The circulation time in the cat, studied by a conductivity method / by J.A.B. Gray and W.D.M. Paton.

  • Gray, J. A. B.
Date:
[1949?]
Catalogue details

Licence: In copyright

Credit: The circulation time in the cat, studied by a conductivity method / by J.A.B. Gray and W.D.M. Paton. Source: Wellcome Collection.

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    into a vein or were blunt needle cannulae which were inserted through small side vessels so that their tips lay in the vessel into which it was desired to inject. In the latter case adjacent branches of the vessel concerned were tied and divided. Injecting system. The injecting system consisted of a graduated pipette fitted to a two-way tap. One arm of the tap was connected with a metal adaptor which could bo plugged into the needle cannulae, and the other with a reservoir. In order to minimize distensibility, the junctions were kept as short as possible and made with plastic tubing. The other end of the pipette was connected with a pressure reservoir which enabled any chosen rate of flow to be maintained uniformly. In some experiments injections were made from a pipette into a glass cannula tied into the main vein. Electrode cannulae. It was necessary to measure the resistance of the blood without interference from the resistance of the vessel wall or of the external fluid, or from changes in the length and diameter of the vessel. For this reason it was decided to mount the electrodes in a cannula which could be tied in continuity with the vessel. Three electrodes were used, the outer two being con- Fig. 1. Diagram of a.c. impedance bridge and cannula. Normal working conditions; A = B =2000 Cl. Final balance of resistance obtained with G and the bridge balanced against earth with the potentiometer W. nected, thus short circuiting the parallel resistance provided by the blood and tissues in contact with the ends of the cannula. As shown in Fig. 1, a glass tube of 3 mm. internal diameter was provided with three side arms 10 mm. apart into which 0-5 mm. diameter silver wires were fixed with de Khotinsky’s cement. When filled with blood the cannula had a resistance of about 2000 Cl.; the true capacity of blood at low frequencies has been shown by Fricke & Morse (1926) to be of the order of 100 jupF. for a cubic centimetre of blood, the same volume having a resistance of the order of 200 Q. This capacity would imply a reactance at 1000 cyc./sec. of about 10 MQ. in parallel with our resistance and can clearly be ignored. Various minor modifications in the cannula were made at different times. Bridge and recording system. The recording cannula formed one arm of a resistance bridge (Fig. 1). Resistances A and B were fixed equal to each other, usually at 2000 Cl. The bridge was balanced with resistance C, and the variable condenser was used to balance the capacity in the cannula. 3 V. r.m.s. 1000 cyc./sec. was supplied to the bridge through a transformer, and the balance was recorded through a transformer coupling with amplifier and cathode-ray oscillograph. A double¬ beam oscillograph was used without time-base deflexion and the spots were photographed on
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