JAMA. 1966;198(13):1362. doi:10.1001/jama.1966.03110260074022.
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Noise is an environmental stress of increasing importance in our urban-centered society. Work efficiency and emotional tranquillity are frequently compromised by the cacophony which characterizes 20th century activity. An enterprising newspaper editor recently described his town as "din city drowned in decibels." It is therefore refreshing to take cognizance of a form of sound which is beneficial rather than detrimental. No one "listens" to this sound since the frequency is in a range beyond that of human hearing. Benefit is related to the reflection of high-frequency sonic energy from organs and tissues with different acoustical impedances. These reflected sound vibrations known as echoes are easily recorded, and a variety of specific echo patterns have been identified. When they are used in diagnostic cardiology, the intensity of ultrasound does not exceed 10% of that required to produce sensations of warmth in man. In recent months a number of communications have been


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