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Biomedical subjects

F F de Mul

Publications and source records attributed to F F de Mul.

At least 19 recordsLinked to original sources
PubMed2001

Detection of photoacoustic transients originating from microstructures in optically diffuse media such as biological tissue.

The generation and detection of broadband photoacoustic (PA) transients may be used for on-axis monitoring or for imaging of optically different structures in the interior of diffuse bodies such as biological tissue. Various piezoelectric sensors are characterized and compared in terms of sensitivity, depth response, and directivity with respect to spherical broadband acoustic pulses. The influence on the sensor output of acoustic interference and refraction of the PA transients at the sample-sensor interface is discussed. Ring detectors are suitable for deep on-axis detection thanks to their strong directional sensitivity, and small disk sensors are most suited for 3-D imaging of microstructures such as the (micro)vascular system. Voltage and charge preamplification schemes are compared in terms of the signal-to-noise ratio (SNR). In all cases, the preamplifier noise turns out to be the limiting factor for the sensitivity. Based on experimental data, for several sensor types and optical wavelengths, the theoretical detectability of PA signals generated by blood-like absorbers in biological tissue is discussed.

Acoustics↗
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

Doppler Monte Carlo simulations of light scattering in tissue to support laser-Doppler perfusion measurements.

Doppler Monte Carlo (DMC) simulations of the transport of light through turbid media, e.g., tissue, can be used to predict or to interpret measurements of the blood perfusion of tissue by laser-Doppler perfusion flowmetry. We describe the physical and mathematical background of Doppler Monte Carlo calculations, and present some comparisons with measurements, performed with experimental flow models, built to mimic skin tissue characteristics and for the calibration of perfusion instruments,which are important goals of the Biomed-I concerted action. The measurements deal with coherence effects.

Calibration↗
PubMed1997

On refraction in Monte-Carlo simulations of light transport through biological tissues.

To obtain reliable results from Monte-Carlo simulations of light scattering experiments, a statistically accurate procedure for positioning the photons after refraction between two different scattering media is necessary. Two statistically equivalent algorithms for calculating the position of the photons immediately after crossing an interface are described and justified.

Algorithms↗
PubMed1992

A monitoring device for pressurised-air-driven diaphragm-based artificial heart assist devices.

A non-invasive device has been developed to monitor the diaphragm position and the blood flow in artificial heart assist devices equipped with a pressurised-air-driven diaphragm. Light scattering from the diaphragm is used as a mechanism for measuring. Information about the position of several points of the diaphragm can be obtained. The completely empty or filled situation can be detected and used for control purposes. Flow data can be extracted and bending characteristics of the diaphragm during operation can be studied.

Heart-Assist Devices↗
PubMed1992

Digital blood flow in cooled and contralateral finger in patients with Raynaud's phenomenon. Comparative measurements between photoelectrical plethysmography and laser Doppler flowmetry.

The effects of cooling of a hand on lateral and contralateral digital skin blood flow were investigated in 18 patients with primary or secondary Raynaud's phenomenon. The aim of the study was to compare photoelectrical plethsmography (PhEP) and laser Doppler flowmetry (LDF). PhEP and LDF were used simultaneously for skin blood flow measurements of the third finger of both hands. One hand was cooled in water from 33 degrees to 3 degrees C in steps of 3 degrees C, each step lasting four minutes. It was followed by a recovery period of ten minutes in room air of 24 degrees C. During stepwise cooling from 33 degrees to 9 degrees C the relative PhEP and LDF values, measured on the cooled hand, decreased to 6.2% +/- 3.2% and 10% +/- 12% respectively. The correlation coefficients between LDF and PhEP varied between 0.79 and 0.99. In the contralateral hand the relative PhEP and LDF values decreased to 38% +/- 30.% and 64% +/- 7.9% respectively. The correlation coefficients between LDF and PhEP values were lower on the contralateral hand and ranged from 0.26 to 0.95. By calculating the LDF/PhEP ratios during cooling and recovery, more specific changes in red blood cell velocities during cooling were studied. Increasing LDF/PhEP ratios suggest increasing red blood cell velocities during cooling at 9 degrees C and a difference in the measuring methods. For testing the severity of Raynaud's phenomenon and the effect of treatment the results of both methods show consistent and quite comparable results when measured on the cooled hand. The effect of indirect cooling on the contralateral hand is, however, less consistent.

Adult↗
PubMed1992

Reflectance pulse oximetry in fetal lambs.

Transmission pulse oximetry is used for monitoring in many clinical settings. However, for fetal monitoring during labor and in situations with poor peripheral perfusion, transmission pulse oximetry cannot be used. Therefore, we developed a reflectance pulse oximeter, which uses the relative intensity changes of the reflected red and infrared light (red/infrared ratio) to measure the arterial oxygen saturation. The performance of the reflectance pulse oximeter was studied in acute experiments in fetal lambs. By stepwise reduction of the inspired oxygen concentration of the ewe, measurements were done at the fetal scalp at various arterial oxygen saturation levels (17-82%). Reflectance pulse oximeter readings were averaged over periods of 15 s and compared with simultaneously taken fetal arterial blood samples. A calibration curve for the relationship between red/infrared ratio and arterial oxygen saturation was obtained from 53 measurements in four fetal lambs, by linear regression analysis [red/infrared = 4.088-(0.038.SaO2), r = 0.96]. In these experiments, the pulse oximeter showed a precision of 4.7% oxygen saturation around the calibration curve, with a 95% confidence interval of +/- 9.4%.

Animals↗
PubMed1991

Laser irradiation and Raman spectroscopy of single living cells and chromosomes: sample degradation occurs with 514.5 nm but not with 660 nm laser light.

In Raman spectroscopic measurements of single cells (human lymphocytes) and chromosomes, using a newly developed confocal Raman microspectrometer and a laser excitation wavelength of 514.5 nm, degradation of the biological objects was observed. In the experiments high power microscope objectives were used, focusing the laser beam into a spot approximately 0.5 micron in diameter. At the position of the laser focus a paling of the samples became visible even when the laser power on the sample was reduced to less than 1 mW. This was accompanied by a gradual decrease in the intensity of the Raman signal. With 5 mW of laser power the events became noticeable after a period of time in the order of minutes. It is shown that a number of potential mechanisms, such as excessive sample heating due to absorption of laser light, multiple photon absorption, and substrate heating are unlikely to play a role. In experiments with DNA solutions and histone protein solutions no evidence of photo damage was found using laser powers up to 25 mW. No degradation of cells and chromosomes occurs when laser light of 660 nm is used. The most plausible explanation therefore seems to be that the sample degradation is the result of photochemical reactions initiated by laser excitation at 514.5 nm of as yet unidentified sensitizer molecules or complexes present in chromosomes and cells but not in purified DNA and histone protein samples.

Animals↗
PubMed1991

Raman microspectroscopic approach to the study of human granulocytes.

A sensitive confocal Raman microspectrometer was employed to record spectra of nuclei and cytoplasmic regions of single living human granulocytes. Conditions were used that ensured cell viability and reproducibility of the spectra. Identical spectra were obtained from the nuclei of neutrophilic, eosinophilic, and basophilic granulocytes, which yield information about DNA and protein secondary structure and DNA-protein ratio. The cytoplasmic Raman spectra of the three cell types are very different. This was found to be mainly due to the abundant presence of peroxidases in the cytoplasmic granules of neutrophilic granulocytes (myeloperoxidase) and eosinophilic granulocytes (eosinophil peroxidase). Strong signal contributions of the active site heme group(s) of these enzymes were found. This paper illustrates the potentials and limitations for Raman spectroscopic analysis of cellular constituents and processes.

Basophils↗
PubMed1990

Studying single living cells and chromosomes by confocal Raman microspectroscopy.

Many indirect methods have been developed to study the constitution and conformation of macromolecules inside the living cell. Direct analysis by Raman spectroscopy is an ideal complement to techniques using directly labelled fluorescent probes or of indirect labelling with mono- and polyclonal antibodies. The high information content of Raman spectra can characterize biological macromolecules both in solution and in crystals. The positions, intensities and linewidths of the Raman lines (corresponding to vibrational energy levels) in spectra of DNA-protein complexes yield information about the composition, secondary structure and interactions of these molecules, including the chemical microenvironment of molecular subgroups. The main drawback of the method is the low Raman scattering cross-section of biological macromolecules, which until now has prohibited studies at the level of the single cell with the exception of (salmon) sperm heads, in which the DNA is condensed to an exceptionally high degree. Ultraviolet-resonance Raman spectroscopy has been used to obtain single cell spectra (and F. Sureau and P. Y. Turpin, personal communication), but in this method absorption of laser light may impair the integrity of the sample. We have avoided this problem in developing a novel, highly sensitive confocal Raman microspectrometer for nonresonant Raman spectroscopy. Our instrument makes it possible to study single cells and chromosomes with a high spatial resolution (approximately less than 1 micron 3).

Animals↗
PubMed1990

Skin blood flow changes, measured by laser Doppler flowmetry, in the first week after birth.

Changes in forehead skin blood flow were determined in 17 healthy, term newborns, using a fiberless diode laser Doppler flow meter (Diodopp). Measurements were carried out three times on each infant, at postnatal ages of 16.8 +/- 7.4 h, 58.9 +/- 6.2 h and 121.5 +/- 14.2 h (mean +/- S.D.), respectively. Skin blood flow, respiration, heart rate and skin temperature were recorded simultaneously, while the newborns were asleep. During the recordings, the behavioural state of the newborns was observed and environmental temperature and humidity were kept constant. Postocclusive hyperaemia of the skin blood flow was obtained by pressing the laser Doppler probe against the skull for 30 or 60 s. The following parameters changed significantly between the first and third measurements (t-test for paired samples): the basal skin blood flow during active and quiet sleep decreased, the average decrease being 29.4% (P = 0.002) and 25.9% (P = 0.01), respectively; skin blood flow during postocclusive hyperaemia also changed: the time taken to reach maximum hyperaemia increased from 17.3 to 22.7 s (P = 0.01), while the halftime recovery increased from 46.1 to 57.1 s (P = 0.02). The changes in skin blood flow between the first and second measurements and between the second and third measurements did not reach the level of statistical significance.

Blood Flow Velocity↗
PubMed1989

Local variation in absolute water content of human and rabbit eye lenses measured by Raman microspectroscopy.

Raman spectra were obtained from fresh, fixed and sliced rabbit lenses and from human lens slices. For all lenses and lens slices the ratio R, defined as the Raman intensity at 3390 cm-1 divided by the Raman intensity at 2935 cm-1, was measured at different locations along the visual and equatorial axis. The ratios R were transformed to absolute water mass percentages by measuring solutions with known protein concentrations. It was shown that fixation and slicing have very little effect on the absolute water content of the lenses. The values obtained for the absolute water content are comparable to values given in literature. It was also shown that the water content in rabbit and human lenses rapidly decreases from the immediate anterior and posterior subsurface region to the deep superficial cortex and is relatively constant in the nucleus. Raman microspectroscopy appears to be a reliable method for the measurement of the absolute water content of small volumes on defined positions in the lens. This can be very useful when analyzing the possible relation between local variations in water content and the occurrence of opacities in the lens.

Animals↗
PubMed1989

Raman microspectroscopy of fixed rabbit and human lenses and lens slices: new potentialities.

Raman spectroscopy is a non-invasive, non-destructive technique for the study of the macromolecular composition of tissues. Raman spectra were obtained from intact fresh and paraformaldehyde fixed rabbit lenses and from thin slices prepared from these lenses. In addition the Raman spectrum of an intact 82-yr-old human lens was compared with a slice of the same lens. It appeared that fixation with paraformaldehyde had only a minor qualitative effect on the Raman spectra and that Raman spectra of intact lenses and lens slices were comparable. It was also shown that in the slice of the old human lens the fluorescence, due to chromophores, could be reduced so that a reliable Raman spectrum could be obtained. The use of slices improves the accuracy of the position at which Raman spectra are recorded and fixation extends the time available for Raman analysis which is particularly important for the study of human lenses. Moreover, slicing enables Raman analysis of old human lenses, which up to now was thought to be impossible due to the overwhelming fluorescence of the chromophores present in these lenses.

Aged↗
PubMed1989

Skin blood flow changes during apneic spells in preterm infants.

Changes in skin blood flow during apneic spells were determined in 18 preterm infants using a diode laser Doppler flow meter without light conducting fibres. Heart rate, nasal air flow, impedance pneumography, skin and incubator temperature and laser Doppler skin blood flow were recorded simultaneously in each infant. During 212 apneic spells with a duration of 11.6 +/- 7.5 s (mean +/- S.D.) (range 6.0-48.0 s), the laser Doppler skin blood flow was measured. In all children except one, the majority of the apneic spells was associated with a decrease in skin blood flow. During 155 apneic spells (73%) skin blood flow decreased significantly P less than 0.025), the maximum decrease being 16.7 +/- 14.8%, 28.5 +/- 23.9% and 18.9 +/- 16.1% (mean +/- S.D.) for central, obstructive and mixed apneic spells, respectively. The decrease in skin blood flow started immediately after the beginning of apneic spells in 71%, the rest started with a mean delay of 3.4 s (range 0.1-7.0 s). No relation was found between the decrease in skin blood flow and the duration of the apneic spells. Thirty-four percent of the apneic spells were accompanied by bradycardia. In apneic spells accompanied by bradycardia the decrease in skin blood flow was not related to the fall in heart rate.

Blood Flow Velocity↗