Leung A, Sehati S, Young J D, McLeod C
Medical Instrumentation Research Laboratory, School of Engineering, Oxford Brookes University, Headington, Oxford OX3 0BP, United Kingdom.
J Appl Physiol (1985). 2000 Dec;89(6):2472-82. doi: 10.1152/jappl.2000.89.6.2472.
This study measured transit time (TT) and attenuation of sound transmitted through six pairs of excised pig lungs. Single-frequency sounds (50-600 Hz) were applied to the tracheal lumen, and the transmitted signals were monitored on the tracheal and lung surface using microphones. The effect of varying intrapulmonary pressure (Pip) between 5 and 25 cmH(2)O on TT and sound attenuation was studied using both air and helium (He) to inflate the lungs. From 50 to approximately 200 Hz, TT decreased from 4.5 ms at 50 Hz to 1 ms at 200 Hz (at 25 cmH(2)O). Between approximately 200 and 600 Hz, TT was relatively constant (1.1 ms at upper and 1.5 ms at lower sites). Gas density had very little effect on TT (air-to-He ratio of approximately 1.2 at upper sites and approximately 1 at lower sites at 25 cmH(2)O). Pip had marked effects (depending on gas and site) on TT between 50 and 200 Hz but no effect at higher frequencies. Attenuation was frequency dependent between 50 and 600 Hz, varying between -10 and -35 dB with air and -2 and -28 dB with He. Pip also had strong influence on attenuation, with a maximum sensitivity of 1.14 (air) and 0.64 dB/cmH(2)O (He) at 200 Hz. At 25 cmH(2)O and 200 Hz, attenuation with air was about three times higher than with He. This suggests that sound transmission through lungs may not be dominated by parenchyma but by the airways. The linear relationship between increasing Pip and increasing attenuation, which was found to be between 50 and approximately 100 Hz, was inverted above approximately 100 Hz. We suggest that this change is due to the transition of the parenchymal model from open to closed cell. These results indicate that acoustic propagation characteristics are a function of the density of the transmission media and, hence, may be used to locate collapsed lung tissue noninvasively.
本研究测量了通过六对切除的猪肺传播的声音的传播时间（TT）和衰减情况。将单频声音（50 - 600赫兹）施加到气管腔内，并使用麦克风在气管和肺表面监测传输信号。使用空气和氦气（He）使肺膨胀，研究了肺内压（Pip）在5至25厘米水柱之间变化对TT和声音衰减的影响。在50至约200赫兹范围内，TT从50赫兹时的4.5毫秒降至200赫兹时的1毫秒（在25厘米水柱时）。在约200至600赫兹之间，TT相对恒定（上部位点为1.1毫秒，下部位点为1.5毫秒）。气体密度对TT影响很小（在25厘米水柱时，上部位点空气与氦气的比例约为1.2，下部位点约为1）。Pip在50至200赫兹之间对TT有显著影响（取决于气体和位点），但在较高频率下没有影响。在50至600赫兹之间，衰减与频率有关，空气时在 - 10至 - 35分贝之间变化，氦气时在 - 2至 - 28分贝之间变化。Pip对衰减也有强烈影响，在200赫兹时最大灵敏度为1.14（空气）和0.64分贝/厘米水柱（氦气）。在25厘米水柱和200赫兹时，空气时的衰减比氦气时高约三倍。这表明声音通过肺的传播可能不是由实质组织主导，而是由气道主导。发现Pip增加与衰减增加之间的线性关系在50至约100赫兹之间，在约100赫兹以上则相反。我们认为这种变化是由于实质组织模型从开放细胞向封闭细胞的转变。这些结果表明，声学传播特性是传输介质密度的函数，因此可用于无创定位肺萎陷组织。
