Acoustic Transmission Characteristics of a Eustachian Tube Volitionally Opened in Two Living Subjects.

OBJECTIVE: To assess the acoustic transmission characteristics of the Eustachian tube (ET) in living subjects in verified patent and closed ET states to facilitate the detection and quantification of ET function using acoustic measures such as sonotubometry. PATIENTS: The two subjects in this study had no history of ear disease nor previous ear surgery and were capable of volitionally opening and closing their ET. INTERVENTIONS: Tympanometry and otologic examinations were used to confirm ET patent and closed states by observing tympanic membrane movement with respiration and by acoustic immitance measurements during forced respiration. A series of 500-ms long chirps containing frequencies from 100 Hz to 10 kHz were introduced into the nasal cavity during both ET states and recorded by microphones in both the contralateral naris and external auditory canal. MAIN OUTCOME MEASURES: Acoustic energy transmission through the ET across the 0.1 to 10 kHz frequency range in the closed state versus the patent state. RESULTS: An increase in acoustic energy transmission occurs across the frequencies of 1 to 4 kHz between the closed and patent ET states, particularly in frequencies below 2.5 kHz. CONCLUSIONS: Results support sonotubometry as a potential diagnostic tool for ET dysfunction. Acoustic differences between the ET states manifest as a general increase in transmitted signal amplitude. Characterizing the acoustic properties in the verified patent and closed ET states allows investigators to more reliably interpret sonotubometric tests of ET function.

Adaptation of tibial structure and strength to axial compression depends on loading history in both C57BL/6 and BALB/c mice.

Tibial compression can increase murine bone mass. However, loading protocols and mouse strains differ between studies, which may contribute to conflicting results. We hypothesized that bone accrual is influenced more by loading history than by mouse strain or animal handling. The right tibiae of 4-month-old C57BL/6 and BALB/c mice were subjected to axial compression (10 N, 3 days/week, 6 weeks). Left tibiae served as contralateral controls to calculate relative changes: (loaded - control)/control. The WashU protocol applied 60 cycles/day, at 2 Hz, with a 10-s rest-insertion between cycles; the Cornell/HSS protocol applied 1,200 cycles/day, at 6.7 Hz, with a 0.1-s rest-insertion. Because sham loading, sedation, and transportation did not affect tibial morphology, unhandled mice served as age-matched controls (AC). Both loading protocols were anabolic for cortical bone, but Cornell/HSS loading elicited a more rapid response that was greater than WashU loading by 13 %. By 6 weeks, cortical bone volume of each loading group was greater than of AC (average + 16 %) and not different from each other. Ultimate displacement and energy to fracture were greater in tibiae loaded by either protocol, and ultimate force was greater with Cornell/HSS loading. At 6 weeks, independent of mouse strain, the WashU protocol produced minimal trabecular bone and the trabecular bone volume fraction of Cornell/HSS tibiae was greater than that of AC by 65 % and that of WashU by 44 %. We concluded that tibial adaptation to loading was more influenced by waveform than mouse strain or animal handling and therefore may have targeted similar osteogenic mechanisms in C57BL/6 and BALB/c mice.

Short-term low-strain vibration enhances chemo-transport yet does not stimulate osteogenic gene expression or cortical bone formation in adult mice.

Development of low-magnitude mechanical stimulation (LMMS) based treatment strategies for a variety of orthopaedic issues requires better understanding of mechano-transduction and bone adaptation. Our overall goal was to study the tissue and molecular level changes in cortical bone in response to low-strain vibration (LSV: 70 Hz, 0.5 g, 300 µÎµ) and compare these to changes in response to a known anabolic stimulus: high-strain compression (HSC: rest inserted loading, 1000 µÎµ). Adult (6-7 months) C57BL/6 mice were used for the study and non-invasive axial compression of the tibia was used as a loading model. We first studied bone adaptation at the tibial mid-diaphysis, using dynamic histomorphometry, in response to daily loading of 15 min LSV or 60 cycles HSC for 5 consecutive days. We found that bone formation rate and mineral apposition rate were significantly increased in response to HSC but not LSV. The second aim was to compare chemo-transport in response to 5 min of LSV versus 5 min (30 cycles) of HSC. Chemo-transport increased significantly in response to both loading stimuli, particularly in the medial and the lateral quadrants of the cross section. Finally, we evaluated the expression of genes related to mechano-responsiveness, osteoblast differentiation, and matrix mineralization in tibias subjected to 15 min LSV or 60 cycles HSC for 1 day (4-h time point) or 4 consecutive days (4-day time point). The expression level of most of the genes remained unchanged in response to LSV at both time points. In contrast, the expression level of all the genes changed significantly in response to HSC at the 4-h time point. We conclude that short-term, low-strain vibration results in increased chemo-transport, yet does not stimulate an increase in mechano-responsive or osteogenic gene expression, and cortical bone formation in tibias of adult mice.

Constrained tibial vibration does not produce an anabolic bone response in adult mice.

Osteoporosis is characterized by low bone mass and increased fracture risk. High frequency, low-amplitude whole-body vibration (WBV) has been proposed as a treatment for osteoporosis because it can stimulate new bone formation and prevent trabecular bone loss. We developed constrained tibial vibration (CTV) as a method for controlled vibrational loading of the lower leg of a mouse. We first subjected mice to five weeks of daily CTV loading (0.5 G maximum acceleration) with loading parameters chosen to independently investigate the effects of strain magnitude, loading frequency, and cyclic acceleration on the adaptive response to vibration. We hypothesized that mice subjected to the highest magnitude of dynamic strain would have the largest bone formation response. We observed a slight, local benefit of CTV loading on trabecular bone, as BV/TV was 5.2% higher in the loaded vs. non-loaded tibia of mice loaded with the highest bone strain magnitude. However, despite these positive differences, we observed significantly lower measures of trabecular structure in both loaded and non-loaded tibias from CTV loaded mice compared to Sham and Baseline Control animals, indicating a negative systemic effect of CTV on trabecular bone. Based on this evidence, we conducted a follow-up study wherein mice were subjected to CTV or sham loading, and tibias were scanned at the beginning and end of the study period using in vivo microCT. Consistent with the findings of the first study, trabecular BV/TV in both tibias of CTV loaded and Sham mice was, on average, 36% and 31% lower on day 36 than day 0, respectively, compared to 20% lower in Age-Matched Controls over the same time period. Contrary to the first study, there were no differences between loaded and non-loaded tibias in CTV loaded mice, providing no evidence for a local benefit of CTV. In summary, 5 weeks of daily CTV loading of mice was, at best, weakly anabolic for trabecular bone in the proximal tibia, while daily handling and exposure to anesthesia was associated with significant loss of trabecular and cortical bone. We conclude that direct vibrational loading of bone in anesthetized, adult mice is not anabolic.