Correlative Observations on Cerebral Metabolism and Cardiac Output in Myxedema 1

Abstract

Patients with myxedema present an unusual opportunity for studying the effect of lowered metabolism on organ blood flow and for observing the effect of changes in peripheral circulation on cardiac output. Studies of cerebral metabolism in myxedema are of interest to the physician because changes in cerebral metabolism may be of importance in understanding the alterations in mental status which occur with this disease (1-3). was recorded with a Hamilton manometer. The nitrous oxide technique for measuring cerebral blood flow has been previously described (4), and the modification in use in this laboratory of collecting simultaneous, continuous samples from the artery and internal jugular bulb, rather than five separate arterial and venous samples, has been reported elsewhere, together with our normal values (7). In the cerebral metabolism study, blood oxygen content was measured by the spectrophotometric method of Hickam and Frayser (8); in the cardiac output study, it was measured by the manometric method of Van Slyke (9). Blood glucose content was measured by Nelson's modification of Somogyi's method (10); in most instances, each arterial cerebral venous glucose difference represents an average of four such arteriovenous differences drawn during the procedure. The calculation of cerebral oxygen consumption, cerebral glucose consumption, and cerebral vascular resistance has been previously described (4, 7). Cerebral venous oxygen tension was not measured directly, but computed from the per cent oxygen saturation of the cerebral venous blood using a standard oxyhemoglobin dissociation curve drawn for pH 7.4. Mean arterial pressures in the cerebral metabolism study were calculated from the formula MP = diastolic pressure plus pulse pressure the readings 3 being obtained at one minute intervals by the standard auscultation procedure with the arm held at heart level. RESULTSCardiac output. The essential data are presented in detail in Table I. The patients with myxedema were compared with a group of normal subjects studied under the same laboratory circumstances (11). The mean decrease in cardiac index from nornal was 47 per cent, and the mean decrease in total oxygen consumption was 37 per cent. There was an excellent correlation between cardiac index and basal metabolic rate, the correlation coefficient (r) being 0.90. The apparent moderate increase in mixed arterial-venous oxygen difference proved not to be statistically significant. The two patients who were restudied after treatment showed sizable increases in both cardiac index and total oxygen consumption. 1139

The Cerebral Circulation and Metabolism in Hyperthyroidism and Myxedema1

“…Scheinberg, Stead, Brannon, and Warren (9) found the mean CBF in subjects with myxedema to be significantly lower than in young normal subjects, an observation in agreement with the findings of Himwich, Daly, Fazekas, and Herrlich (10) who studied the rate of blood flow in cretins by means of a thermostromuhr placed in an internal jugular vein. In 1951, Madison, Sensenbach, and Ochs (11) reported the results of a preliminary study of cerebral circulatory and metabolic functions in hyperthyroidism and myxedema, in which the values for these functions, obtained after euthyroidism had been achieved, served as controls for comparison with pre-treatment findings.…”

Cerebral Blood Flow and Metabolism in the Wernicke-Korsakoff Syndrome*

“…In this event the elevated vascular resistance is another example of the well-known and remarkable property of the cerebral vasculature to regulate itself to meet the lessened demand of the tissues for blood. This is consistent with what is known to occur in other metabolic and toxic encephalopathies such as myxedema, methyl alcohol poisoning, general anesthesia, pernicious anemia, and insulin hypoglycemia (25)(26)(27)(28)(29)(30). Although mean jugular venous Po2 was normal in this study, in four instances a striking reduction from normal of CBF and CMRo2 was associated with jugular Po2 values well above the usual normal range, further suggesting the inability of the cerebral cells to extract oxygen normally.…”

Cerebral Blood Flow and Oxygen Consumption in Hyperthyroidism Before and After Treatment 1

“…This effect in the mature brain, however, may be normally not detectable because of the low turn-over rate of these protein systems compared to that of the carbohydrates. When the thyroid hormone is insufficient adequately to maintain these systems, as, for example, in myxedema, then secondarily, the energy producing carbohydrate metabolism may be impaired and this reflected in a lowered cerebral oxygen consumption (14,18). SUMMARY 1.…”

“…By means of the nitrous oxide method, quantitative determinations of cerebral blood flow and oxygen consumption in patients with hyperthyroidism have failed to demonstrate any significant differences from normal young men (15)(16)(17). On the other hand, in myxedema, a markedly reduced cerebral blood flow and metabolism and an elevated cerebral vascular resistance have been reported by Scheinberg and associates (18). Recently, Madison, Sensenbach and Ochs (19) have reported the results of a similar study on four hyperthyroid and four myxedematous subjects, the latter studied both before and after therapy.…”