THE BLOOD FLOW AND OXYGEN CONSUMPTION OF THE HUMAN BRAIN IN DIABETIC ACIDOSIS AND COMA

Brain metabolism during fasting

Catheterization of cerebral vessels in three obese patients undergoing 5-6 wk of starvation demonstrated that beta-hydroxybutyrate and acetoacetate replaced glucose as the predominant fuel for brain metabolism. A strikingly low respiratory quotient was also observed, suggesting a carboxylation mechanism as a means of disposing of some of the carbon of the consumed substrates.

Severe metabolic acidemia in infants: clinical and therapeutic aspects

A study of 10 infants in severe metabolic acidemia (pH below 7) led to the conclusion that the clinical signs-hyperventilation, coma or lethargy, peripheral vascular collapse, a significantly palpable liver, and abdominal distension-may all be directly related to the metabolic acidemia. In five of 10 infants, an initial erroneous diagnosis of congestive heart failure or pneumonia was made. Dramatic clinical improvement followed correction of the acidemia with rapid intravenous administration of sodium bicarbonate. This rapid administration of sodium bicarbonate was safe, provided hypocalcemia was recognized and treated in its early stages. In severe metabolic acidemia the measurement of blood bicarbonate alone does not reflect adequately the magnitude of the acid-base derangement and repeated measurements of hydrogen ion concentration, Pco(2) and bicarbonates are needed to evaluate and treat such infants correctly.

Rapid Serial Angiography in the Investigation of the Pharmacology of Brain Circulation in the Dog

The values of cerebral circulation time were determined by means of rapid serial angiography in the chloralosed dog under control conditions, after administration of strychnine and after injection of ergotamine. These results were compared with those obtained by the simultaneous registration of the intracranial venous pressure. Confirming previous observations made by means of this latter technique, the angiographic results showed that strychnine reduces the cerebral circulation time by provoking an increase in cerebral blood flow, whereas ergotamine causes a cerebral vasoconstriction, thereby increasing intracranial circulation time. Moreover, a statistically significant inverse correlation exists between the values of the intracranial pressure and the cerebral circulation time. New evidence of the relationship between the extra- and the intracranial circulation was obtained by the angiographic observations; these latter data are discussed in relation with the problem of the lability of cerebral vasoconstrictor reactions.

The Humoral Regulation of Breathing: A concept based on the physicochemical composition of mixed venous and arterial blood is presented

The clasic concept that breathing is regulated only by chemoreceptor mechanisms in the arterial blood stream- the respiratory center, the carotid and aortic bodies-has been modified in two ways. It has been expanded by postulating another chemoreceptor which reacts to the composition of mixed venous blood. It has been qualified by questioning the assumption that the respiratory center has physiologically significant chemosensitivity. (The respiratory center is considered to be, on the contrary, primarily a computing mechanism that integrates information received from chemoreceptors responding to both arterial and mixed venous blood.) By postulating a chemoreceptor mechanism which reacts to the composition of mixed venous blood, a variety of ventilatory responses can be accounted for with a unified and semiquantitative concept based on the ventilatory response to exercise. For the quantitative description of exercise, data obtained from normal men at rest and during exercise have been used to develop several equations which describe the ventilatory response to exercise in terms of P(co)(2) and H(+) of arterial and mixed venous blood. The simplest of these equations, yet a useful one, is the following: V = 1.1 H(+)a + 2.3 Pv(co)(2) - 135 (5a) which states that the volume of breathing is determined by the algebraic summation of influences in arterial and mixed venous blood. Ventilatory responses, as measured in several experimental and clinical situations characterized by acid-base imbalance and associated hyperpnea, have been compared with the ventilation predicted by this equation and by the equation which quantifies Gray's multiple-factor theory. Equation 5a estimated the various ventilatory responses as closely as the multiple-factor theory equation did. Equation 5a was also able to predict ventilation during exercise. It is concluded, therefore, that the hyperpnea of muscular exercise may be a generally applicable expression of the ventilatory response to alterations of the composition of both arterial and mixed venous blood. When applied to the ventilatory responses of cross-perfused animals during exercise, the concept gives a satisfactory qualitative explanation of the various observations. Although there is strong indirect evidence that a chemoreceptor mechanism exists which reacts to the composition of mixed venous blood and whose activity can be quantified, the equations that have been developed are not definitive expressions of the stimuli which regulate breathing. That the equations apply as well as they do, in view of the known errors of fact in their development, is probably the best evidence yet adduced for the essential validity of the present concept.