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Biomedical subjects

H Schmid-Schönbein

Publications and source records attributed to H Schmid-Schönbein.

At least 19 recordsLinked to original sources
PubMed2004

Coordination dynamics of circulatory and respiratory rhythms during psychomotor drive reduction.

A 0.15-Hz rhythm band in cutaneous blood oscillations in awake human subjects was studied in cardiovascular-respiratory time series of five subjects relaxing naïvely or practicing hypnoid relaxation (autogenic training, or AT). Time series analysis used nonlinear algorithms, time-frequency distribution (TFD), postevent scan (PES) method, and linear fast Fourier transform (FFT) algorithm. This 0.15-Hz rhythm band caused phase synchronization with respiration at 1:2, 1:1, and 2:1 integer number (n/m) ratios for extended periods. During wave epochs, the 0.15-Hz rhythm band was amplified, causing the 0.15-Hz rhythm band to also appear in interbeat intervals and arterial blood pressure fluctuations. If phase synchronization of the 0.15-Hz rhythm band with respiration was established at a 1:1 integer number ratio, it was maintained and resulted in consensualization of all cardiovascular-respiratory oscillations at this frequency. Simultaneous cardiovascular and respiratory oscillations at about 0.1 Hz did not affect the appearance of the 0.15-Hz rhythm band in the photoplethysmography (PPG) signal. Recent evidence suggests the emergence of the 0.15-Hz rhythm band and n/m phase synchronization to result from nonequilibrium phase transitions operational in the network of lower brainstem neurons and associated parasympathetic neuronal effectors. These findings corroborate our notion of the 0.15-Hz rhythm band as a marker of the trophotropic mode of operation.

Adult↗
PubMed2001

Standardized ultrasound as a new method to induce platelet aggregation: evaluation, influence of lipoproteins and of glycoprotein IIb/IIIa antagonist tirofiban.

Most of the published studies concerning platelet aggregation were performed with chemical stimulation procedures, however, mechanical stimulation might be a better simulation of physiological activation of platelets. In order to evaluate the influence of ultrasound on platelet aggregation in vitro, we developed an ultrasound device in a standardized set-up, and we evaluated the influence of lipoproteins and the glycoprotein IIb/IIIa inhibitor tirofiban on ultrasound induced platelet aggregation. A cylindrical shaped plastic test tube with 1 ml of platelet-rich plasma was placed in an ultrasound bath (35 kHz) for 5 s. The ultrasound energy transfer into the sample (Delta W=3.77 J) was calculated using the average temperature increase (averaged by 0.935 degrees C) of the sample. Platelet aggregation was quantified immediately after stimulation with ultrasound or adenosine diphosphate (ADP 2.1 and 4.2 microM) by the Myrenne Aggregometer PA2 at low (40 s(-1)) and afterwards at high (2500 s(-1)) shear. To evaluate the influence of lipoproteins, seven healthy male volunteers were investigated before and after a fat load (50 g fat per m(2) body surface), and 11 patients suffering from hypercholesterolemia and atherosclerotic disease before and after a single low-density lipoprotein (LDL) apheresis. Platelet aggregation after ultrasound stimulation was well correlated with platelet aggregation after ADP (r between 0.50 and 0.95). However, when exposed to high shear, the low shear-induced platelet aggregates were more stable after ultrasound stimulation compared with ADP stimulation either with or without tirofiban. After the fat load triglyceride concentration increased from 0.86+/-0.39 to 2.10+/-1.10 mmol l(-1) (P<0.05) resulting in a reduced formation of platelet aggregates after weak (ADP 2.1 microM) but not after strong (ADP 4.2 microM or ultrasound) stimuli. After a single LDL apheresis LDL cholesterol dropped from 3.99+/-0.90 to 1.06+/-0.55 mmol l(-1) (P<0.005). No changes in platelet aggregation were observed with the exception of a lower aggregation when exposed to high shear after stimulation with 2.1 microM ADP. In conclusion, we found the ultrasound stimulation of platelet-rich plasma easy to perform. The platelet aggregation after ultrasound stimulation correlated well with stimulation after ADP. While a reduction in LDL cholesterol concentration had only slight effects on platelet aggregation, an increase in triglyceride concentration resulted in a reduced formation of platelet aggregates after weak stimulation.

Blood Platelets↗
PubMed1999

Effect of local anesthetics on red blood cell deformability.

The deformability of human red blood cells under the influence of local anesthetics is studied in vitro. Red blood cells obtained from blood samples of healthy adult volunteers are treated with two local anaesthetics, procain and tetracaine, at varied concentrations. Deformability of red blood cells, in terms of its elongation index, were then examined by laser light shear stress diffractometer both at low and high shear forces. Results show that the deformability of local anesthetic-treated red blood cells is decreased when compared to that of control samples. At low shear forces and at low concentrations of the anesthetic agent, the decrease in deformability is not significant, whereas it is significant for high shear forces and at high concentrations. These effects are similar for both anesthetic agents studied.

Adult↗
PubMed1999

Evaluation of hemorheological risk factor profile in plasmacytoma patients.

The hemorheological parameters, plasma viscosity, hematocrit, erythrocyte aggregation and deformability of blood samples obtained from plasmacytoma patients are measured by capillary viscometer, microcentrifuge, Myrenne aggregometer, and filtrometer, respectively. These parameters are significantly altered in patients compared to those of normal subjects. The plasma viscosity and erythrocyte aggregation are increased, whereas erythrocyte deformability and hematocrit are decreased. Based on these parameters the hemorheological risk factor profiles are developed and by their overall risk factors, the patients with low and high risk factors are identified.

Blood Viscosity↗
PubMed1999

Influence of local anaesthetics on the aggregation and deformability of erythrocytes.

The effects of two local anaesthetics, procain and tetracaine, on erythrocyte aggregation and deformability under in vitro conditions are analysed. Fresh blood samples from healthy volunteers are obtained by venepuncture in test tubes containing heparin as anticoagulant. After centrifugation, plasma and cells are separated and buffy coat is discarded. The erythrocyte suspensions for aggregation and deformability measurement are prepared at hematocrit 34 and at 8% in buffered medium containing glucose and albumin, respectively. A part of the suspending medium in these samples is replaced by an equal volume of anaesthetic solution to obtain its final concentration ranging from 0.001 to 1 g/l. The results show that with the increase of anaesthetic concentration the deformability index and the aggregation index are reduced. The change in erythrocyte shape may contribute to the decrease in aggregation. The combined effect of these parameters may affect blood flow under varied experimental conditions.

Anesthetics, Local↗
PubMed1998

Thrombolysis of mural thrombus by ultrasound: an experimental in vitro study.

RATIONALE AND OBJECTIVES: The authors perform an in vitro evaluation of the thrombus fragmentation to determine the efficacy and degree of downstream clot fragment embolization that occurs during transcatheter ultrasound treatment of fibrin-rich mural thrombus in a peripheral venous flow model with variable diameter tubing. METHODS: The authors used a 22.5-kHz prototype intravascular ultrasound device with a flexible 0.8-mm (.032-inch) titanium wire probe encased in a 7-French teflon guide catheter, at the tip of which is a 2-mm ball. In 50 silicone tube segments (inner diameter 3, 5, 7, 9, and 11 mm; n = 10 each), firmly adherent mural thrombus was produced using bovine blood in a modification of the Chandler's loop technique. Ultrasound energy (30-36 watts/cm), maximal longitudinal catheter tip amplitude 70 m) was applied to the thrombus while a continuous flow of water was maintained in the closed loop system. Clot fragment emboli were trapped in "downstream" polyethylene filters. RESULTS: The mean rate of thrombus removal ranged from 99% +/- 0.3% in the 3-mm segments to 76% +/- 6% in the 11-mm segments. The average weight of the fragments that embolized "downstream" and were trapped in the filters, expressed as a percentage of the initial clot weight, was 11% in the 3-mm segment, 14% in the 5-mm segment, 30% in the 7-mm segment, 29% in the 9-mm segment, and 28% in the 11-mm segments. The majority of the embolized fragments appear to be larger than 1 mm. CONCLUSIONS: In this in vitro venous flow model a lack of catheter steerability was the major obstacle to complete thrombus fragmentation in vessel calibers larger than two times the tip diameter. The rate of embolism and the amount of remaining thrombus that could not be removed from the vessel were higher in the larger vessels.

Animals↗
PubMed1998

[In vivo ICG fluorescence photometry for quantification of warm ischemia damage of to the liver in a rat model].

The clearance of indocyanine green (ICG) from the peripheral blood has been used for the study of hepatic function in clinical and experimental investigations. We describe a method of simultaneous, semiquantitative measurement of the kinetics of ICG in the peripheral blood, liver, kidney and bile system following intraoperative bolus injection. The method is based on the fluorescence of ICG in the near infrared spectrum. Using this method, we have recognized a temporary extrahepatic storage of ICG within the kidney. Our first results prove changes in the ICG-metabolism fifteen minutes after reperfusion following a 30-minute hepatic ischemia and partial liver resection in the rat.

Animals↗
PubMed1998

Haemorheological behaviour of erythrocytes & risk factor profile in patients suffering from Waldenström's macroglobulinaemia.

The plasma viscosity, haematocrit, and erythrocyte aggregation and deformability of blood samples of patients of Waldenström's macroglobulinaemia were measured by capillary viscometer, microcentrifuge, Myrenne aggregometer and filtrometer respectively and correlated with the serum IgM concentrations. The observed increase in plasma viscosity and erythrocyte aggregation and decrease in their deformability were attributed to the increase in the concentration of IgM. Haematocrit was also decreased compared to normal subjects. Based on these parameters a haemorheological risk factor profile was developed and an overall risk factor calculated. An increase in the risk factor in these patients was observed. The haemorheological profile and the calculated risk factors not only help in establishing the inter-relationship of these parameters in the disease state but also to evaluate the severity of the disease.

Aged↗
PubMed1996

Attractors and quasi-attractors in the cutaneous perfusion in human subjects and patients: "chaotic" or adaptive behaviour?

The causes of the aperiodic fluctuations in the perfusion of the skin (volar hand, measured by the Laser-Doppler (LD) technique) of healthy human subjects were studied were studied by simultaneous recording of the fluctuations of local blood content (reflectiophotoplethysmography (rPPG)) and those in the skin of the glabella. Various thermoregulatory situations were provoked by exposing 12 subjects to 18, 21, 24 and 27 degrees C ambient temperature; in addition, the hands were placed at, below and above heart level. In mentally relaxed subjects (evidenced by a stable approx. 0.015-Hz rhythm in the glabellar rPPG signal), there was perfect temporal correlation between aperiodic LDA and rPPG signal under all thermoregulatory conditions. Clearly identifiable episodes of retardation associated with skin bleaching, asymmetrical shape of LDA and rPPG signals were taken as indicators of episodic sympathetic skin constrictor (SSC) activity. In synergetic terms, the modulated SSC activity operates as transient "quasi-attractor'. A notable exception occurred: when the hand was placed below heart at 27 degrees C ambient temperature, a sinusoidal periodic fluctuation (approx. 0.03 Hz) in the LDA evolved. These were not seen the rPPG signal, i.e., coherence between LDA and rPPG dynamics was lost). Lack of coherency between LDA-rPPG, also observed in patients with autonomic neuropathy and decompensated forms of peripheral arterial disease, suggesting predominance of spontaneously oscillating myogenic vasomotion after removal of temporally variable SSC drive. Stable vasomotion is regarded as a synergetically stereotyped reaction rather than as "well-ordered' stable attractor mode of operation.

Blood Flow Velocity↗
PubMed1994

Complex dynamic order in ventricular fibrillation.

Self-sustained circus movement of excitation has long been discussed as the underlying mechanism of ventricular fibrillation. This concept now appears to have found general acceptance. Mapping studies are very expensive and do not permit observations to be isolated from varying external influences. The authors have therefore used a simple cellular automation for studying the basic principles of excitation spreading during ventricular fibrillation under various conditions. Highly ordered spiral waves, described in other computer models, previously interpreted as fibrillation were encountered. Comparisons of pseudo-electrocardiograms created by the cellular automaton with original electrocardiographic recordings showed similarity in the time series and in fast Fouriér transformation. Modulation of refractory times often led to the termination of model fibrillation. Clinical evidence suggests that maintenance of the 1/f (RR-variability) variations produced by the autonomic nervous system exerts a protective effect on the evolution of ventricular fibrillation.

Computer Simulation↗
PubMed1992

Custom-tailored hemodilution with albumin and crystalloids in acute ischemic stroke.

BACKGROUND AND PURPOSE: Hemodilution in the acute phase of ischemic stroke is still controversial. Multicenter studies have failed to demonstrate any benefit. The present study focuses attention on analysis of circulation in stroke and on individual restabilization of circulation. METHODS: The Amsterdam Stroke Study is a prospective, single-center, randomized clinical trial (n = 300). Normovolemic hemodilution is accomplished in a customized procedure by administration of 20% albumin plus crystalloids under hemodynamic and rheological monitoring in the acute phase of stroke. All patients receive general intensive care treatment and monitoring with a pulmonary artery catheter. This custom-tailored fluid therapy is guided on the basis of a target pulmonary capillary wedge pressure (12 +/- 3 mm Hg) and hematocrit (0.32 +/- 0.02). The control group receives only customized rehydration by infusion of crystalloids. RESULTS: We obtained significant (p less than 0.05) reduction in mortality at 3 months (from 27% to 16%) and an increase in independence at home (from 35% to 48%) after viscosity reduction by means of hemodilution with albumin in the subgroup with a hematocrit less than 0.45 (n = 201) (specific viscosity effect). We also obtained a significant (p less than 0.005) reduction in mortality at 3 months (from 27% to 8%) and an increase in independence (from 35% to 59%) after only rehydration with crystalloids in the subgroup with overt dehydration (hematocrit greater than or equal to 0.45; n = 51) as compared with the normal-hematocrit group without signs of dehydration (hematocrit less than 0.45; n = 103) (specific rehydration effect). CONCLUSIONS: This study may provide an explanation for the failures in former hemodilution trials and may re-establish proper hemodilution and rehydration as a valuable therapy in the acute phase of stroke, thus reducing mortality and improving independence after 3 months.

Acute Disease↗
PubMed1992

Active and passive modulation of cutaneous red cell flux as measured by laser Doppler anemometry.

1) We have found that the fluctuations in blood motion and blood content in cutaneous microvessels in man can be related to either active vasomotion (an order parameter for this system) or to a passive penetration of arterial (or venous, not shown) pressure waves (the control parameters for the microvascular blood motion). Arterial, respiratory (not shown), neuronal and myogenic rhythms can be clearly differentiated. 2) Spectral analysis of the signal fluctuations of a LDA method (monitoring phasic shifts in blood velocity) in combination with a photoplethysmographic method (monitoring shifts in blood content) can be used to identify the "normal state". In normal human subjects, it is characterized by broad band synergetic liberty (a wide spectrum of rhythmic activities between 0.01 and 5 Hz). The spectrum readily responds to changes in thermoregulatory state and/or myogenic activation by positional changes of the extremity. 3) The spectral analysis of LDA and photoplethysmographic records of the volar finger reveals predominance of active vasoconstriction during heat conserving thermoregulatory reflexes (18 degrees C ambient), predominantly passive reactions are seen at 27 degrees C. At 21-24 degrees C ("thermoregulatory indifference temperature range"), a mixed reaction pattern is seen. 4) Functional or irreversible elimination of the activity of subsystems leads to the elimination of circumscript spectral bands and/or potentiation of others. The functional differentiation of active and passive components can be utilized in the future for differential diagnosis of vascular and nervous disease state on the basis of spectral shifts and/or spectral narrowing.

Blood Flow Velocity↗