Biomedical subjects

K Horch

Publications and source records attributed to K Horch.

At least 19 recordsLinked to original sources

PubMed2005

[People's interest in health information].

Well-informed citizens and patients regard health policy innovations as a key element when it comes to reforms in the health service--both in health economics and with regard to prevention issues. We evaluated the data provided by the 2003 Telephone Health Survey (GSTel03) to examine demographic and social distinctions in the use of different information sources. At the same time we examined whether there are any population-related differences in people's interest in health information depending on their levels of health awareness, attitudes to prevention and related modes of behaviour. The data generated by the survey show that there is considerable interest in health-related topics. Only 2% of the people questioned used no information sources for this purpose. In addition to more traditional media (books, newspapers, information from pharmacies), information provided by health insurance companies and via the Internet is becoming increasingly important. With the exception of the Internet, all other sources of information are used more frequently by women than by men, and demand for most of the information media increases with age. The frequency of information use and the number of different media used increase from the lower to the upper strata of society. As far as selected variables of health-related behaviour are concerned (smoking, sport, alcohol), the results show a link between a more positive attitude to health and a greater interest in information.

Adolescent↗

PubMed2002

Evidence for a two pigment visual system in the fiddler crab, Uca thayeri.

Intraocular recordings were made from the eyestalks of dark-adapted fiddler crabs (Uca thayeri) during presentation of monochromatic light flashes of different wavelengths and intensities. Two types of signals were recorded in different experiments: slow potentials (electroretinogram) and fast potentials (spikes). The latter were also recorded in the presence of a continuous green or red adapting light. The resulting visual spectral-sensitivity curves, when fitted to rhodopsin-based visual pigment absorption spectra (from Dartnall nomograms), indicated the presence of two visual pigments, one with an absorption maximum near 430 nm, and the other with a peak absorption between 500 nm and 540 nm. The data also provided evidence for some differential bleaching of the pigments in the presence of a colored adapting light, but most of the adaptation effect was probably due to changes in screening pigment and neural desensitization or inhibition. These two observations suggest that an adequate substrate for color vision may exist in this and other species of fiddler crabs. The electroretinogram and spike-recording methods produced similar visual-sensitivity data, suggesting that latter technique, a much more efficient way of collecting data that is physiologically relevant, may be the method of choice for determining spectral sensitivity in crustaceans.

Animals↗

PubMed2001

Electrical resistivity of the upper arm and leg yields good estimates of whole body fat.

Single frequency bioelectrical impedance analysis is an inexpensive, quick and painless means of estimating body composition. However, current approaches to estimating body composition from segment resistivity have some drawbacks. The purpose of this study was to overcome these limitations by developing a better model of the relationship between resistivity and body composition. A three-compartment model of body mass and body segment resistivity is presented and calibrated to predict %Fat estimated by underwater weighing. The subject population from which the data were obtained was heterogeneous. Both sexes were represented, as were a range of ages (21-44 years), ethnic backgrounds, body masses (47.0-129.0 kg) and body compositions (%Fat = 8.7-50.7%). Based on resistivity measurements from the upper arm and upper leg, and measurements of subject height and weight, the model predicted %Fat with errors comparable to those reported for other methods based on segmental resistivity. All the terms in the calibrated model represented a physical component of the body and show reasonable agreement with resistivity measured in tissue samples. In short, predicting %Fat from resistivity of the proximal arm and leg segments compares favourably with other methods based on segment resistivity.

Adipose Tissue↗

PubMed1999

Extrinsic muscles of the hand signal fingertip location more precisely than they signal the angles of individual finger joints.

Studies have demonstrated that muscle spindle organs provide the majority of the proprioceptive information available to the nervous system about limb position. Other studies suggest that a sense of position may be lacking in the fingers, as subjects were unaware of rather large excursions of finger joints if the excursions were made slowly enough. We sought to investigate the basis for this unexpected finding with a biomechanical model of the human long finger and the forearm muscles which actuate it, in order to study potential contributions of spindle organs in the extrinsic muscles of the hand to a sense of position of the finger. The model, based on cadaver data, allowed us to determine how precisely estimates of the lengths of the extrinsic finger muscles can be transformed into estimates of: (1) the flexion/extension angles of the individual finger joints, and (2) the location of the fingertip in the flexion/extension plane. We found that, for some finger positions, length information from all three extrinsic muscles was not sufficient to precisely estimate the flexion angles of all finger joints. Precision of joint angle estimates could be as poor as +/- 18% of joint range of motion. However, length information from just two of the extrinsic muscles taken together could always provide information sufficient to estimate the location of the fingertip relative to the metacarpophalangeal joint within a reasonably small tolerance (+/- one-half thickness of the fingertip). Furthermore, it was possible to make this estimate without determining any of the finger joint angles. These results suggest that spindles in the extrinsic muscles alone can signal fingertip location, even though they may not provide sufficient information to estimate the individual joint angles that set the position of the fingertip. Thus, an absence of position sense for individual joints (the sense many studies have tried to measure) may say little about a sense of location of the tip of the finger.

Biomechanical Phenomena↗

PubMed1999

A three-dimensional kinematic model of the human long finger and the muscles that actuate it.

A kinematic model of the human long finger and the six muscles that actuate it is presented. The model transforms finger pose into estimates of muscle excursions and fingertip location. The effects of abduction/adduction about the metacarpo-phalangeal joint are accounted for, as are the effects of flexion of the three finger joints. A set of parameters are provided which approximate kinematics of the segments and muscles of a cadaver finger over the range of finger poses humans normally assume.

Biomechanical Phenomena↗

PubMed1999

Biomechanical model predicts directional tuning of spindles in finger muscles facilitates precision pinch and power grasp.

Humans have a sense of static limb position derived primarily from the output of secondary muscle spindle endings. The features of finger pose these proprioceptors signal best were predicted by singular value decomposition of a kinematic model of the human long finger and the six muscles that actuate it. The analysis indicated that muscle spindles signal the location of the fingertip with less error than they signal angles of individual finger joints. The fingertip displacements for which proprioceptors have greatest sensitivity were also predicted. These fingertip displacements seem to correspond to the fine positioning of an object pinched between the fingertip and distal phalanx of the thumb. The analysis also predicted the directions in which subjects can displace the fingertip most rapidly. The directions seem to correspond to rapid closure of precision pinch or power grasp.

Biomechanical Phenomena↗

PubMed1997

Recognition of temporally changing action potentials in multiunit neural recordings.

We present a method to iteratively train an artificial neural network (ANN) or other supervised pattern classifier in order to adaptively recognize and track temporally changing patterns. This method uses recently acquired data and the existing classifier to create new training sets, from which a new classifier is then trained. The procedure is repeated periodically using the most recently trained classifier. This scheme was evaluated by applying it to simulated situations that arise in chronic recordings of multiunit neural activity from peripheral nerves. The method was able to track the changes in these simulated chronic recordings and to provide better unit recognition rates than an unsupervised clustering method suited to this problem.

Action Potentials↗

PubMed1996

Closed-loop control of ankle position using muscle afferent feedback with functional neuromuscular stimulation.

This paper describes a closed-loop functional neuromuscular stimulation system that uses afferent neural activity from muscle spindle fibers as feedback for controlling position of the ankle joint. Ankle extension against a load was effected by neural stimulation through a dual channel intrafascicular electrode of a fascicle of the tibial nerve that innervated the gastrocnemius muscle. Ankle joint angle was estimated from recordings of tibialis anterior and lateral gastrocnemius spindle fiber activity made with dual channel intrafascicular electrodes. Experiments were conducted in neurally intact anesthetized cats and in unanesthetized decerebrate cats to demonstrate the feasibility of this system. The system was able to reach and maintain a fixed target ankle position in the presence of a varying external moment ranging in magnitude between 7.3 and 22 N-cm opposing the action of the ankle extensor, as well as track a sinusoidal target ankle position up to a frequency of 1 Hz in the presence of a constant magnitude 22- or 37-N-cm external moment.

Anesthesia, General↗

PubMed1994

Classification of action potentials in multi-unit intrafascicular recordings using neural network pattern-recognition techniques.

Neural network pattern-recognition techniques were applied to the problem of identifying the sources of action potentials in multi-unit neural recordings made from intrafascicular electrodes implanted in cats. The network was a three-layer connectionist machine that used digitized action potentials as input. On average, the network was able to reliably separate 6 or 7 units per recording. As the number of units present in the recording increased beyond this limit, the number separable by the network remained roughly constant. The results demonstrate the utility of neural networks for classifying neural activity in multi-unit recordings.

Action Potentials↗

PubMed1993

Biocompatibility of silicon-based electrode arrays implanted in feline cortical tissue.

The passive biocompatibility of silicon-based electrode arrays was studied in feline cortical tissue. Three types of arrays were used: uncoated, coated with polyimide, and coated with polyimide over an adhesion promoter. Fifteen arrays were implanted for 24 h to determine early tissue reaction to the implantation procedure, and twelve arrays were implanted for 6 months to determine structural and material biocompatibility. Edema and hemorrhage were present around the short-term implants, but involved less than 6% of the total area of the tissue covered by the array. With chronic implants, leukocytes were rarely present and macrophages were found around roughly one-third of the tracks. Remnants of foreign material from the electrodes could be identified in less than 10% of the tracks. Gliosis was found around all tracks, forming an annulus between 20 and 40 microns thick. A capsule was not always present, and never exceeded a thickness of 9 microns. These results suggest that the implantation procedure produces limited amounts of tissue damage, and that the arrays are biocompatible. However, the arrays insulated with polyimide over a primer had significantly greater involvement of macrophages, gliosis, and capsule formation than uncoated arrays and arrays insulated with polyimide without printer, perhaps indicating a reaction to aluminum oxide in the primer.

Animals↗

PubMed1993

Selective stimulation of peripheral nerve fibers using dual intrafascicular electrodes.

We have studied activation of nerve fibers by pairs of Pt-Ir wire electrodes implanted within single fascicles of the nerve innervating the gastrocnemius muscle in cats. The purpose of this study was to determine if these intrafascicular electrodes can activate nerve fibers in different fascicles independently of each other and if they can also be used to activate separate subsets of axonal populations within a single fascicle. The average overlap of activated nerve fiber populations was 5.5% between fascicles and 27% within a fascicle, indicating that such selective activation is possible with these electrodes.

Animals↗

PubMed1992

Simulation of a phosphene-based visual field: visual acuity in a pixelized vision system.

A visual prosthesis for the blind using electrical stimulation of the visual cortex will require the development of an array of electrodes. Passage of current through these electrodes is expected to create a visual image made up of a matrix of discrete phosphenes. The quality of the visual sense thus provided will be a function of many parameters, particularly the number of electrodes and their spacing. We are conducting a series of psychophysical experiments with a portable "phosphene" simulator to obtain estimates of suitable values for electrode number and spacing. The simulator consists of a small video camera and monitor worn by a normally sighted human subject. To simulate a discrete phosphene field, the monitor is masked by an opaque perforated film. The visual angle subtended by images from the masked monitor is 1.7 degrees or less, depending on the mask, and falls within the fovea of the subject. In the study presented here, we measured visual acuity as a function of the number of pixels and their spacing in the mask. Visual acuity was inversely proportional to pixel density, and trained subjects could achieve about 20/26 visual acuity with a 1024 pixel image. We conclude that 625 electrodes implanted in a 1 cm by 1 cm area near the foveal representation of the visual cortex should produce a phosphene image with a visual acuity of approximately 20/30. Such an acuity could provide useful restoration of functional vision for the profoundly blind.

Blindness↗

PubMed1992

An Automated Tactile Tester for evaluation of cutaneous sensibility.

The Automated Tactile Tester (ATT) is a computer-controlled device designed to measure patients' cutaneous perception of touch, vibration, temperature, and pain. The ATT provides repeatable and precise control of the amplitude, rate of application, and duration of stimuli. Threshold values for skin indentation (touch), high- and low-frequency vibration, pinprick (sharpness), warmth, and two-point discrimination were obtained with the ATT from the fingers of 62 normal subjects. Manual monofilament and two-point discrimination tests were also performed on the same subjects. All the tests with the ATT, except pinprick, showed a statistically significant increase in threshold with age. There were no significant differences attributable to the hand or digit tested or the sex of the subject. These data were used to derive age-adjusted criteria for normal sensory function in the glabrous skin of the fingers. Thresholds were found to remain within normal limits when these subjects were retested at various time intervals. We conclude that the ATT provides repeatable and reliable measurements of sensory function in the skin and has potential application in the diagnosis and evaluation of compression and other peripheral neuropathies.

Adolescent↗

PubMed1992

Evaluation of nerve compression with the Automated Tactile Tester.

The Automated Tactile Tester (ATT) was used to measure threshold values for trapezoidal skin indentation (light touch), low- and high-frequency vibration (50 and 150 Hz), pinprick (sharp-dull transition point), warming (temperature awareness), and two-point discrimination in 61 patients with symptoms of median nerve compression at the wrist. We compared these data with values obtained in the same patients with manual monofilament tests, manual two-point discrimination measurements, and electrophysiologic nerve conduction studies. The ATT detected abnormal sensation in 71% of the hands tested, nerve conduction velocity was abnormal in 44% of the cases, and the manual tests indicated abnormality in 42% of the hands. The most indicative single test among those included in the present study for detecting sensory abnormality in these patients was threshold to a 50 Hz vibration administered by the ATT. We conclude that the ATT is a sensitive tool for the diagnosis and evaluation of compressive peripheral neuropathy and may allow objective documentation in a higher percent of patients than do more traditional testing methods.

Adult↗

PubMed1991

Chronically implanted intrafascicular recording electrodes.

A newly designed intrafascicular electrode for chronic neural recording was studied by implanting 12 electrodes in the radial nerves of 6 cats for 6 months. Action potentials were monitored at specified intervals throughout the experiment. The number and size of the signals recorded suggest that this type of electrode provides information that is appropriate for feedback control in functional electrical stimulation (FES) systems. Histology of the nerve revealed that the implants are biocompatible and that little damage is caused by the presence of the electrode.

Action Potentials↗

PubMed1991

Muscle recruitment with intrafascicular electrodes.

We have studied muscle recruitment with Teflon-insulated, 25 microns diameter, Pt-Ir intrafasicular electrodes implanted in nerves innervating the gastrocnemius and soleus muscles of cats. The purpose of this study was to measure the performance of these bipolar electrodes, which had been designed to optimize their ability to record unit activity from peripheral nerves, as stimulating electrodes. Recruitment curves identified the optimal stimulus configuration as a biphasic rectangular pulse, with an interphase separation of about 500 microseconds and a duration of about 50 microseconds. The current required for a half-maximal twitch contraction was on the order of 50 microA. Current and charge densities needed for stimulation were well below levels believed to be safe for the tissue and electrode materials involved. When the spinal reflex pathway was interrupted by crushing the nerve, the force produced by a given stimulus changed in some cases, but not in others, implying that the spinal reflex contribution was not the same in all the implants. We conclude that intrafascicular recording electrodes are also a potentially valuable technology for functional neuromuscular stimulation, and warrant further development.

Animals↗

PubMed1991

Coding of vibrotactile stimulus frequency by Pacinian corpuscle afferents.

Psychophysical and electrophysiological techniques were used to study the encoding and processing of information about the frequency content of vibrational stimuli applied to glabrous skin in humans and cats. Trained human subjects were asked to discriminate changes in stimulus frequency and harmonic content for pairs of mono- and diharmonic sinusoidal vibrations applied to the fingertips. These psychophysical tests supplied data on what information is available to the central nervous system about the frequency components of vibratory stimuli. Electrophysiological recordings from nerves innervating the glabrous skin of the paw in cats during presentation of the same stimuli used in the psychophysical study provided data on how the peripheral nervous system encodes information about the physical parameters of cutaneous vibratory stimuli. The two sets of data indicated that the subjects derived information about the frequency of vibrotactile stimuli from the mean interval between action potentials in afferent nerve fibers activated by the stimulus.

Acoustic Stimulation↗

PubMed1983

Effects of chronic denervation in type I cutaneous mechanoreceptors (Haarscheiben).

Cutaneous type I receptor sites (Haarscheiben or tactile domes) were examined at intervals of 4 to 275 days after chronic denervation of the skin. The number of domes decreased with denervation time, and only about one-third of the domes originally present were still visible at 275 days. Most but not all of the Merkel cells from these domes were absent by 48 days, and the epithelium was significantly thinner than in nondenervated domes. Only a few of the examined domes appeared to be completely devoid of Merkel cells. It is concluded that after nerve transection, domes degenerate but do not always disappear entirely. The remnants may thus act as target sites which either attract regenerating type I nerve fibers or facilitate the formation of new dome structures after nerve regeneration.

Animals↗