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Biomedical subjects

A Hufschmidt

Publications and source records attributed to A Hufschmidt.

10 recordsLinked to original sources
PubMed1991

Contractile properties of lower leg muscles are normal in Parkinson's disease.

Contraction parameters (time-to-peak and half relaxation time), responses to short tetani and resistance to stretch were studied in the lower leg muscles of Parkinsonian patients and in age-matched controls. It was possible to distinguish between muscle groups of different fibre type composition in normal subjects on the basis of their contraction and relaxation velocities. These parameters, however, failed to show any abnormalities in the patient group. The only abnormal finding in Parkinsonian subjects was an increased resistance to passive stretch under static conditions, presumably elastic in origin. The results are evidence against a contribution of altered contractile properties to muscular rigidity in Parkinsonism.

Aged↗
PubMed1990

Statistical evaluation of slow brain potentials on the basis of single trials.

The amplitude of slow brain potentials is related to the complexity of the task performed. Therefore, the large potentials related to the processing of complex tasks (tracking, writing, mental acts) may be analysed statistically on a single trial basis. This opens up a range of new facilities for within-session tests of significance. Prior to evaluation, signals are passed through several automatic error compensation routines: smoothing, trend removal, subtraction of eye artifacts, rejection of trials with random artifacts. The shape of the task potential approximates well to a rectangular elevation of cortical negativity, with the mean amplitude over a pre-event baseline being used as the main statistical parameter. Non-parametric statistical tests are preferred for evaluation. Application of the method is demonstrated for a tracking paradigm.

Electroencephalography↗
PubMed1987

Short-range elasticity and resting tension of relaxed human lower leg muscles.

1. Tension responses of relaxed human lower leg muscles were recorded during applied triangular stretch cycles at a range of constant angular velocities which were below the threshold for inducing stretch reflexes. 2. Length-tension curves so obtained begin with a steep initial rising phase which is demonstrated to be equivalent to the 'short-range elastic component' (s.r.e.c.) observed in resting frog muscle (Hill, 1968). The s.r.e.c. develops only gradually following a stretch-release cycle. The time course can be described by a saturation function. It is suggested that this can be explained as resulting from a slow shift of the kinetic equilibrium between attached and detached cross-bridges towards attached cross-bridges. A kinetic model is presented, by which the sum of the cross-bridge formation and decay rate constants can be calculated from the saturation curves. 3. The recovery of resting tension following a stretch-release cycle proceeds at a significantly higher rate than the development of the s.r.e.c. Resting tension is also selectively influenced by passive movements of very small amplitude. This further suggests that the s.r.e.c. and resting tension are generated by different sources.

Ankle Joint↗
PubMed1985

Acoustic phenomena in the latent period of skeletal muscle: a simple method for in-vivo measurement of the electro-mechanic latency (EML).

An in-vivo method for the assessment of the latency of muscular contraction is presented. It is based on acoustic registration of muscular thickening by a microphone. It was found that the recorded sound wave is often preceded by a small wave of opposite polarity (flattening of the muscle belly) which is an acoustic correlate of the latency relaxation. Strong direct stimulation produced another small sound wave at the beginning of the latent period. The physiological significance of these findings is discussed.

Biomechanical Phenomena↗
PubMed1985

Chronic transformation of muscle in spasticity: a peripheral contribution to increased tone.

Mechanical properties of relaxed lower leg muscles were assessed by torque measurements during imposed constant velocity dorsiflexion-plantarflexion cycles. At low angular velocities, they exhibited an elastic and an energy-consuming, velocity-independent (plastic) resistance. In most patients with long-standing spasticity, both of these were enhanced. The results support the hypothesis of secondary structural changes of muscles in spasticity.

Adult↗
PubMed1981

Treatment of acute inflammatory polyneuropathy.

Most patients with acute inflammatory polyneuropathy (AIP) recover spontaneously, but the time course of the illness is unpredictable so that the results of treatment are difficult to assess. Three decades of retrospective reports of steroid treatment fail to demonstrate any striking beneficial effect. In a randomized trial of prednisolone, starting dose 60 mg daily, 21 treated patients improved more slowly than 19 untreated patients. By contrast, in rats immunized with bovine nerve root myelin, prednisolone at 10 mg/kg reduced the severity and duration of experimental allergic neuritis (EAN), the putative animal model for AIP. This discrepancy might reflect the greater difficulty of clinical as opposed to animal therapeutic trials or indicate that EAN is not the appropriate model for the human disease. Immunosuppressive drugs, plasmapheresis and other agents have also been employed, but their efficacy cannot be decided from the available case report. The role of similar agents in chronic progressive and relapsing inflammatory neuropathy cannot yet be resolved, but in some patients steroids do appear to be valuable.

Adrenocorticotropic Hormone↗
PubMed1979

Quantitative analysis of stance in late cortical cerebellar atrophy of the anterior lobe and other forms of cerebellar ataxia.

(1) Methods have been developed to measure, analyse and document postural sway. The main parameters studied were: average sway amplitude; length of the sway path per unit time; sway direction and sway position histograms; and the frequency spectra of the antero-posterior and lateral sway components. (2) Postural ataxia was quantitatively studied in three groups of patients with cerebellar lesions: (a) late atrophy of the anterior lobe, (b) tumours of the cerebellar hemisphere and (c) tumours within the vestibulo-cerebellum. Characteristic differences were found. (3) Patients with anterior lobe lesion show a specific 3 Hz postural tremor in the antero-posterior direction. The tremor can be evoked by sudden destabilization in incipient cases. Less characteristic and smaller in amplitude is a mainly lateral sway component with an average frequency of 0.5 Hz. This is also seen in cases with spinal ataxia. Visual stabilization of posture is frequently preserved. Its amount does not correlate with general instability of posture. Tremor and characteristically exaggerated intersegmental responses between head, trunk, hips and legs are interpreted as the consequence of hyper-excitability of postural reflexes in these patients. (4) Patients with lesions of the hemispheres show only slight postural instability without directional preference. Their sway parameters with eyes open are within the 2 sigma range of normals and there is no significant difference from normals in these parameters even when the eyes are closed. Therefore these patients cannot be distinguished from normals by means of their platform recordings. (5) Two patients with posterior vermal and flocculo-nodular lesions were very unstable without preferred axis or frequency of instability. In contrast to the anterior lobe group the instability was characterized by the absence of intersegmental movements.

Adult↗
PubMedDate not supplied

Automatic recognition of random artifacts in recordings of slow brain potentials: a bias-free method.

A method for computerized recognition of random artifacts in recordings of slow brain potentials is presented. It is based on systematic comparison of the shape of single trial EEG segments with all other trials obtained in the same experiment. This is possible because, in contrast to short-latency event related potentials, a plateau of EEG negativity during complex tasks can often be detected in single trails. After linear trend removal and subtraction of EOG artifacts, similarity of pairs of single trials is established by point-to-point linear regression analysis, the total score of a trial being defined as the mean correlation coefficient (R) resulting from comparison to all other trials. Selection is then performed by setting a critical value for R, admitting for averaging only trials with a mean correlation coefficient above the critical value. An example is given in which the method is applied to recordings of slow brain potentials during a manual tracking task.

Brain↗