Gait and balance of transfemoral amputees using passive mechanical and microprocessor-controlled prosthetic knees.

BACKGROUND: Microprocessor-controlled knee joints appeared on the market a decade ago. These joints are more sophisticated and more expensive than mechanical ones. The literature is contradictory regarding changes in gait and balance when using these sophisticated devices. METHODS: This study employed a crossover design to assess the comparative performance of a passive mechanical knee prosthesis compared to a microprocessor-controlled knee joint in 15 subjects with an above-knee amputation. Objective measurements of gait and balance were obtained. RESULTS: Subjects demonstrated significantly improved gait characteristics after receiving the microprocessor-controlled prosthetic knee joint (p<0.01). Improvements in gait were a transition from a hyperextended knee to a flexed knee during loading response which resulted in a change from an internal knee flexor moment to a knee extensor moment. The participants' balance also improved (p<0.01). All conditions of the Sensory Organization Test (SOT) demonstrated improvements in equilibrium score. The composite score also increased. CONCLUSIONS: Transfemoral amputees using a microprocessor-controlled knee have significant improvements in gait and balance.

Motion of the whole body's center of mass when stepping over obstacles of different heights.

Tripping over obstacles and imbalance during gait were reported as two of the most common causes of falls in the elderly. Imbalance of the whole body during obstacle crossing may cause inappropriate movement of the lower extremities and result in foot-obstacle contact. Thus, this study was performed to investigate the effect of obstacle height on the motion of the whole body's center of mass (COM) and its interaction with the center of pressure (COP) of the stance foot while negotiating obstacles. Six healthy young adults were instructed to perform unobstructed level walking and to step over obstacles of heights corresponding to 2.5, 5, 10, and 15% of the subject's height, all at a comfortable self-selected speed while walking barefoot. A 13-link biomechanical model of the human body was used to compute the kinematics of the whole body's COM. Stepping over the higher obstacles resulted in significantly greater ranges of motion of the COM in the anterior-posterior and vertical directions, a greater velocity of the COM in the vertical direction, and a greater anterior-posterior distance between the COM and COP. In contrast, the motion of the COM in the medial-lateral direction was less likely to be affected when negotiating obstacles of different heights.

The canalith repositioning procedure for the treatment of benign paroxysmal positional vertigo: a randomized controlled trial.

OBJECTIVE: To compare the canalith repositioning procedure (CRP) with a sham maneuver for the treatment of benign paroxysmal positional vertigo. PATIENTS AND METHODS: We recruited 50 patients with a history of positional vertigo and unilateral positional nystagmus on physical examination (Dix-Hallpike maneuver). Patients were randomized to either the CRP (n = 24) or a sham maneuver (n = 26). Measured outcomes included resolution of vertigo and positional nystagmus at follow-up examination. RESULTS: The mean duration of follow-up was 10 days for both groups. Resolution of symptoms was reported by 12 (50%) of the 24 patients in the CRP group and by 5 (19%) of the 26 patients in the sham group (P = .02). The results of the Dix-Hallpike maneuver were negative for positional nystagmus in 16 (67%) of 24 patients in the CRP group and in 10 (38%) of 26 patients in the sham group (P = .046). CONCLUSION: The CRP is effective treatment of benign paroxysmal positional vertigo, and this procedure can be performed by general internists on outpatients with this disorder.

Cochlear implantation after labyrinthectomy.

OBJECTIVE: The goal was to report a method used for intraoperative ear selection for cochlear implantation using electrical brainstem response. Initial patient response and the longer-term results of cochlear implantation after labyrinthectomy were compared. STUDY DESIGN: This was a specific retrospective review of a single case of cochlear implantation after labyrinthectomy. SETTING: The study involved a tertiary referral center in both an ambulatory and a hospital setting. PATIENT: The study involved a report of a single patient who was evaluated for a possible cochlear implant and successfully underwent cochlear implantation. INTERVENTIONS: A case study of a profoundly deaf individual is presented, including the diagnostic measures used to determine the candidacy for cochlear implantation, the ear selected, and the rehabilitation. MAIN OUTCOME MEASURES: Both early (3 months) and later (14 months) postoperative results clearly demonstrate that a cochlear implant in a patient with a previous labyrinthectomy can be beneficial. RESULTS: The early and later results after cochlear implantation are compared in a single case study. CONCLUSION: This case study demonstrates that there is improvement in sound awareness, speech recognition, and communication after cochlear implantation in a previously labyrinthectomized ear.

Benign paroxysmal positional vertigo: the canalith repositioning procedure.

As much as 20 percent of patients presenting with dizziness may have benign paroxysmal positional vertigo. This condition, which may be caused by otoliths lodged in the semicircular canals of the ear, tends to be persistent or recurrent. Traditionally, it has been treated symptomatically with medication. The canalith repositioning procedure, a series of defined head positions, is designed to shift the location of the otoliths to afford relief from the nausea, vomiting and dizziness often experienced by patients with this disorder.

Cochlear implantation in the senior citizen age group using the Nucleus 22-channel device.

Cochlear implantation has become a recognized beneficial method of assisting in the rehabilitation of the profoundly deaf individual. The only device that is currently approved by the Food and Drug Administration for implantation in children and adults in the United States is the Nucleus 22-channel device. Since 1988, the Nucleus is the only device that has been implanted at the Mayo Clinic, Rochester, Minnesota. Fifty-six patients ranging in age from 3 to 85 have received implants. Twenty-five (45%) were over 55 and 14 (25%) were 65 or older. All of the patients over 55 are currently using their implants. Several of the patients over 65 are continuing to be gainfully employed. The benefits, complications, and results are addressed.

Vestibular effects associated with implantation of a multiple channel cochlear prosthesis.

This study revealed that some patients with cochlear implants have symptoms of vertigo and imbalance following implant surgery. Although most experience a resolution of these symptoms, some patients have more persistent disturbances of balance. A total of 52 patients were implanted with a Nucleus 22 channel cochlear implant device between September 1988 and February 1994. Preoperatively, all but five of the patients received a vestibular evaluation. Twenty-two of the 52 patients received both pre- and postoperative vestibular evaluation. The cochlear implant was worn and activated during the postoperative vestibular assessment. The vestibular assessment included electronystagmography, computerized dynamic posturography, and harmonic acceleration testing. Five of the 22 patients demonstrated bilateral vestibular weakness preoperatively; that is, no response to caloric stimulation or a total of less than 30 degrees per second for the four irrigations. These patients were not included in the caloric analysis portion of the study. The remaining 17 were divided into groups under 60 years of age (7 patients) and over 60 years of age (10 patients). Analysis of the pre-and postoperative caloric response of the implanted ear showed a significant drop in output for the group over 60 years of age. The difference for the group under 60 years of age was not significant. Forty percent of the patients in the over 60 age group and 43% of those in the under 60 age group developed a peripheral vestibular weakness postoperatively. However, younger individuals in general did not seem to have balance complaints and did not require vestibular rehabilitation as frequently as the older group. Potential cochlear implant candidates should be advised of the possibility of postoperative vestibular effects following cochlear implantation. Most of the symptoms are transient; however, there may be persistent symptoms of imbalance that may be benefited by vestibular rehabilitation.

Averaged electrode voltages used to identify nonfunctioning electrodes in cochlear implants: case study.

We present the case of an adult male whose internal cochlear implant unit failed. Several months elapsed following initial stimulation with the implant before the problem was identified and corrected. The sequence of the failure and its detection are detailed. Following reimplantation, the patient did not initially report improved sound quality. However, within a week of the initial stimulation of the second device, he reported being able to identify environmental sounds, and speech began to sound the way he remembered it before he lost his hearing. We suggest a method of detection that might improve the early identification of a nonfunctioning device or of nonfunctioning individual electrodes. Knowledge of specific nonfunctioning electrodes is important in device adjustment, especially for young children.

The Mayo Clinic experience with the cochlear implant.

The implantation of a cochlear electronic prosthetic device is an acceptable means of improving the communication ability of pre- and postlingually deafened children and adults. A significant number of patients in this series are in the senior citizen age group. It has been beneficial in improving communication ability in selected profoundly deafened individuals. There has been a significant improvement in the cochlear electronic prosthetic device since the initial report of Djourno in 1957.

Influence of masker bandwidth on binaural masking level differences.

Masking level differences (MLDs) were investigated using masking noise with 160 Hz (amplitude-modulated noise) and 600 Hz (filtered-random noise) bandwidth. One hundred normally hearing subjects received the MLD test under both types of noise. Significant differences between noise types were observed in both N0S pi and N pi S0 conditions; MLDs were larger in amplitude-modulated noise. Consideration of these differences would indicate that older MLD norms based solely on filtered-random noise are invalid for amplitude-modulated noise especially where bandwidth differences in the noise exist. Were the norms for 600-Hz-wide filtered-random noise to be applied to results of MLD testing performed using 160-Hz-wide amplitude-modulated noise, patients with lesions in the central auditory pathway might exhibit normal or borderline normal results. Clinical MLD norms established on one type of noise should not be used to interpret MLD results obtained using a different type of noise.

The effects of digital quantization error on speech intelligibility and perceived speech quality.

The effects of digital quantization error upon speech intelligibility and perceived speech quality, for normally hearing subjects, were investigated for digitized speech processed to simulate 6-, 8-, 10-, 12-, 14-, and 16-bit integer conversion and 2-, 3-, 4-, 5-, 6-, and 7-bit floating-point conversion. For the integer data, there were no significant differences in speech intelligibility for 8- to 16-bit conversion. Only 6-bit integer conversion at 55 dB SPL resulted in a significant degradation in speech intelligibility. For the floating-point data, there were no significant differences in speech intelligibility for 2- to 7-bit floating-point conversion. However, results of the perceived quality experiment appeared to be more sensitive to differences among the various conditions. Speech processed using 12-, 14-, and 16-bit integer conversion was judged to be superior to speech processed using the 6-, 8-, and 10-bit integer conditions. Speech processed using 5-, 6-, and 7-bit floating-point conversion was judged to be superior to speech processed using 2-, 3-, and 4-bit floating-point conversion.

Influence of dietary magnesium on the amplitude of wave V of the auditory brainstem response.

Thirty-six weanling guinea pigs were fed either a low (600 ppm) or normal (3000 ppm) diet of magnesium for 8 weeks. One half of each diet group received intramuscular injections of magnesium-depleting drugs, furosemide and gentamicin. The other half were controls and received equal intramuscular injections of saline. Auditory brainstem responses were obtained from all animals before and after 8 weeks of treatment of diet and drugs to examine the effects of treatment upon hearing and auditory brainstem function. A three-way analysis of variance of dietary magnesium, by drug and by sex, showed no significant differences in auditory brainstem wave V thresholds, wave V latencies, or interpeak wave I-V latencies between the control and experimental groups. The low magnesium diet group, which received drugs, had significantly greater wave V auditory brainstem response amplitudes. Results can be explained on the basis of magnesium influencing the uptake of calcium into both the hair cells and associated brainstem pathways.

Use of adaptive digital signal processing to improve speech communication for normally hearing and hearing-impaired subjects.

A two microphone adaptive digital noise cancellation technique was used to improve word-recognition ability of normally hearing and hearing-impaired subjects in the presence of varying amounts of multitalker speech babble noise and speech spectrum noise. Signal-to-noise ratios varied from -8 dB to +12 dB in 4 dB increments. The adaptive noise cancellation technique resulted in reducing both the speech babble and speech spectrum noises 18 to 22 dB. This reduction in noise resulted in average improvements in word recognition, at the poorest signal-to-noise ratios, ranging from 37% to 50% for the normally hearing subjects and 27% to 40% for the hearing-impaired subjects. Improvements in word recognition in the presence of speech babble noise as a result of adaptive filtering were just as large or larger than improvements found in the presence of speech spectrum noise. The amount of improvement of word-recognition scores was most pronounced at the least favorable signal-to-noise ratios.

Application of adaptive digital signal processing to speech enhancement for the hearing impaired.

A major complaint of individuals with normal hearing and hearing impairments is a reduced ability to understand speech in a noisy environment. This paper describes the concept of adaptive noise cancelling for removing noise from corrupted speech signals. Application of adaptive digital signal processing has long been known and is described from a historical as well as technical perspective. The Widrow-Hoff LMS (least mean square) algorithm developed in 1959 forms the introduction to modern adaptive signal processing. This method uses a "primary" input which consists of the desired speech signal corrupted with noise and a second "reference" signal which is used to estimate the primary noise signal. By subtracting the adaptively filtered estimate of the noise, the desired speech signal is obtained. Recent developments in the field as they relate to noise cancellation are described. These developments include more computationally efficient algorithms as well as algorithms that exhibit improved learning performance. A second method for removing noise from speech, for use when no independent reference for the noise exists, is referred to as single channel noise suppression. Both adaptive and spectral subtraction techniques have been applied to this problem--often with the result of decreased speech intelligibility. Current techniques applied to this problem are described, including signal processing techniques that offer promise in the noise suppression application.

Improvement in speech intelligibility in noise employing an adaptive filter with normal and hearing-impaired subjects.

It is well known that communication in noisy environments with reverberation present is a difficult problem to solve, particularly for the hearing-impaired listener. Two-microphone noise cancelling using an LMS adaptive filter in real time was used to process speech recorded in the presence of speech-spectrum noise at six different signal-to-noise ratios, -8, -4, 0, 4, 8, and 12 dB. Twelve normal-hearing and 11 sensorineural hearing-impaired subjects were tested. Results indicated mean improvement of 37.34 percent for the 12 normal-hearing subjects and 38.3 percent for 5 of the sensorineural hearing-impaired subjects. Individual data for the 5 remaining hearing-impaired subjects revealed severe speech intelligibility deficits when noise and reverberation contaminated the speech signal. It is proposed that rehabilitative audiological assessments include evaluation of an individual's ability to cope with reverberation and noise.

The effects of alcohol on the acoustic Reflex Relaxation Index.

Normal-hearing young adults (6 M, 5 F) ingested 1.5 ml alcohol per Kg body weight over 90 min (blood alcohol level then being 0.104 +/- 0.016%), then tested for contralateral acoustic reflex (AR) threshold using an otoadmittance meter, and given the acoustic Reflex Relaxation Index (RRI) test of Norris, Stelmachowicz and Taylor. Each stimulus for the RRI was a 4-sec train of pulses at a level 10 db above AR threshold at .5, 1, or 2 kc/s, with equivalent on-time of 166.7 msec and off-time of 200 msec. AR responses were displayed on an X-Y recorder. RRI was taken as the percentage of total relation of the AR during off-times. The AR relaxed relatively more during off-times, and the RRI consequently significantly increased, in the alcohol vs the control condition, mean differences in RRI score in percent being 5.0, 12,9, and 21.3% for .5, 1, and 2 kc/s, respectively. Group mean RRI at all 3 frequencies under alcohol was close to the cut-off score suggested as "normal" by the test originators, but in 6 of the 11 Ss RRI interpretation by that criterion changed from "normal" to "not normal" under alcohol at one or more frequencies. There are unresolved differences in the effect of specific temporal stimulus patterning on RRI. Caution is recommended in interpreting RRI in the clinic as suggestive of sensorineural hearing impairment if S is at the time under the influence of a CNS depressant.

High frequency Bekesy audiometry. I: equipment and calibration.

A simple, straightforward and inexpensive conversion of the high-frequency (HF) range (up to 20 kc/s) of the Grason-Stadler E-800 Bekesy audiometer is described, incorporating as transducer a 1/2-inch condenser microphone loosely coupled to the ear canal by an adjustable headband, which provides also for a standard audiometric earphone-cushion unit on the non-test ear. A free field calibration is recommended. The system has a dynamic range of 135 db. Step-by-step instructions are provided for the conversion and for calibrations. Repeated calibrations of a prototype unit showed acceptable stability and validity. The HF E-800 audiometer could provide a valuable and cost-effective source of HF diagnostic information for the audiologist.

Effects of the visual modality on acoustic reflex magnitude.

Acoustic reflex magnitude for nine normal hearing subjects was measured with eyes opened and closed under three visual modality conditions: (1) in darkness; (2) in light without the ability to focus; and (3) in light with the ability to focus. Reflex magnitude decreased with eyes open for all three visual modality conditions; however, greater magnitude reduction occurred when the eyes were able to focus. Magnitude reduction for the three visual conditions was: 7% in darkness; 11% without visual focusing; and 20% with visual focusing. Additional data presented suggests reflex magnitude changes occur when eyes are held open with visual stimulation as a variable.