Abstract
From an analysis of the method of measuring blood flow by the Rein 1 2 thermostromuhr it became evident that the passage of the high frequency current through the intact blood vessel, on which a diathermy thermoelement is placed, results essentially in a localized heating of the wall of the blood vessel. Hence it was of interest to construct a thermostromuhr unit similar to the modified type introduced by Baldes, Herrick and Essex 1 in which a direct current heater replaced the platinum electrodes and likewise was spaced midway between the differential thermocouple. This arrangement of the Rein unit differs somewhat from the thermostromuhr described by Schmidt and Walker 4 in which the hot thermojunction is a silver trough interposed between a direct current heater and the blood vessel.
The arrangement of the direct current heater and the thermocouple in the bakelite block is shown in Fig. 1. The heating unit is made of No. 36 or 38 B. & S. gauge nichrome wire rolled to a ribbon 0.75 mm. to 0.5 mm. wide. This unit consists of a folded loop ‘c’ soldered to copper wires ‘b’(2 strands number 38 B. & S. gauge), the resistance of the loop being at least one ohm. The unit is held in place by bakelite lacquer. The thermojunctions at ‘a’ are made by soldering copper wires (0.0016 in.) to a constantan wire (0.002 in.) which is embedded in the groove ‘d.’ The fine copper wires as well as the copper wires attached to the heater are then soldered to braided copper wires (17 strands 0.003 in. tinned copper). All grooves are filled by several applications of bakelite lacquer 3128 or Sterling varnish M-472, each application being followed by suitable air drying and baking.
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