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Biomedical subjects

W Kroll

Publications and source records attributed to W Kroll.

At least 19 recordsLinked to original sources
PubMed2000

Enzyme immunoassay for the measurement of human tenascin-C on the Bayer Immuno 1 analyzer.

OBJECTIVES: To evaluate a new tenascin-C assay performed on the Bayer Immuno 1 system. DESIGN AND METHODS: The precision was measured using three levels of serum pools. Linearity was tested by diluting patient serum samples containing high tenascin-C concentrations, and the minimal detectable concentration determined by repetitive analysis of the zero calibrator. Preliminary reference intervals were determined by testing serum samples from 220 healthy individuals. Biovariability was estimated in a cohort of 20 apparently healthy subjects over 18 days. The levels of tenascin-C in patients with different liver diseases was tested. RESULTS: The detection limit was 2 ng/mL. At concentrations ranging from 325 to 1957 ng/mL the assay demonstrated within-run and between-run CVs ranging from 4% to 3.6% and 8.4% to 6.7%, respectively. Dilutions of sera were linear and parallel to the standard curve with recoveries ranging from 97% to 100%. The reference interval (central 95% interval) for tenascin-C in serum of healthy adults was 199-906 ng/mL. The variability study yielded an analytical variability, CV(A), of 1.8%; a within-subject variability, CV(I), of 11.7%; and a between-subject variability, CV(G), of 39.3%. Tenascin-C concentrations in sera of liver disease patients were significantly increased. CONCLUSIONS: The novel assay provides a rapid and reliable procedure for the determination of tenascin-C levels in human sera.

Adult↗
PubMed1999

Neuromuscular control mechanisms and strategy in arm movements of attempted supranormal speed.

Rapid, goal-directed elbow flexion movements were examined under interacting conditions of inertial loading and resistance to movement initiation. The resistance ceased when movement began, resulting in quick release movements. Inertial load slowed the movement and lengthened the agonist and antagonist electromyographic (EMG) burst durations. The quick release resulted in larger accelerations but only minimal changes in peak velocity. Most aspects of the triphasic EMG pattern were little affected by the quick release, but the build up of agonist EMG and the corresponding rate of static force development differed markedly between load and quick release conditions. These and other data suggest that the specific pattern of agonist muscle activation is set according to neuromuscular constraints of the antagonist muscle and the expectation of movement dynamics.

Acceleration↗
PubMed1998

Epitope-specific monoclonal antibodies against human C-terminal procollagen alpha1(III)-propeptide.

We have generated monoclonal antibodies against recombinant C-terminal human procollagen alpha1(III) propeptide (PIIICP), produced in E. coli in high yields. The monoclonal antibodies were screened for epitope specificity using recombinant truncated PIIICP. Several antibodies were identified which recognized different regions of the PIIICP molecule. The ability of the antibodies to detect PIIICP antigens in human cell line lysates and supernatants was demonstrated. As PIIICP antigens are a key marker of extracellular matrix metabolism, the monoclonal antibodies described here should be of value for clinical and basic research.

Antibodies, Monoclonal↗
PubMed1992

[An aortopulmonary shunt after a knife wound].

An extensive hemopneumothorax developed in a 23-year-old man after having been knifed in the region of the left nipple. After general surgical care a Bülau suction drain was inserted. Cardiological examination became necessary a week later when a chest X-ray film demonstrated an enlarged cardiac silhouette. Echocardiography revealed pericardial effusion (about 600 ml) which was removed by pericardial aspiration. Cross-sectional and colour Doppler echocardiography showed a shunt between the aorta and right ventricular outflow tract at the origin of the pulmonary artery. At surgery a fistula between the root of the aorta and the pulmonary artery was identified (the posterior sinus near the anulus was nearly completely detached). The fistula was closed and the pulmonary valve reconstructed. The early and late postoperative course was unremarkable.

Adult↗
PubMed1991

[Young patient with left brain infarct and transient right sided hemiparesis in cardiac papillary fibroelastoma].

This is a case report of a 25-year-old female with recurrent episodes of transient cerebral ischemia accompanied by transient hemiparesis. Cardiac ultrasound examination revealed a small left-ventricular tumor located between the chordae tendineae. The echocardiographic finding was subsequently confirmed by surgery. The entire tumor was removed and the mitral valve remained intact. Due to the histological and immunohistochemical findings a papillary fibroelastoma was diagnosed. The early and late postoperative course was without event.

Adult↗
PubMed1989

A flow cytometric assay for the determination of cell proliferation with a monoclonal antibody directed against DNA-methyltransferase.

The enzyme DNA-methyltransferase is responsible for the methylation of a newly synthesized DNA-strand. A monoclonal antibody directed against DNA-methyltransferase was used to determine cell proliferation by means of flow cytometry. The reactivity of DNA-methyltransferase antibody was compared with the known proliferation markers transferrin-receptor and Ki67. All three methods showed comparable reactivity with the erythroblastic cell line K562 (86%, 81%, 76% respectively). In a second set of experiments peripheral blood mononuclear cells were stimulated with phytohaemagglutinin; in three experiments, a mean of 63% of the cells reacted with DNA-methyltransferase antibody after 72 h of culture as compared to a mean of 6% in the case of unstimulated control cells. HL60 cells were incubated with DMSO and harvested on day 5 of culture. The results obtained show that in differentiated cells the fraction positive with DNA-methyltransferase antibody decreased to levels below 10%. It is concluded that the technique described is a fast and easy method for the flow cytometric determination of cellular proliferation.

Antibodies, Monoclonal↗
PubMed1984

Modification of the BrdU/H33258 technique for flow cytometry based on the pH-dependence of the fluorescence of H33258 stained DNA.

A simple analytical method is described for the evaluation of cell cycle progression data by modification of the BrdU/H33258 technique for flow cytometry. This procedure allows to obtain quenched and unquenched DNA-histograms of cells containing BrdU-substituted DNA by staining with one dye only, namely H33258. Quenched histograms are obtained at pH = 7 and give information about how far cells have passed the cell cycle since the beginning of the incubation. The unquenched ones obtained at pH less than or equal to 4 of the staining solution give information about the actual position of the cells in the cell cycle.

Animals↗
PubMed1983

On the stability of delay equation models of simple human stretch reflexes.

Human stretch reflexes (SRs) are often too weak and ineffectual to provide adequate postural regulation or rhythmic movement boosting (e.g. in ankle pushoff at the end of stance phase in fast running). Recent improvements in methods of artificially enhancing skeletomotor responses, especially in therapeutic regimens, should not be widely employed until the clonus-resisting stability properties of SRs are better understood. We formulate an idealized linear servo model of a segmentally-mediated SR system which includes the often ignored electromechanical coupling delay. For typical closed-loop (delay/gain) ratios, the model is shown to be unstable for all values of loop gain when operating as a position servo, but maximally stable when operating as a velocity servo. We claim that the velocity servo or more of its nonlinear relatives is a better model for some well studied SRs than, e.g., Houk's stiff muscle hypothesis. We also present evidence that even feeble and quickly saturating monosynaptic postural servos are always unstable if operated as pure position regulators.

Humans↗
PubMed1982

An EMG-level muscle model for a fast arm movement to target.

A model of human muscle action is presented for a maximally fast, large-amplitude forearm movement to target. The inputs to the model are approximately the biceps and triceps EMG envelopes over a single movement. The model's output gives the corresponding displacement angle of the forearm about a fixed elbow position as a function of time. The idea of the model is to conceive of both EMG input drives as successions of millisecond input pulses, with each pulse resulting in a muscle tension twitch. Every twitch is amplitude-scaled, parametrically-shaped, and duration-limited as a function of the muscle's contractile history thus far in the movement. The muscle tension at any time t is the sum of the residual tension levels of all twitches begun before t. The model was developed and tested with special reference to two subjects: one, according to the model dynamics, was a comparatively slow-twitch type and the other modelled as a fast-twitch type. Good agreement was found between model output and subject response data whenever the subject's EMG's were "synchronous". The model can be used to characterize each subject's responses by a suite of twitch characteristics. This will enable us to check the accepted but now suspect correlation between muscle biopsy- and performance-determined muscle twitch type.

Animals↗
PubMed1982

Isokinetic strength, endurance, and fiber type composition in elite American paddlers.

Muscle fiber type and isokinetic strength and fatigue were examined in nine highly trained canoe and kayak paddlers. Needle biopsies were taken from the right vastus lateralis and biceps brachii muscles and the samples stained for myofibrillar ATPase. Baseline elbow flexion and knee extension isometric (0 degrees . s-1) and isokinetic (60 degrees . s-1 or 1.05 rad . s-1 and 180 degrees . s-1 or 3.14 rad . s-1) peak torques were determined. Each subject then performed two series of 50 isokinetic contractions at an angular velocity of 180 degrees . s-1: elbow flexion and knee extension series, separated by 3 h. The percentage of slow twitch fibers was similar in the biceps brachii (43.9%) and the vastus lateralis (43.3%). The fast twitch/slow twitch fiber area ratio was significantly higher in the more highly trained biceps brachii due to larger FT fibers. No relationship was found between fiber type composition and baseline peak torques or decline in peak torque due to the fatigue regimens. Baseline peak torque correlated with initial strength level, body weight, and limb girth. The results suggested that for these paddlers muscle strength and the decline in strength induced by repetitive isokinetic contractions were more dependent on characteristics of body size than on fiber type composition.

Adult↗
PubMed1982

The relationship of serum creatine kinase, fiber type, and isometric exercise.

In 11 untrained subjects (mean age = 22.5 yr) serum creatine kinase (CK) was measured before and after two types of knee extension exercise regimens. One regimen consisted of 35 10-s maximal isometric contractions separated by a 20-s rest (10:20). This regimen provided adequate recovery time between trials so that strength loss amounted to only 23.4% over the 35 contractions. The other exercise regimen consisted of the same 35 maximal isometric contractions but separated by 5 s between trials (10:5), resulting in a 54.6% strength loss. Muscle fiber type was also determined to assess the relationship of fiber type with serum CK and strength loss. The fast-twitch (FT)/slow-twitch (ST) area ratio correlated with resting CK. Baseline strength correlated with strength loss over the 10:5 condition but not with strength loss over the 10:20 condition suggesting different mechanisms responsible for strength decline for the two exercise conditions. Although a greater strength loss was found for the 10:5 condition, serum CK levels were significantly higher following the 10:20 exercise. An analysis of covariance showed that the mean strength level over the 35 contractions was significantly related to CK increase in the two exercise conditions. Results suggest that mechanical factors associated with high tension levels may be responsible for CK efflux following isometric exercise.

Adult↗
PubMed1981

Fractioned reaction time in power-trained and endurance-trained athletes under conditions of fatiguing isometric exercise.

Fractionated knee extensor and plantar flexor reaction time (RT) components were assessed in a group of eight weightlifters and eight long distance runners. Following a 4-day period of baseline stabilization for each muscle group, a 50% maximal voluntary contraction (MVC) holding-time exercise was administered. Results showed that the runners had longer premotor times (PMT) than the weightlifters in the knee extensors, but had much faster PMTs than the lifters in the plantar flexor condition. Compared to previously reported investigations using non-athletes, the data for the present sample of athletes indicated faster total reaction times(TRT) in both the knee extensors and the plantar flexors. A resistance of 15% MVC applied during the RT task resulted in a lengthening of the motor time (MT) component in both groups prior to exercise. However, while knee extensor resisted motor time was lengthened by the exercise task, no such lengthening occurred in plantar flexor resisted RT. It is concluded that power-trained and endurance-trained athletes exhibit difference in response to a fractionated RT task, under both baseline and fatiguing exercise conditions.

Journal Article↗
PubMed1981

Age, isometric strength, rate of tension development and fiber type composition.

Knee extension isometric strength, rate of absolute and relative tension development, and vastus lateralis muscle fiber type composition was examined in 15 old (means = 64.5 years) and 9 young (means = 23.2 years) subjects. Strength was assessed using a 5-sec maximal voluntary contraction (MVC) and a fast maximal voluntary contraction (FMVC). MVC and FMVC were not significantly different in the Young group while in the Old group the FMVC was 19% greater than the MVC. These data suggested that usual strength testing methodology may considerably overestimate age-related strength loss. MVC, FMVC, and FT/ST muscle fiber area ratio were significantly lower in the Old group; rate of relative tension development was similar in Young and Old groups. FT/ST area ratio correlated with strength in the Young group and with rate of relative tension development in both groups. It was concluded that relative rate of tension development is unimpaired and related to FT fiber size while absolute tension level is impaired and unrelated to FT fiber size in the Old group.

Age Factors↗
PubMed1981

Exercise effects upon reflex time components in weight lifters and distance runners.

In an effort to identify neuromuscular parameters which differentiate between power-type and endurance-type athletes, an investigation was conducted to determine the effects of an isometric exercise task upon patellar and Achilles fractionated reflex time components in a group of weight lifters and long-distance runners. A reflex hammer was used to deliver a tendon tap stimulus to the patellar tendon (sitting position) and the Achilles tendon (prone position). Under resting conditions, no differences in Achilles reflex components existed between the two subject groups. However, patellar reflex latency was significantly shorter in the weight lifters than in the distance runners. Following knee extensor exercise consisting of three bouts of a 50% MVC holding-time task, the power group manifested a marked lengthening in total reflex time and reflex motor time. In the endurance group, reflex time lengthened after the first bout, but became shorter after the last two bouts. A similar Achilles reflex pattern was seen in both groups after plantar flexor exercise--an initial elongation of the peripheral components of reflex time, followed by a trend towards shorter reflex components in the later bouts. It was suggested that several factors may be competing to produce the bi-directional results observed in reflex time components following isometric exercise.

Achilles Tendon↗
PubMed1980

Maximal isometric strength and fiber type composition in power and endurance athletes.

The relationship between maximum isometric strength and muscle fiber type composition was examined in seven endurance and eight power trained athletes. Knee extension strength and ankle extension strength was assessed on 10 separate days and muscle biopsies were taken from the vastus lateralis and gastrocnemius muscles. The percent composition of slow twitch (ST) fibers and fast twitch (FT) fibers was determined from the biopsy samples. Correlation between maximal knee extension strength and percent ST fibers of the vastus lateralis was found to be 0.80 (n = 8,p less than 0.05) for the power group and 0.63 (n = 7,N.S.) for the endurance group. Corresponding correlation coefficients for the relationship between ankle extension strength and gastrocnemius percent ST fibers were -0.94 (p less than 0.01) and -0.19 (N.S.), respectively. The results suggest that the relationship to be expected between muscle fiber type composition and maximum isometric strength may well depend upon the muscle group under study as well as the type of athlete in terms of specific training adaptations.

Humans↗