Pathology and mechanisms of cochlear aging

Presbycusis, or age-related hearing loss (ARHL), occurs in most mammals with variations in the age of onset, rate of decline, and magnitude of degeneration in the central nervous system and inner ear. The affected cochlear structures include the stria vascularis and its vasculature, spiral ligament, sensory hair cells and auditory neurons. Dysfunction of the stria vascularis results in a reduced endocochlear potential. Without this potential, the cochlear amplification provided by the electro-motility of the outer hair cells is insufficient, and a high-frequency hearing-loss results. Degeneration of the sensory cells, especially the outer hair cells also leads to hearing loss due to lack of amplification. Neuronal degeneration, another hallmark of ARHL, most likely underlies difficulties with speech discrimination, especially in noisy environments. Noise exposure is a major cause of ARHL. It is well-known to cause sensory cell degeneration, especially the outer hair cells at the high frequency end of the cochlea. Even loud, but not uncomfortable, sound levels can lead to synaptopathy and ultimately neuronal degeneration. Even in the absence of a noisy environment, aged cells degenerate. This pathology most likely results from damage to mitochondria and contributes to degenerative changes in the stria vascularis, hair cells, and neurons. The genetic underpinnings of ARHL are still unknown and most likely involve various combinations of genes. At present, the only effective strategy for reducing ARHL is prevention of noise exposure. If future strategies can improve mitochondrial activity and reduce oxidative damage in old age, these should also bring relief.     

The Clinical Incidence and Significance of Myopotential Sensing with Unipolar Pacemakers

Myopotential oversensing by unipolar pulse generators can cause patient symptoms ranging from dizziness and syncope to ventricular tachycardia. Seventy-seven patients with implanted unipolar pacemakers from three manufacturers participated in isometric and reach exercises to evaluate their pacemakers susceptibility to myopotentials. Myopotential inhibition occurred in 47% of the patients performing the reach maneuver. Testing revealed a wide difference in level of susceptibility to myopotentials between pacemakers of different manufacture (a low of 33% inhibition for the least susceptible to a high of 78% inhibition for the most susceptible during the reach maneuver). The normal pacing interval was extended by myopotential oversensing for each manufacturer's model within a range of 0.3–3.9 seconds. Pulse generators incorporating additional automatically-adjusting threshold and reversion circuits in the sense amplifier along with standard bandpass filtering exhibited: a) two-to-three times less susceptibility to myopotentials; and b) a 75% reduction in the maximum pacing interval extension as compared with pacemakers with bandpass filtering alone. The effectiveness of insulative coating in reducing myopotential inhibition was substantiated as coated pulse generators had a 22% lower incidence of muscle sensing than those than were uncoated. Six out of seven patients tested had symptoms during Holter monitoring which correlated with pacemaker myopotential inhibition. Selecting pulse generators with improved sensing amplifiers, clinical testing of patients with unipolar pacemakers using the reach method, and reprogramming of sensitivity will significantly reduce the incidence of myopotential inhibition.     

Energy Flux in the Cochlea: Evidence Against Power Amplification of the Traveling Wave

Traveling waves in the inner ear exhibit an amplitude peak that shifts with frequency. The peaking is commonly believed to rely on motile processes that amplify the wave by inserting energy. We recorded the vibrations at adjacent positions on the basilar membrane in sensitive gerbil cochleae and tested the putative power amplification in two ways. First, we determined the energy flux of the traveling wave at its peak and compared it to the acoustic power entering the ear, thereby obtaining the net cochlear power gain. For soft sounds, the energy flux at the peak was 1 ± 0.6 dB less than the middle ear input power. For more intense sounds, increasingly smaller fractions of the acoustic power actually reached the peak region. Thus, we found no net power amplification of soft sounds and a strong net attenuation of intense sounds. Second, we analyzed local wave propagation on the basilar membrane. We found that the waves slowed down abruptly when approaching their peak, causing an energy densification that quantitatively matched the amplitude peaking, similar to the growth of sea waves approaching the beach. Thus, we found no local power amplification of soft sounds and strong local attenuation of intense sounds. The most parsimonious interpretation of these findings is that cochlear sensitivity is not realized by amplifying acoustic energy, but by spatially focusing it, and that dynamic compression is realized by adjusting the amount of dissipation to sound intensity.     

Phase III results with a totally implantable piezoelectric middle ear implant: Speech audiometry,spatial hearing and psychosocial adjustment

Objective To evaluate the treatment efficacy of an electromechanical middle ear amplifier implant (AI) in patients with chronic moderate-to-severe sensorineural hearing loss (SNHL). The AI is a piezoelectric system with a sound processor and a rechargeable battery within a hermetically sealed titanium canister. Its titanium-sealed microphone is placed in the bony region of the ear canal. The incus-coupled transducer (actuator), which is also inside a titanium casing, is fastened to the adjacent bone.

Material and Methods This was a phase III study comprising 20 intention-to-treat patients. Telemetrical adjustments followed electromechanical amplifier implantations. We used a word recognition test as our primary efficacy measure (Freiburg Speech Recognition Test; DIN 45621). Secondary efficacy measures were the sentence comprehension test (Goettinger Satztest, 1996) for auditory orientation within noisy and quiet environments and a psychosocial adjustment test (Gothenburg Profile Test, 1998). The 6-month follow-up comprised a complete medical examination. Nineteen patients completed the study (per-protocol patients; 100% reference).

Results Seventeen patients (89%) demonstrated improved binaural recognition of phonetically balanced monosyllables. Fourteen postoperative patients (74%) attained a perfect score (100%) on this test, compared to only 3 preoperative patients (16%). Thirteen patients (68%) reached the sentence recognition threshold at a 2:1 dB signal-to-noise ratio during noisy trials. Correct identification of the noise source direction in the horizontal plane occurred in 89% of the trials. The Gothenburg Profile Test scores showed that the subjective evaluation of hearing, orientation, social behavior and self-confidence increased from 48% to 88%. Three patients did not benefit from the implant.

Conclusion Treatment of SNHL with a totally implantable hearing system can be an efficient method for those patients unable to wear hearing aids. However, in order to avoid implantation in non-responders, there is a need for more specific audiological indication criteria.     

Wireless amplified NMR detector for improved visibility of image contrast in heterogeneous lesions

To demonstrate the capability of a wireless amplified NMR detector (WAND) to improve the visibility of lesion heterogeneity without the use of exogenous contrast agents, a cylindrically symmetric WAND was constructed to sensitively detect and simultaneously amplify MR signals emitted from adjacent tissues. Based on a two‐leg high‐pass birdcage coil design, this WAND could be activated by a pumping field aligned along the main field (B₀), without perturbing MR signal reception. Compared with an equivalent pair of external detectors, the WAND could achieve more than 10‐fold gain for immediately adjacent regions. Even for regions with 3.4 radius distance separation from the detector's cylindrical center, the WAND was at least 1.4 times more sensitive than an equivalent pair of surface arrays or at least twice as sensitive as a single‐sided external surface detector. When the WAND was inserted into a rat's rectum to observe adjacent tumors implanted beneath the mucosa, it could enhance the detection sensitivity of lesion regions, and thus enlarge the observable signal difference between heterogeneous tissues and clearly identify lesion boundaries as continuous lines in the intensity gradient profile. Hyperintense regions observable by the WAND existed due to higher levels of blood supply, which was indicated by a similar pattern of signal enhancement after contrast agent administration. By better observing the endogenous signal contrast, the endoluminal WAND could characterize lesions without the use of exogenous contrast agents, and thus reduce contrast‐induced toxicity.     

A New Computer Assisted Orthopaedic Surgery System： WATO

Background： The traditional manual orthopaedic technology heavily re- lies on a surgeon＇s experience, so it certainly increases the instability of the surgery. Therefore, computer assisted orthopaedic surgery （CAOS） is becoming a hot research topic for its high accuracy and stability. We developed a new CAOS system WATO, which is mainly designed for total knee replacement （TKR）. Methods： WATO system provides the interactive software for a surgeon＇s preoperative planning. Based on its two infrared cameras, infrared markers and infrared probe, WATO system gives a simple surgical positioning procedure of femur and tibia without additional surgery for the placement of fiducial markers. According to the reference alignment axis from positioning procedure, a surgeon can move the robot of WATO system to do accurate bone resection. Safety checking is also considered in WATO system. Results： Extensive experiments were conducted on phantoms and cadaver bones to verify the accuracy and stability of WATO system. Experimental results showed that TKR using WATO system had better performance compared with traditional and navigated TKR. Conclusion： WATO system shows its superiority in TKR, and has a broad application prospect in the future. We will develop its new functions for other orthopaedic surgery such as total hip replacement （THR）. Current disadvantages such as bigger skin incision have to be resolved in the future.     

主动模拟肺的运动及控制部分仿真研究

目的：对于基于主动模拟肺的呼吸机测试平台的运动及控制部分进行分析与仿真研究,为进一步研究和功能扩展打下基础。方法：对步进电动机、丝杠滑台和活塞摩擦力的数学模型进行分析,在 SimuLink 内建立仿真模型,采用PID 控制方法实现步进电动机控制,使用纤维肺的呼吸数据进行模拟,对控制和运动模型进行分析。结果：经过初步的仿真模拟,所设计的控制及运动模型能够实现较为准确的控制,实现初步的呼吸运动仿真。结论：所建立的主动模拟肺的运动和控制部分的数学模型及仿真模型能够较真实地反映控制及运动规律,基于这一仿真模型可以实现主动模拟肺的运动及控制模拟,同时为下一步各种呼吸模型的建立提供良好的分析平台。     

Meet the challenge of high-pass filter and ST-segment requirements with a DC-coupled digital electrocardiogram amplifier

Background

The high-pass filter (HPF) in an electrocardiogram (ECG) amplifier can distort the ST segment required for ischemia interpretation. Therefore, the current standards and guidelines require −3 dB for monitoring and −0.9 dB for diagnostic purposes at 0.67 Hz. In addition, a minimal reaction to a rectangular pulse of 300 μV has to be proven. We raise the question of why the design of a DC-coupled digital ECG amplifier is reasonable when today the AC-coupled digital ECG amplifier including a 0.05-Hz HPF works so well, meets all required standards, and is already safe. We make the hypothesis that a digital DC-coupled ECG amplifier can as well meet the requirements and guarantee the same safety levels at the same time provide a higher degree of freedom for future improvements of the ECG signal quality.

Methods

Firstly, a historical research of the origin of the 0.05-Hz requirement has been made. Secondly, triangular pulses simulating unipolar QRS complexes have been passed through a digital filter to get qualitative results of the HPF response. And finally, to quantitatively describe the filter response, corresponding test requirement signals have been passed through a digital filter to simulate the HPF behavior, therefore understanding the reasons for the required tests.

Results

The oldest reference found to the 0.05-Hz filter dates from 1937. At that time, DC-coupled analogue ECG amplifiers were used. The simulation of the AC-coupled ECG amplifier with a first-order analogue HPF shows that the rectangular 300-μV pulse is a phase requirement and more restrictive than the frequency requirements. The phase requirement in fact corresponds to the requirement of a 0.05-Hz first-order analogue HPF (−3 dB) even if −0.9 dB at 0.67 Hz is required. The DC-coupled ECG amplifier (without an analogue HPF and during online and off-line acquisition) fulfils the phase and frequency requirements, just as the digital AC-coupled ECG amplifier does.

Conclusions

An AC-coupled ECG amplifier based on a first-order analogue HPF must have a maximum cutoff frequency of 0.05 Hz or requires a phase equalizer causing a delay of the acquired ECG. Because the desired delay during online acquisition should be short, the solution is practical but could be improved. Not the frequency cutoff of the HPF but the phase distortion of such a filter should be discussed. The DC-coupled ECG amplifier is as safe as the AC-coupled ECG amplifier; but it provides a higher degree of freedom for future filter designs certainly improving the ECG signal quality, while the safety can be guaranteed. Furthermore, the DC-coupled ECG amplifier allows investigation of the HPF, which is not easily possible when an AC-coupled ECG amplifier including the HPF is to be investigated.     

电阻抗参数成像数据采集系统中三种电流-电压转换器的比较

目的 寻找一种能在2-380kHz间提供2MΩ以上的等效输出阻抗和０.1％以上精度的电压－电流转换电路（ＶＩＣ）。为电阻抗参数成像数据采集系统的建立打下基础。方法 在分别对单运放ＶＩＣ＝三运放ＶＩＣ和由仪表放大器的成的ＶＩＣ的工作原理进行了分析的基础上，根据各自的要求建立了这３个ＶＩＣ，并在不同频率点进行了测量。结果 在低频端，基于仪表放大器的ＶＩＣ具有极高的输出阻抗和很低的噪声水平，在高频时只有三运放ＶＩＣ性能能接近要求。结论 在电阻抗参数成像数据采集系统中应采用三运放ＶＩＣ。