Acoustic mechanisms: canal wall-up versus canal wall-down mastoidectomy.

The contribution of the middle ear air spaces to sound transmission through the middle ear in canal wall-up and canal wall-down mastoidectomy was studied in human temporal bones by measurements of middle ear input impedance and sound pressure difference across the tympanic membrane for the frequency range 50 Hz to 5 kHz. These measurements indicate that, relative to canal wall-up procedures, canal wall-down mastoidectomy results in a 1 to 5 dB decrease in middle ear sound transmission below 1 kHz, a 0 to 10 dB increase between 1 and 3 kHz, and no change above 3 kHz. These results are consistent with those reported by Gyo et al. (Arch Otolaryngol Head Neck Surg 1986;112:1262-8), in which umbo displacement was used as a measure of sound transmission. A model analysis suggests that the reduction in sound transmission below 1 kHz can be explained by the smaller middle ear air space volume associated with the canal wall-down procedure. We conclude that as long as the middle ear air space is aerated and has a volume greater than 0.7 ml, canal wall-down mastoidectomy should generally cause less than 10 dB changes in middle ear sound transmission relative to the canal wall-up procedure.

Calbindin D-28k immunoreactivity in the medial nucleus of the trapezoid body declines with age in C57BL/6, but not CBA/CaJ, mice.

This study compared calbindin D-28k immunoreactivity in the medial nucleus of the trapezoid body (MNTB) in young (3-4 month old) and old (24-26 month old) CBA/CaJ mice, and young (3-4 month old), middle-aged (6.5-8.5 month old), and old (24-29 month old) C57BL/6 mice. C57BL/6 mice exhibit progressively more severe peripheral (sensorineural) hearing loss between 4 and 12 months of age, whereas CBA/CaJ mice show little change in peripheral sensitivity until very late in life. We obtained auditory brainstem response audiograms on all subject mice. Old CBA mice were selected for study whose audiograms matched those of young CBA and C57 controls. Middle-aged C57 mice showed elevated thresholds indicative of peripheral degeneration. Brain sections were reacted with anti-calbindin D-28k (CB). Staining patterns in Nissl and anti-CB material were characterized and cells were counted. We found no significant change in the number of CB+ cells or the total number of cells in the MNTB of old CBA mice compared to young controls. However, the mean number of CB+ cells decreased by 11% in middle-aged, and by 14.8% in old C57 mice. Since the decline in C57 mice was significant by 6.5-8.5 months of age, the decrease could be the consequence of a loss of input from the cochlear nucleus where cell numbers are known to decline by this age in this strain. The total number of neurons in MNTB assessed from Nissl material showed a more modest 7.1% decline with age in C57 mice, implying that the greater loss of CB immunoreactive cells with age cannot be completely attributed to a reduction in the total number of cells.

Analysis of middle ear mechanics and application to diseased and reconstructed ears.

OBJECTIVE: To review current concepts of the mechanical processes of the human middle ear, and to apply them to practical issues in clinical otology and tympanoplasty surgery. BACKGROUND: The wide range of conductive hearing losses associated with middle ear pathology and reconstruction cannot be adequately explained by simple models of middle ear function. METHODS: Variables used to describe the system are sound pressure, volume velocity, and acoustic impedance. The relationship between specific middle ear structures and these variables is described such that inferences can be drawn regarding sound conduction in the normal, diseased, and reconstructed middle ear. RESULTS AND CONCLUSIONS: Sound can be transmitted from the car canal to the cochlea via two mechanisms: the tympano-ossicular system (ossicular coupling) and direct acoustic stimulation of the oval and round windows (acoustic coupling). Acoustic coupling is negligibly small in normal ears, but can play a significant role in some diseased and reconstructed ears. In the normal ear, middle ear pressure gain (which is the result of ossicular coupling) is frequency-dependent and less than generally believed. The severity of conductive hearing loss due to middle-ear disease or after tympanoplasty surgery can be predicted by the degree to which ossicular coupling, acoustic coupling, and stapescochlear input impedance are altered. Hearing after type IV and V tympanoplasty is determined solely by acoustic coupling. The difference in magnitude between the oval- and round-window pressures is more important than the difference in phase in determining cochlear input. In tympanoplasty types I, II, and III, adequate middle-ear and round-window aeration is necessary and the tympanic membrane-ossicular configuration may be less crucial.

Photosensitization and tissue distribution studies of the picket fence porphyrin, 3,1-TPro, a candidate for photodynamic therapy.

From a structurally distinct set of o-substituted tetraphenylporphyrins, the picket fence porphyrin (PFP), 3,1-meso-tetrakis(o-propionamidophenyl)porphyrin (3,1-TPro) has been selected as a potential candidate for use in the photodynamic therapy (PDT) of cancer. In this report, the time-dependent tissue distribution of 14C-labeled 3,1-TPro is described along with the results of various treatment regimens. The tissue distribution of radiolabeled 3,1-TPro is comparable to that of other porphyrin photosensitizers with the advantage of being most effective at 4 h and being cleared rapidly from most tissues. The results of the various treatment regimen experiments, as well as other studies, indicate that the 3,1-TPro mechanism of action is similar to that of other photosensitizers, but may include some minor differences. The conclusion is that 3,1-TPro and other PFP offer a class of effective photosensitizers that may be exploited for their structural versatility, straightforward synthesis leading to a compound of high purity and known structure, and stability (both in terms of shelf-life and in vivo metabolism) as potential candidates for PDT.