Imaging the human tympanic membrane using optical coherence tomography in vivo.

OBJECTIVE: Optical coherence tomography (OCT) is a diagnostic imaging modality that combines low coherence light with interferometry to produce high-resolution cross-sectional images of living tissues. Using this technology, we have imaged in vivo the human tympanic membrane (TM) in the office clinic setting and characterized TM microstructure in normal and pathologic conditions. STUDY DESIGN: Prospective clinical trial. MATERIALS AND METHODS: The normal and diseased TMs in 10 adult subjects were examined. Each subject underwent direct microscopic examination before OCT imaging to provide visual coregistration of associated subsites including the anulus fibrosus, pars tensa, pars flaccida, and umbo. The probe from the imaging system (1,310-nm central wavelength, 15-microm coherence length, Niris; Imalux, Cleveland, OH, USA) was introduced into the ear canal to obtain lateral cross-sectional images. RESULTS: Systematic imaging of the TM was performed with characterization of the epithelial and collagenous layers. The overall TM thickness was clearly demonstrated and quantified. CONCLUSION: The ability to noninvasively study middle ear microstructures in vivo is essential in the treatment of diseases of the ear. OCT may provide the otologist/neurotologist with the ability to 1) image pathology such as cholesteatoma, dimeric TMs, and chronic otitis media; 2) gauge the response to pharmacological therapy; and 3) monitor postsurgical changes after tympanoplasty and other procedures. OCT may provide a means to optimize the diagnosis and management of patients with middle ear disease.

Tympanic membrane collagen fibers: a key to high-frequency sound conduction.

OBJECTIVE: To investigate the significance of tympanic membrane collagen fiber layers in high frequency sound transmission. STUDY DESIGN: Human cadaver temporal bone study. METHODS: Laser Doppler vibrometry was used to measure stapes footplate movement in response to acoustic stimulation. The tympanic membrane was altered by creating a series of slits and applying paper patches to isolate the effects of specifically oriented collagen fibers. Three groups of membrane alterations were evaluated: 1) circumferentially oriented slits involving each quadrant to primarily disrupt radial fibers, made sequentially within superior-anterior, inferior-anterior, inferior-posterior, and superior-posterior quadrants; 2) the same slits made in the reverse order; and 3) radially oriented slits from the umbo to the annulus to primarily disrupt circumferential fibers. For each group, measurements of the middle-ear cavity pressure, ear canal pressure, and stapes velocity were made each time the tympanic membrane was altered. RESULTS: Regardless of the order in which the circumferentially oriented slits were made, there was a consistent decrease in stapes velocity above 4 kHz for the third and fourth cuts compared to the control. The mean decrease in the range of 4 to 12.5 kHz was 11 dB for the third patched slit and 14 dB for the fourth patched slit (P < .01). Radially oriented slits appear to produce smaller effects. CONCLUSIONS: Radial collagen fibers in the tympanic membrane play an important role in the conduction of sound above 4 kHz.

Nicotinamide modulates energy utilization and improves functional recovery from ischemia in the in vitro rabbit retina.

The central nervous system depends critically on a regular supply of oxygen and glucose for the formation of adenosine triphosphate (ATP) and the sustenance of its energy metabolism. Consequently, a significant reduction in the supply of oxygen and glucose to neuronal tissue causes an imbalance between the energy supply and demand, inducing the onset of neuronal ischemia and triggering many metabolic cascades leading to irreversible injury and cell death. Nicotinamide (NAm), an essential precursor to nicotinamide adenine dinucleotide (NAD+), which raises brain ATP levels, may improve cerebral blood flow and is neuroprotective against ischemia-induced injury. We therefore chose to examine the metabolic and electrophysiologic/functional effects of NAm (0.1 mM, 1.0 mM, 10.0 mM) under normal, control, and ischemic conditions, as well as following the early stages of reperfusion ("return-to-control" conditions) using an in vitro rabbit retina model where blood flow effects are excluded. Under nonischemic, control conditions, the protective concentration of NAm (10.0 mM) increased glucose utilization (34%, P < 0.01) and decreased lactate production (44%, P < 0.01), but had no significant effect on electrophysiologic function. After 2 h of ischemia, glucose utilization was significantly decreased (41%, P < 0.01) and lactate production was unaffected by NAm (10 mM). Following 3 h of "reperfusion", NAm (10 mM) significantly improved glucose utilization (217%, P < 0.01), lactate production (40%, P < 0.01), and electrophysiologic function (264%, P < 0.01) relative to controls. Thus, the functional neuroprotective effects of NAm may be independent of blood flow effects, but related, at least in part, to its improvement of tissue glucose utilization and lactate production.