In 1954 we reported in The Journal1 the use of an externally applied throat microphone and amplifier to amplify the sounds of respiration in anesthetized patients. The throat microphone proved to be somewhat impractical for surgery of the neck and related operations that might disturb or momentarily move the throat microphone. In addition, the presence of an endotracheal tube prevented the larynx from vibrating sufficiently to energize the microphone. The apparatus described here requires no contact whatsoever with the patient. We have named it the Breathophone. It consists of a hearing-aid transistor amplifier, a hearingaid earphone that does not have to be worn in the ear, and a microphone that is removed from the hearing aid and placed, by means of a T-tube, anywhere within the anesthesia breathing circuit (fig. 1).
Amplifying the sounds of breathing is highly desirable, since it affords the most accurate means of communication with
Shane SM, Ashman H. AN IMPROVED DEVICE TO AMPLIFY THE SOUNDS OF RESPIRATION OF ANESTHETIZED PATIENTS. JAMA. 1957;163(4):261. doi:10.1001/jama.1957.82970390002013a