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Biomedical subjects

M Voigt

Publications and source records attributed to M Voigt.

At least 55 records · Page 3Linked to original sources
PubMed1999

Prefabrication of bilaminar-epithelialized composite flap with tissue expander and cultured keratinocytes.

This study investigated the feasibility of prefabrication of a bilaminar-epithelialized flap by using a tissue expander and cultured keratinocytes, for reconstruction of perforate defects in the oral cavity and upper aerodigestive tract. In each of six rats, a 10-ml volume expander was implanted under the inferior epigastric flap and a thin silicon catheter was introduced into periexpander space. Seven days after implantation, 10 x 10(6) cultured keratinocytes, isolated from inbred donor rats, were suspended in fibrin glue and injected into the periexpander space through the catheter (n = 4 of 6). The expansion was started immediately after cell inoculation and lasted at least 3 weeks at the speed of 2 to 3 ml every 5 to 7 days. At the end of expansion, the periexpander space was opened and the capsule around the tissue expander was found to be covered completely with a neoepithelium. Thus, a bilaminar-epithelialized flap based on femoral vessels was elevated and successfully transferred to cover the excisional perforate defect in the oral cavity with the neoepithelial side as inner lining. All flaps treated with 10 x 10(6) cultured keratinocytes survived with complete wound healing during a 1-week follow-up (n = 4 of 6). Both macroscopic and histologic findings demonstrated that a bilaminar-epithelialized composite flap can be fabricated by using a tissue expander and keratinocyte-fibrin glue suspension.

Animals↗
PubMed1999

Choice of jumping strategy in two standard jumps, squat and countermovement jump--effect of training background or inherited preference?

Six male subjects, three professional ballet dancers and three elite volleyball players, performed maximal vertical jumps from 1) a static preparatory position (squat jump), 2) starting with a countermovement (countermovement jump) and 3) a specific jump for ballet and for volleyball, respectively. The jumps were recorded on highspeed film (500 Hz) combined with registration of ground reaction forces, and net joint moments were calculated by inverse dynamics. The purpose was to investigate the choice of strategy in two standard jumps, squat jump and countermovement jump. The volleyball jump was performed with a sequential strategy and the ballet jump was performed with a simultaneous strategy. In the two standard jumps, the choice of strategy was individual and not related to training background. This was additionally confirmed in a test of seven ballet dancers and seven volleyball players.

Biomechanical Phenomena↗
PubMed1999

[Free microsurgical flap-plasty in reconstructive therapy of diabetic foot ulcer].

The diabetic foot ulcer is a significant clinical problem often resulting in frustranous conservative treatment or early amputation. In certain cases transfer of well vascularized tissue can improve wound healing and lead to a length-spearing therapy. In this study the concept of microsurgical tissue transfer in the treatment of diabetic foot ulcers is introduced. Following a radical debridement and, if necessary a atypical length-spearing amputation the wound is covered by a free transplanted muscle flap followed by a split-thickness skin graft. In six patients treated with this procedure the extremity could be saved. The perioperative mortality was 0%, average hospitalization was 47.6 days. One flap was lost, two vascular revision were necessary. Several necrectomies and skin grafts were performed and one donor side seroma was drained. One hernia was observed after free rectus abdominus transfer. Compared to conservative treatment or amputation this concept leads to a length-spearing therapy and can increase success rates of rehabilitation and quality of life.

Amputation, Surgical↗
PubMed1999

[Keratinocyte transplantation and tissue engineering. New approaches in treatment of chronic wounds].

Cultured keratinocytes have been used for the treatment of extensive burns since disease lethality is reduced. Consequently, the treatment of chronic wounds with keratinocytes may be promising. Cell culture technology allows to expand keratinocytes up to 6000-fold in vitro after taking a single biopsy from patient. Today the transplantation of these in vitro cultured keratinocytes in different modifications is an established clinical treatment regimen for therapy of extensive wounds. For example, keratinocyte-fibrin-glue-suspensions, mainly consisting of proliferative epidermal basal cells, were used for the treatment of burns in experimental and clinical settings to bypass the disadvantages of conventional sheet grafts. Other approaches in tissue engineering for wound healing aim at the (epi-)dermal repair by the combination of allodermis and biomaterials, i.e. collagen-sponges and microspheres. Due to most recent efforts in keratinocyte culture techniques, developments in tissue engineering, research for novel biomaterials and gene therapy, therapy of chronic wounds may prove to be more efficient. Furthermore, from the socio-economical point of view, overall costs for treatment of chronic wounds could be reduced.

Cell Division↗
PubMed1998

Non-noxious stimulation of the glenohumeral joint capsule elicits strong inhibition of active shoulder muscles in conscious human subjects.

Information about the function of joint afferents in humans is scarce. Therefore, we investigated the influence of non-noxious electrical stimulation of the glenohumeral joint capsule on the activity of shoulder muscles in conscious human subjects. Stimulation electrodes were inserted in the joint capsule during arthroscopy. Only when the anterior inferior part of the capsule including the glenohumeral ligament was stimulated a strong and rather long latent general inhibition in voluntarily activated shoulder muscles was observed (average latency and duration: 33 ms and 76 ms, respectively). The inhibition was followed by an excitation and a few but inconsistent oscillations in the muscle activity. The results suggests a potent proprioceptive feedback pathway for the motor control of the human shoulder joint. However, further investigations are needed to clarify the involvement of several possible afferent pathways.

Adult↗
PubMed1998

The H-reflex in the passive human soleus muscle is modulated faster than predicted from post-activation depression.

The purpose of the present study was to investigate the influence of afferent activity (mainly homonymous Ia-afferent activity) on the modulation (post-activation depression) of the soleus H-reflex during isolated and passive sinusoidal ankle joint rotations at a speed and amplitude comparable to slow walking. The H-reflex modulation was measured in the relaxed soleus muscle on human subjects during different imposed patterns of 20 degrees haversine ankle joint rotations (0.5-0.6 Hz) while they were sitting comfortably in a chair. Eighteen healthy males and four male patients with clinically complete spinal cord lesion above the soleus motoneuron pool participated in the study. During a single dorsi-plantar flexion rotation the H-reflex was depressed to 27+/-7% (mean+/-S.E.M.) of the initial level within 600 ms. The course of this depression was reversed when the dorsi-flexion velocity started to decrease. At the end of the dorsi-flexion movement the depression was already relieved to a level of 73+/-6% of the initial level. The H-reflex returned more slowly to the initial level within 2 s after the end of the movement cycle. During two consecutive ankle joint rotations and continuous ankle joint rotations both at 0.5 Hz the H-reflex was modulated but also generally depressed while the movement was imposed. The reflex only returned to the reference level after the movements were stopped. These observations indicate the action of a fast and a slow mechanism in the post-activation depression of the soleus H-reflex. The H-reflex modulations observed in the spinal cord injured patients were comparable to the reflex modulations observed in the healthy subjects, except the depressions were smaller. This suggests that a major part of the amplitude of the H-reflex modulation observed in healthy subjects was caused by peripheral and spinal influences. The fast 500 ms recovery of the H-reflex had a time course comparable to presynaptic inhibition. The slow 2 s recovery after the end of a given imposed movement may be explained by a change in the probability of transmitter release from the homonymous soleus Ia-afferent synaptic terminals after repeated activations.

Adult↗
PubMed1998

Subjective, physiological and biomechanical responses to prolonged manual work performed standing on hard and soft surfaces.

The aim of this laboratory study was to examine the subjective, physiological and biomechanical responses to prolonged light repetitive manual work during standing on soft (polyurethane standard mat) and hard (aluminum casting) surfaces. The subjects stood on the hard (10 subjects) and on the soft surfaces (11 subjects) for 2 h. Intensity of unpleasantness, shank circumference, electromyograph (EMG) activities from the right soleus and tibialis anterior muscles, mean amplitude and total angular displacement around the left and right ankle in the saggital plane, centre of pressure (CoP) displacement in the frontal and saggital planes, calf surface temperature, and pain intensity in experimentally induced muscle pain were recorded. Maximal voluntary contraction and fatigue tests were performed before and after the 2 h experiment. Standing on a soft surface caused a lower intensity of unpleasantness. During standing on a hard surface compared to a soft one the results showed an enhanced swelling of the shank, an increased EMG activity (right soleus muscle) of the lower leg, a greater amplitude and total angular displacement, and a larger CoP displacement in the frontal plane. Indications of more pronounced muscle fatigue while standing on the hard surface were also noticed. After 105 min, experimental muscle pain was elicited by injecting hypertonic saline. The intensity of the induced pain was lower when standing on the soft surface. Amplitude, angular distance and CoP displacement showed a tendency to be greater after injection of the hypertonic saline. It was found that the experimentally induced pain influenced postural activity, underlining central interactions between proprioceptors and nociceptors. The results highlighted a higher feeling of comfort when standing on the soft surface. In addition, postural activity was lower when standing on the soft surface, but the activity was sufficient to prevent swelling of the lower legs.

Adult↗
PubMed1998

Changes in the excitability of soleus muscle short latency stretch reflexes during human hopping after 4 weeks of hopping training.

Changes in the excitability of the human triceps surae muscle short latency stretch reflexes were investigated in six male subjects before and after 4 weeks of progressive two-legged hopping training. During the measurements the subjects performed 2-Hz hopping with: preferred contact time (PCT) and short contact time. The following reflex parameters were examined before and after the training period: the soleus muscle (SOL) Hoffmann-reflex (H-reflex) at rest and during hopping, the short latency electromyogram (EMG) components of the movement induced stretch reflex (MSR) in SOL and medial gastrocnemius muscle (MG), and the EMG amplitude of the SOL and MG tendon reflexes (T-reflexes) elicited at rest. The main results can be summarized as follows: the SOL T-reflex had increased by about 28% (P < 0.05) after training while the MG T-reflex was unchanged; the SOL MSR (always evident) and the MG MSR (when observable) did not change in amplitude with training, and before training the SOL H-reflex in both hopping situations was significantly depressed to about 40% of the reference value at standing rest (P < 0.05). After training the H-reflex during PCT hopping was no longer depressed. As the value of the measured mechanical parameters (the total work rate, joint angular velocity and the ankle joint work rate) was unchanged after training in both hopping situations, the reflex changes observed could not be ascribed to changes in the movement pattern. To explain the observed changes, hypotheses of changes in the excitability of the stretch reflex caused by the training were taken into consideration and discussed.

Adult↗
PubMed1998

Sensory manifestations in experimental and work-related chronic neck-shoulder pain.

Little is known about the mechanisms leading to chronic neck-shoulder musculo-skeletal disorders. The aim of the present study was to investigate and compare the sensory manifestations of experimental or chronic neck-shoulder pain under controlled, low load, repetitive work. Experimental and clinical experiments were carried out. In Experiment 1, experimental muscle pain was induced in healthy subjects by intramuscular injection of hypertonic saline in the trapezius (n = 10) and infraspinatus (n = 10) muscles. Experiment 2 was performed on 18 workers with (n = 12) and without (n = 6) chronic neck-shoulder pain. Sensory assessments were performed before and/or after a session of controlled, low load, repetitive work. The pain intensity was assessed by a visual analogue scale. The pain quality and location(s) were monitored together with pressure-pain thresholds. Moderate-to-strong deep pain intensity was experienced in the experimental and clinical part of the working session (six patients out of 12). The verbal descriptors used to describe the experimental or chronic pain qualities were partially similar, i.e. first of all verbal descriptors from the sensory class. The patterns of local and referred pain characteristics were similar (around the shoulder girdle), but it is difficult to evoke pain in extensive areas with hypertonic saline. Patients exhibited hypersensitivity or tenderness to pressure stimuli in both sides of the upper body, i.e. in the trapezius, supraspinatus, infraspinatus and pectoralis major muscles (p < 0.05). This hypersensitivity was only seen at the referred pain site in the healthy volunteers exposed to infraspinatus experimental muscle pain. In conclusion, the present study demonstrated similar sensory manifestations in the experimental and clinical neck-shoulder pain experiments. The presented experimental model can most likely be used to investigate the underlying pain mechanisms involved in work-related chronic musculoskeletal pain.

Journal Article↗
PubMed1998

Modulation of short latency stretch reflexes during human hopping.

To gain insight into central and peripheral reflex control mechanisms in moving humans we have investigated short latency stretch reflex activity in m. triceps surae during two legged hopping. The objectives were: (1) to compare movement induced short latency stretch reflexes in soleus and medial gastrocnemius (MG) muscles, (2) to determine the relationship between the size of these reflexes and the muscle spindle stretch velocities, and (3) to compare the size of the movement induced short latency stretch reflexes and the H-reflexes simultaneously. Six well-trained healthy male subjects participated and they hopped at three different work rates. Surface electromyogram (EMG) and H-reflexes were recorded during hopping. Muscle spindle length changes were estimated as the difference between estimated origin-to-insertion length changes and tendon length changes. The important findings were that during hopping: (1) movement induced short latency stretch reflexes were observed consistently in soleus, (2) the EMG amplitude of this stretch reflex was negatively correlated with the estimated peak muscle spindle stretch velocity (rs = -0.52, P < 0.02), and (3) the amplitude of the soleus H-reflex at touchdown did not change in parallel with the stretch reflex. The negative correlation observed between the stretch reflex and the estimated peak muscle spindle stretch velocity in soleus is opposite to the basic velocity sensitive behaviour of stretch reflexes mechanically elicited during resting conditions. Possible control mechanisms are discussed. Additionally, muscle spindle length changes estimated from changes in the skeletal movements (joint angles) should be inferred cautiously because of tendon compliance, especially at high tendon forces.

Adult↗
PubMed1998

A model to examine the validity of the 6-month abstinence criterion for liver transplantation.

Six months of abstinence from alcohol is a commonly used criterion for liver transplantation eligibility for patients with alcoholic cirrhosis. There is limited evidence to document the validity of this criterion with regard to risk of alcoholism relapse. Ninety-one patients with alcoholic cirrhosis were interviewed for relapse risk using the High Risk Alcoholism Relapse (HRAR) Scale. The HRAR model can be used to predict relapse risk independent of duration of sobriety and therefore can be used to examine the validity of the 6 months of abstinence criteria in this clinical population. The two methods demonstrated poor to fair agreement. Agreement was highest with a cutoff allowing a 5% 6-month relapse risk when 79% agreement (c = 0.56) was demonstrated between the two methods. Using the 6-month abstinence criterion alone disallows a significant number of candidates who have a low relapse risk based on their HRAR score. The validity of the 6-month abstinence criterion is supported somewhat by comparison with the HRAR model. However, use of the 6-month abstinence criterion alone forces a significant number of patients with a low relapse risk by HRAR to wait for transplant listing. A relapse risk model based on an estimate of alcoholism severity in addition to duration of sobriety may more accurately select patients who are most likely to benefit from liver transplantation.

Adult↗
PubMed1998

[Biological wound tissue glue systems in wound healing].

Tissue engineering relies on in vitro cell culture, biocompatible matrix materials and genetic engineering with growth and differentiation factors for guided tissue regeneration. Biogenic or semisynthetic biomaterials are an alternative as cell carriers: To circumvent the disadvantages of conventional keratinocyte sheet grafts, a keratinocyte fibrin glue suspension KFGS (H. W. Kaiser et al., Burns 20: 23, 1994), which mainly consists of epidermal stem cells, has been tested experimentally in nude mice and clinically in extensive burns and chronic wounds. In the "in vivo culture" on the wound, the non-confluent keratinocytes form a differentiated epithelium within days. Current research aims at guided dermal regeneration by a combination with allodermis or biomaterials (collagen sponges like TissueFaszie, Microspheres etc.). Fibrin glue (Tissuecol) has also been tested successfully as matrix for other cells like chondrocytes and fibroblasts transfected with growth factor genes (EGF/KGF).

Animals↗
PubMed1998

[Surgically-induced angiogenesis as basic principle in treatment ov hypovascularized wounds--the nutritive flap].

Chronic wounds of the lower extremity as a result of diabetes, arteriosclerosis and microangiopathy are of significant clinical relevance, as they result in immobilization, extended hospitalization and cost-intensive treatment. Via transfer of well-vascularized tissue onto chronic wounds as a free transplanted muscle flap, if necessary connected to a venous bypass, angiogenesis is induced and wound healing improved. This concept leads to nonamputational therapy.

Arteriosclerosis↗
PubMed1997

Mechanisms contributing to different joint moments observed during human walking.

The present study investigated factors that contribute to the formation of a previously reported knee joint flexor moment during the stance phase of walking. Contradictory results have been reported on this flexor moment, which some but not all individuals exhibit. Seven healthy male subjects were high speed filmed while walking across a force platform, and EMG recordings were obtained from five leg muscles. To investigate segment interactions, net joint moments about the ankle, knee and hip joint were calculated by inverse dynamics and each term in the equation used for the moment calculation was evaluated during the time-course of the step cycle. To test the hypothesis that net joint moments are balanced by an external moment formed by the resulting ground reaction vector multiplied by the perpendicular distance to the actual joint, external moment arms were calculated by the floor reaction force vector approach (FRFV). Contrasting two subjects with different net joint moments about the knee and ankle joint revealed that the knee joint flexor moment could not be explained by an opposite external moment. The external moments were calculated by a simplified method (FRFV) in which the point of force application is incorrect for joints above the ankle joint. However, at the ankle joint the net joint moment was always opposed by an external moment of opposite polarity. A detailed examination of the equation used for the net joint moment calculation showed that a knee joint flexor moment can be caused directly by a large plantar flexor moment about the ankle joint. For example. the soleus muscle can pull the tibia and generate an extensor moment about the knee joint, which in turn has to be opposed by a knee flexor moment from the hamstring muscles. Otherwise the desired joint angles cannot be obtained during human walking. It is therefore suggested that the kinematics regarding how the foot is placed on the ground may influence the net ankle joint moment, while the moment patterns about the knee and hip joint are determined by segment interaction and the requirements for controlling the direction of the resulting ground reaction vector. In vertical jumping it is advantageous to generate extensor moments about the knee and hip joint simultaneously, while in horizontal locomotion this would result in inefficient vertical movements.

Adult↗
PubMed1997

Hepatitis C virus infection rate in volunteer blood donors from the Western Cape--comparison of screening tests and PCR.

INTRODUCTION: Hepatitis C virus (HCV) antibody seroprevalence studies overestimate the true infection rate. No data exist on the incidence of HCV or its clinical features in blood donors of sub-Saharan Africa. AIMS: To establish the true incidence of HCV infection in volunteer blood donors in the Western Cape, and compare risk factors and clinical and biochemical features of viraemic and non-viraemic subjects. METHODS: All donors attending the Western Province Blood Transfusion Service between December 1992 and August 1994 were screened prospectively for anti-HCV using the Abbott second-generation assay. Positive donors were evaluated clinically and biochemically. Their sera were examined for HCV-RNA by the polymerase chain reaction (PCR). RESULTS: Of 66314 donors screened, 275 (0.41%) were anti-HCV-positive. Of these 13.6% were PCR-positive (0.056% of all donors). PCR-positive patients had more risk factors for HCV acquisition (P < 0.01), symptoms of hepatitis (P = 0.02) and clinical signs of liver disease (P = 0.05) and higher alanine (P < 0.0001) and aspartate aminotransferase levels (P < 0.0001) than PCR-negative donors. However, clinical and biochemical features did not discriminate adequately between PCR-positive and negative donors. Liver biopsies performed in 9 of 13 PCR-positive cases showed mild inflammation, but no cirrhosis.

Blood Donors↗
PubMed1996

[Analysis of a 1992 birth sample in Germany. 1: New percentile values of the body weight of newborn infants].

14 of the 16 German Federal "Lands" ("Bundesländer") participated in the first assessment in perinatal medicine in reunited Germany. A total of stored data representing 563,480 single births were used to calculate percentile values for birth weight, size (length) at birth and circumference of the head from the 23rd week of pregnancy, presented in tabulated and graphic form. Only data of German Population were evaluated; no other selective criteria were applied. The percentile values were calculated via the cumulative frequencies. Besides the conventional somatic data, the length-related birth weight percentile values were also stated, since these enable a classification more in accordance with the fetal development of the newborn. A cursory comparison with other German standard value determinations and with Lubchenco's curve is carried out.

Birth Weight↗
PubMed1995

Mechanical and muscular factors influencing the performance in maximal vertical jumping after different prestretch loads.

The objective of the present work was to study the interaction between the tendon elasticity, the muscle activation-loading dynamics, specific actions of the biarticular muscles, preloading and jumping performance during maximal vertical jumping. Six male expert jumpers participated in the study. They performed maximal vertical jumps with five different preloads. The kinematics and dynamics of the jumping movements were analysed from force plate and high speed film recordings. The amount of elastic energy stored in the tendons of the leg extensor muscles was calculated by a generalised tendon model, and the muscle coordination was analysed by surface EMG. The best jumping performances were achieved in the jumps with low preloads (counter movement jumps and drop jumps from 0.3 m). A considerable amount of the energy imposed on the legs by prestretch loading was stored in the tendons (26 +/- 3%), but the increased performance could not be explained by a contribution of elastic energy to the positive work performed during the push off. During the preloading, the involved muscles were activated at the onset of the loading. Slow prestretches at the onset of muscle activation under relatively low average stretch loads, as observed during counter movement jumps and drop jumps from 0.3 m, prevented excessive stretching of the muscle fibres in relation to the tendon length changes. This consequently conserved the potential of the muscle fibres to produce positive work during the following muscle-tendon shortening in concert with the release of the tendon strain energy. A significant increase in the activity of m. rectus femoris between jumps with and without prestretch indicated a pronounced action of m. rectus femoris in a transport of mechanical energy produced by the proximal monoarticular m. gluteus maximus at the hip to the knee and thereby enhanced the transformation of rotational joint work to translational work on the mass centre of the body. The changes in muscle activity were reflected in the net muscle powers. Vertical jumping is like most movements constrained by the intended direction of the movement. The movements of the body segments during the prestretches induced a forward rotation and during the take off, a backward rotation of the body. A reciprocal shift in the activities of the biarticular m. rectus femoris and m. semitendinosus indicated that these rotations were counteracted by changes in the direction of the resultant ground reaction vector controlled by these muscles.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗