Stethoscope acoustics. II. Transmission and filtration patterns.

T HERE are no reliable acoustical data to aid physicians in their selection or use of a stethoscope. Yet, the sole medical utility of any stethoscope is derived from its acoustical performance. It is the purpose of this paper to provide clinicians with objective acoustical performance data on intact and current stethoscopes. Frederick and Dodge' first recognized that the stethoscope was deserving of acoustical study in 1924. They studied the intact stethoscope, but their data understandably reflected the limitations of acoustical test instruments of the time. In 1940, Johnston and Kline2 made an objective acoustical study of stethoscope components. Their test method was physiologically oriented and employed a sound source implanted within a cadaver heart. They concluded that the design of the chestpiece was an important determinant in shaping the response of a stethoscope. Rappaport and Sprague3 4 studied stethoscope tubing. They interpreted their data to indicate that the physical properties of tubing had considerable influence on stethoscope efficiency. Groom5' 6 investigated stethoscope performances through well-executed subjective studies. He called attention to the importance of well-fitting earpieces and cited the impairment of stethoscope performances caused by air leaks and ambient noise levels. However, we have been unable to find any fully calibrated objective data published on the acoustics of intact stetho-