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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 25 (1987), S. 207-211 
    ISSN: 1741-0444
    Keywords: Blood flow measurements ; Laser Doppler flowmetry ; Signal processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The performance of different signal processors for laser Doppler tissue flowmeters was evaluated by the use of a well defined flow model comprising a segment of the feline intestinal wall. The processor that, apart from being based on the calculation of the first moment of the power spectral density, also takes into account the effect of multiple scattering in a number of blood cells gave an output signal that was linearly related to the intestinal wall perfusion as recorded independently by a drop-counting technique. At a recording bandwidth of 12 kHz, this linear relationship was valid for the entire flow range 0–300 ml min−1 100 g−1 (r=0·98). The processor based on the first moment of the power spectral density alone under-estimated the highest flow rates by about 35 per cent, while within the flow range 0–100 ml min−1 100 g−1 this processor also gave an output signal linearly related to flow at a recording bandwidth of 12 kHz (r=0·96). When the bandwidth was limited to 4 kHz, the output signals from both processors were linearly related to flow only within the range 0–100 ml min−1 100 g−1 (r=0·90). The output signals recorded with the 4 kHz systems were, however, generally only about 65 per cent of those recorded with the 12 kHz systems.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 31 (1993), S. 301-307 
    ISSN: 1741-0444
    Keywords: Laser Doppler flowmetry ; Light scattering ; Monte Carlo model ; Sampling depth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Monte Carlo simulation of photon migration in tissue was used to assess the sampling depth, measuring depth and photon pathlength in laser Doppler flowmetry. The median sampling depth and photon pathlength in skin, liver and brain tissue were calculated for different probe geometries. The shallowest median sampling depth found was 68 μm for a 120 μm diameter single fibre probe applied to a one-layered skin tissue model. By using separate transmitting and receiving fibres, the median sampling depth, which amounted to 146 μm for a 250 μm fibre centre separation, by be successively increased to 233 μm when the fibres' centres are separated by 700 μm. Total photon pathlength and thereby the number of multiple Doppler shifts increase with fibre separation, thus favouring the choice of a probe with a small fibre separation when linearity is more important than a large sampling depth. Owing mainly to differences in the tissue g-value and scattering coefficient, the median sampling depth is shallower for liver and deeper for brain, in comparison with skin tissue. For skin tissue, the influence on the sampling depth of a homogeneously distributed blood volume was found to be limited to about 1 per cent per percentage increase in tissue blood content, and may, therefore, be disregarded in most practical situations. Simulations show that the median measuring depth is strongly dependent on the perfusion profile.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 24 (1986), S. 415-419 
    ISSN: 1741-0444
    Keywords: Laser Doppler flowmetry ; Integrating probe ; Skin blood flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Methods to measure microvascular blood flow usually probe small volumes of tissue. Therefore, spatial differences in skin blood flow alter the signal, when the sensing element is moved a short distance. To reduce the effects of spatial differences in skin blood flow, but yet record its temporal variability, a new integrating probe for laser Doppler flowmeters was developed. The probe receives light from seven different scattering volumes simultaneously, and the instrument processes an integrated signal which is ultimately taken as the average flow value. Significant spatial integration is found, as spatial variability is reduced by the square root of the number of scattering volumes.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 168 (1998), S. 619-623 
    ISSN: 1432-136X
    Keywords: Key words Endothelin ; Gill ; Oncorhynchus mykiss ; Osmoregulation ; Respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The lamellae of the fish gill are the primary sites for oxygen uptake from the water. Here, only two very thin layers of cells separate the blood from the water. Therefore, energetically costly ion-fluxes will also occur between blood and water, and it has been hypothesised that the blood flow within the lamellae can be regulated through vasoconstriction, but evidence for this has been lacking. Through direct observations of the lamellae of rainbow trout (Oncorhynchus mykiss) in vivo, using epi-illumination microscopy, we show here that an endothelium-derived vasoactive peptide, endothelin-1 (ET-1, 0.2 μg kg−1 or 1.0 μg kg−1), is able to completely constrict the vascular sheet in the lamellae, probably by inducing contraction of pillar cells. This coincided with a dose-dependent increase in ventral aortic blood pressure (rising from 6.6 kPa to 12.0 kPa in response to the high ET-1 dose). However, blood continued to flow through the marginal channel that circumvents each lamella. Thus, ET-1 caused an intralamellar blood shift from the lamellar sheet towards the marginal channels. Vasoconstriction in the lamellae is likely to provide the fish with a mechanism for matching its respiratory surface area with its respiratory needs, thereby minimising ion-fluxes.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 15 (1977), S. 209-218 
    ISSN: 1741-0444
    Keywords: Evaporation ; Hygrometry ; Insensible perspiration ; Transepidermal water loss ; Sweat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Description / Table of Contents: Sommaire Une nouvelle méthode pour mesurer les échanges hydriques à travers la peau a été mise au point. Cette méthode, fondée sur l'estimation du gradient de pression de la vapeur adjacente à la surface de la peau, permet d'exposer cette surface à l'air ambiant normal pendant toute la durée de la mesure. L'humidité et la température du microclimat entourant la peau sont ainsi minimisées. Sur la base de cette nouvelle méthode, un instrument pour mesurer de petites quantité d'eau s'evaporant d'une surface ou absorbées par elle, calculées par unités de temps et de surface, a été mis au point et sa précision est examinées. Cet instrument, qui est destiné à être utilisé dans une gamme de températures allant de 15 à 40°C. et pour des valeurs de la pression atmosphérique comprises entre 98 et 104 kPa, s'est révélé offrir une mesure de haute précision et une sensibilité améliorée par comparaison avec les systèmes prélablement employés. Il a tout d'abord servi aux recherchest portant sur le taux d'évaporation à la surface de la peau des nouveaux-nés, de malades présentant des troubles de la thyroide et de brûlés. La construction de l'instrument le rend néanmoins particulièrement bien adapté pour mesurer les taux d'évaporation dans de nombreux autres domaines d'application.
    Abstract: Zusammenfassung Es wurde eine neue Methode zur Messung des Wasseraustausches durch die mensch liche Haut entwickelt. Die auf der Schätzung des Dampfdruckgradienten in unmittelbarer Nachbarschaft der Hautoberfläche beruhende Methode gestattet es, die zu untersuchende Oberfläche der normalen Umgebungsluft während der gesamten Meßperiode auszusetzen. Dadurch wird ein minimaler Einfluß auf die Feuchtigkeit und Temperatur des die Haut umgebenden Mikroklimas erzielt. Auf der Grundlage des neuen Verfahrens wird ein Instrument zur Messung kleiner Mengen von Wasser beschrieben, das von einer Oberfläche pro Zeit- und Flächeneinheit absorbiert oder verdampft wird, und seine Genauigkeit wird besprochen. Das für Verwendung im Temperatur-bereich von 15–40°C und im Luftdruckbereich von 98–104 kPa bestimmte Gerätzeigte im Vergleich mit vorher verwendeten Geräten eine hohe Genauigkeit und verbesserte Empfindlichkeit. Es wurde vor allem fur die Untersuchung der Verdampfungsrate von der Hautoberfläche Neugeborener wie auch thyrotoxischer und Bunddwunden-Patienten verwendet. Der Bau des Instrumentes macht es aber auch für die Messung von Verdampfungsraten bei vielen anderen Anwendungen sehr gut geeignet.
    Notes: Abstract A new method for the measurement of the water exchange through the human skin has been developed. The method, based on the estimation of the vapour-pressure gradient immediately adjacent to the surface of the skin, permits the surface investigated to be exposed to normal ambient air during the entire period of measurement. A minimal influence on the humidity and the temperature of the microclimate surrounding the skin is thereby achieved. On the basis of the new method an instrument for measuring small amounts of water evaporated from or absorbed by a surface per unit time and area is described and its accuracy discussed. The instrument, which is intended for use in the temperature range 15–40°C and the atmospheric pressure range 98–104 kPa, has proved to offer a high accuracy and an improved sensitivity in comparison with devices previously employed. It has been used primarily for investigations of the rate of evaporation from the skin surface of newborn infants as well as of thyrotoxic and burned patients. The construction of the instrument, however, makes it well suited for the measurement of evaporation rates in many other fields of application.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 22 (1984), S. 343-348 
    ISSN: 1741-0444
    Keywords: Blood flow ; Laser Doppler flowmetry ; Signal processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Laser Doppler flowmeter for the assessment of tissue blood flow are generally equipped with a signal processor which generates the first moment of the unnormalised power spectral density as a continuous output signal. This signal is related to blood flow for low and moderate flow rates. At higher flow rates the interpretation of the output signal becomes ambiguous as a consequence of the multiple scattering in moving blood cells and the homodyne mixing of waves on the detector surface. The paper describes a new signal processor which takes these effects into account and establishes a linear relationship between the flowmeter output signal and blood flow for all flow rates. The performance of the signal processor was evaluated by an experimental fluid model which optically resembled the blood flow through the microvasculature. The transiently high blood flow in the initial phase of reactive hyperaemia, recorded from palmar skin, gave peak values which were almost double those recorded with the original signal processor of the flowmeter. In conjunction with these high peak values a high concentration of moving blood cells was recorded, indicating that the initially high flow rate is produced by an increased number of moving blood cells due to vasodulation rather than by a change in average velocity.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2007-02-22
    Print ISSN: 0722-4028
    Electronic ISSN: 1432-0975
    Topics: Biology , Geosciences
    Published by Springer
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