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In 1928, Boas described the cardiotachometer, an apparatus designed to count automatically and record the heart rate for prolonged periods of time. Using this instrument, Boas and Goldschmidt report studies based on continuous records over periods of from twelve to forty-eight hours on 356 persons. The heart rate was studied during sleep, during the normal activities of the day, during anesthesia and operations and in certain diseases, particularly cardiac insufficiency, exophthalmic goiter and neurogenic sinus tachycardia. Almost one third of the book is devoted to a study of the heart rate during sleep.
In an attempt to establish normal values for healthy men and women, respectively, the authors computed the minimum, maximum, average and basal rates. The basal rate was the rate recorded early in the morning, shortly after the subject awakened and before arising. The average heart rates in the sleeping and waking states demonstrate clearly the marked slowing
The Heart Rate.. Arch NeurPsych. 1933;29(6):1386-1387. doi:10.1001/archneurpsyc.1933.02240120209022