Measurement of heart rate in white rat. I. The effects of anesthetization.

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Abstract
The apparatus comprises a crystal microphone "relatively insensitive to air-borne sounds and designed to respond to the frequency range covered by heart beats" coupled to a high-gain amplifier which activates a signal magnet recording on a kymograph. 15 [male] and 15 [female] animals were investigated. After anesthetization had attained adequate depth, the stethophone was placed in a position over the site of good pulsation and records were taken for at least 120 secs. In this manner mean heart rates were detd. with ether, with Na amytal, with nembutal, and with phenobarbital anesthesia. There were no statistically significant differences in mean heart rate among the 1st three of these (mean about 374 per min., standard deviation about 38). Under nembutal, heart rates were found to be significantly lower than under the other anesthetics.