebral blood flow, oxygen, and glucose metabolism. Analysis of cerebral metabolic disorder in stroke and some therapeutic trials in human volunteers

More accurate methods for monitoring cerebral blood flow, oxygen, and glucose metabolism with results of their application in human volunteers are described.

Subjects with various types of cerebral vascular disease showed decreased cerebral blood flow and oxygen and glucose metabolism but anaerobic glycolysis appeared to be increased. Inhalation of 100% oxygen decreased anaerobic glycolysis, and mixtures of oxygen, 5% CO 2 plus oxygen, 5% CO 2 plus air, and hyperventilation all showed that cerebral vascular reactivity is reduced in cerebrovascular disease. Nevertheless, inhalation of 5% mixtures of CO 2 in air or oxygen significantly increased cerebral blood flow. Inhalation of 5% CO 2 plus oxygen significantly increased cerebral oxygen consumption in cerebrovascular disease within 10 minutes of its institution. The depression of cerebral glucose metabolism and oxygen consumption appears to be amenable to rapid improvement in some subjects with stroke. Intravenous administration of nylidrin hydrochloride decreased cerebral vascular resistance but did not increase cerebral blood flow or metabolism, presumably by autoregulation. Intravenous injection of 100 ml of low molecular-weight dextran increased cerebral blood flow and oxygen consumption but not to the level of statistical significance. A case of brain-stem ischemia showed a large increase of cerebral blood flow, oxygen metabolism, and glucose consumption after surgical reconstruction of the left vertebral artery accompanied by clinical recovery.