Biomedical subjects

J J Wertsch

Publications and source records attributed to J J Wertsch.

At least 19 recordsLinked to original sources

PubMed2005

Biomechanical implications of the negative heel rocker sole shoe: gait kinematics and kinetics.

Rocker sole shoes are commonly prescribed to diabetic patients with insensate feet. Recent passage of the therapeutic shoe bill has drawn an increased focus to prescription rehabilitative footwear. The purpose of this work is to investigate the dynamics of lower extremity joints (hip, knee and ankle) with the application of a negative heel rocker sole shoe under controlled lab conditions. Forty normal adults volunteered for gait evaluations using controlled baseline and prescription negative heel rocker sole shoes. Three-dimensional motion analysis techniques were used to acquire kinematic and kinetic data using a six-camera Vicon 370 motion system and two AMTI force plates. No significant change in walking speed or stride length was seen with the negative heel rocker shoe, although cadence was increased. The most significant kinematic changes with the application of the negative heel shoe occurred at the ankle in the sagittal plane with increased plantarflexion at terminal stance. Significant hip and knee changes were also noted with increased mid-stance hip extension and knee flexion. The most significant kinetic effects were seen in the transverse plane followed by changes in the sagittal and coronal planes. Changes in power were mostly noted in the sagittal plane. Other statistically significant changes in gait kinematics and kinetics were observed, although the magnitudes and durations were limited and as a result were not considered clinically significant. The study results indicated the negative heel rocker shoe significantly altered proximal joint metrics (hip and knee). The most significant distal joint alterations were seen in sagittal plane ankle kinetics. These kinematic and kinetic changes, along with previously studied effects of pressure relief at the metatarsal heads, should aid medical professionals in prescribing prophylactic footwear.

Adult↗

PubMed2001

Digit distribution of proper digital nerve action potential.

Antidromic sensory nerve action potential testing is well characterized and commonly used to assess the sensory component of the upper limb median and ulnar nerves. The final terminal segments of these nerves are the proper digital nerves. Ring recording electrodes are commonly used to detect the proper digital nerves' antidromic responses. Attempts to record the separate contributions of individual digital nerves along the lateral aspects of each finger, using small surface electrodes, is shown to be unreliable for determining the integrity of a single terminal digital branch. We found between 50% to 77% of the stimulated terminal branch's response amplitude when recorded at electrodes positioned over the nonstimulated branch located 180 degrees from the activated terminal branch. Detecting a single terminal nerve response was achieved by using the fourth digit and the second digit with one of the second digit's branches neurophysiologically blocked by local anesthetic. The volume-conducted response from the opposite side of the finger resulted in this relatively large recorded response, which remains within the range of reference values precluding the simple use of antidromic techniques to assess injury to a single proper digital nerve. Techniques are proposed to avoid such pitfalls and to assess most accurately the desired response.

Action Potentials↗

PubMed2001

Acute hypothalamic instability in traumatic brain injury: a case report.

. Acute hypothalamic instability occurs in patients with traumatic brain injury (TBI). It usually occurs in the form of autonomic dysfunction syndrome (also known as diencephalic seizures or paroxysmal sympathetic storms); however, there are other causes of acute hypothalamic instability of which the clinician must be aware. Neuroleptic malignant syndrome, malignant hyperthermia, autonomic dysfunction syndrome, and lethal catatonia are all syndromes that clinically present as signs and symptoms of acute hypothalamic instability. Because of the lethal potential of these syndromes, clinicians who care for patients with TBI must be aware of the various syndromes, their clinical presentation, and their treatment. We present a case of life-threatening acute hypothalamic instability in a patient with TBI.

Accidents, Traffic↗

PubMed1999

Instantaneous postural stability characterization using time-frequency analysis.

Postural stability assessment is critical to a more accurate understanding of sway and balance control. The center of pressure (COP) metric has been shown to be a suitable output measure for time and frequency analysis. However, the center of pressure is a non-stationary signal. Standard time and frequency analysis methods may not be adequate for monitoring the dynamic changes in the center of pressure signal. In this study a time-frequency method, based on data-adaptive evolutionary spectral estimation, is applied to monitor the dynamic changes of the center of pressure in a non-stationary environment. Metrics including the instantaneous mean frequency (IMF), instantaneous spectral bandwidth (ISB), and instantaneous average power (IAP) are analyzed to characterize the center of pressure signal in both the anterior-posterior (AP) and the medial-lateral (ML) planes. Within the confines of this study, the IMF was found to be inversely proportional to IAP. The inverse proportionality factors were calculated in both eyes-open and eyes-closed trials during upright quiet standing. These findings suggest that the time-frequency analysis provides instantaneous metrics which describe the amplitude changes and frequency shift of the center of pressure under a variety of environmental conditions, thus providing a more reliable quantification of postural control.

Adult↗

PubMed1998

Anatomical and technical considerations in surface electromyography.

Despite the technical and clinical limitations of surface EMG, it is essential in the physical medicine and rehabilitation field. Surface EMG has evolved from a secondary means of clinical assessment to a primary factor in determining and predicting clinical outcomes. Computer models of electrical muscular activity are currently implemented to assist in designing proper instrumentation and electrode with optimum dimensions. These models could be expanded to simulate pathological motor functions to help understand functional abnormalities even before clinical interventions. Currently, several groups all over the world are investigating the use of multichannel surface EMG. This technological advancement would have an immediate impact on several medical fields. For instance, tendon transfers are performed to improve function in peripheral nerve injury, brachial plexus lesion, spinal cord injury, and cerebral palsy. There are potential uses for multichannel surface EMG, both preoperatively and postoperatively. Preoperatively choosing the muscle for transfer has been largely based on clinical grounds. Multichannel surface EMG could give a more objective database to assess prognosis and determine which muscle to transfer. Postoperatively, multichannel surface EMG can provide a systematic way of assessing changes in gross muscle topography caused by the tendon transfer. Other applications of multichannel surface EMG would be for bony and soft tissue deformity from arthritis, heterotopic ossification, amputation, or burns. Multichannel surface EMG would allow clinicians to get a broader picture of the skeletal muscle activity despite the fact that it is physically impossible for the patient to assume the anatomic position used for traditional isolated electrode placement. Individuals with physical disabilities that affect their ability to assume the usual posture for electrophysiologic testing may benefit considerably from development of multichannel electrophysiologic testing. Patients with abnormalities of tone from various causes such as stroke, traumatic brain injury, and cerebral palsy are at times evaluated with kinesiologic EMG to assess motor control. Multichannel surface EMG could potentially give us much greater insight into motor control disorders.

Cerebral Palsy↗

PubMed1997

A Holter-type, microprocessor-based, rehabilitation instrument for acquisition and storage of plantar pressure data.

A Holter-type, microprocessor-based, portable, in-shoe, plantar pressure data acquisition system has been developed. The system allows continuous recording of pressure data between the sole of the foot and the shoe during the performance of daily living activities. Fourteen conductive polymer sensors acquire the plantar pressure history, which is then stored in the system memory. Pressures are sampled at a rate of 40 Hz from each of the 14 sensors for up to 8 hrs. The extended recording and processing capacity of the system developed in this study allows quantitative analysis of cumulative plantar pressure and temporal gait data necessary for characterization of event-related alterations in plantar pressures. The alterations that could be examined with the system include rehabilitative, therapeutic, surgical, and nonsurgical treatment. The system is fully portable and does not disrupt the natural gait pattern of the subject during ambulation. Peak plantar pressures, pressure-time integrals, and contact durations are determined for each of the insole sensors.

Equipment Design↗

PubMed1996

A Holter-type microprocessor-based rehabilitation instrument for acquisition and storage of plantar pressure data in children with cerebral palsy.

A multichannel, portable data acquisition system has been developed to measure discrete plantar pressures in the rehabilitation of children who have cerebral palsy and planovalgus foot deformity. The microprocessor-based system is designed to be lightweight (350 g with batteries) and portable (no umbilicus) in order to minimize encumbrances to gait patterns. It provides an improved method for obtaining accurate and reliable data during extended recording and rehabilitative periods that is not available from commercial systems. Twelve conductive polymer force (pressure) sensors are used to acquire pressure data, which are then stored in the system memory. Plantar pressures are sampled at a rate of 40 Hz from each of the 12 sensors for up to 2 h. The system consists of 16 analog amplifiers, a 12 b sampling analog-to-digital converter, an 8 b Dallas semiconductor microprocessor (DS5001FP-16, Dallas, TX), 4 MB of pseudo static RAM, and serial and parallel I/O interfaces. The interfaces are used to upload data into a PC for further processing, analysis, and display. During subject testing, sensors are located at predetermined anatomic areas under the calcaneus, medial and lateral midfoot, medial and lateral metatarsal heads, and hallux. Foot pressure data has been acquired from two pediatric subjects during multiple walking trials to illustrate system application in the normal and planovalgus foot. The system is considered to be appropriate for further clinical application and for characterization of event related alterations including rehabilitative, therapeutic, surgical, and nonsurgical treatment.

Cerebral Palsy↗

PubMed1996

An optoelectric plantar "shear" sensing transducer: design, validation, and preliminary subject tests.

A prototype miniature plantar shear sensing transducer was developed, characterized, and tested in this study. Electro-optical components were chosen for the design because of the fast response time, low cost, small size, low power requirements, and adaptability to this application. The optoelectric circuit employed a 660 nm wavelength light source and photodiode solar cell. Signal amplification and sensitivity were adjusted to provide an output voltage proportional to light power. The sensor shell was designed to encapsulate the electro-optical sensing components while providing mechanical resistance to shear through a spring mechanism. A naval bronze was chosen for the shell due to its strength and nonreflective characteristics (alloy of copper and tin). Static and dynamic characteristics of the shear sensor were determined through a series of calibration tests. Mechanical crosstalk sensitivity ranged from 14.34 to 30.51 mV/N. This represented 1% full-scale/Newton sensitivity. Nonlinearity averaged 5.6% in the forward direction and 7.6% in the reverse direction. Overall sensor output hysteresis was 1.1 +/- 3.1% while the natural frequency of the sensor to an input shear transient was approximately 5 Hz. Temperature sensitivity was -7.0 mV/degree C or 3.5% full-scale/degree C. Testing of five adult subjects revealed peak anterior-posterior shear ranging from 6.7 kPa (posterior heel) to 51.4 kPa (great toe) and medial-lateral shear ranging from 5.4 kPa (great toe) to 43.5 kPa (first metatarsal head). Stress-time integral values ranged from 0.78 kPa-sec (posterior shear at the posterior heel) to 37.3 kPa-sec (medial shear at the posterior heel). Contact durations ranged from 0.28 sec (posterior shear at the posterior heel) to 1.25 sec (medial shear at the posterior heel). Further application of the sensor for plantar shear characterization in able-bodied subjects and those with pathology is suggested.

Adult↗

PubMed1995

Walking cadence effect on plantar pressures.

OBJECTIVE: Prior studies have examined the effect of cadence on ground reaction forces by use of a force plate. Force plate studies generally analyze isolated steps and do not provide insight into ongoing step-to-step variations or in-shoe plantar pressures. The objective of this study was to evaluate the effect of walking cadences on in-shoe plantar pressures over extended periods of continuous walking. DESIGN: Nonrandomized control trial. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: Volunteer sample of 8 able-bodied subjects. INTERVENTIONS: In-shoe plantar pressures were studied during four minutes of continuous walking at controlled cadences of 70, 80, 90, 100, 110, and 120steps/min. For each cadence more than 200 steps were analyzed for each of the 8 subjects. MAIN OUTCOME MEASURES: Pressure-time integrals, foot-to-floor contact durations, and peak pressures at all 14 locations were processed for each step. Changes were calculated compared to values at 70steps/min. RESULTS: With increasing cadence, mean pressure-time integrals continuously decreased (45% at 120steps/min); mean foot-to-floor contact durations continuously decreased (64% at 120steps/min); and mean peak pressures increased (119% at 120steps/min). CONCLUSIONS: Our results show that as walking cadence increases, pressure-time integrals and foot-to-floor contact durations decrease, and peak plantar pressures increase. This is clinically relevant to all kinetic gait studies because our results suggest that normal values should be established for each cadence.

Adult↗

PubMed1995

Plantar pressures with total contact casting.

Total contact casting has been used to aid in the healing of plantar neurotrophic ulcerations. The efficacy of total contact casts in promoting ulcer healing is presumably due to a reduction in the load over high pressure areas with pressure redistribution over the entire surface of the foot. The purpose of this study was to quantify the effectiveness of total contact casting in reducing plantar pressures. A portable microprocessor-based data-acquisition system was used for recording plantar pressures. Plantar pressures were collected from six nondisabled individuals with and without total contact casting at cast-walking cadence. In our study, there was a decrease in plantar loading under the metatarsal heads (first, fourth, fifth), the great toe, and the heel. The average decrease was 32% under the fifth metatarsal, 63% under the fourth metatarsal, 69% under the first metatarsal, 65% under the great toe, and 45% under the heel. Our study quantitatively showed that total contact casting does reduce vertical plantar pressures in high load areas.

Adolescent↗

PubMed1994

Electrophysiologic analysis of snap amplitude in orthodromic and antidromic studies.

In 1966, Buchthal and Rosenfalk established that the sensory nerve action potential (SNAP) amplitude increased with increasing number of nerve fibers. Lambert and Dyck's in vitro study of the sural nerve, however, found the SNAP amplitude of a single fascicle was equivalent to the SNAP amplitude of the entire nerve. The current study confirmed Buchthal and Rosenfalk's original findings, and discovered an in vivo equivalent to Lambert and Dyck's findings. Ten subjects were used as their own controls. Orthodromic stimulation of both the index and middle fingers stimulated individually versus simultaneously revealed a significant increase in amplitude (p < 0.001). When the recording and stimulating electrodes were reversed, without physically changing the electrodes on the subject, there was no significant difference between the antidromic SNAP amplitudes recorded from separate fingers, or from both fingers simultaneously. Although in both cases the number of recorded nerve fibers approximately doubled, the effect on the SNAP amplitude was very different. This seemingly paradoxical result can be explained by electrophysiologic differences in the recording methods, without using the concept of fiber density.

Action Potentials↗

PubMed1994

Use of devices for mobility by the elderly.

Our study examined the use of devices for mobility by the elderly. We looked at whether the device was prescribed, who prescribed it, and how it was obtained. Seventy elderly people, age 75 years or older, who were current users of canes, walkers, or wheelchairs were interviewed. Seventy-one percent of the devices had been prescribed. The prescribed devices were chosen 45% of the time by physical therapists, 32.5% by physicians, and 22.5% by nurses. An exceptionally high percentage of wheelchair users (93%) in the skilled care facility may reflect economics (wheelchair and standard walkers are provided free) and perceived socialization benefits. This study shows that many elderly begin using devices for mobility on their own (94.3%). Clinicians need to be alert to these non-prescribed devices to assure their appropriateness and safe use.

Aged↗

PubMed1994

Development of a model of the premotor potential.

This study explored the sensory nature of the small negative premotor potential (PMP) that is often seen preceding the compound muscle action potential. We developed a model of the PMP, using the ulnar and superficial radial sensory (SRS) nerves. Standard conduction studies of the deep ulnar motor nerve recording over the first dorsal interosseous manus (FDIM) and of the SRS nerve recording over the same site were done separately, then simultaneously, on 20 normal hands. In all subjects, there was no FDIM PMP, but with simultaneous stimulation of both nerves, there was a potential in all subjects that appeared similar to their median thenar and ulnar hypothenar PMPs. Reference data for the median thenar, ulnar hypothenar, and model PMP were generated. Findings from this study are discussed and appear to support the concept of the PMP being either a sensory potential or a junctional potential.

Action Potentials↗

PubMed1994

Procedures for gait analysis.

Observational gait analysis is clinically useful with videotape slow-motion replay and freeze-frame, offering significant improvement over unaided visual observation. Any form of observational gait analysis, however, has limited precision and is more descriptive than quantitative. This article reviews procedures that are available for gait analysis. Gait analysis systems have evolved from cine with manual digitization, electrogoniometry, and video technology to sophisticated automated tracking systems. When used in conjunction with biomechanical models, these systems allow quantitative analysis of many specific gait characteristics such as joint moments and powers (kinetic analysis), joint angles, angular velocities, and angular accelerations (kinematic analysis). Analysis of dynamic electromyographic activity and energy consumption adds useful clinical information to gait analysis. The combination of a careful clinical assessment and gait analysis can be a powerful tool for the clinician.

Biomechanical Phenomena↗

PubMed1993

Multifrequency characteristics of disposable and nondisposable EMG needle electrodes.

The physical properties of recording electrodes coupled with the input characteristics of recording amplifiers can affect motor unit parameters. In recent years, there has been increased use of disposable needle electrodes; thus, a comparison of impedance characteristics with disposable types is of interest. Impedances at 10, 100, 1000, and 10,000 Hz of eight different electrode models including concentric and monopolar, both disposable and reusable, were measured. For all models of monopolar electrodes, no significant difference in impedance was found between disposable and nondisposable types. Intramodel variability was seen, however, with a twofold difference between minimum and maximum impedances for each model. For concentric electrodes, a moderate difference in impedance was found between disposable and nondisposable types, but less intramodel variability was seen; there was also more intermodel variability. To determine whether the measured impedances could affect recorded motor unit potentials, a theoretical analysis was conducted using typical waveforms along with circuit analysis techniques. Electrode impedances as high as 50 times nominal values caused no significant waveform distortion.

Action Potentials↗

PubMed1993

Sensate and insensate in-shoe plantar pressures.

In the individual with loss of protective sensation, the presence of high plantar pressures has been considered a risk factor for the development of plantar ulceration. Previous studies of insensate plantar pressures have measured a limited number of isolated, barefoot steps in a laboratory setting. Such isolated snapshots of barefoot plantar pressures do not give us insight into possible step-to-step variations or what plantar pressures occur when wearing shoes. The purpose of this study was to quantitatively examine and compare in-shoe plantar pressures during continuous walking by normal sensate and diabetic insensate subjects. A portable, insole data-acquisition system was used for pressure measurement during 4 minutes of normal continuous walking. Seven pressure sensors were placed in each insole under posterior and anterior heels, the metatarsal heads, and hallux. Twelve sensate and five insensate subjects were studied. We found that the insensate group had higher plantar pressures under posterior and anterior heels and the first metatarsals compared with the sensate group. From the study of the coefficients of variation, we demonstrated a larger step-to-step variation in plantar pressures for the insensate during continuous walking, suggesting the need for caution in interpreting the data from isolated force plate steps when studying insensate individuals.

Adult↗

PubMed1992

AAEM case report #25: anterior interosseous nerve syndrome.

A case study is reported regarding a 57-year-old woman, chose chief complaint was weakness in her thumb that she had noted while gardening. The patient described difficulty pulling weeds out because of an inability to get a firm grip when using the thumb. Physical examination showed weakness of the flexor pollicis longus and flexor digitorum profundus to the index finger. There was no other weakness and no clinical sensory deficit. Electrodiagnostic studies revealed normal median motor and sensory nerve conduction studies with needle examination abnormalities noted only in the flexor pollicis longus, flexor digitorum profundus, and pronator quadratus. The literature on anterior interosseous nerve syndrome (AINS) is reviewed. It is important to differentiate those with idiopathic AINS as part of a neuralgic amyotrophy picture from those with an anatomic cause such as a fibrous band or anomalous muscle. Electrodiagnostic examination can be useful to help make this distinction.

Electromyography↗

PubMed1992

A portable insole plantar pressure measurement system.

To analyze plantar pressures during activities of daily living, one needs a fully portable system capable of measuring many steps over extended periods. This paper presents an inexpensive, reliable, portable plantar pressure acquisition system which we have developed. It allows the long-term recording (up to 2 hours) of pressure-time data from 14 pressure sensors within insoles. The sensor chosen is an inexpensive, conductive polymer sensor that is only 0.25 mm thick yet able to withstand sudden overloads. The portable, battery-powered, microprocessor-based data acquisition system has a memory space of 480 kbytes for data storage. It can collect pressure data from 14 insole sensors at a 20 Hz sample frequency for 5 seconds every minute over a 2-hour period. It enables the long-term measurement of plantar pressures during normal activities in a natural unrestricted environment. The design and development of this portable insole plantar pressure measurement system is described.

Foot↗