Picker Engineering Program, Ford Hall, Smith College, Northampton, Massachusetts 01063, USA.
Ear Hear. 2012 Mar-Apr;33(2):195-208. doi: 10.1097/AUD.0b013e31823235b5.
Reflectance measured in the ear canal offers a noninvasive method to monitor the acoustic properties of the middle ear, and few systematic measurements exist on the effects of various middle-ear disorders on the reflectance. This work uses a human cadaver-ear preparation and a mathematical middle-ear model to both measure and predict how power reflectance R is affected by the middle-ear disorders of static middle-ear pressures, middle-ear fluid, fixed stapes, disarticulated incudostapedial joint, and tympanic-membrane perforations.
R was calculated from ear-canal pressure measurements made on human-cadaver ears in the normal condition and five states: (1) positive and negative pressure in the middle-ear cavity, (2) fluid-filled middle ear, (3) stapes fixed with dental cement, (4) incudostapedial joint disarticulated, and (5) tympanic-membrane perforations. The middle-ear model of Kringlebotn (1988) was modified to represent the middle-ear disorders. Model predictions are compared with measurements.
For a given disorder, the general trends of the measurements and model were similar. The changes from normal in R, induced by the simulated disorder, generally depend on frequency and the extent of the disorder (except for the disarticulation). Systematic changes in middle-ear static pressure (up to 6300 daPa) resulted in systematic increases in R. These affects were most pronounced for frequencies up to 1000 to 2000 Hz. Above about 2000 Hz there were some asymmetries in behavior between negative and positive pressures. Results with fluid in the middle-ear air space were highly dependent on the percentage of the air space that was filled. Changes in R were minimal when a smaller fraction of the air space was filled with fluid, and as the air space was filled with more saline, R increased at most frequencies. Fixation of the stapes generally resulted in a relatively small low-frequency increase in R. Disarticulation of the incus with the stapes led to a consistent low-frequency decrease in R with a distinctive minimum below 1000 Hz. Perforations of the tympanic membrane resulted in a decrease in R for frequencies up to about 2000 Hz; at these lower frequencies, smaller perforations led to larger changes from normal when compared with larger perforations.
These preliminary measurements help assess the utility of power reflectance as a diagnostic tool for middle-ear disorders. In particular, the measurements document (1) the frequency ranges for which the changes are largest and (2) the extent of the changes from normal for a spectrum of middle-ear disorders.
耳道内测量的反射率提供了一种非侵入性的方法来监测中耳的声学特性，而关于各种中耳疾病对反射率的影响的系统测量却很少。本研究使用人尸体耳朵标本和中耳数学模型，分别测量和预测静态中耳压力、中耳积液、镫骨固定、砧镫关节分离和鼓膜穿孔等中耳疾病对功率反射率 R 的影响。
在正常状态和 5 种状态下，对人尸体耳朵的耳道压力进行测量，计算 R：（1）中耳腔正、负压；（2）充满液体的中耳；（3）用牙科水泥固定的镫骨；（4）砧镫关节分离；（5）鼓膜穿孔。对 Kringlebotn（1988 年）的中耳模型进行了修改，以代表中耳疾病。将模型预测与测量结果进行比较。
对于给定的疾病，测量值和模型的总体趋势相似。模拟疾病引起的 R 从正常状态的变化通常取决于频率和疾病的严重程度（除了关节分离）。中耳静态压力的系统变化（高达 6300 达帕）导致 R 的系统增加。这些影响在 1000 至 2000Hz 频率范围内最为显著。在大约 2000Hz 以上，负压和正压之间的行为存在一些不对称性。中耳气腔充满液体的结果高度依赖于充满的气腔百分比。当气腔的较小部分充满液体时，R 的变化最小，当气腔充满更多盐水时，R 在大多数频率上增加。镫骨的固定通常会导致 R 在低频时出现相对较小的增加。砧骨与镫骨的分离导致 R 在低频时持续下降，在 1000Hz 以下有一个明显的最小值。鼓膜穿孔导致 2000Hz 以下频率的 R 下降；在这些较低的频率下，与较大穿孔相比，较小穿孔导致的正常变化更大。
这些初步测量有助于评估功率反射率作为中耳疾病诊断工具的效用。特别是，这些测量记录了（1）变化最大的频率范围和（2）一系列中耳疾病的正常反射率变化程度。
