Development of an autonomic portable single-board computer based high resolution NIRS device for microcirculation analysis

Near Infrared Spectroscopy (NIRS) is a wellestablished non-invasive technique for measuring metabolic changes in biological tissue. In this paper we describe the design and development of an autonomic portable single board computer based high resolution NIRS device, which allows quantification of these changes. The sensor-patch consisting of 8LEDs and 2photo-detectorsprovides8 channels for each detector, offering increased depth resolution for monitoring microcirculatory activity..NIRS data is acquired with a sampling rate of about 2Hz per channel using the data acquisition board which consists of a 16 bit ADC, a LED driver and programmable gain amplifiers. The components on the data acquisition board are controlled via the Advantech's PCM-3355L SBC based on Windows XP platform. The software was created using Visual Basic 6.0 and Microsoft Visual C++ 6.0. It offers optionally a real time 'monitoring' and a static data (offline) visualization mode. The most unique feature of the system is its ability to auto-calibrate itself i.e. Adopt the intensity of the LEDs output light to different experimental conditions, e.g. local melanin content, density of the tissue, and emitter-detector distances. To validate the device various experiments have been carried out such as measurements on resting and working gastrocnemius and biceps muscle in ambulatory situations. The achieved results confirmed adequate performance and reliability of the device.

Usefulness of simultaneous EEG-NIRS recording in language studies

One of the most challenging tasks in neuroscience in language studies, is investigation of the brain's ability to integrate and process information. This task can only be successfully addressed by applying various assessment techniques integrated into a multimodal approach. Each of these techniques has its advantages and disadvantages, but help to elucidate certain aspects of the capacity of neural networks to process information. These methods provide information about changes in electrical, hemodynamic and metabolic activities. Ideally, they should be noninvasive in order to facilitate their use particularly in children. In the present review, we describe the advantages of simultaneous electroencephalographic (EEG) acquisition with near infrared spectroscopy (NIRS) to provide a better understanding of the mechanisms involved in cerebral activation. This coregistration is also useful to avoid misleading interpretation of NIRS, notably during the various phases of sleep. Development and implementation of the various tools required and assessment strategies are also discussed.

Development of the human choriocapillaris

Vasculogenesis and/or angiogenesis are thought to be the major mechanisms for new vessel formation during development. A third mechanism, haemo-vasculogenesis, has been described in which blood vessel and blood cells (haematopoiesis (expression of CD34(+)) and erythropoiesis (presence of epsilon chain of haemoglobin or Hb-epsilon(+))) differentiate from a common precursor, the haemangioblast. This review describes the mechanism(s) for development of human choroidal vascular from 6 until 22 weeks gestation (WG). Endothelial cell or EC (CD31, CD34, CD39, VEGFR-2) and angioblast (CD39, VEGFR-2) markers were present in choriocapillaris (CC) by 7 WG through 22 WG. From 6 to 8 WG, many erythroblasts (nucleated Hb-epsilon(+) RBCs) were observed in the CC layer. Erythroblasts (Hb-epsilon(+)) were also positive for CD34, CD31, and/or VEGFR-2. Proliferation of vascular cells (Ki67+), suggesting angiogenesis, was not observed until 12 WG. TEM analysis demonstrated that CC was structurally immature even at 11 WG: no basement membrane, absence of pericytes, and poorly formed lumens that were filled with filopodia. Contiguous fenestrations and significant PV-1 (protein in diaphragms of fenestrations) were not observed until 21-22 WG. Smooth muscle actin was prominent at 20 WG and the maturation of pericytes was confirmed by TEM. Therefore, the embryonic CC appears to form initially by haemo-vasculogenesis (Hb-epsilon(+)/CD31(+) cells), whereas angiogenesis (CD34(+)/Ki67(+)) appears to be the mode of intermediate and large choroidal vessel development later in the foetus. Contiguous fenestrations, mature pericytes, and EC basal lamina occur late in development, around 22 WG, which coincides with photoreceptors developing inner segments.

Neonatal probabilistic models for brain, CSF and skull using T1-MRI data: preliminary results

Inappropriate results may be produced if one uses adult or pediatric atlases for evaluation of neonatal cerebral images for morphological studies. This is mainly due to anatomical particularities typical for this early stage of development. In this paper, we describe the construction of a digital neonatal brain atlas from a set of images of neonates aged between 39 and 42 weeks. It consists of probabilistic models for brain, cerebrospinal fluid (CSF) and skull. In the first step, the selected images are segmented automatically followed by manual correction. In the second step, the images are normalized to a stereotaxic space defined by the neonatal brain atlas template GRAMFC_T(39-42) using a popular normalization algorithm implemented in Statistical Parametric Mapping (SPM). The normalization parameters of individual subjects are then used to resample the corresponding brain, CSF and skull. Finally, to construct the probabilistic models, the average is computed for each voxel location. The atlas might be used for different applications such as source localization or neonatal structural image analysis.

Segmentation of scalp and skull in neonatal MR images using probabilistic atlas and level set method

In this paper, we present a novel automatic algorithm for scalp and skull segmentation in T1-weighted neonatal head MR images. First, the probabilistic scalp and skull atlases are constructed. Second, the scalp outer surface is extracted based on an active mesh method. Third, maximum number of boundary points corresponding to the scalp inner surface is extracted using the constructed scalp probabilistic atlas and a set of knowledge based rules. In the next step, the skull inner surface and maximum number of boundary points of the outer surface are extracted using a priori information of the head anatomy and the constructed skull probabilistic atlas. Finally, the fast sweeping, tagging and level set methods are applied to reconstruct surfaces from the detected points in three-dimensional space. The results of the new segmentation algorithm on MRI data acquired from nine newborns (including three atlas and six test subjects) were compared with manual segmented data provided by an expert radiologist. The average similarity indices for the scalp and skull segmented regions were equal to 89% and 71% for the atlas and 84% and 63% for the test data, respectively.

Coupled oxygenation oscillation measured by NIRS and intermittent cerebral activation on EEG in premature infants

Electroencephalography of premature neonates shows a physiological discontinuity of electrical activity during quiet sleep. Near infrared spectroscopy (NIRS) shows spontaneous oscillations of hemoglobin oxygenation and volume. Similar oscillations are visible in term neonates and adults, with NIRS and other functional imaging techniques (fMRI, Doppler, etc.), but are generally thought to result from vasomotion and to be a physiological artifact of limited interest. The origin and possible relationship to neuronal activity of the baseline changes in the NIRS signal have not been established. We carried out simultaneous EEG-NIRS recordings on six healthy premature neonates and four premature neonates presenting neurological distress, to determine whether changes in the concentration of cerebral oxy- and deoxy- and total hemoglobin were related to the occurrence of spontaneous bursts of cerebral electric activity. Bursts of electroencephalographic activity in neonates during quiet sleep were found to be coupled to a transient stereotyped hemodynamic response involving a decrease in oxy-hemoglobin concentration, sometimes beginning a few seconds before the onset of electroencephalographic activity, followed by an increase, and then a return to baseline. This pattern could be either part of the baseline oscillations or superimposed changes to this baseline, influencing its shape and phase. The temporal patterns of NIRS parameters present an unique configuration, and tend to be different between our healthy and pathological subjects. Studies of physiological activities and of the effects of intrinsic regulation on the NIRS signal should increase our understanding of these patterns and EEG-NIRS studies should facilitate the integration of NIRS into the set of clinical tools used in neurology.

A new method to model change in cutaneous blood flow due to mechanical skin irritation

Mechanical skin irritation, for example a light scratch with a needle, induces histamine and neuropeptide release on the line of stroke and in the surrounding tissue. Both histamine and neuropeptides are vasodilators. They cause vasodilation by changing the contraction state of the vascular smooth muscles and hence vessel compliance. Smooth muscle contraction state is very difficult to measure in vivo. For that reason we propose in this article an identification procedure to establish an irritation law. The law gives change in vessel compliance as a function of space, time and the intensity of the stroke. We have showed that vessel compliance increases immediately after the stroke not only on the line of stroke, but also in the surrounding tissue. Then, after a short delay, vessel compliance starts decreasing in the surrounding tissue, whereas vessel compliance on the line of stroke keeps increasing. Hence, blood is transported from the surrounding tissue to the line of stroke. In this way, higher blood volume on the line of stroke can be obtained than by only changing vessel compliance locally.

A new method to model change in cutaneous blood flow due to mechanical skin irritation

Mechanical skin irritation creates vasodilation. Vasodilation of vascular networks induces increase in blood volume and blood velocity. Both can be measured by Laser Doppler Velocimetry. We propose in this article a method permitting comparison between experimental and numerical results. Experimental data was obtained by Laser Doppler Velocimetry. Numerical results were obtained by a continuous model of the vascular network. The model consists of three layers. First and last layer are described by anisotropic and heterogeneous porous media. They represent the irrigation and the drainage of the vascular system. The intermediate layer is described by a lumped parameter model that does not permit horizontal fluxes. All vessels are compliant. The permeabilities depend on the volumes of the specific layer. Skin irritation is modeled by a change in compliance of small arterial blood vessels. The comparison between experimental and numerical data is based on the model proposed by Bonner and Nossal [1981. Model for laser Doppler measurements of blood flow. Appl. Opt. 20, 2097-2107]. The model describes the Doppler frequency spectrum S(omega) as a function of the optical phenomena creating the frequency shift. The comparison is based on the model of the first moment M1 approximately integralomegaS(omega)domega. The variables of the first moment can be determined by results of the numerical model. We have shown, that it exists a linear relation between the change in compliance and the following increase in first moment. Using this linear relation experimental and numerical data can be compared.

Automated neonatal seizure detection: A multistage classification system through feature selection based on relevance and redundancy analysis

OBJECTIVE

Automatic seizure detection obtains valuable information concerning duration and timing of seizures. Commonly used methods for EEG seizure detection in adults are inadequate for the same task in neonates because they lack the specific age-dependant characteristics of normal and pathological EEG. This paper presents an automatic seizure detection system for newborn with focus on feature selection via relevance and redundancy analysis.

METHODS

Two linear correlation-based feature selection methods and the ReliefF method were applied to parameterized EEG data acquired from six neonates aged between 39 and 42 weeks. To evaluate the effectiveness of these methods, features extracted from seizure and non-seizure segments were ranked by these methods. The optimized ranked feature subsets were fed into a backpropagation neural network for classifying. Its performance was used as indicator for the feature selection effectiveness.

RESULTS

Results showed an average seizure detection rate of 91%, an average non-seizure detection rate of 95%, an average false rejection rate of 95% and an overall average detection rate of 93% with a false seizure detection rate of 1.17/h.

CONCLUSIONS

This good performance in detecting newborn ictal activities has been achieved based on an optimized subset of 30 features determined by the ReliefF-based detector, which corresponds to a reduction of the number of features of up to 75%.

SIGNIFICANCE

The presented approach takes into account specific characteristics of normal and pathological EEG. Thus, it can improve the accuracy of conventional seizure detection systems in newborn.

Relationship between ultrastructure and biomechanical properties of the knee meniscus

The purpose of this study was to determine the biomechanical properties of the knee meniscus and to relate them to its ultrastructure. The knee joint menisci are semicircular, fibrocartilaginous structures interposed between the femoral and tibial condyles. For a long time, they were considered to be embryologic vestiges. This study describes the response of the knee joint meniscus to circumferential, radial and axial compressive forces. The results show an anisotropic response of the knee joint meniscus to unconfined compression. The Young's modulus increased approximately twofold between vertical and circumferential or radial directions with a 10 mm/min-compression rate. This response is probably a direct consequence of the orientation of collagen fibres.

A three-layer continuous model of porous media to describe the first phase of skin irritation

Mechanical skin irritation induces vasodilation on the line of scratch and in the neighboring zone. In order to model the effect of an irritation on the microcirculation, the vascular network has been described using a three-layer model. The first and last layer, considered as horizontal two-dimensional porous media, describe irrigation and drainage of the system, respectively. The intermediate layer, described by means of a lumped parameter method, does not permit horizontal fluxes. Hierarchical fluxes are directed from the first to the second layer and then towards the drainage layer in order to take into account physiological flow direction. Irritation is modeled by changing compliance of vessels situated at the entrance of the micro-circulation. The model permits to investigate the influence of change in compliance on flow and pressure behavior at microscopic and macroscopic level.

First phase microcirculatory reaction to mechanical skin irritation: a three layer model of a compliant vascular tree

Mechanical skin irritation creates vasodilatation in the line of a stroke and in the surrounding tissue. To obtain further insight on underlying physiological mechanisms we developed a model of the vascular network comprised of three layers, where the first and the last one have a tree structure. They represent the arterial and the venous system, respectively. Both are connected via an intermediate zone representing the core of the microcirculation, which is described by means of a compliant compartment model. Irritation induces change in compliance of vessels situated at the entrance of the intermediate zone. Thus the model describes flow and pressure behavior due to mechanical skin irritation.

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.

Influence of age and osteoporosis on calcaneus trabecular bone structure: a preliminary in vivo MRI study by quantitative texture analysis

Recent developments in high-resolution MR imaging techniques have opened up new perspectives for structural characterization of trabecular bone by non-invasive methods. In this study, 3-D MR imaging was performed on 17 healthy volunteers and 6 osteoporotic patients. Two different MR sequences were used to evaluate the impact on MR acquisition on texture analysis results. Images were analyzed with four automated methods of texture analysis (grey level histogram, cooccurrence, runlength and gradient matrices) enabling quantitative analysis of grey level intensity and distribution within three different regions of interest (ROI). Texture analysis is not very frequently used since the interpretation of the large number of calculated parameters is difficult. We applied multiparametric data analyses such as principal component analysis (CFA) and hierarchical ascending classification (HAC) to determine the relevant parameters to differentiate between three sets of images (healthy young volunteers, healthy postmenopaused and osteoporotic patients). The results suggest that relevant texture information (depending on the ROI localization in the calcaneus) can be extracted from calcaneus MR images to evaluate osteoporosis and age effects on trabecular bone structure if strictly the same acquisition sequences are used for all patients' examination.

Viscoelastic deformation response of red blood cells under conditions of oscillating centrifugal field

The red cell deformation under the conditions of oscillating centrifugal fields was studied. Experiments were carried out with a modified Cell-Elastometer operating in oscillating mode (0.02 to 0.30 Hz). Gravitational acceleration was sinusoidally modulated between 620 g and 2250 g. At low frequencies (below 0.08 Hz), native red cells followed the applied stress without delay. At 0.09 Hz and up, the cellular deformation was still periodical and included an additional perturbation due to intracellular movements. This perturbation was analysed and quantified. The influence of alterations on the erythrocyte membrane by diamide was analysed to verify the sensitivity of this method. On increasing the membrane stiffness with low concentrations of diamide, the response to oscillatory centrifugal stress was impaired characteristically in terms of amplitude deformation. Based on tangential and centrifugal accelerations, a physical model was developed that describes the basic observable changes on varying the oscillation frequency. From the data it can be concluded that viscoelastic properties of red cells can be analysed and quantified using oscillatory centrifugal accelerations. The described method can become a valid tool to differentiate between membrane alterations or intracellular viscous modifications.

Viscoelastic and biochemical properties of erythrocytes during storage with SAG-M at +4 degrees C

During storage at +4 degrees C, red blood cells undergo biochemical and physicochemical modifications, which alter their rheological characteristics especially the deformability. Even so until now not precisely defined deformability is undoubtedly a function of whole cell elasticity and viscosity. In a previous study we have investigated changes of elasticity of whole RBCs during a 6 weeks storage by quasi-static experiments using our Cell-Elastometer method. Since the changes in deformability we observed with that experimental approach have not been significant we extended the hard/software capabilities of this instrument to enable dynamic measurements also. We applied this modified hard-/software set-up to examine again changes in viscoelasticity of erythrocytes from concentrates during a six weeks storage at a blood bank. The cells were resuspended in CPD-SAG-M and stored at +4 degrees C. Quasi-static and dynamic experiments were performed on stored erythrocytes and showed for both significant changes in elasticity and viscoelasticity from the fourth week on. So it can be stated that due to our experimental results decrease in deformability of RBCs during storage occurs after a four weeks period of relative stability. To get further insight in changes of underlying or related biochemical properties according experiments have been performed in parallel. Especially the decrease in ATP showed a nearly parallel time course with a significant decrease after the 4th week. All other parameters especially the 2,3 DPG level showed a nearly linear de- or increase with time which are in accordance with the results of the additionally performed elongation experiments. Our quasi-static and dynamic deformability measurements have been proven to provide a simple and reliable tool to follow up erythrocyte senescence during storage where a pronounced change in mechanical properties may be used as an indicator for a change in bioviability. This has to be verified in further experiments.

Cyclic AMP-dependent cell shape changes induced by mechanical forces

Biomaterials used in some biomedical devices are exposed to flow of physiological fluids. The flow-induced forces may influence the morphological and the biochemical responses of adhering cells. The objective of this work is to examine the capacity of a mechanical stress to cause changes in cell/substratum and cell/cell interactions via the second messenger cAMP pathway (cyclic Adenosine Monophosphate). Cyclic AMP is known to modulate cell shape, cell adhesion and intercellular communication in static conditions. A specially designed flow chamber was used to analyze the responses of mouse 3T3 fibroblasts spread on biocompatible substrata and submitted to controlled shear stresses. A 1.1-Pa shear stress induced: cell rounding, disruption of vitronectin receptors clusters and clustering of connexins 43 at cell-cell apposition points. These cell responses were cAMP-dependent. These investigations should help provide a better understanding of the early biochemical events triggered by mechanical forces.

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.

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.

[Three-dimensional modelling of thoracic aortic aneurysm. A case report]

The anatomical forms of aneurysms are sometimes complex. Three-dimensional modelisation may be valuable in understanding the configuration and spatial orientation on one hand and also help in therapeutic decision making on the other. Two types of modelisation are reported with details of their methods and their respective values.

Automated surface and volume measurement of fused cells

OBJECTIVE

To design and evaluate an algorithm to automatically calculate membrane area, volume and derived values from grey scale microscopic images of pairs of spheroid fused cells, especially human erythrocytes.

STUDY DESIGN

Pairs of fused cells ("doublets") were identified by their high optical contrast, which resulted from their unhemolysed state. Global thresholding and noise-removing algorithms were applied to the image and resulted in a binary, "8"-shaped contour. The contour was used as a base for the calculation of a two-dimensional weighted distance histogram, the hilltops of which could be identified as center points of the contour's spheres. This allowed calculation of the distance of both center points and of the spheres' radii. With these three values, calculation of membrane area, volume and other derived values of the doublets became possible. High-speed time series were created based on consecutive images of the postfusion swelling and hemoglobin ejection from erythrocyte doublets at different temperatures.

RESULTS

The influence of observation temperature on the dynamics of electrofused erythrocytes was measured with the algorithms given, and results were in agreement with physical changes in cell plasma viscosity. Images taken by optical and electron microscopy were in agreement with the two-spheres model of a doublet. The algorithm was not affected by fragmented contours.

CONCLUSION

The velocity of hemoglobin ejection from electrofused erythrocytes and the relative change in static membrane area increase with temperature. The algorithm delivered reliable geometric values of fused cell configurations.

Nonstationary time-series analysis applied to investigation of brainstem system dynamics

Previous investigations of the dynamic organization of the lower brainstem and its relation to peripheral and other central nervous systems were predominantly performed by linear methods. These are based on time-averaging algorithms, which merely can be applied to stationary signal intervals. Thus, the current concept of the common brainstem system (CBS) in the reticular formation (RF) of the lower brainstem and basic types of its functional organization have been developed. Here, we present experiments where neuronal activities of the RF and the nucleus tractus solitarii (NTS, first relay station of baroreceptor afferents) were recorded together with related parameters of electroencephalogram (EEG), respiration, and cardiovascular system. The RF neurons are part of the CBS, which participates in regulation and coordination of cardiovascular, respiratory, and motor systems, and vigilance. The physiological time series, thus acquired, yield information about the internal dynamic coordination of the participating regulation processes. The major problem in evaluating these data is the nonlinearity and nonstationarity of the signals. We used a set of especially designed time resolving methods to evaluate nonlinear dynamic couplings in the interaction between CBS neurons and cardiovascular signals, respiration and the EEG, and between NTS neurons (influenced by baroreceptor afferents) and CBS neurons.

Herbimycin A in the treatment of experimental proliferative vitreoretinopathy: toxicity and efficacy study

BACKGROUND

Proliferative vitreoretinopathy (PVR) is partially caused by peptide growth factors, stimulating the cell by binding to a transmembrane tyrosine kinase receptor. We studied the effects of herbimycin A (HA), a tyrosine kinase inhibitor, in PVR.

METHODS

Toxicity studies: Electroretinography and histological studies were performed after intravitreal injection of HA. Efficacy studies: Homologous rabbit dermal fibroblasts were injected intravitreally, followed by injection of HA. The presence of tractional retinal detachment (TRD) and severity of inflammation were assessed.

RESULTS

Toxicity studies: Eyes injected with HA exhibited decrease in B-wave amplitude initially, with subsequent recovery. Histologically, damage to photoreceptors was evident after injection of high but not of low doses of HA. Efficacy studies: Inflammatory response and the development of TRD were significantly reduced with all doses of HA.

CONCLUSIONS

HA (20 microM) was found to be effective and safe in preventing the development of inflammation and TRD.

Phase transitions in the common brainstem and related systems investigated by nonstationary time series analysis

Neuronal activities of the reticular formation (RF) of the lower brainstem and the nucleus tractus solitarii (NTS, first relay station of baroreceptor afferents) were recorded together in the anesthized dog with related parameters of EEG, respiration and cardiovascular system. The RF neurons are part of the common brainstem system (CBS) which participates in regulation and coordination of cardiovascular, respiratory, somatomotor systems, and vigilance. Multiple time series of these physiological subsystems yield useful information about internal dynamic coordination of the organism. Essential problems are nonlinearity and instationarity of the signals, due to the dynamic complexity of the systems. Several time-resolving methods are presented to describe nonlinear dynamic couplings in the time course, particularly during phase transitions. The methods are applied to the recorded signals representing the complex couplings of the physiological subsystems. Phase transitions in these systems are detected by recurrence plots of the instationary signals. The pointwise transinformation and the pointwise conditional coupling divergence are measures of the mutual interaction of the subsystems in the state space. If the signals show marked rhythms, instantaneous frequencies and their shiftings are demonstrated by time frequency distributions, and instantaneous phase differences show couplings of oscillating subsystems. Transient signal components are reconstructed by wavelet packet time selective transient reconstruction. These methods are useful means for analyzing coupling characteristics of the complex physiological system, and detailed analyses of internal dynamic coordination of subsystems become possible. During phase transitions of the functional organization (a) the rhythms of the central neuronal activities and the peripheral systems are altered, (b) changes in the coupling between CBS neurons and cardiovascular signals, respiration and the EEG, and (c) between NTS neurons (influenced by baroreceptor afferents) and CBS neurons occur, and (d) the processing of baroreceptor input at the NTS neurons changes. The results of this complex analysis, which could not be done formerly in this manner, confirm and complete former investigations on the dynamic organization of the CBS with its changing relations to peripheral and other central nervous subsystems.

Characteristics of the osmotically induced membrane rupture

The phenomenon of reciprocating mechanical oscillations of electrofused erythrocytes was used to investigate the mechanical characteristics of ruptures induced in erythrocyte membranes by colloid osmotic pressure. The rupture characteristics follow an exponentially decaying time function. Time constants determined for opening times of ruptures decreased from 5.5 ms at 10 degrees C to 3.8 ms and 2.0 ms at 40 degrees C for the first and the last observable rupture, respectively. Evidence is given that the diameter of the membrane rupture exceeds the size of a haemoglobin molecule. With repetitive membrane rupturing, the ability of the membrane bilayer and associated structures to heal decreases, owing to the reduced ability to withstand pressure gradients. This change allows oscillating doublets to be classified according to one of three groups: group A showing no development in response to swell times, group B showing a continuous decrease in response to swell times, and group C showing a spontaneous decrease in response to swell times. These results suggest that oscillations cease as a result of defects of membrane healing. Calculations of respective temperature ranges are in agreement with temperature ranges for spectrin denaturation. Thus, conclusions obtained from this study suggest that the spectrin network plays a key role in membrane healing processes after mechanical membrane rupture.

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.

[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.

Long-term registration of cutaneous microcirculation during general anesthesia

The temporal dynamics of the systemic arterial pressure can be monitored noninvasively from the skin of the earlobe or forehead by photoplethysmography under the provision that the active control of the microcirculatory perfusion is eliminated. Using this approach, we have been able to detect a highly stable blood pressure rhythm in the range of 0.15 Hz during psychophysical relaxation or sleep. The aim of the present study was to investigate the occurrence and behavior of blood pressure rhythms below 0.2 Hz during general anesthesia. In 30 patients (ASA groups I-II) undergoing basic surgical procedures, photoplethysmographic recordings from the earlobe were made during the whole time of anesthesia. The recorded signals were divided into segments of 200 s of duration, the temporal structure of which was analyzed by fast Fourier transform. Different characteristic patterns of rhythmical behavior were detected: (1) absence of activity below 0.2 Hz ('low-frequency range'); (2) slow sinusoidal rhythmicity below 0.05 Hz; (3) 'chaotic' behavior, i.e. multiple incoherent fluctuations without stationary periods or amplitudes; (4) short-term rhythmical activity at about 0.15 Hz, and (5) long-term rhythmical activity at about 0.15 Hz. In patients sufficiently sedated to eliminate low-frequency activity, rhythmicity could sometimes be triggered by certain surgical stimuli, the response to which was suppressed by injection of opioids. The data presented strongly suggest that rhythmical perfusion patterns of the cutaneous microcirculation could serve as an indicator for the depth of anesthesia.

Synergetic interpretation of patterned vasomotor activity in microvascular perfusion: discrete effects of myogenic and neurogenic vasoconstriction as well as arterial and venous pressure fluctuations

Synergetic concepts allow to identify emergent coordination phenomena between interacting physiological systems, for example between the cutaneous microcirculation, the sympathetic nervous system and the cardiac and pulmonary systems. The temporal patterns (oscillations of various frequencies) that are found in the data obtained with laser-Doppler anemometers (LDA; e.g. Periflux 2 used in the study) can be investigated by simultaneous recording of photoplethysmographic data obtained in the identical region of interest, as well as in cutaneous regions treated with vasoparalytic procedures which permit to record the dynamics of the arterial system. These strategies were applied to studies in the cutaneous microcirculation (volar side of the index fingers) as well as to mucosal microcirculation (maxillar gingiva) in healthy subjects and in patients suffering from autonomic dysfunction (cutaneous microcirculation) or gingivitis. By this procedure, it could be corroborated that - contrary to popular notions - the temporal fluctuations in the LDA records do not necessarily reflect myogenic vasomotion, but can have multiple causes. In a confirming recent study [Schmid-Schönbein et al., J Auton Nerv Syst, 57, 136-140, 1996], we have demonstrated that the LDA fluctuations under conditions of normal ambient temperature and hand position most likely reflect neurogenic vasoconstriction. Under exceptional conditions, different patterns emerge. Prolonged exposure to ambient temperature (18 degrees C) leads to marked vasoconstriction, with occasional vasodilator escape ('miniature hunting reaction'). Normal subjects under gravitational load and in warm environment (28 degrees C ambient) silence their neurogenetic vasoconstriction reactions, which allows sinusoidal vasomotion to dominate. A similar phenomenon is seen in neuropathic patients at 21-24 degrees C (presumably due to structural defects). Fluctuations in LDA signal taken from the healthy gingiva are entrained to arterial, those taken from inflamed gingiva to respiratory activity. The theory and practice of nonlinear analysis is discussed, and data compression procedures allowing to portray characteristic temporal patterns for future diagnostic procedures are presented.