PubMed Health⌕ Search

Biomedical subjects

A Liebert

Publications and source records attributed to A Liebert.

17 recordsLinked to original sources
PubMed2006

Decomposition of a laser-Doppler spectrum for estimation of speed distribution of particles moving in an optically turbid medium: Monte Carlo validation study.

A method for measurement of distribution of speed of particles moving in an optically turbid medium is presented. The technique is based on decomposition of the laser-Doppler spectrum. The theoretical background is shown together with the results of Monte Carlo simulations, which were performed to validate the proposed method. The laser-Doppler spectra were obtained by Monte Carlo simulations for assumed uniform and Gaussian speed distributions of particles moving in the turbid medium. The Doppler shift probability distributions were calculated by Monte Carlo simulations for several anisotropy factors of the medium, assuming the Hanyey-Greenstein phase function. The results of the spectra decomposition show that the calculated speed distribution of moving particles match well the distribution assumed for Monte Carlo simulations. This result was obtained for the spectra simulated in optical conditions, in which the photon is scattered with the Doppler shift not more than once during its travel between the source and detector. Influence of multiple scattering of the photon is analysed and a perspective of spectrum decomposition under such conditions is considered. Potential applications and limitations of the method are discussed.

Blood Flow Velocity↗
PubMed2006

Non-invasive detection of fluorescence from exogenous chromophores in the adult human brain.

This is the first report on results proving that fluorescence of exogenous dyes inside the human brain can be excited and detected non-invasively at the surface of the adult head. Boli of indocyanine green (ICG) were intravenously applied to healthy volunteers, and the passage of the contrast agent in the brain was monitored by detecting the corresponding fluorescence signal following pulsed laser excitation at 780 nm. Our hypothesis that the observed fluorescence signal contains a considerable cortical fraction was corroborated by performing measurements with picosecond temporal resolution and analyzing distributions of times of arrival of photons, hence taking advantage of the well-known depth selectivity of that method. Our experimental findings are explained by Monte Carlo simulations modeling the head as a layered medium and taking into account realistic bolus kinetics within the extra- and intracerebral compartment. Although a particular non-specific dye (ICG) was used, the results clearly demonstrate that fluorescence-mediated imaging of the adult human brain is generally feasible. In particular, we will discuss how these results serve as proof of concept for non-invasive fluorescence brain imaging and may thus open the door towards optical molecular imaging of the human brain.

Adult↗
PubMed2004

Bed-side assessment of cerebral perfusion in stroke patients based on optical monitoring of a dye bolus by time-resolved diffuse reflectance.

We present a minimally invasive optical method, that is, multi-channel time-domain diffuse near-infrared reflectometry of the head to assess cerebral blood perfusion that is applicable at the bed-side and repetitively at short intervals. Following intravenous injection of an ICG bolus, its transit through intra- and extracerebral tissue is monitored based on changes in moments of distributions of times of flight of photons, recorded with a 4-channel instrument simultaneously on both hemispheres. In healthy volunteers, we found that variance of distributions of times of flight of photons is well suited to assess latency and initial slope of the increase in absorption of intracerebral tissue due to the bolus. We successfully applied our method in two patients demonstrating a reversible cerebral perfusion deficit in an ischemic stroke patient who was treated by thrombolysis and in another patient with a permanent impaired unilateral perfusion due to ipsilateral internal carotid artery occlusion. In either case, we observed a difference in bolus transit time between the hemispheres. In the stroke patient, this difference resolved when re-evaluated 1 day after thrombolysis. The study demonstrates the necessity of a technique with sub-nanosecond time resolution to allow for depth discrimination if clinical perfusion monitoring of cerebrovascular diseases is addressed by optical methods.

Adult↗
PubMed2000

Manifestation of internal organs malfunction by laser Doppler study on microcirculation.

Monitoring of microvascular blood perfusion provides very specific information on the proper function or malfunction of some internal organs, e.g. the pancreas and kidney. The laser Doppler method was used to measure microperfusion in the skin of the lower limb of diabetic patients and patients undergoing hemodialysis. This method offers non-invasive, real-time monitoring and is already accepted in many clinical experiments. The method and the laser Doppler instruments used are described. Special attention is paid to the investigation of microvascular abnormality in diabetes by using a multichannel laser Doppler system during postocclusive reactive hyperemia. The study group consisted of 41 diabetes and 24 healthy subjects with no history of family diabetes. The most valuable data were obtained from the probe located on the most distal part of the foot. Some hyperemic parameters (maximum of hyperemic response, time to peak flow) were significantly different for the diabetic group as comparing to the norm. In the microcirculation study during hemodialysis, three patients with kidney dysfunction were investigated. Increase in red blood cell velocity was observed, probably caused by better distribution of blood to the peripheral circulation.

Blood Flow Velocity↗
PubMed1999

Spectral analysis of laser-Doppler perfusion signal measured during thermal test.

The method of spectral analysis of laser-Doppler perfusion signal measured during thermal test is proposed. During three 20 min phases with 40, 5, and 40 degrees C of thermal test laser-Doppler perfusion signal was recorded. For each signal phase frequency spectra were calculated using the FFT method. Quantitative parameter Spectral Factor for results evaluation was proposed. In total 94 patients were measured: 69 with Raynaud's phenomenon and 25 normal subjects. Additionally in 18 Raynaud's patients the influence of Nifedipine was studied. Results suggest that proposed parameter is able to differentiate between Raynaud's patients and normal subjects and that is useful for evaluation of Nifedipine effectiveness. However, further studies are needed to improve the method to differentiate between primary and secondary Raynaud's patients.

Adult↗
PubMed1998

Multichannel laser-Doppler probe for blood perfusion measurements with depth discrimination.

The laser-Doppler method is frequently used in clinical experiments for blood perfusion measurement. A multichannel laser-Doppler probe was constructed, and calibrated and evaluated using a flow model and real examination of healthy subjects. Results obtained on a three-capillary flow model suggest that the probe can be used to obtain information from superficial and deeper layers of the tissue. The influence of the optical arrangement of the laser-Doppler probe on the parameters of post-occlusive reactive hyperaemia was investigated in a group of 15 healthy subjects. A statistically significant increase of biological zero with distance between emitting and detecting fibres was noted.

Humans↗
PubMed1998

[Use of laser-doppler perfusion for evaluation of microcirculation in patients with diabetes type I].

UNLABELLED: The purpose of this study was to investigate the foot skin microcirculation in type 1-diabetic patients. The study group comprised 67 patients divided into four subgroups: 13 women and 11 men healthy and had no family history of diabetes; 19 women and 24 men had type 1-diabetes. The studied measurements included 7 parameters determined during rest and post occlusive hyperaemia. They were performed with laser Doppler fluxmetry using surface probe localised in distal part of the lower limbs. The most significant data localised the probe in thumb. The maximum of hyperaemic response (MAX) was significantly lower in the diabetic patients as compared to the healthy subjects (p < 0.01). The time of peak flow (TM) was higher (p < 0.01) in diabetic patients as compared to the control subjects. The half time of hyperaemia (TH) was significant longer (p < 0.05) for diabetic groups. CONCLUSION: The laser Doppler method is helpful to identify patients with risk development diabetic complications. The most valuable data is MAX, TM and TH, the best localisation of the probe seems to be the most distal point of thumb.

Adult↗
PubMed1988

[The clinical use of polyvalent immunoglobulin preparations].

A short survey is given of the indication for the use of polyvalent human immunoglobulin (human gamma globulin). The effect for the prophylaxis in hepatitis A is ascertained. The indication in the primary antibody deficiency syndrome is obligatory. In the secondary antibody deficiency syndrome with a moderate decrease of the immunglobulins as a rule a substitution is not indicated. A general prophylaxis or adjuvant therapy in surgical interventions, in polychemotherapy and in the framework of an intensive therapy without presence of an immune defect is to be refused. If in individual cases in sepsis, burn diseases or therapy-refractory infections additionally immunoglobulins are given, this must be done in high dosage. The modulation of immune reactions in autoimmunopathies is a new indication. Hyperimmunoglobulin and monoclonal antibodies will in future determine the immunoglobulin therapy.

Autoimmune Diseases↗
PubMed1987

[Variation in nocturnal blood pressure behavior in stage III (WHO) hypertension--a case report].

In some cases of hypertensive men the authors obtained 24-hour blood pressure profiles by easy non-invasive technique (Mercury manometer) and under the usual atmosphere and activities of a hospital. The control Group, 32 normotensive men, showed a normal circadian blood pressure variability with systolic acrophases at 10.00 h and 16.00 h and a bathyphase around 3.00 h. The diastolic blood pressure had a smaller variability. One patient with essential hypertension stage II (WHO), case 1, kept the normal day-night rhythm. By case 2, a man with essential hypertension stage III (WHO), the authors refer to the possibility of considerable differences of blood pressure behaviour during the night in cases of severe hypertension in contrary to normal blood pressure variability. After a supplementary fourth medication this patient showed a significant decrease of blood pressure during the night. Nevertheless he kept his acrophase at night. The recording of day-night profiles of blood pressure seems to be useful in relation to the judgement of classification of severity, of the mode of anti-hypertensive medication and of the success in therapy.

Antihypertensive Agents↗
PubMed1986

[Immunomodulation with apheresis technics].

The use of apheresis therapy (plasmapheresis/plasmafiltration or cytopheresis) was successful in numerous immunological diseases. Autoimmune and immune complex diseases as well as paraproteinemias with hyperviscosity syndrome (M. Waldenström, plasmocytoma) are the main indications. The several modifications of apheresis and its indications are outlined, and possible immune regulatoric effects of apheresis therapy are discussed. Finally this paper refers to beginning changes from unspecific to more selective methods of apheresis (cascade filtration, cryofiltration, immunoadsorption, enzymatic degradation, continuous electrophoresis) and its significance for clinical and experimental immunology.

Adjuvants, Immunologic↗
PubMed1984

[Plasma exchange therapy (plasmapheresis/plasmafiltration). II. Indications and complications].

On the basis of an extensive study of references as well as of own experiences the present state of the plasma exchange therapy, its success, problems and tendencies are represented. In the 1st part the essential modifications of the technique (plasmapheresis/plasma filtration), problems of anticoagulation, kind and quantity of the substitution as well as tendencies to more specific separation methods are explained. The 2nd part gives a survey of all essential indications (Goodpasture's syndrome, myasthenia gravis, hyperviscosity syndrome, lupus erythematodes visceralis, intoxications) and shows the main complications.

Connective Tissue Diseases↗
PubMed1984

[Plasma exchange therapy (plasmapheresis/plasma filtration). I. Technic].

With the help of an extensive study of literature as well as of own experiences the technical aspects of the plasma exchange therapy are described. Issuing from their hitherto existing course of the development and corresponding to their present significance the essential signs of the nowadays usual modifications (plasmapheresis by means of sedimentation in transfusion containers or by means of blood cell separator as well as plasma filtration) are explained. The discussion of problems of anticoagulation, the kind and quantity of substitution solutions as well as of developmental tendencies to more specific separation techniques leads over to the survey of essential indication areas (part II).

Anticoagulants↗
PubMedDate not supplied

Comparison of the tumor associated proteases cathepsin D (CATH D) and urokinase-type plasminogen activator (uPA) in cytosols of human breast cancer patients.

As a matter of routine, prepared cytosols of human primary breast cancer specimens (n = 230) are analysed for both CATH D and hormone receptor status (ER,PR). Retrospectively, uPA was determined in the samples. The selection criterion for the retrospective analysis was the possibility of a longitudinal follow-up of the patients. All tumor stages were included, but the main emphasis was on lower tumor stages (T1, and T2) as well as nodal negative stages (N0). The results of the hormone receptor status (ER,PR) were: ER+PR+ 66.37%; ER+PR- 10.18%, ER-PR+ 10.18%, ER-PR- 13.27%. The CATH D results ranged from 5 to 246 pmol/mg protein. 30.97% of these results rose above 50 pmol/mg protein (positive), 42.48% were below 35 pmol/mg protein (negative). The uPA results ranged from 0.05 to 3.74 ng/mg protein. 27.43% of the uPA results rose above 0.71 ng/mg protein (positive), 58.85% were below 0.53 ng/mg protein (negative). Raised results of uPA are distinct in the higher tumor stages (T1N0 > T2N0 > T2N1 > T4Nx). Although the CATH D and uPA measurements showed similar results (positive/negative distribution) in the general survey, the confirmity of both factors is rather limited if it is focused to single cases. Between CATH D and uPA there was a confirmity of 50% (T1N0) of 45.5% (T2N0) respectively in the range of positive results, and there was a confirmity of 60.3% (T1N0) and 65.8% (T2N0), respectively, in the range of negative results. Differences were seen in 19.2% (T1N0) and 22.7% (T2N0), respectively, in the range of positive results, and in 20.6% (T1N0) in 1508% (T2N0), respectively, in the range of negative results. The prospectively diagnostic value of these is still under observation.

Biomarkers, Tumor↗
PubMedDate not supplied

Effectiveness of high resolution ECG spectral analysis in discrimination of patients prone to ventricular tachycardia and fibrillation.

INTRODUCTION: To improve the diagnostic power of high resolution electrocardiography for discriminating patients at risk of ventricular arrhythmias, new methods based on spectral analysis have been used in recent years. The purpose of this study was to evaluate the effectiveness of these methods for predicting the risk of ventricular tachycardia and ventricular fibrillation in patients after myocardial infarction. MATERIAL AND METHODS: High resolution ECG were recorded in 129 post-infarction patients and 23 healthy volunteers. Of the post-infarction patients: 62 presented with ventricular tachycardia, 23 with ventricular fibrillation, while 44 had no clinically relevant arrhythmias. The ECG signals were recorded in three orthogonal X, Y, Z leads and averaged using cross-correlation method. Spectral analysis was performed by fast Fourier transform and the parametric modeling method with autoregressive model. Spectral analysis data were evaluated quantitatively by computing normality factor for FFT and spectral factor for AR. RESULTS: Both methods were found to be useful for evaluating the risk of arrhythmias. The sensitivity of ventricular tachycardia risk evaluation was higher (81%--FFT, 73%--AR) than that of evaluating the risk of ventricular fibrillation (30%--FFT, 48%--AR). The specificity in post-infarction patients without arrhythmias (93%--FFT, 84%--AR) was as high as that in healthy subjects (96%--FFT, 87%--AR). CONCLUSIONS: Spectral analysis of HRECG is an effective method for evaluating the risk of VT and VF in patients after myocardial infarction.

Adult↗
PubMedDate not supplied

[Near infrared spectroscopy: a noninvasive optical method for monitoring cerebral oxygenation and hemodynamics].

The Near Infrared Spectroscopy (NIRS) has been established as a non-invasive method for monitoring the oxygenation state of human brain at the bedside. This possible by observing spectral changes in the tissue caused by presence of oxygenated hemoglobin, deoxygenated hemoglobin and cytochrome aa3. In this paper the technical data of the NIRS instrument and its clinical application particularly in investigation of cerebral oxygenation and hemodynamic has been described.

Brain↗