PubMed Health⌕ Search

Biomedical subjects

R Maniewski

Publications and source records attributed to R Maniewski.

16 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↗
PubMed2004

Near-infrared spectroscopy in evaluation of cerebral oxygenation during vasovagal syncope.

Near-infrared spectroscopy (NIRS) offers a non-invasive, real-time monitoring of cerebral oxygenation. This method is based on the oxygenation and the light wavelength dependent absorption of near-infrared light by tissue chromophores, e.g. oxyhaemoglobin and deoxyhaemoglobin. The objective of the present study was the application of NIRS for evaluation of the brain function during vasovagal syncope (VVS). The VVS is a clinical syndrome affecting ca 3.5% of the population and for which the widely used diagnostic examination in this disease entity is the head-up tilt table test (HUT). In this study 69 patients with a history of VVS were examined using HUT. In 42 patients VVS was provoked. Results of the examination have shown that the changes in cerebral oxygenation measured by the NIRS technique are distinctly visible before the syncope. A gradual decrease of oxyhaemoglobin followed by its sudden drop was observed in all the VVS patients. Changes in the oxyhaemoglobin concentration measured by NIRS were observed on average 3.3 min before the syncope. They preceded the presyncope symptoms about 1.3 min (p < 0.005), the blood pressure and heart rate drop 2.2 min (p < 0.0001) and the arterial blood saturation 2.6 min (p < 0.00001).

Adolescent↗
PubMed2000

Risk evaluation of ventricular tachycardia using wavelet transform irregularity of the high-resolution electrocardiogram.

A new method for analysis of high-resolution ECG signals using a wavelet transform based on a modified Morlet function is presented. A polynomial filter is used to reduce low-frequency, high-amplitude noise components in the analysed signals. The method is tested on test ECG signals with simulated late potentials and finally verified on two post-infarction patient (PP) groups: 62 PPs with ventricular tachycardia and 44 PPs without arrhythmia. A new quantitative parameter, the irregularity factor, is proposed for discrimination between the study groups. The results show a significant difference in the parameter values for tachycardia patients compared with those for patients without arrhythmia. The sensitivity of the proposed method is 85%, and the specificity is 93%.

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

Principles and practice of the laser-Doppler perfusion technique.

This paper reviews the development and use of laser-Doppler perfusion monitors and imagers over the past two decades. The enormous interest in microvascular blood perfusion coupled with the 'ease of use' of the technique has led to 1500+ publications citing its use. However, useful results can only be achieved with an understanding of the basic principles of the instrumentation and its application in the various clinical disciplines. The basic theoretical background is explored and definitions of blood perfusion and laser-Doppler perfusion are established. The calibration method is then described together with potential routes to standardisation. A guide to the limitations in application of the technique gives the user a clear indication of what can be achieved in new studies as well as possible inadequacy in some published investigations.

Artifacts↗
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↗
PubMed1991

Tests of EEG localization accuracy using implanted sources in the human brain.

The accuracy with which electrical sources in the brain can be localized by using electroencephalograms measured on the scalp is not well known. In this study, tests of localization accuracy were performed by using implanted dipolar sources in the human brain. These dipoles are created by passing a weak (subthreshold) current through intracerebral electrodes implanted in the brains of epileptic patients for seizure monitoring. The locations of these dipoles are accurately known from roentgenographs. First, 16 electroencephalograms produced by these dipoles were recorded, then inverse solutions were calculated for the apparent sources of these electroencephalograms. Finally, the locations of the apparent sources were compared with the known locations of the implanted dipoles to determine localization error. The average localization error for a total of 28 dipoles in 3 subjects was 1.1 cm. These results indicate that good localization accuracy for focal sources in the brain can be provided by scalp electroencephalograms.

Brain↗
PubMed1991

Magnetic studies on mechanical activity of the heart.

Magnetic measurement offers a new noninvasive technique for monitoring cardiac mechanical activity and for evaluation of important hemodynamic parameters, e.g., heart volume changes and cardiac output. The magnetic signal is observed with a sensitive magnetometer when an external magnetic field is applied to the thorax. The magnitude of the signal is usually in the order of a few picoteslas when an applied magnetic field of about 250 A/m is used. This signal is due to the differences in magnetic susceptibilities of intracardiac blood, heart muscle, and surrounding lung tissues. In the present paper, the origin of the magnetic susceptibility signal is theoretically analyzed and various measurement techniques are reviewed. The measurement results reported by different authors are compared and discussed. The spatial variation of the magnetic signal is analyzed in terms of mathematical models and its temporal behavior is compared with the results obtained from other measurement techniques. Three independent experimental methods are proposed in order to separate the magnetic plethysmogram from the other components in the total magnetic susceptibility signal recorded above the heart. The results suggest that usually about 65 to 80% of the signal originates directly from cardiac volume changes, and that the cardiac plethysmogram can be separated easily by surrounding the thorax with the medium whose magnetic susceptibility is about -5.10(-6), or by preventing motion of the chest wall of the subject.

Biomechanical Phenomena↗
PubMed1990

MEG versus EEG localization test using implanted sources in the human brain.

It is believed that the magnetoencephalogram (MEG) localizes an electrical source in the brain to within several millimeters and is therefore more accurate than electroencephalogram (EEG) localization, reported as 20 mm. To test this belief, the localization accuracy of the MEG and EEG were directly compared. The signal source was a dipole at a known location in the brain; this was made by passing a weak current pulse simulating a neural signal through depth electrodes already implanted in patients for seizure monitoring. First, MEGs and EEGs from this dipole were measured at 16 places on the head. Then, computations were performed on the MEG and EEG data separately to determine the apparent MEG and EEG source locations. Finally, these were compared with the actual source location to determine the MEG and EEG localization errors. Measurements were made of four dipoles in each of three patients. After MEGs with weak signals were discounted, the MEG average error of localization was found to be 8 mm, which was worse than expected. The average EEG error was 10 mm, which was better than expected. These results suggest that the MEG offers no significant advantage over the EEG in localizing a focal source. However, this does not diminish other uses of the MEG.

Adult↗
PubMed1987

On the accuracy of source localisation in cardiac measurements.

This paper describes a localisation study of the sources of bioelectrical activity in the human heart. In particular, the atrial activation (P wave) and the activation of an extra pre-excitation area in the WPW syndrome are investigated. Different models based on the current multipole expansion are used to calculate the inverse solution. A comparison between calculated results, invasive electrophysiological studies and known physiological data is performed. The best results were obtained by the current multipole model with dipole and quadrupole terms. Non-invasive localisation of cardiac electric sources can be useful in studies of arrhythmia patients in the future.

Atrial Function↗
PubMed1982

Hall effect transducer for apexcardiography and sphygmography.

Recording of mechanograms (Recording of mechanical activity of internal organs and vessels, often non-invasively eg. apex cardiogram) can be performed by applying different kinds of mechano-electric transducers. In this paper the idea and construction of a new transducer with Hall-generator are presented. This transducer is self-adjusting in the range of its linear characteristics, and exerts practically constant touching pressure independent of the configuration of the patients thorax. This facilitates the measuring process and allows for calibration of the obtained records. The sensitivity of the transducer is 250 mV/mm, frequency bandwidth 0-45 Hz and it has a linearity of +/- 1.5% in the range of displacements +/- 1.5 mm. The transducer also generates the signal of the first derivative of the investigated vibrations. Assessment of the transducer was carried out in a cardiology clinic on 27 patients with a normal heart and with different kind and degree of heart damage. The mechanograms obtained from different transducers for each patient were compared in respect of the essential time intervals and morphological elements. The comparison shows a good detecting capability, correctness and reproducibility of the data obtained by means of the Hall-effect transducer. Some recordings of mechanograms (apexcardiograms and different kinds of pulse) from patients with normal heart, valvular aortic stenosis and atrial heart defect are shown and discussed in the paper.

Heart Diseases↗
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↗