Tuned vibration modes in a miniature hearing organ: Insights from the bushcricket.

Bushcrickets (katydids) rely on only 20 to 120 sensory units located in their forelegs to sense sound. Situated in tiny hearing organs less than 1 mm long (40× shorter than the human cochlea), they cover a wide frequency range from 1 kHz up to ultrasounds, in tonotopic order. The underlying mechanisms of this miniaturized frequency-place map are unknown. Sensory dendrites in the hearing organ (crista acustica [CA]) are hypothesized to stretch, thereby driving mechanostransduction and frequency tuning. However, this has not been experimentally confirmed. Using optical coherence tomography (OCT) vibrometry, we measured the relative motion of structures within and adjacent to the CA of the bushcricket Mecopoda elongata We found different modes of nanovibration in the CA that have not been previously described. The two tympana and the adjacent septum of the foreleg that enclose the CA were recorded simultaneously, revealing an antiphasic lever motion strikingly reminiscent of vertebrate middle ears. Over the entire length of the CA, we were able to separate and compare vibrations of the top (cap cells) and base (dorsal wall) of the sensory tissue. The tuning of these two structures, only 15 to 60 µm (micrometer) apart, differed systematically in sharpness and best frequency, revealing a tuned periodic deformation of the CA. The relative motion of the two structures, a potential drive of transduction, demonstrated sharper tuning than either of them. The micromechanical complexity indicates that the bushcricket ear invokes multiple degrees of freedom to achieve frequency separation with a limited number of sensory cells.

A narrow ear canal reduces sound velocity to create additional acoustic inputs in a microscale insect ear.

Located in the forelegs, katydid ears are unique among arthropods in having outer, middle, and inner components, analogous to the mammalian ear. Unlike mammals, sound is received externally via two tympanic membranes in each ear and internally via a narrow ear canal (EC) derived from the respiratory tracheal system. Inside the EC, sound travels slower than in free air, causing temporal and pressure differences between external and internal inputs. The delay was suspected to arise as a consequence of the narrowing EC geometry. If true, a reduction in sound velocity should persist independently of the gas composition in the EC (e.g., air, [Formula: see text]). Integrating laser Doppler vibrometry, microcomputed tomography, and numerical analysis on precise three-dimensional geometries of each experimental animal EC, we demonstrate that the narrowing radius of the EC is the main factor reducing sound velocity. Both experimental and numerical data also show that sound velocity is reduced further when excess [Formula: see text] fills the EC. Likewise, the EC bifurcates at the tympanal level (one branch for each tympanic membrane), creating two additional narrow internal sound paths and imposing different sound velocities for each tympanic membrane. Therefore, external and internal inputs total to four sound paths for each ear (only one for the human ear). Research paths and implication of findings in avian directional hearing are discussed.

The influence of tympanic-membrane orientation on acoustic ear-canal quantities: A finite-element analysis.

Assuming plane waves, ear-canal acoustic quantities, collectively known as wideband acoustic immittance (WAI), are frequently used in research and in the clinic to assess the conductive status of the middle ear. Secondary applications include compensating for the ear-canal acoustics when delivering stimuli to the ear and measuring otoacoustic emissions. However, the ear canal is inherently non-uniform and terminated at an oblique angle by the conical-shaped tympanic membrane (TM), thus potentially confounding the ability of WAI quantities in characterizing the middle-ear status. This paper studies the isolated possible confounding effects of TM orientation and shape on characterizing the middle ear using WAI in human ears. That is, the non-uniform geometry of the ear canal is not considered except for that resulting from the TM orientation and shape. This is achieved using finite-element models of uniform ear canals terminated by both lumped-element and finite-element middle-ear models. In addition, the effects on stimulation and reverse-transmission quantities are investigated, including the physical significance of quantities seeking to approximate the sound pressure at the TM. The results show a relatively small effect of the TM orientation on WAI quantities, except for a distinct delay above 10 kHz, further affecting some stimulation and reverse-transmission quantities.

Differential effects of mass-loading the eardrum and stiffening the middle ear on wideband absorbance.

The current work investigated the effects of mass-loading the eardrum on wideband absorbance in humans. A non-invasive approach to mass-loading the eardrum was utilized in which water was placed on the eardrum via ear canal access. The mass-loaded absorbance was compared to absorbance measured for two alternative middle ear states: normal and stiffened. To stiffen the ear, subjects pressurized the middle ear through either exsufflation or insufflation concurrent with Eustachian tube opening. Mass-loading the eardrum was hypothesized to reduce high-frequency absorbance, whereas pressurizing the middle ear was hypothesized to reduce low- to mid-frequency absorbance. Discriminant linear analysis classification was performed to evaluate the utility of absorbance in differentiating between conditions. Water on the eardrum reduced absorbance over the 0.7- to 6-kHz frequency range and increased absorbance at frequencies below approximately 0.5 kHz; these changes approximated the pattern of changes reported in both hearing thresholds and stapes motion upon mass-loading the eardrum. Pressurizing the middle ear reduced the absorbance over the 0.125- to 4-kHz frequency range. Several classification models based on the absorbance in two- or three-frequency bands had accuracy exceeding 88%.

Applying video motion magnification to reveal spontaneous tympanic membrane displacement as an indirect measure of intracranial pressure in patients with brain pathologies.

BACKGROUND: The observation of tympanic membrane displacement (TMD) opens up the possibility of indirect intracranial pressure (ICP) estimation. In this study, we applied a phase-based video motion magnification (VMM) algorithm to reveal spontaneous pulse TMD waveforms (spTMD) and compare them with invasively measured ICP in patients with intracranial pathologies. METHODS: Nine adults (six traumatic brain injury and three aneurysmal subarachnoid haemorrhage; median age 44 (29-53) years admitted to the intensive care unit of Wroclaw Medical University between October 2021 and October 2022 with implanted ICP sensors were included in this retrospective study. Video recordings of the tympanic membrane were performed using a portable otoscope with a video camera and analysed by a custom-written VMM algorithm. ICP was monitored using intraparenchymal sensors and arterial blood pressure (ABP) was measured in the radial arterial lines. ICP, ABP, and spTMD videos were captured simultaneously. The pulse amplitudes of ICP (Amp_ICP), ABP (Amp_ABP) and spTMD (Amp_spTMD) were estimated using fast Fourier transform within the heart rate (HR)-related frequency range. RESULTS: Amp_spTMD was significantly correlated with mean ICP (rS = 0.73; p = 0.025) and with Amp_ICP (rS = 0.88; p = 0.002). Age was not a significant moderator of this association. There were no significant relationships between Amp_spTMD and either mean ABP, HR, or Amp_ABP. CONCLUSIONS: The study suggests that Amp_spTMD increases with the increase in mean ICP and Amp_ICP. Estimation of Amp_spTMD using the VMM algorithm has the potential to allow for non-invasive detection of the risk of elevated ICP; however, further investigation in a larger group of patients is required.

Statistical analysis of the human middle ear mechanical properties.

Many experimental data on the human middle ear (ME) mechanics and dynamics can be found in the literature. Nevertheless, discussions about the uncertainties of these data are scarce. The present study compiles experimental data on the mechanical properties of the human ME. The summary statistics of mean and standard deviation of the data were collected and the coefficients of variation were computed and pooled. Moreover, the linear correlation and distribution were assessed for the ossicles' mass. Results show that, generally, the uncertainties of the stiffness properties of the tympanic membrane, ligaments, and tendons are larger than the uncertainties of the ossicles' mass. In addition, the uncertainties of the ME response vary across frequency. The vibration measures, such as the stapes' velocity normalized by the sound pressure at the tympanic membrane, are more uncertain than ME input impedance and reflectance. It is expected that the results presented in this study will provide the basis for the development of probabilistic models of the human ME.

The eardrums move when the eyes move: A multisensory effect on the mechanics of hearing.

Interactions between sensory pathways such as the visual and auditory systems are known to occur in the brain, but where they first occur is uncertain. Here, we show a multimodal interaction evident at the eardrum. Ear canal microphone measurements in humans (n = 19 ears in 16 subjects) and monkeys (n = 5 ears in three subjects) performing a saccadic eye movement task to visual targets indicated that the eardrum moves in conjunction with the eye movement. The eardrum motion was oscillatory and began as early as 10 ms before saccade onset in humans or with saccade onset in monkeys. These eardrum movements, which we dub eye movement-related eardrum oscillations (EMREOs), occurred in the absence of a sound stimulus. The amplitude and phase of the EMREOs depended on the direction and horizontal amplitude of the saccade. They lasted throughout the saccade and well into subsequent periods of steady fixation. We discuss the possibility that the mechanisms underlying EMREOs create eye movement-related binaural cues that may aid the brain in evaluating the relationship between visual and auditory stimulus locations as the eyes move.

Tympanic thermometers support fast and accurate temperature monitoring in acute and alternative care.

This article explores body temperature and the physiological process of thermoregulation. Normal body temperature and body temperature changes are discussed, including comorbidities associated with body temperature and signs of hyperthermia and hypothermia, and the factors that affect intraoperative temperature regulation. The evidence base behind thermometry is discussed and is applied to contemporary clinical conditions and symptoms, including: sepsis and suspected COVID-19. After discussing clinical considerations and regulations that encompass thermometry, three case studies present the use of the Genius 3 Tympanic Thermometer in clinical practice, with user feedback supporting its benefits, which include speed, accuracy and ease of use.

Developmental aspects of the tympanic membrane: Shedding light on function and disease.

The ear drum, or tympanic membrane (TM), is a key component in the intricate relay that transmits air-borne sound to our fluid-filled inner ear. Despite early belief that the mammalian ear drum evolved as a transformation of a reptilian drum, newer fossil data suggests a parallel and independent evolution of this structure in mammals. The term "drum" belies what is in fact a complex three-dimensional structure formed from multiple embryonic cell lineages. Intriguingly, disease affects the ear drum differently in its different parts, with the superior and posterior parts being much more frequently affected. This suggests a key role for the developmental details of TM formation in its final form and function, both in homeostasis and regeneration. Here we review recent studies in rodent models and humans that are beginning to address large knowledge gaps in TM cell dynamics from a developmental biologist's point of view. We outline the biological and clinical uncertainties that remain, with a view to guiding the indispensable contribution that developmental biology will be able to make to better understanding the TM.

On the tympanic membrane impedance of the katydid Copiphora gorgonensis (Insecta: Orthoptera: Tettigoniidae).

Katydids (bush-crickets) are endowed with tympanal ears located in their forelegs' tibiae. The tympana are backed by an air-filled tube, the acoustic trachea, which transfers the sound stimulus from a spiracular opening on the thorax to the internal side of the tympanic membranes (TM). In katydids the sound stimulus reaches both the external and internal side of the membranes, and the tympanal vibrations are then transferred to the hearing organ crista acustica (CA) that contains the fluid-immersed mechanoreceptors. Hence the tympana are principally involved in transmitting and converting airborne sound into fluid vibrations that stimulate the auditory sensilla. Consequently, what is the transmission power to the CA? Are the TM tuned to a certain frequency? To investigate this, the surface normal acoustic impedance of the TM is calculated using finite-element analysis in the katydid Copiphora gorgonensis. From this, the reflectance and transmittance are obtained at the TM. Based on the impedance results obtained from the pressure recordings at TM and the velocity field calculations in the AT, in the frequency range 5-40 kHz, it is concluded that the tympana have considerably higher transmission around 23 kHz, corresponding to the dominant frequency of the male pure-tone calling song in this species.

Air- and Bone-Conducted Sources of Feedback With an Active Middle Ear Implant.

OBJECTIVES: Active middle ear implants (AMEI) have been used to treat hearing loss in patients for whom conventional hearing aids are unsuccessful for varied biologic or personal reasons. Several studies have discussed feedback as a potential complication of AMEI usage, though the feedback pathway is not well understood. While reverse propagation of an acoustic signal through the ossicular chain and tympanic membrane constitutes an air-conducted source of feedback, the implanted nature of the device microphone near the mastoid cortex suggests that bone conduction pathways may potentially be another significant factor. This study examines the relative contributions of potential sources of feedback during stimulation with an AMEI. DESIGN: Four fresh-frozen, hemi-sectioned, human cadaver specimens were prepared with a mastoid antrostomy and atticotomy to visualize the posterior incus body. A Carina active middle ear implant actuator (Cochlear Ltd., Boulder, CO) was coupled to the incus by two means: (1) a stereotactic arm mounted independently of the specimen and (2) a fixation bracket anchored directly to the mastoid cortical bone. The actuator was driven with pure-tone frequencies in 1/4 octave steps from 500 to 6000 Hz. Acoustic sound intensity in the ear canal was measured with a probe tube microphone (Bruel & Kjær, Nærum, Denmark). Bone-conducted vibration was quantified with a single-axis laser Doppler vibrometer (Polytec Inc., Irvine, CA) from both a piece of reflective tape placed on the skin overlying the mastoid and a bone-anchored titanium screw and pedestal (Cochlear Ltd., Centennial, CO) implanted in the cortical mastoid bone. RESULTS: Microphone measurements revealed ear-canal pressures of 60-89 dB SPL, peaking in the frequency range below 2 kHz. Peak LDV measurements were greatest on the mastoid bone (0.32-0.79 mm/s with mounting bracket and 0.21-0.36 mm/s with the stereotactic suspension); peak measurements on the skin ranged from 0.05 to 0.15 mm/s with the bracket and 0.03 to 0.13 mm/s with stereotactic suspension. CONCLUSION: AMEI produce both air- and bone-conducted signals of adequate strength to be detected by the implanted device microphone, potentially resulting in reamplification. Understanding the relative contribution of these sources may play an important role in the development of targeted mitigation algorithms, as well as surgical techniques emphasizing acoustic isolation.

Sound pressure distribution within human ear canals: II. Reverse mechanical stimulation.

This work is part of a study of the interactions of ear canal (EC) sound with tympanic membrane (TM) surface displacements. In human temporal bones, the ossicles were stimulated mechanically "in reverse" to mimic otoacoustic emissions (OAEs), and the sound field within the ear canal was sampled with 0.5-2 mm spacing near the TM surface and at more distal locations within the EC, including along the longitudinal EC axis. Sound fields were measured with the EC open or occluded. The reverse-driven sound field near the TM had larger and more irregular spatial variations below 10 kHz than with forward sound stimulation, consistent with a significant contribution of nonuniform sound modes. These variations generally did not propagate more than ∼4 mm laterally from the TM. Longitudinal sound field variations with the EC open or blocked were consistent with standing-wave patterns in tubes with open or closed ends. Relative contributions of the nonuniform components to the total sound pressure near the TM were largest at EC natural frequencies where the longitudinal component was small. Transverse variations in EC sound pressure can be reduced by reducing longitudinal EC sound pressure variations, e.g., via reducing reflections from occluding earplugs.

Tympanic membrane surface motions in forward and reverse middle ear transmissions.

Characterization of Tympanic Membrane (TM) surface motions with forward and reverse stimulation is important to understanding how the TM transduces acoustical and mechanical energy in both directions. In this paper, stroboscopic opto-electronic holography is used to quantify motions of the entire TM surface induced by forward sound and reverse mechanical stimulation in human cadaveric ears from 0.25 to 18.4 kHz. The forward sound stimulus was coupled to an anatomically realistic artificial ear canal that allowed optical access to the entire TM surface, and the reverse mechanical stimulus was applied to the body of the incus by a piezo-electric stimulator. The results show clear differences in TM surface motions evoked by the two stimuli. In the forward case, TM motion is dominated by standing-wave-like modal motions that are consistent with a relatively uniform sound-pressure load over the entire TM surface. With reverse mechanical stimulation, the TM surface shows more traveling waves, consistent with a localized mechanical drive applied to the manubrium embedded in the TM. With both stimuli, the manubrium moves less than the rest of the TM, consistent with the TM acting like a compliant membrane rather than a stiff diaphragm, and also consistent with catenary behavior due to the TM's curved shape.

Sound localization by the internally coupled ears of lizards: From biophysics to biorobotics.

As they are generally small and only hear low frequencies, lizards have few cues for localizing sound. However, their ears show extreme directionality (up to 30 dB direction-dependent difference in eardrum vibrations) created by strong acoustical coupling of the eardrums, with almost perfect internal transmission from the contralateral ear over a broad frequency range. The activity of auditory nerve fibers reflects the eardrum directionality, so all auditory neurons are directional by default. This suggests that the ensuing neural processing of sound direction is simple in lizards. Even the simplest configuration of electrical analog models-two tympanic impedances connected via a central capacitor-produces directional patterns that are qualitatively similar to the experimental data on lizard ears. Several models, both analytical and (very recently) finite-element models, have been published. Robotic implementations using simplified models of the ear and of binaural comparison show that robust phonotaxic behavior can be generated with little additional processing and be performed by simple (and thus small and cheap) units. The authors review lizard directional processing and attempts at modeling and robotics with a twofold aim: to clarify the authors' understanding of central processing of sound localization in lizards, and to lead to technological developments of bioinspired robotics.

On the calculation of reflectance in non-uniform ear canals.

Ear-canal reflectance is useful for quantifying the conductive status of the middle ear because it can be measured non-invasively at a distance from the tympanic membrane. Deriving the ear-canal reflectance requires decomposing the total acoustic pressure into its forward- and reverse-propagating components. This decomposition is conveniently achieved using formulas that involve the input and characteristic impedances of the ear canal. The characteristic impedance is defined as the ratio of sound pressure to volume flow of a propagating wave and, for uniform waveguides, the plane-wave characteristic impedance is a real-valued constant. However, in non-uniform waveguides, the characteristic impedances are complex-valued quantities, depend on the direction of propagation, and more accurately characterize a propagating wave in a non-uniform ear canal. In this paper, relevant properties of the plane-wave and spherical-wave characteristic impedances are reviewed. In addition, the utility of the plane-wave and spherical-wave reflectances in representing the reflection occurring due to the middle ear, calibrating stimulus levels, and characterizing the emitted pressure in simulated non-uniform ear canals is investigated and compared.

In that vein: inflated wing veins contribute to butterfly hearing.

Insects have evolved a diversity of hearing organs specialized to detect sounds critical for survival. We report on a unique structure on butterfly wings that enhances hearing. The Satyrini are a diverse group of butterflies occurring throughout the world. One of their distinguishing features is a conspicuous swelling of their forewing vein, but the functional significance of this structure is unknown. Here, we show that wing vein inflations function in hearing. Using the common wood nymph, Cercyonis pegala, as a model, we show that (i) these butterflies have ears on their forewings that are most sensitive to low frequency sounds (less than 5 kHz); (ii) inflated wing veins are directly connected to the ears; and (iii) when vein inflations are ablated, sensitivity to low frequency sounds is impaired. We propose that inflated veins contribute to low frequency hearing by impedance matching.

Experimental Simulation of Clinical Borderline Situations in Temporal Bone Specimens After Ossiculoplasty.

OBJECTIVES: One reason for insufficient hearing improvement with a distinct air-bone gap after ossiculoplasty with implantation of partial or total ossicular replacement prostheses can be the dislocation or minimal shifting of the prosthesis. The aim of this study was the simulation of common clinical borderline situations with minimal shifting of the prosthesis in temporal bone specimens after ossiculoplasty. It was furthermore the goal to identify these specific situations through imaging by cone beam computed tomography (cbCT) and direct visual inspection using the operation microscope. Additionally, the functional status was evaluated using laser-Doppler vibrometry (LDV). DESIGN: We used a total of four temporal bone specimens for this study. A reconstruction with a partial ossicular replacement prostheses was performed in three specimens and with a total ossicular replacement prostheses in one specimen, with good initial acoustic properties. Subsequently, one specific type of prosthesis failure was simulated in each specimen, respectively, by minimally shifting, tilting, or bending the prostheses from their initial positions. These changes were introduced step-by-step until a borderline situation just short of complete acoustic decoupling was reached. Each step was examined using both LDV and cbCT and observed through the operation microscope. RESULTS: LDV was able to quantify the mechanic function of the ossicular chain after most of the manipulation steps by demonstrating the effect of any shifting of the prosthesis on the middle ear transfer function. However, in some situations, the middle ear transfer function was better with a visually more advanced failure of the prosthesis. In addition, cbCT showed most of the steps with excellent resolution and was able to delineate changes in soft tissue (e.g., cartilage covering). CONCLUSION: cbCT seems to be a promising imaging technique for middle ear problems. As cbCT and LDV exhibited slightly different advantages and disadvantages regarding the demonstration of borderline situations, the combination of both techniques allowed for a more precise evaluation of middle ear reconstructions. Knowledge of the specific characteristics of these methods and their possible combination might help otologists and otosurgeons to refine indications for revision surgery and improve their personal patient counseling.

Pure-Tone Audiometry With Forward Pressure Level Calibration Leads to Clinically-Relevant Improvements in Test-Retest Reliability.

OBJECTIVES: Clinical pure-tone audiometry is conducted using stimuli delivered through supra-aural headphones or insert earphones. The stimuli are calibrated in an acoustic (average ear) coupler. Deviations in individual-ear acoustics from the coupler acoustics affect test validity, and variations in probe insertion and headphone placement affect both test validity and test-retest reliability. Using an insert earphone designed for otoacoustic emission testing, which contains a microphone and loudspeaker, an individualized in-the-ear calibration can be calculated from the ear-canal sound pressure measured at the microphone. However, the total sound pressure level (SPL) measured at the microphone may be affected by standing-wave nulls at higher frequencies, producing errors in stimulus level of up to 20 dB. An alternative is to calibrate using the forward pressure level (FPL) component, which is derived from the total SPL using a wideband acoustic immittance measurement, and represents the pressure wave incident on the eardrum. The objective of this study is to establish test-retest reliability for FPL calibration of pure-tone audiometry stimuli, compared with in-the-ear and coupler sound pressure calibrations. DESIGN: The authors compared standard audiometry using a modern clinical audiometer with TDH-39P supra-aural headphones calibrated in a coupler to a prototype audiometer with an ER10C earphone calibrated three ways: (1) in-the-ear using the total SPL at the microphone, (2) in-the-ear using the FPL at the microphone, and (3) in a coupler (all three are derived from the same measurement). The test procedure was similar to that commonly used in hearing-conservation programs, using pulsed-tone test frequencies at 0.5, 1, 2, 3, 4, 6, and 8 kHz, and an automated modified Hughson-Westlake audiometric procedure. Fifteen adult human participants with normal to mildly-impaired hearing were selected, and one ear from each was tested. Participants completed 10 audiograms on each system, with test-order randomly varied and with headphones and earphones refitted by the tester between tests. RESULTS: Fourteen of 15 ears had standing-wave nulls present between 4 and 8 kHz. The mean intrasubject SD at 6 and 8 kHz was lowest for the FPL calibration, and was comparable with the low-frequency reliability across calibration methods. This decrease in variability translates to statistically-derived significant threshold shift criteria indicating that 15 dB shifts in hearing can be reliably detected at 6 and 8 kHz using FPL-calibrated ER10C earphones, compared with 20 to 25 dB shifts using standard TDH-39P headphones with a coupler calibration. CONCLUSIONS: These results indicate that reliability is better with insert earphones, especially with in-the-ear FPL calibration, compared with a standard clinical audiometer with supra-aural headphones. However, in-the-ear SPL calibration should not be used due to its sensitivity to standing waves. The improvement in reliability is clinically meaningful, potentially allowing hearing-conservation programs to more confidently determine significant threshold shifts at 6 kHz-a key frequency for the early detection of noise-induced hearing loss.

Does the Variability of Evoked Tympanic Membrane Displacement Data (V m) Increase as the Magnitude of the Pulse Amplitude Increases?

OBJECTIVES: Evoked tympanic membrane displacement (TMD) measurements, quantified by V m, record small volume changes in the ear canal following stimulation of the acoustic reflex. V m shows a correlation with intracranial pressure (ICP) and has been proposed as an option to non-invasively measure ICP. The spontaneous pulsing of the tympanic membrane, driven by the cardiovascular pulse, may contaminate the recordings and contribute to high measurement variability in some subjects. This study hypothesised that the larger the spontaneous vascular pulse, the larger the variability in V m. MATERIALS AND METHODS: Spontaneous and evoked TMD data from each ear in the sitting and supine position were recorded from 100 healthy volunteers using the MMS-14 CCFP analyser. ECG was also recorded to identify each heartbeat. Using bespoke software written in Matlab, spontaneous data were analysed to produce average pulse amplitude (PA) waveforms and evoked data were analysed to calculate average V m and its standard deviation. Averaged spontaneous PA was plotted against V m variability and Pearson's correlation coefficient was calculated to test for a significant linear relationship. RESULTS: There was a strong positive correlation between PA and V m variability in all conditions: left sitting, r = 0.758; left supine, r = 0.665; right sitting, r = 0.755; right supine, r = 0.513. All were significant at p < 0.001. CONCLUSION: This study shows that large V m variability is associated with a large spontaneous vascular pulse. This suggests that efforts to reduce vascular pulsing from recordings, either by a subtraction technique during post-processing or ECG-gating of the evoking stimulus, may improve reliability of the V m measurement.

Improvement of cerebral blood perfusion in certain cerebral regions after cranioplasty could be monitored via tympanic membrane temperature changes.

OBJECTIVE: Delayed neurological deficit was often observed in patients underwent craniectomy, which could be improved by cranioplasty. Little is known about hemodynamic improvement before and after cranioplasty. METHODS: Cerebral blood perfusion, tympanic membrane temperature (TMT), neuropsychological and cognitive function were assessed in eleven craniectomy patients before and after cranioplasty. RESULTS: Before cranioplasty, the cerebral blood volume (CBV) on the decompressed side was significantly lower than that of the contralateral side. The cranioplasty led to instant improvement (7 days after cranioplasty) of cerebral perfusion at the cranioplasty side in the frontal lobe, parietal lobe, temporal lobe, mesencephalon, basal ganglia and thalamus, but not the occipital lobe and epencephalon. Interestingly, CBV of the thalamus and basal ganglia gradually decreased to pre-surgical status 6 months later while the frontal lobe, parietal lobe, temporal lobe, mesencephalon remained well perfused. Meanwhile, the TMT changes acquired positive correlation with the perfusion of temporal lobe and mesencephalon as well as the GCS and MMSE score. CONCLUSION: The cranioplasty remarkably improves neurological and cognitive function by ameliorating cerebral perfusion in certain regions. The TMT could be used as a non-invasive method to monitor the cerebral perfusion improvement after the cranioplasty.