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Biomedical subjects

U Hoffmann

Publications and source records attributed to U Hoffmann.

At least 145 records · Page 8Linked to original sources
PubMed1995

[Fast MRI contrast medium dynamics for characterization of tumors. Experiences with functional MR-mammography].

METHODS: MRI studies with high temporal resolution can be achieved with an optimized saturation recovery TurboFLASH sequence, which allows a more detailed characterization of contrast enhancement in tissue as is available with the current FLASH 3D techniques. A two compartment model allows characterization of signal time curves with three parameters, Amp (amplitude), k21 (distribution rate constant) and kel (elimination rate constant). RESULTS: In a prospective study on 314 patients with indetermined breast lesions signal-time-curves revealed differences in the k21 parameter between benign (0.56 +/- 0.46) and malignant lesions (1.25 +/- 0.80) (p < 0.0001) as well as between different histological classifications. CONCLUSION: The introduced MR-technique enables a better evaluation of the vascular permeability for the MR contrast media in lesions. Distinct differences were detected, which are influenced by elevated expression of angiogenesis factors such as the vascular endothelial growth factor.

Breast↗
PubMed1995

Segmental flexibility of cardiac myosins.

Conventional and saturation transfer electron paramagnetic resonance spectroscopy (EPR and ST EPR) and differential scanning calorimetry (DSC) were used to study the motional dynamics and structural stability of cardiac myosins. Cardiac myosins isolated from bovine and human heart muscle were spin-labelled with a maleimide- or an iodoacetamide-based probe molecule at the reactive sulhydryl sites (Cys-697 and Cys-707). The probe molecules rotated with an effective rotational correlation time of 0.04 microsecond which was at least six times shorter than the rotational correlation time of the same label on skeletal myosin. In the presence of MgADP, flexibility changes in the multisubunit structure of myosins were detected, but this did not lead to changes of the overall rotational property of the myosin heads. Temperature dependence of the EPR spectra of maleimide spin-labelled myosin showed continuous decrease of the spectral parameters (amplitude ratio of the diagnostic peak heights in the ST EPR time domain and hyperfine splitting constant) at increasing temperature. In contrast, marked changes were obtained at about 17 degrees C in light chain-2 deficient myosin. DSC measurements supported the view that the removal of the light chain-2 produced additional loosening in the multisubunit structure of cardiac myosin. It is postulated that the light chain-2 is an integral part of myosin, and there is an intersite communication between light chain-2 and the 20 kDa subunit.

Animals↗
PubMed1994

Postural effect on cardiac output, oxygen uptake and lactate during cycle exercise of varying intensity.

Owing to changes in cardiac output, blood volume distribution and the efficacy of the muscle pump, oxygen supply may differ during upright and supine cycle exercise. In the present study we measured, in parallel, circulatory (heart rate, stroke volume, blood pressure) and metabolic parameters (oxygen uptake, lactic acid concentration [la]) during incremental-exercise tests and at constant power levels ranging from mild to severe exercise. In supine position, cardiac output exceeded the upright values by 1.0-1.5 l.min-1 during rest, light ([la] < 2 mmol.l-1) and moderate ([la] = 2-4 mmol.l-1) exercise. At higher exercise intensities the cardiac output in an upright subject approached and eventually slightly exceeded the supine values. For both rest-exercise transitions and large-amplitude steps (delta W > or = 140 W) the cardiac output kinetics was significantly faster in upright cycling. The metabolic parameters (VO2 and [la]) showed no simple relationship to the circulatory data. In light to moderate exercise they were unaffected by body position. Only in severe exercise, when cardiac output differences became minimal, could significant influences be observed: with supine body posture, [la] started to rise earlier and maximal power (delta W = 23 W) and exercise duration (64 s) were significantly reduced. However, the maximal [la] value after exercise was identical in both positions. The present findings generally show advantages of upright cycling only for severe exercise. With lower workloads the less effective muscle pump in the supine position appears to be compensated for by the improved central circulatory conditions and local vasodilatation.

Adult↗
PubMed1994

Prediction of individual oxygen uptake on-step transients from frequency responses.

Power-oxygen uptake (VO2) frequency responses can be used to predict VO2 responses to arbitrary exercise intensity patterns. It is still an open question for which range of exercise intensities such computed VO2 response patterns yield valid predictions. In the present study, we determined the power-VO2 frequency response of nine sports students by means of pseudo-randomised switching between 20 W and 80 W during upright and supine cycle exercise. Starting from a baseline of 20 W each subject also performed sustained step increases to 40 W, 80 W, 120 W, and 160 W in both positions. The individual VO2 step responses were then compared with the expected VO2 time-courses predicted on the basis of the individual VO2 frequency responses. The comparison showed a close agreement for the 20 W-40 W and 20 W-80 W steps in both positions. With larger step amplitudes the VO2 kinetics became increasingly slower than the predicted VO2 time course in both positions. During additional ramp tests (10 W.30 s-1) whole blood lactic acid concentration [la-]b tended to be higher in the supine position at exercise intensities higher than 160 W. The mean power at 4 mmol.l-1 [la-]b amounted to 234 (SD 32) W and 253 (SD 44) W (P < 5%) in the supine and the upright position, respectively. The maximal oxygen uptake relative to body mass was not found to be significantly different [upright, mean 57 (SD 10) ml.(min.kg)-1; supine, mean 54 (SD 10) ml.(min.kg)-1].(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

[A pharmacokinetic analysis of Gd-DTPA enhancement in MRT in breast carcinoma].

Dynamic Gd-DTPA enhanced MR of the breast was performed in one single slice in 27 patients with suspicious nodular lesions. The results could be histologically verified in all cases. A rapid spin-echo sequence with a time resolution of 8.75 s was used for the dynamic examination. The signal changes were analysed using a pharmacokinetic model which allowed parametrization of the contrast enhancement and transformation of the data into colour coded parameter images. The parameters allowed reliable distinction of 9 benign from 18 malignant lesions (p < 0.05 for "amplitude", p < 0.001 for "k21"). One fibroadenoma could not be distinguished from the carcinomas. Lymph node metastases and the pharmacokinetic parameter amplitude correlated significantly (p < 0.05).

Adult↗
PubMed1994

[Detection of coronary calcification by ultrafast CT compared with coronary angiography].

The angiographical findings of 24 patients with coronary artery disease were compared with qualitative and quantitative detection of coronary calcification by ultrafast CT. Doubts concerning the capabilities of the ultrafast CT for a screening of coronary artery disease arise when the results of one third false positive and false negative findings are considered. Variations in the quantification of coronary calcification were too great to allow a realistic assessment of the degree of stenosis of the coronary arteries.

Adult↗
PubMed1994

VO2 kinetics determined by PRBS-technique and sinusoidal testing.

The PRBS-technique is a useful tool to investigate muscle VO2 kinetics within the aerobic range. However, the validity of this kind of multi-frequent testing may be limited by non-linearities generated by the circulatory and pulmonary system. To check for such non-linear effects we compared the frequency responses computed from the multi-frequent PRBS with the results of pure sinusoidal testings (periods between 75 s and 450 s). Both methods show a good agreement for periods in the range between 113 s and 450 s. For shorter periods the results slightly diverged. The harmonic analyses of the sinusoidal data indicate increased stimulation of higher harmonics with increase in frequency. It is concluded that the VO2 in the lower frequency range shows only little, if any, influence of the circulatory and pulmonary system. Differences between the methods in the higher frequency range may be caused by non-linearities at the same or even lower frequencies. Therefore, periods shorter than 100 s are not suitable for assessing the muscle VO2 kinetics.

Adult↗
PubMed1994

VO2 and cardiac output during rest-exercise and exercise-exercise transients.

The dynamics of external gas exchange during exercise is influenced by pulmonary, cardiovascular, and metabolic factors. During rest-exercise transitions the interaction of these factors is more complex than during exercise-exercise transients. In the present study, we directly compared oxygen uptake (VO2) and cardiac output (CO) responses to step changes in exercise intensity. Nine students performed the following step changes on a bicycle ergometer in upright body position: rest-20W, 20W-80W, 20-140W. VO2 was measured breath-by-breath while CO was determined beat-by-beat by means of a Doppler device. The probe was positioned in the suprasternal notch and directed towards the aortic root. When starting from the 20 W baseline the VO2 responses showed a first, mainly cardio-vascular component over the first 30 s, followed by a second, metabolic component at constant CO. The rest-exercise transients displayed two additional early features. First, there was a very rapid VO2 increase during the initial breathing cycles of the on-transient. This was probably caused by events in the lungs or the pulmonary circulation. Second, the CO attained its steady-state level in about 10 s. This suggests a sudden increase in venous return. The present results generally show that both the VO2 and CO kinetics are faster when exercise in the upright body position is started from rest.

Adult↗
PubMed1994

Low frequency oscillations of skin blood flux in peripheral arterial occlusive disease.

Using the laser Doppler technique patterns of spontaneous oscillations of skin blood flux within the low frequency band (< 10 min-1; LF waves) were analysed in 12 healthy controls and 24 patients with different degrees of peripheral arterial occlusive disease (PAOD). Measurements were performed at 5 different sites at the dorsum of the foot in healthy controls and patients with severe claudication or rest pain and/or gangrene due to PAOD. Patterns were classified as "periodic", "aperiodic" or "no flux motion". The aperiodic pattern was characteristic for skin blood flux of controls. In severe claudication prevalence of periodic LF oscillations significantly increased (p < 0.05) whereas it decreased again in patients with severe ischemia. In the latter group, LF waves often were completely absent. Periodic LF waves mainly occurred between an ankle/arm pressure ratio of 0.4 to 0.8. We suggest that periodic LF waves most likely ar the result of a synchronized vasomotor activity of different arterioles within the sample volume, whereas the aperiodic pattern may resemble the net effect of simultaneous activities of different control mechanisms on skin blood flow. Based on animal experiments it is hypothesized that decreased postocclusive driving pressure and flow in patients with advanced PAOD may be the stimulus for synchronized arteriolar vasomotion.

Adult↗
PubMed1994

[Diagnosis of sympathetic reflex dystrophy. Comparison of ischemia test and modified guanethidine blockade].

Recently, the ischemia-test (IT) had been suggested to be part of the diagnostic procedure for reflex sympathetic dystrophy (RSD). The present study investigated, for the first time whether pain suppressing, as typically occurring under the IT, would correlate in RSD to the pain relieving effect following a diagnostic guanethidine blockade. For this purpose, both IT and guanethidine blockade were applied to 40 RSD-patients. A high correlation was found between the results of both procedures: 89% of those cases, who showed a positive IT (38 out of 40 patients) also reported acute pain relieve following the guanethidine blockade. Thus, both procedures have the same diagnostic value for pain in RSD. These results are in agreement with new pathophysiological considerations, assuming an indirectly (via the microvascular system) mediated sympathetic-afferent coupling as a cause of pain in RSD.

Adult↗
PubMed1993

Effects of microgravity on interstitial muscle receptors affecting heart rate and blood pressure during static exercise.

Afferent nerve fibers from receptors situated in the interstitium of skeletal muscles can induce cardiovascular reflexes. It has been shown that these interstitial muscle receptors are also sensitive to the local state of hydration: increased heart rates and blood pressure values were seen during dynamic and static exercise after local dehydration on earth. Since weightlessness leads to a persisting fluid loss in the lower part of the body, we hypothesized that leg exercise in space would augment heart rate and blood pressure responses to a similar extent as during local, interstitial dehydration on earth. Initial measurements during weightlessness were obtained in one subject after 6 days of space flight. Heart rate and blood pressure responses to light static foot plantar flexion (18% of maximal voluntary contraction) were recorded in two sessions. To eliminate the influence of muscle perfusion, exercise was performed during a period of arterial occlusion obtained by means of pneumatic cuffs at mid-thigh level. Identical protocols were used in the pre- and postflight controls, which were performed both in the sitting posture and in a -90 degrees tilted sitting posture assumed 30-40 min before arterial occlusion. During weightlessness the exercise responses of heart rate and systolic and diastolic blood pressure closely followed the tracings obtained with the tilted sitting posture on ground. The response amplitudes in these states of reduced lower limb volumes (about 20/min and 20 mmHg, respectively) exceeded the responses in the supine position by a factor of at least 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure↗
PubMed1993

[Polypoid malignant melanoma. An aggressive, seldom observed variant of nodular malignant melanoma].

We describe a 54-year-old man with a polypoid melanoma. The tumour had developed within 1 year. Physical examination showed an eroded pedunculated nodule approximately 2.5 x 3 cm in size. Histopathology revealed a pedunculated, sharply demarcated tumour with an eroded surface; it was composed of atypical melanocytes in sheets and nests. Physical examination 11 months after excision of the tumor with 3-cm safety margin disclosed no evidence for enlarged lymph nodes or cutaneous metastases. No metastases were seen on computer tomography. To our knowledge, this patient represents the first case of polypoid melanoma reported in the German literature.

Biopsy↗
PubMed1993

Variability of different patterns of skin oscillatory flux in healthy controls and patients with peripheral arterial occlusive disease.

Variability of patterns of laser Doppler flux motion was analysed at 5 different sites at the foot of 12 healthy controls and 24 patients with different degrees of ischemia due to peripheral arterial occlusive disease. Patterns were evaluated by means of the frequency histogram method. Three main flux motion components were detected at mean frequencies of 3.5 +/- 1.1 min-1 (low frequency waves, LF), 17.2 +/- 2.7 min-1 (high frequency waves, HF) and at 62.6 +/- 8.5 min-1 (pulsatile waves, PF). The characteristic pattern in normals consisted of LF and PF waves. In severe ischemia oscillatory flux was predominantly characterized by the combination of LF and HF waves and loss of pulsatile flux, or by the absence of any flux motion. Claudicants covered the entire spectrum of the flux motion patterns. In controls spatial variations were mainly due to the occasional presence of HF waves at one of the 5 sites. With increasing ischemia spatial variability of HF waves decreased due to more homogeneous presence. Loss of pulsatile flux was inhomogeneous in claudicants but almost complete in severe ischemia. Whereas LF waves were almost always observed at all sites of controls and claudicants there was considerable spatial variability in severe ischemia due to inhomogeneous loss of LF waves. Prevalence of the distinct flux motion patterns was well reproducible in controls and patients. Patterns showed a marked day to day variability when sites of measurement were compared.

Adult↗