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Biomedical subjects

U Hoffmann

Publications and source records attributed to U Hoffmann.

At least 109 records · Page 6Linked to original sources
PubMed1997

[Heart tumors].

Tumors of the heart are very rare. Due to the nonspecific clinical presentation the diagnosis is usually made by radiological procedures. Cardiac myxomas and thrombi are the most common cardiac masses. Two-dimensional echocardiography is the method of choice for the initial evaluation of cardiac tumors, because it permits the accurate determination of the tumor's size, localization, point of attachment, mobility and haemodynamic significance. Inadequate or nondiagnostic ultrasound examination and the need for preoperative assessment are indications for further examinations, such as magnetic resonance imaging (MRI) and computed tomography. Both these methods are helpful in the assessment of paracardiac structures and of the tumor invasion into great vessels and the mediastinum. MRI allows a limited degree of assessment of whether or not the tumor is malignant by soft tissue characterization. In the case of resectable, symptomatic, cardiac tumors surgical excision should be performed.

Diagnostic Imaging↗
PubMed1997

[Methodological approaches to quantitative evaluation of microcirculation in tissues with dynamic magnetic resonance tomography].

The development of rapid magnetic resonance imaging (MRI) sequences makes it possible to detect the fast kinetics of tissue response after intravenous administration of paramagnetic contrast media (CM), reflecting the status of tissue microcirculation. In this paper, the basic physical and tracer kinetic principles of dynamic relativity and susceptibility contrast MRI techniques are reviewed. The quantitative analysis of the acquired dynamic image data is broken up into an MR specific part, in which the observed signal variations are related to the CM concentration in the tissue, and an MR independent part, in which the computed concentration-time-courses are analyzed by tracer kinetic modeling. The purpose of the applied models is to describe the underlying physiological processes in mathematical terms and thus to enable the estimation of tissue specific parameters from measured dynamic image series. Whereas the capillary permeability can be estimated from dynamic relativity contrast enhanced MRI studies, the regional blood volume as well as the regional blood flow can be determined from dynamic susceptibility contrast enhanced image series. However, since there are no intravascular but only diffusible CM available at present, the application of the susceptibility technique is currently restricted to brain tissues with intact blood brain barrier. The practical realization of both dynamic MRI techniques is demonstrated by case studies.

Blood Flow Velocity↗
PubMed1997

Popliteal artery compression and force of active plantar flexion in young healthy volunteers.

PURPOSE: To define the prevalence of popliteal artery occlusion during active plantar flexion in normally active and highly trained young volunteers by measuring plantar flexion force and to assess the force level associated with popliteal artery occlusion. METHODS: Eighty-four limbs of 42 healthy subjects were studied. Eighteen subjects were highly trained athletes, and 24 were normally active persons. Plantar flexion was progressively performed in prone position against a scale. Plantar flexion force was measured in kilograms. After determination of the maximum strength (Pmax) of plantar flexion force, the level necessary to occlude the popliteal artery (Poccl) was assessed by continuously monitoring that vessel using color duplex sonography. RESULTS: Occlusion of the popliteal artery during plantar flexion was observed in 88.1% of the subjects and 77.4% of the limbs. No significant differences in prevalence were found between athletes and normally active subjects. The popliteal artery occluded at a mean plantar flexion force of 45.1 +/- 11.5 kg, which corresponded with 70.1% +/- 16.8% of the maximum force exerted during the provocation test. Poccl was not significantly different between lower limbs of athletes and nonathletes. Although in lower limbs of athletes the popliteal artery occluded at a significantly lower relative force as compared with normally active subjects (65.6% +/- 17.4% vs 74.5% +/- 17.4% of Pmax; p < 0.02), the difference was a result of two extremely low values found in a female athlete. CONCLUSION: Positional occlusion of the popliteal artery during active plantar flexion is commonly found in young healthy volunteers. Prevalence of the phenomenon depends on the force level exerted during active plantar flexion. Popliteal artery occlusion during active plantar flexion is not more frequent in athletes and occurs at a similar force level than in normally active subjects.

Adult↗
PubMed1997

Sympathetic nervous system and pain: a clinical reappraisal.

The target article discusses various aspects of the relationship between the sympathetic system and pain. To this end, the patients under study are divided into three groups. In the first group, called "reflex sympathetic dystrophy" (RSD), the syndrome can be characterized by a triad of autonomic, motor, and sensory symptoms, which occur in a distally generalized distribution. The pain is typically felt deeply and diffusely, has an orthostatic component, and is suppressed by the ischemia test. Under those circumstances, the pain is likely to respond to sympatholytic interventions. In a second group, called "sympathetically maintained pain" (SMP) syndrome, the principal symptoms are spontaneous pain, which is felt superficially and has no orthostatic component, and allodynia. These symptoms, typically confined to the zone of a lesioned nerve, may also be relieved by sympathetic blocks. Since the characteristics of the pain differ between RSD and SMP, the underlying kind of sympathetic-sensory coupling may also vary between these cases. A very small third group of patients exhibits symptoms of both RSD and SMP. The dependence or independence of pain on sympathetic function reported in most published studies seems to be questionable because the degree of technical success of the block remains uncertain. Therefore, pain should not be reported as sympathetic function independent until the criteria for a complete sympathetic block have been established and satisfied.

Aged↗
PubMed1997

Urinary excretion of apo(a) in patients after kidney transplantation.

BACKGROUND: Increased plasma Lipoprotein (a) (Lp(a)) levels are strongly associated with premature cardiovascular disease and stroke. The kidney is purported to play an important role in apo(a) catabolism. Therefore we investigated plasma Lp(a) levels in relation to kidney function and urinary apo(a) excretion. METHODS: One hundred and sixteen kidney transplant patients with normal or impaired renal function and 109 age- and sex-matched healthy controls were investigated. Plasma Lp(a) and urinary apo(a) levels were determined immunochemically and all other parameters were determined by routine laboratory methods. RESULTS: Transplant recipients were found to have significantly elevated total cholesterol and LDL-C values, but equal HDL-C values compared to controls. Plasma Lp(a) values were higher and urinary apo(a) excretion was lower in transplant recipients compared to controls, independent of renal function. When the patient group was subdivided into 'normal' and 'impaired creatinine clearance', only the latter group secreted less apo(a) than normal controls. CONCLUSION: These data suggest that urinary apo(a) excretion is reduced in transplant recipients with impaired excretory graft function, which may contribute to the elevation of plasma Lp(a) levels in these patients.

Aged↗
PubMed1997

Interleukin-2 increases transcapillary diffusion of sodium fluorescein in human skin.

Immunotherapy with interleukin-2 (IL-2) has been limited by dose-dependent systemic toxicities secondary effects inducing a "vascular leak" syndrome. The purpose of our study was directly to observe and to quantitate changes in skin capillary permeability in response to microinjection of IL-2 by measuring transcapillary diffusion of sodium fluorescein. Twelve healthy volunteers were studied. IL-2 (2.5 microliters; 45,000 i.u.) was injected into the subepidermal skin layer of the distal tibial plateau by using a new microinjection technique. At the opposite leg, an equivalent amount of the solvent was injected to serve as the intraindividual control site. Three and 24 h after injection, Na-fluorescein was given intravenously, and transcapillary diffusion of the dye was simultaneously recorded with two different video microscopes. Perivascular fluorescent light intensities (FLI) corresponding to transcapillary diffusion of the dye were measured in arbitrary units (AU) by videodensitometry around the sites of microinjection during playback of the videotapes. Mean FLI values representing microvascular permeability 10 s after dye appearance were at 3 h, 1,504 +/- 592 AU for IL-2 and 983 +/- 652 AU for the solvent; and at 24 h, 2,450 +/- 447 AU for IL-2 and 658 +/- 329 AU for the solvent. At 3 and 24 h, the mean values after IL-2 application were significantly enhanced (p < 0.05-0.005) when compared with the mean values after injection of the solvent. The results document that IL-2, as compared with the solvent, significantly increases transcapillary diffusion of Na-fluorescein, reflecting capillary permeability in human skin. The increase in capillary permeability may explain the edema-promoting effect of IL-2 after systemic application.

Administration, Cutaneous↗
PubMed1997

Changes in arterial and transcutaneous oxygen and carbon dioxide tensions during and after voluntary hyperventilation.

The purposes of our study were (1) to investigate whether a 3-min short-term hyperventilation leads to posthyperventilatory hypoxemia and (2) to assess the role of transcutaneous blood gas measurements for monitoring oxygen and carbon dioxide changes during the after the test. In 10 male volunteers arterial and transcutaneous blood gases were measured simultaneously before, during and after a 3-min voluntary hyperventilation maneuver. Baseline arterial PO2 increased from 13.7 +/- 0.4 kPa (103 +/- 3 mm Hg) to 18.6 +/- 0.3 kPa (139 +/- 2.3 mm Hg; p < 0.005 compared to baseline) during hyperventilation. After the provocation test posthyperventilatory hypoxemia occurred with a minimal mean value of 7.8 +/- 1.3 kPa (58.5 +/- 9.8 mm Hg; p < 0.05 compared to baseline). Whereas close agreement between arterial and transcutaneous measurements was obtained for carbon dioxide values before hyperventilation, transcutaneous O2 consistently underestimated arterial O2. A short-term over-breathing of 3 min causes a significant posthyperventilatory hypoxemia. We hypothesize that posthyperventilatory hypoxemia is caused by hypopnea as a result of depleted CO2 body stores. Noninvasive transcutaneous blood gas measurements are not reliable for monitoring blood gas changes during and after hyperventilation, most probably because of the slow response time of the electrodes and the reflex vasoconstriction of the skin vessels.

Adult↗
PubMed1997

Microvascular changes in venous disease: an update.

In an overview the microvascular involvement in chronic venous insufficiency (CVI) is described. Microangiopathy in the lower leg areas is characterized by the presence of typical enlarged and ramified blood capillaries, reduced capillary number, microvascular thrombosis and obliterations, and/or increased permeability of microlymphatics. Transcutaneous oxygen tension (tcPO2) is decreased and directly correlated to the number of perfused capillaries, whereas laser Doppler flux is enhanced. This apparent paradox may be explained by hyperperfusion in the deeper skin layers (mainly shunt vessels) and hypoperfusion in the superficial nutritive vessels. Microvascular changes are of patchy distribution. Trophic changes up to overt venous ulceration are mainly caused by microvascular ischemia and edema formation due to increased capillary permeability and deficient lymphatic drainage.

Capillary Permeability↗
PubMed1997

Noninvasive method for measuring thrombus formation in patients after peripheral angioplasty using three-dimensional B-mode and color-coded Doppler ultrasonography.

Clinical investigations studying the effect of newer medications on such complex pathophysiology as the formation of an arterial or venous mural thrombus have been limited to clinical symptomatic endpoints. Biochemical markers so far have not been convincing in quantifying ongoing thrombus formation. Consequently, clinical development of new antithrombotic compounds has had to rely on clinical symptoms that occur either comparably late in the course of the disease and may therefore be influenced by many other factors, or on those symptoms that occur at a relatively low incidence rate. Both circumstances make studies for dose-finding and determination of optimal drug regimens more difficult and time consuming. Using conventional clinical noninvasive ultrasonography, the volume and geometry of a peripheral arterial segment can be measured with high sensitivity and reproducibility in healthy volunteers (% coefficient of variation = 8.01%). In patients, thrombus volume was monitored after peripheral transluminal angioplasty of the femoral artery. All patients received a standard anticoagulant treatment with heparin for 24 hours after the procedure. Volume measurements were performed at 20, 29, 44, 53, and 68 hours after angioplasty. When compared with the obstruction volume at 20 hours, a slight increase could be detected at 29, 44, and 53 hours. At 68 hours there was a significant increase in obstruction volume. This indicates that volume measurements may detect changes in the course of thrombus formation, related to the antithrombotic treatment regimen, at a level at which clinical symptoms may not be present.

Aged↗
PubMed1997

Skin hyperemia in a habitual blusher.

Blushing, a vascular skin response to emotion is difficult to investigate since subjects are not able to blush on demand in a laboratory setting. Laser Doppler fluxmetry measures blood flux changes noninvasively. In a 28 year old lady distressed by habitual blushing we were able to document changes in skin blood flux during blushing. Forehead skin blood flux increased suddenly from 20 to 45 arbitrary units and returned to baseline values after about 3 minutes. It is the first time that emotionally provoked hyperemia in head skin is documented.

Blushing↗
PubMed1997

Exercise capacity during and after spaceflight.

UNLABELLED: Our aim was to elucidate why astronaut's exercise capacity after spaceflight is reduced. Therefore, the kinetics of oxygen uptake (VO2) as a measure for muscular aerobic capacity, as well as maximal oxygen uptake (VO2peak), and anaerobic threshold (PAT) as overall measures for exercise capacity were determined. Measurements of VO2peak and AT were restricted to pre- and postflight sessions. METHODS: Four crew-members of the D-2 mission (10 d) were cycling with steady state phases at 20 W and 80 W, followed by 450s of pseudo random binary sequence (PRBS) changes between 20 W and 80 W, and an incremental exercise test (10 W every 30 s) up to subjective exhaustion. Breath-by-breath VO2, VCO2, ventilation, HR, and blood pressure were continuously recorded. Blood lactate samples were drawn only during the incremental phase. The VO2 kinetics were determined by evaluation of the relationship between the workload and the instantaneous oxygen uptake of each subject. The cross-correlation function between both variables showed two characteristic items, the maximum as a measure for the muscular aerobic capacity, and its lag representing time consuming processes. RESULTS AND DISCUSSION: Each subject showed an individual characteristic of VO2 kinetics. In flight, no significant changes were detected compared to preflight data. Decreases in lags of cross-correlation function maxima and decreases in mean blood pressure during exercise indicate lowered blood volumes 2 d after the flight. Lowered blood volumes can explain the losses in exercise capacity. The maximum of the cross-correlation function did not change significantly which indicates unchanged muscular oxidative capacity.

Adult↗
PubMed1996

[Secondary prevention of arteriosclerosis].

Secondary prevention of arteriosclerosis tries to inhibit progression of the atherosclerotic process. Therapeutic measures focus on modification of cardiovascular risk factors and antithrombotic treatment. Hypercholesterolemia is the main risk factor for coronary artery disease. The risk of a coronary event is correlated to the plasma cholesterol level. Lowering plasma cholesterol results in reduction of vascular morbidity and mortality. Cigarette smoking is the predominant risk factor for peripheral arterial occlusive disease (PAOD). Smoking cessation reduces progression of PAOD and lowers cardiovascular morbidity and mortality. The preventive effect of antihypertensive therapy in hypertensive patients is most pronounced for cerebrovascular events. Antihypertensive measures improve prognosis after stroke and myocardial infarction. The increased cardiovascular risk in diabetics is in part explained by hyperglycemia and hyperinsulinemia, but also depends on coexisting dyslipidemia and hypertension. Intensive treatment of elevated blood glucose levels, dyslipidemia and hypertension are important preventive measures. Aspirin is highly effective in secondary prevention of vascular events. For the coronary arteries, low-dose aspirin is well established. Whether low-dose aspirin is equally effective for reducing progression of arteriosclerosis in the cerebrovascular and in the peripheral vessels is questionable. Ticlopidine serves as an alternative to aspirin; however, neutropenia may occur, which requires supervision of the patient.

Anticholesteremic Agents↗
PubMed1996

Microinjection technique for pharmacological evaluation of microvascular permeability in human skin.

A new technique which combines skin microinjection of minute amounts of drugs (0.5 microliter) and measurement of capillary permeability by intravital fluorescence videomicroscopy and densitometry is introduced. Glass micropipettes with a tip diameter of 7-9 microns are inserted by a micromanipulator into the stratum papillare containing the capillary loops and used for microinjection by microsyringe and special dispenser. Transcapillary diffusion of sodium fluorescein applied by intravenous bolus injection is visualised by fluorescence videomicroscopy and stored on videotape. Perivascular fluorescent light intensity (FLI) is measured in arbitrary units (AU) by videodensitometry around the site of microinjection during playback of the videotapes. The method was tested by microinjection of 0.5 microliter histamine (1% solution) at the distal tibial plateau. Mean FLI values representing microvascular permeability were 2186 AU 10 min after microinjection of histamine, 420 AU after physiologic saline and 1228 AU after histamine combined with oral intake of 20 mg cetirizine. Cetirizine significantly reduced (P < 0.01) the increased permeability induced by histamine. However, the mean values after injection of the H1-blocker were still significantly enhanced (P < 0.01) when compared to the mean values observed after injection of physiologic saline solution, which provoked only minor microtrauma. The technique offers new scope for pharmacological testing in man.

Adult↗