Abstract
Schmitz and Loevenhart 1 published a method for judging the onset and duration of anesthesia in the sciatic nerve of rabbits by the disappearance of changes in respiration when the distal portion of the nerve was stimulated. They recorded the respiration with a tambour attached to a cannula introduced into the trachea.
In order to study anesthesia (general, local and spinal) analgesia and hyperalgesia in small laboratory animals, without performing surgical operations, we have devised the apparatus shown in Fig. 1.
The respiration is recorded using a modified blood pressure cuff which is laced around the chest and abdomen and connected with a tambour in the manner described below. Ordinary platinum electrodes are applied to the shaved skin (moistened with 0.9% NaCl) over the area to be tested. The stimulus is furnished by induction shocks from a Harvard induction coil, either faradic or break shocks being used. The coil distance is noted, so as to furnish a fairly quantitative measure of the stimulus.
For purposes of comparison, the threshhold of sensation can be taken as the minimal stimulus which causes a definite change in amplitude or rate of respiration.
The elastic sac of the respiration cuff for rabbits consists of a small toy balloon 18 cm. in diameter, covered with a linen sac (Fig. 1). The sac is placed inside of an ordinary tire boot through which a hole is made for the tube leading to the recording apparatus. The tire boot bears lacings and is applied to the animal's chest and abdomen. The rubber sac is connected by a rubber tubing and a T tube whose one branch inflates a rubber condom enclosed in a glass bulb. The other branch of the T tube is connected with a pressure bottle in which the pressure is kept constant by a slow stream of compressed air provided with a water valve maintaining about 15 cm. H2O pressure as shown in the figure.
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