Automatic recording of cerebral blood flow by nitrous oxide inhalation without blood loss

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Abstract
In a modification of the method of Kety and Schmidt nitrous oxide gas was rapidly removed from arterial and cerebral blood by a diffusion coil. The nitrous oxide contents were measured colorimetrically or by means of infrared nitrous oxide gas analyzers and the curves were automatically recorded. The arterial and cerebral venous blood were then returned to the brachial veins by a pump so that no blood loss resulted. The method was applied to 41 subjects with various diseases without ill effect. The colorimetric nitrous oxide method for measuring cerebral blood flow was made during saturation and desaturation in 30 subjects. Statistically significant correlation was found between saturation and desaturation values. The reason for higher desaturation values was discussed. Comparisons of this method with the conventional Scheinberg and Stead''s modification of the Kety-Schmidt method and the hydrogen method were in good agreement. Cerebral blood flow determinations using infrared nitrous oxide gas analyzers were made with inhalation of 15% nitrous oxide during saturation and desaturation in 13 subjects. Cerebral blood flow during saturation and desaturation using this method also showed good correlation; comparison of this method with the colorimetric nitrous oxide method also showed good agreement. Cerebral blood flow measurements in subjects with occlusive cerebrovascular disease using the automatic nitrous oxide method were obtained and were in good agreement with other reported values. In the monkey, comparison of cerebral blood flow values determined by the colorimetric nitrous oxide method with values for total internal jugular flow measured by electromagnetic flowmeters showed good agreement despite the different principles used.

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