The behavior of the heart during operations has always been of vital interest to surgeons as an index to the general condition of the patient. Especial attention has been paid to the rate and quality of the pulse as well as to the blood pressure. The technic available heretofore has consisted largely of the palpation of the radial or temporal pulse by the anesthetist. The surgeon is informed of changes in the pulse only when a dramatic significant alteration has occurred.
One of us1 has devised an instrument, the cardiotachometer, by means of which the heart rate can be continuously recorded irrespective of the posture or degree of activity of the subject. The principle of the apparatus can be briefly described. The action current of the heart is led off from the chest by a pair of small electrodes. Ordinary green soap is used to improve the contact between
BOAS EP, GOLDSCHMIDT EF. CONTINUOUS RECORDING OF THE HEART RATE DURING OPERATIONS. JAMA. 1930;94(16):1210–1213. doi:10.1001/jama.1930.02710420022008