Hayden C. Nicholson

Effects of Low Oxygen Pressure on Respiratory Phenomena.

Eight per cent oxygen mixtures were administered for a period of approximately 30 minutes to 3 dogs anesthetized with morphine and urethane. Such administration produced an initial decrease in oxygen consumption which was followed by an increase slightly in excess of normal. This excess oxygen consumption was ascribed to the increased muscular effort of augmented ventilation. The augmented ventilation increased the elimination of carbon dioxide considerably above normal. On readministration of room air there was a decrease in pulmonary ventilation, a relative retention of carbon dioxide and an oxygen consumption above normal. In one experiment the expiratory quotient rose to 2.86 during the period of oxygen lack and fell on readministration of room air to 0.24. During oxygen lack there was a substantial decrease in the carbon dioxide capacity of the blood which was promptly followed by an increase approaching or exceeding the initial carbon dioxide capacity. There was a similar increase and decrease in blood lactic acid. The blood lactic acid content at the end of the period of oxygen lack was only moderately increased. The lactic acid changes occurred earlier than and were smaller than the changes in blood carbon dioxide capacity. The lactic acid content of the testicle and the rectus femoris muscle before and after the period of oxygen lack was determined. The tissue was dropped in liquid air and a satisfactory suspension was obtained by sectioning in the frozen state with a rotary microtome. The lactic acid content of the testicle and of the muscle was increased during the period of oxygen lack. The amount of lactic acid in the muscle was greater than in the blood. In the testicle it was less than in the blood.

Respiratory Effects from the Passage of Polarizing Currents Through the Medulla Oblongata.

In a series of experiments now extending over several years we have been attempting to investigate the site and functioning of the central respiratory mechanism by exposing the posterior portion of the floor of the fourth ventricle and studying the effects of local cooling of that region and the effects of the application of certain drugs to it. It was felt that additional information might be gained by studying the effects of the passage of polarizing currents through this part of the brain stem for it seemed likely that if too great current density was avoided, it might be possible in this way to produce temporary depression of function without causing irreparable tissue damage. Twenty experiments have been performed. In all these, dogs anesthetized either with morphine and urethane or with pentobarbital were used. As one electrode we used the instrument which had previously served as our applicator in the experiments on central cooling. The silver chloride plated silver tip of this electrode, triangular in shape, measuring about 3 mm on a side, was placed in light contact with the floor of the fourth ventricle in the calamus scriptorius. A large, indifferent electrode, also silver-silver chloride was wrapped in cotton soaked in saline and placed, in some experiments, in the mouth, in others beneath the skin over the occiput. With the electrodes so placed, a current of only a few milliamperes resulted in profound changes in respiration. In some cases the effects were completely reversible while in other cases recovery did not occur, suggesting that permanent damage had been done. Inspection of the brain in these latter cases frequently revealed gross tissue destruction. The results, somewhat variable, seem to fall into 2 groups. In the majority of the experiments, the effect of the passage of such a current was a decrease in amplitude of respiration proportional to the current strength and independent of the direction of current flow. When respiration ceased, it was with the chest in the expiratory position. These results we believe represent the effect of depression of the entire respiratory center—inspiratory as well as expiratory parts. Two examples of this type of response are illustrated in Fig. 1 A and B.

Effects of Low Alveolar Oxygen and High Alveolar Carbon Dioxide on Rate of Flow of Cerebro-Spinal Fluid of the Dog.

The fluid was obtained either by placing a cannula in the cisterna magna or by lumbar puncture, in most cases the former method being used. The rate of flow was recorded by the drop method. High percentages of carbon dioxide in room air (8-14%) invariably increased the rate of flow, in one case reaching 1000%. This increase appeared promptly on administration of the gas, rapidly increased to a maximum, and persisted practically undiminished up to the readministration of room air, when the flow quickly returned to the preadministrational rate. The effects of low oxygen are somewhat more complex. Low oxygen almost invariably caused a decrease in flow, followed, after prolonged administration, by a gradual increase, approaching, but practically never reaching, the preadministrational rate. The initial decrease in flow was usually preceded by a slight and very brief increase. When room air was again administered there was usually a brief but distinct decrease in flow, followed by a marked increase above the rate during administration of low oxygen and approaching the preadministrational rate. These results seem to be in agreement with those obtained by Eddy 1 on salivary secretion. The effects of high carbon dioxide resemble the results of Gesell 2 on the rate of flow of lymph but the resemblance does not hold for low oxygen.