Rice D A, Rice J C
Department of Biomedical Engineering, Tulane University, New Orleans, Louisiana 70118.
J Acoust Soc Am. 1987 Oct;82(4):1139-44. doi: 10.1121/1.395249.
The time it takes audible sound to travel from the trachea to the pleura in five intact, excised horse lungs and one dog lung inflated with several gases was measured. Regression estimates of sound speed at total lung capacity (TLC) using straight line distance from the carina to the pleura are: helium, 775 +/- 60.5 m/s (means +/- 95% confidence limits); air, 282 +/- 23.5; carbon dioxide, 219 +/- 25.5; sulfur hexafluoride, 142 +/- 43.5. With the exception of sulfur hexafluoride, these speeds are 15%-20% less than the free-field speed of sound in each gas. Total airway length did not predict time delay any better or worse than straight line distance, but the high correlation between these two predictors (r = 0.94) prevents showing either to be the more predictive. In one lung, airway length was partitioned according to airway diameter. A regression using partitioned airway lengths significantly improved time delay prediction (p less than 0.001) over an unpartitioned model. Sound speed in the trachea equals free-field sound speed. Sound speed in air-filled airways 1 to 25 mm in diameter equals 268 +/- 44 m/s. We conclude that the first sound to reach the surface travels in the airways for at least 90% of the distance, spending at least 87% of the total travel time there.
测量了在五个完整的、切除的马肺和一个用几种气体充气的狗肺中，可听声音从气管传播到胸膜所需的时间。使用从隆突到胸膜的直线距离对总肺容量（TLC）下的声速进行回归估计结果如下：氦气，775±60.5米/秒（均值±95%置信限）；空气，282±23.5；二氧化碳，219±25.5；六氟化硫，142±43.5。除六氟化硫外，这些速度比每种气体在自由场中的声速低15% - 20%。总气道长度对时间延迟的预测效果并不比直线距离更好或更差，但这两个预测指标之间的高度相关性（r = 0.94）使得无法表明哪一个更具预测性。在一个肺中，根据气道直径对气道长度进行了划分。与未划分的模型相比，使用划分后的气道长度进行回归显著改善了时间延迟预测（p < 0.001）。气管中的声速等于自由场声速。直径为1至25毫米的充气气道中的声速等于268±44米/秒。我们得出结论，到达表面的第一个声音在气道中传播的距离至少占总距离的90%，在气道中花费的时间至少占总传播时间的87%。
