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Biomedical subjects

J Stegemann

Publications and source records attributed to J Stegemann.

At least 73 records · Page 4Linked to original sources
PubMed1987

Automated DNA sequencing: ultrasensitive detection of fluorescent bands during electrophoresis.

A simple system has been designed enabling ultrasensitive on-line detection of fluorescently labelled macromolecules, e.g. nucleic acids, proteins and peptides during electrophoretic separations in gels. An important application is the automated DNA sequence determination without radioactivity. Drying of gels, film exposure and handling are not necessary. A sulphydryl containing M13 sequencing primer has been synthesised and end-labelled in a reaction with fluorescein iodoacetamide. This is then used in the dideoxy reactions. In particular no moving parts or complicated software are required for data collection and analysis. Compared to our first automated device detection sensitivity has been improved by a factor of thirty to about 3 X 10(-18) mol per band. The resolution has increased to about 400 bases in 5 hours, with the possibility to read up to about 500 bases when they are properly labelled. Gels shorter than 20 cm may be used for resolution of about 300 bases. The single gel system may be upgraded for simultaneous running and reading of six or ten sequencing samples.

Autoanalysis↗
PubMed1987

VO2 kinetics in subjects differing in aerobic capacity: investigation by spectral analysis.

The power-VO2 transfer functions of 38 subjects differing in aerobic capacity have been determined on the basis of breath-by-breath total oxygen uptake (VO2,t) measurements during light cycle ergometer exercise (lactic acid concentrations below 2 mmol.l-1). At constant pedalling frequency (1 Hz) pseudorandom binary sequences (PRBS) of workload were used as the testing signal. The VO2,t response was analysed by autocorrelating the ergometer power input and crosscorrelating the power input and VO2,t output. From the spectra of these functions the amplitude ratios and phase relationships were computed for the first six harmonics of the PRBS fundamental (14 mrad X s-1). We found that differences in aerobic capacity are associated with significant differences in the amplitude plots of the VO2 transfer function.

Adult↗
PubMed1987

Metabolic changes during volleyball matches.

Urinary and/or serum concentrations of electrolytes (sodium, potassium, calcium, magnesium), hormones (aldosterone, cortisol, catecholamines), and metabolic parameters (lactate, glucose, free fatty acids) were determined during different volleyball matches. While [Na+]s was slightly increased-not exceeding the hemo-concentration effect-[K+]s, and [Ca2+]s were diminished after the matches. Due to a lowered glomerular filtration rate (GFR), urinary excretion of water, sodium, and potassium was decreased. In addition, the tubular resorption and secretion of fluid and electrolytes was influenced by different hormones leading to a lowered [Na+]u and an increase of [K+]u after exercise. Low concentrations of lactate (2.54 +/- 1.21 mmol/l) during and after the matches and an increase of [FFA]s indicate that energy during the short exercise periods (9 s) is mainly supplied by a breakdown of creatine phosphate, while aerobic pathways restore the energy sources during the resting periods (12 s). Serum concentrations of aldosterone and cortisol as well as the excretion of adrenaline are enhanced on the same scale as after endurance sports. The excretion of noradrenaline corresponds to values during exercise of high intensity.

Adult↗
PubMed1987

Heart volume during short-term head-down tilt (-6 degrees) in comparison with horizontal body position.

The immediate effect of head-down tilt (5 min., -6 degrees) on heart volume was investigated in nine healthy male volunteers. Heart volumes were determined by the X-ray method of Kahlstorf and Rohrer as modified by Musshoff and Reindell. Biplane chest orthodiagrams were taken after 5 min of rest in a prone horizontal position (control values) and 5 min after tilting the examination table into a -6 degrees head-down tilt position. After 5 min head-down tilt, cardiac volumes had increased significantly (+ 5.2%). The results indicate that head-down tilt leads to an immediate increase in heart volume, which is similar in terms of elapsed time to results of immersion experiments conducted by other researchers, but not in terms of percent of increase.

Adaptation, Physiological↗
PubMed1986

The influence of furosemide on heart rate and oxygen uptake in exercising man.

We recently observed that heart rate (HR) related methods for assessing physical fitness lead to an overestimation of endurance capacity in subjects treated with furosemide. To gain a more detailed description of this effect, the relationships between work load (WL), oxygen uptake (VO2), and HR were determined in the present study. To this end, nine healthy male subjects performed two incremental exercise tests (10 W increase per 30 s) on a bicycle ergometer. In one test 40 mg furosemide (Lasix) was applied orally 90 min before exercise started. Compared with control conditions, furosemide led to a change in mean blood volume of -4.5% (range: +7.8% to -11.5%). Neither the maximal VO2 (VO2max) nor the maximal work load (WLmax) were significantly altered after furosemide application. Though the WL-VO2 relationship was not significantly affected, the HR-VO2 relationship showed significant alterations which depended on both the loss of blood volume (BV) and work intensity: When the reduction in BV was less than approximately 5%, HR was found to be lowered at all workloads. When the BV reduction was greater than about 5% HR was significantly reduced only in the lower ranges of work load but significantly increased at the higher work intensities. Since BV reductions are known to increase HR during exercise, our findings suggest that, in addition to the blood volume induced changes in HR, furosemide exerts further direct or indirect effects on heart rate adjustment.

Adult↗
PubMed1986

A non-radioactive automated method for DNA sequence determination.

A method and instrument for automated DNA sequencing without radioactivity have been developed. In spite of the success with radioactive labels there are drawbacks attached to the technique, such as hazards in the handling, storage and disposal of radioactive materials, and the considerable cost of the radiolabelled nucleoside triphosphates. In addition, there is deterioration of sample quality with time. A sulphydryl containing M13 sequencing primer has been synthesised and subsequently conjugated with tetramethylrhodamine iodoacetamide. The fluorescent primer is used to generate a nested set of fluorescent DNA fragments. The fluorescent bands are excited by a laser and detected in the gel (detection limit about 0.1 fmol per band) during electrophoresis, and sequence data from the four tracks are transferred directly into a computer. Standard gels, 200 mm wide with 20 sample slots have also been used. The device contains no moving parts. At present 250-300 bases can be read in 6 h. The system is capable of single base resolution at a fragment length of at least 400 bases.

Autoanalysis↗
PubMed1985

Force kinetics and oxygen consumption during bicycle ergometer work in racing cyclists and reference-group.

The forces acting on the right crank of a bicycle ergometer were measured in 18 male subjects (6 racing cyclists, 8 students of physical education, 4 long distance runners) during an incremental exercise test. Oxygen consumption (VO2) was simultaneously determined by means of a breath-by-breath method. Differences in peak values of the typical force record might indicate a different force distribution during each cranking cycle. When compared to the reference group, the racing cyclists showed peak values that were significantly lower at all levels of work load. Oxygen consumption during the initial 20 min of the test was found to be significantly lower in the cyclist group (cyclists: 37.2 +/- 3.2 1, reference group: 41.1 +/- 3.9 1). These results suggest that a different force distribution during a crank revolution might lead to an improved gross efficiency in the cyclist group. The findings might be due to different fractions of ST-fibres in the exercising muscle.

Bicycling↗
PubMed1985

Effects of a 7-day head-down tilt (-6 degrees) on the dynamics of oxygen uptake and heart rate adjustment in upright exercise.

Oxygen uptake (VO2) kinetics and heart rate (HR) kinetics were studied in six healthy male students before and on days 1,3 and 5 after a continuous 7-d antiorthostatic bedrest (-6 degrees). The exercise test protocol consisted of pseudorandom binary sequences (PRBS) of workload (W) performed on a bicycle ergometer in the upright position (20 W - 80 W, 15 bits, 30 s per bit; the sequence was repeated three times). Amplitude ratio and phase of the W-VO2 and W-HR relations were computed at six harmonic frequencies in the range 0.014 - 0.084 rad X s-1. After bedrest the VO2 kinetics was found to be impaired at the harmonic frequencies greater than 0.056 rad X s-1. Additionally, the mean heart rate during the PRBS cycles was increased (108 +/- 15 as compared to 92 +/- 10 min-1). There were no significant effects on HR kinetics and on the static W-VO2 relation. During an endurance training program both VO2 and HR changes were restored to the pre-bedrest levels. It is concluded that the impairment of VO2 kinetics can be attributed mainly to muscular factors.

Adult↗
PubMed1983

A new fluid switching flow sorter.

Conventional cell sorters produce potentially hazardous microdroplets containing dyes and radiolabeled compounds commonly used to identify and trace subpopulations of cells. Many of these substances are potential toxins, mutagens, or carcinogens constituting a risk to personal associated with the sorting device. The separation of living cells for continued study of cell growth from an "in air" sample stream includes the risk of contamination with microorganisms altering the following cultures. To avoid those risks, we have constructed a new capsular flow cytometer sorter which consists of a small chamber completely encasing the sorting mechanism. Data acquisition, analysis, and processing are accomplished by using a microcomputer-based pulse height analyser.

Animals↗
PubMed1983

CO2-H+ stimuli and neural muscular drive to ventilation during dynamic exercise: comparison of stimuli at constant levels of ventilation.

In exercising man, the ventilatory responses to CO2-H+ stimuli and neural muscular drives were compared at constant ventilation (VE). For that purpose, a small increase of the CO2-H+ stimulus in exercise was to be counterbalanced by work load reductions in such a way that the magnitude of ventilation remained unchanged. Control of end-tidal PO2 and PCO2 (PETO2, PETCO2) was established to minimize the influence of changed mixed venous gas tensions on the arterial levels. Only in metabolic acidosis could the additional CO2 stimulus be compensated by work load reduction. This compensation was due to the concomitant decrease of acidosis. Below the 2 mmol X l-1 [La]a threshold, decrements of work load, VO2, and VCO2 showed no effect on VE, when PETCO2 and PETO2 were regulated at constant levels. After the termination of end-tidal clamps, the proportional relation of VE to VO2, VCO2, and work load was largely reestablished. The results show that neural muscular drives cannot decrease ventilation against a background of constant arterial feedback stimuli. Transient decreases of the CO2-H+ stimulus seem to be necessary to readjust the ventilation to a decreased CO2 flow to the lungs. It is suggested that the overall effect of decreasing CO2 is to inhibit the respiratory centers and that positive ventilatory effects of CO2 are the result of a disinhibitory influence.

Acidosis↗
PubMed1976

[Relation between training status and orthostatic tolerance].

Investigations on orthostatic tolerance and physical fitness prior to and after 6-8 h immersion experiments surprisingly revealed that all untrained subjects endured pre- and postimmersion tilt table tests without subjective complaints, whereas after immersion all trained participants collapsed within the first minutes of erect position displaying symptoms of a vasovagal syncope. Assuming that this impaired orthostatic tolerance of trained subjects can partially be referred to influences of an altered blood pressure control system we decided to record the blood pressure characteristics of both groups. Thereby, the transmural pressure of the carotid artery was changed by applying from outside either reduced or exceeding pressures. The controller sensitivity in the untrained group was almost twice as high as in the trained one. This implies a better regulatory response to disturbing interference in the untrained. Under normal conditions the controlling capacity of both groups is sufficient to cope with body position changes. However, during stress situations--in this case, reduction of aldosterone concentration as well as losses of plasma volume due to the 'Gauer-Henry-Reflex'--blood pressure regulation first fails in the trained subjects.

Blood Pressure↗
PubMed1975

A mathematical model of the ventilatory control system to carbon dioxide with special reference to athletes and nonathletes.

The ventilatory response curve (VRC) as a function of alveolar and arterial pCO2 was recorded in 6 high-performance athletes and 6 nonathletes. The best fit to the data points could be found for an equation of the form (see article) showing that the results are strongly related to a Gaussian probability density function (PDF). After normalizing the equation to a form (see article) (M = mean value of PDF), sigma, A and M could be determined for both groups. Sigma and A are smaller in the athletic group, whereas M did not show any systematic difference. Regarding the respiratory center consisting of functional "elements" responding indirectly to variable pCO2 it can be concluded that the frequency distribution of the different active elements is greater and spread over a wider pCO2 range in the nonathletes with the same mean value in both groups. Using Loeschcke's model (1960), the open loop gain factor for different V CO2 as a function of p(A)CO2 was computed; the gain factor showed a maximum in the physiological range of pCO2.

Adult↗
PubMed1975

Effects of a multi-hour immersion with intermittent exercise on urinary excretion and tilt table tolerance in athletes and nonathletes.

The circulatory and diuretic responses of athletes and non-athletes to 6-h water i-mersion with intermittent swimming exercise (series I) as well as to 8-h inactive immersions (series II) were studied. With simultaneous intermittent exercise, the normally arising diuresis during a water bath was strongly suppressed in athletes and even abolished in nonathletes. In subsequent tilt table tests, 3 of 11 (27.3%) athletes of series I and 3 of 4 (75%) of series II collapsed, whereas all nonathletes tolerated the vertical position without any subjective complaints. By use of the so-called "orthostatic index" (4) the later group, however, was also shown to yield a substantially better orthostatic stability in series I than in series II. The protective effect of intermittent physical activity for simulation of the weightless state can possibly be explained by assuming a less-reduced plasma volume via a diminished urinary excretion.

Adaptation, Physiological↗