The impact of size on middle-ear sound transmission in elephants, the largest terrestrial mammal.

Elephants have a unique auditory system that is larger than any other terrestrial mammal. To quantify the impact of larger middle ear (ME) structures, we measured 3D ossicular motion and ME sound transmission in cadaveric temporal bones from both African and Asian elephants in response to air-conducted (AC) tonal pressure stimuli presented in the ear canal (PEC). Results were compared to similar measurements in humans. Velocities of the umbo (VU) and stapes (VST) were measured using a 3D laser Doppler vibrometer in the 7-13,000 Hz frequency range, stapes velocity serving as a measure of energy entering the cochlea-a proxy for hearing sensitivity. Below the elephant ME resonance frequency of about 300 Hz, the magnitude of VU/PEC was an order of magnitude greater than in human, and the magnitude of VST/PEC was 5x greater. Phase of VST/PEC above ME resonance indicated that the group delay in elephant was approximately double that of human, which may be related to the unexpectedly high magnitudes at high frequencies. A boost in sound transmission across the incus long process and stapes near 9 kHz was also observed. We discuss factors that contribute to differences in sound transmission between these two large mammals.

The impact of size on middle-ear sound transmission in elephants, the largest terrestrial mammal.

Elephants have a unique auditory system that is larger than any other terrestrial mammal. To quantify the impact of larger middle ear (ME) structures, we measured 3D ossicular motion and ME sound transmission in cadaveric temporal bones from both African and Asian elephants in response to air-conducted (AC) tonal pressure stimuli presented in the ear canal (P EC ). Results were compared to similar measurements in humans. Velocities of the umbo (V U ) and stapes (V ST ) were measured using a 3D laser Doppler vibrometer in the 7-13,000 Hz frequency range, stapes velocity serving as a measure of energy entering the cochlea-a proxy for hearing sensitivity. Below the elephant ME resonance frequency of about 300 Hz, the magnitude of V U /P EC was an order of magnitude greater than in human, and the magnitude of V ST /P EC was 5x greater. Phase of V ST /P EC above ME resonance indicated that the group delay in elephant was approximately double that of human, which may be related to the unexpectedly high magnitudes at high frequencies. A boost in sound transmission across the incus long process and stapes near 9 kHz was also observed. We discuss factors that contribute to differences in sound transmission between these two large mammals.

Management of N0 neck in early oral squamous cell carcinoma: A systematic review and meta-analysis.

OBJECTIVE: The role of elective neck dissection (END) in patients with stage I (T1N0) and II (T2N0) squamous cell carcinoma of the oral cavity remains a controversial topic. We investigate the need for END by establishing a true incidence of occult nodal disease as a function of T stage DATA SOURCES: MEDLINE, Google Scholar, Scopus. REVIEW METHODS: Studies were selected using a set of inclusion and exclusion criteria. Meta-analysis using a random-effects model was employed to generate an odds ratio (OR) comparing the incidence of occult metastasis between T1 and T2 tumors, as well as regional recurrence rates between patients receiving END versus observation. RESULTS: Thirty-nine publications comprising five randomized controlled trials and 34 retrospective studies were selected for inclusion, yielding over 4,300 patients for analysis. The overall incidence of occult nodal metastasis, weighted by study size, was found to be 23%. Patients with T2 tumors have a significantly higher odds of having occult nodal disease (OR: 2.6, 95% confidence interval [CI]: 2.0-3.4) over patients with T1 tumors. We also demonstrate that for patients who are observed, the odds of recurrence are significantly higher (OR: 4.18, 95% CI: 2.78-6.28) compared to those who undergo END, although statistically significant interstudy heterogeneity was observed. CONCLUSIONS: END should be reserved for stage II tumors given the significantly higher rate of occult metastasis. Observation may be more appropriate for stage I cancers. Laryngoscope, 129:E284-E298, 2019.