Laser Doppler velocimetry: The problem of fibre movement artefact

The problem of fibre movement artefact in laser Doppler velocimetry recordings of skin blood flow has been investigated. Beat frequency spectra were obtained for a stationary target, unheated skin, heated skin (43.5°C), with and without blood flow occluded for various induced amounts of fibre movement. Possible methods for either eliminating, or obtaining an indicator of, fibre movement artefact were considered. The solution proposed is to incorporate additional fibres terminating within the transducer to permit an index of fibre movement to be obtained that is independent of blood flow.     

Cyclic Alternating Pattern Is Associated with Cerebral Hemodynamic Variation: A Near-Infrared Spectroscopy Study of Sleep in Healthy Humans

The cyclic alternating pattern (CAP), that is, cyclic variation of brain activity within non-REM sleep stages, is related to sleep instability and preservation, as well as consolidation of learning. Unlike the well-known electrical activity of CAP, its cerebral hemodynamic counterpart has not been assessed in healthy subjects so far. We recorded scalp and cortical hemodynamics with near-infrared spectroscopy on the forehead and systemic hemodynamics (heart rate and amplitude of the photoplethysmograph) with a finger pulse oximeter during 23 nights in 11 subjects. Electrical CAP activity was recorded with a polysomnogram. CAP was related to changes in scalp, cortical, and systemic hemodynamic signals that resembled the ones seen in arousal. Due to their repetitive nature, CAP sequences manifested as low- and very-low-frequency oscillations in the hemodynamic signals. The subtype A3+B showed the strongest hemodynamic changes. A transient hypoxia occurred during CAP cycles, suggesting that an increased CAP rate, especially with the subtype A3+B, which may result from diseases or fragmented sleep, might have an adverse effect on the cerebral vasculature.     

Estimation of monopolar signals from sphincter muscles and removal of common mode interference

The detection of surface electromyogram (EMG) by multi-electrode systems is applied in many research studies. The signal is usually recorded by means of spatial filters (linear combination of the potential under at least two electrodes) with vanishing sum of weights. Nevertheless, more information could be extracted from monopolar signals measured with respect to a reference electrode away from the muscle. Under certain conditions, surface EMG signal along a curve parallel to the fibre path has zero mean (property approximately satisfied when EMG is sampled by an array of electrodes that covers the entire support of the signal in space). This property allows estimating monopolar from single differential (SD) signals by pseudoinversion of the matrix relating monopolar to SD signals. The method applies to EMG signals from the external anal sphincter muscle, recorded using a specific cylindrical probe with an array of electrodes located along the circular path of the fibres. The performance of the algorithm for the estimation of monopolar from SD signals is tested on simulated signals. The estimation error of monopolar signals decreases by increasing the number of channels. Using at least 12 electrodes, the estimation error is negligible. The method applies to single fibre action potentials, single motor unit action potentials, and interference signals.The same method can also be applied to reduce common mode interference from SD signals from muscles with rectilinear fibres. In this case, the last SD channel defined as the difference between the potentials of the last and the first electrodes must be recorded, so that the sum of all the SD signals vanishes. The SD signals estimated from the double differential signals by pseudoinvertion are free of common mode.     

Reliability of muscle fibre conduction velocity distribution estimation from surface EMG

Most of the neuromuscular diseases induce changes in muscle fibre characteristics. For example, Duchenne dystrophy is characterized by a specific loss of fast fibres, and an increase in small diameter fibres. These morphological changes may lead to large modifications in the distribution of fibre diameters, possibly producing bimodal distributions. It has already been shown that it is possible to reveal these morphological modifications through the distribution of muscle fibre conduction velocity (MFCV) as estimated from needle electromyography (EMG) recordings. In this paper, we investigate whether such changes can be extracted from surface EMG signals.

Simulation allows generation of surface EMG signals in which features are well described especially at a morphological level. Therefore, we generated a database of simulated signals both in voluntary and electrically elicited contraction conditions using a bimodal distribution of muscle fibre diameters. MFCV distributions were computed using two short-term methods based on cross-correlation and peak-to-peak techniques for voluntary contraction signals, and using a deconvolution method in time domain for electrically elicited signals. MFCV distributions were compared with true ones, as generated from modelling.

This work reveals that estimating MFCV distribution through these methods does not appear yet as precise and robust enough to accurately characterize changes in redistribution of various muscle fibre diameters. However, it opens to new experimental protocols that can be explored in order to improve the robustness of MFCV distribution estimation for the follow-up of patients suffering from neuromuscular disorders.     

Ultra‐low background Raman sensing using a negative‐curvature fibre and no distal optics

Measuring Raman spectra through an optical fibre is usually complicated by the high intrinsic Raman scatter of the fibre material. Common solutions such as the use of multiple fibres and distal optics are complex and bulky. We demonstrate the use of single novel hollow‐core negative‐curvature fibres (NCFs) for Raman and surface‐enhanced Raman spectroscopy (SERS) sensing using no distal optics. The background Raman emission from the silica in the NCF was at least 1000× smaller than in a conventional solid fibre, while maintaining the same collection efficiency. We transmitted pump light from a 785‐nm laser through the NCF, and we collected back the weak Raman spectra of different distal samples, demonstrating the fibre probe can be used for measurements of weak Raman and SERS signals that would otherwise overlap spectrally with the silica background. The lack of distal optics and consequent small probe diameter (<0.25 mm) enable applications that were not previously possible.      

Esophageal wall blood perfusion during contraction and transient lower esophageal sphincter relaxation in humans

We recently reported that esophageal contraction reduces esophageal wall perfusion in an animal study. Our aim was to determine esophageal wall blood perfusion (EWBP) during esophageal contraction and transient lower esophageal sphincter relaxations (TLESRs) in humans. We studied 12 healthy volunteers. A custom-designed laser Doppler probe was anchored to the esophageal wall, 4-6 cm above the LES, by use of the Bravo pH system so that the laser light beam stay directed toward the esophageal mucosa. A high-resolution manometry equipped with impedance electrodes recorded esophageal pressures and reflux events. Synchronized pressure, impedance, pH, and EWBP recordings were obtained during dry and wet swallows and following a meal. Stable recordings of laser Doppler EWBP were only recorded when the laser Doppler probe was firmly anchored to the esophageal wall. Esophageal contractions induced by dry and wet swallows resulted in 46 ± 9% and 60 ± 10% reduction in the EWBP, respectively (compared to baseline). Reduction in EWBP was directly related to the amplitude (curvilinear fit) and duration of esophageal contraction. Atropine reduced the esophageal contraction amplitude and decreased the EWBP reduction associated with esophageal contraction. TLESRs were also associated with reduction in the EWBP, albeit of smaller amplitude (29 ± 3%) but longer duration (19 ± 2 s) compared with swallow-induced esophageal contractions. We report 1) an innovative technique to record EWBP for extended time periods in humans and 2) contraction of circular and longitudinal muscle during peristalsis and selective longitudinal muscle contraction during TLESR causes reduction in the EWBP; 3) using our innovative technique, future studies may determine whether esophageal wall ischemia is the cause of esophageal pain/heartburn.     

Real-time vibrational dynamics in chlorophyll a studied with a few-cycle pulse laser

We use a 6.8-fs laser as the light source for broad-band femtosecond pump-probe real-time vibrational spectroscopy to investigate both electronic relaxation and vibrational dynamics of the Q_y-band of Chl-a at 293 K. More than 25 vibrational modes coupled to the Q_y transition are observed. Eleven of them have been clarified predominantly due to the excited state, and six of them are concluded to be nearly exclusively resulting from the ground-state wave-packet motion. Moreover, thanks to the broad-band detection over 5000 cm⁻¹, the modulated signals due to the excited state vibrational coherence are observed on both sides of the 0-0 transition with equal separation. The corresponding nonlinear process has been studied using a three-level model, from which the probe wavelength dependence of the phase of the periodic modulation can be calculated. The probe wavelength dependence of the vibrational amplitude is interpreted in terms of the interaction between the “pump” or “laser,” Stokes, and anti-Stokes field intermediated by the molecular vibrations. In addition, an excited state absorption peak at ∼709 nm has been observed. To the best of our knowledge, this is the first study of broad-band real-time vibrational spectroscopy in Chl-a.     

Real-time cortical cerebral blood flow follow-up in conscious,freely moving rats by laser Doppler flowmetry

This article describes a laser Doppler flowmetry (LDF) system that enables repeated measurements and thereby long-term followup of cortical cerebral blood flow (CBF) in awake and freely moving rats. The system consists of a specially designed flow probe adapter, a flow probe connector, and a LDF flow probe, which may thereby rotate through its own axis. During the experiment, the flow adapter is permanently mounted onto the rat's skull bone. A thin layer of skull bone is left intact at the site for cortical CBF measurements. The probe connector and the flow probe may be repeatedly detached and remounted to the adapter, which allows for cortical cerebral blood flow recording from exactly the same anatomical location. The laser Doppler flowmetry system enables stable cortical CBF recordings in the conscious rat while it moves freely in a bowl cage.     

Calcium-induced calcium release mechanism from the sarcoplasmic reticulum in skinned crab muscle fibres

Mechanically skinned skeletal muscle fibres of the crab Carcinus maenas have been used to investigate the mechanism of calcium release from the sarcoplasmic reticulum. Calcium release has been monitored by the amplitude and kinetics of the tension developed by the fibre. Results show that a very low calcium concentration, insufficient to directly activate contractile proteins, induces a release of calcium from the SR. This release is stimulated by low concentrations of caffeine and inhibited by small amounts of EGTA. Thus, a graded calcium-induced calcium release mechanism dependent on extrareticular calcium concentration has been demonstrated in skinned crab muscle fibre.     

Pulsed Doppler ultrasound system for the measurement of velocity distributions and flow disturbances in arterial prostheses

For the investigation of flow through prosthetic arteries a pulsed Doppler ultrasound system has been characterized. Preliminary in vitro experiments using this system are described; they verify its suitability for making velocity profile and flow disturbance measurements. The output from a frequency tracker is compared with spectral analysis of Doppler signals for both laminar and turbulent flow regimes and the root mean square fluctuations on the tracker output signal are used to identify transition from laminar to turbulent flow. In addition, the turbulent itensity of poststenotic flow is quantified at several axial locations and for different rates of flow. Finally, we present velocity profile measurements which were obtained using a deconvolution technique to account for the finite size of the sample volume.     

Laser shock wave‐induced visible mechanoluminescence from semi‐transparent organic crystals

Indirect focusing of the output from a pulsed infrared Nd³⁺:YAG laser through a shock‐generating layer onto organic crystals results in the emission of an intense microsecond duration pulse of mechanoluminescence (ML). The ML appears after a threshold laser fluence has been reached and increases sharply above this threshold. This specifies that there is a corresponding amplitude of a laser‐induced shock wave that is necessary to induce crystal fracturing. Thus, the intensity of ML can be controlled by varying the laser fluence. Piezoelectric charges produced on the surfaces of a fractured crystal create the foundation for luminescence. Initially, the ML intensity increases with the shock wave pressure and time due to the creation of more surfaces in the crystal; the ML intensity reaches a peak value and then decreases over time. Thus, laser shock wave‐induced ML provides a new optical technique for the study of materials under high pressure. Expressions explored for the characteristics of laser shock wave‐induced ML satisfactorily explain the experimental results. Copyright © 2016 John Wiley & Sons, Ltd.     

Mean power frequency and amplitude of the mechanomyographic and electromyographic signals during incremental cycle ergometry.

The purpose of this investigation was to determine the relationships for mechanomyographic (MMG) amplitude, MMG mean power frequency (MPF), electromyographic (EMG) amplitude, and EMG MPF versus power output during incremental cycle ergometry. Seventeen adults volunteered to perform an incremental test to exhaustion on a cycle ergometer. The test began at 50 W and the power output was increased by 30 W every 2 min until the subject could no longer maintain 70 rev min(-1). The MMG and EMG signals were recorded simultaneously from the vastus lateralis during the final 10 s of each power output and analyzed. MMG amplitude, MMG MPF, EMG amplitude, EMG MPF, and power output were normalized as a percentage of the maximal value from the cycle ergometer test. Polynomial regression analyses indicated that MMG amplitude increased (P<0.05) linearly across power output, but there was no change (P>0.05) in MMG MPF. EMG amplitude and MPF were fit best (P<0.05) with quadratic models. These results demonstrated dissociations among the time and frequency domains of MMG and EMG signals, which may provide information about motor control strategies during incremental cycle ergometry. The patterns for amplitude and frequency of the MMG signal may be useful for examining the relationship between motor-unit recruitment and firing rate during dynamic tasks.     

Continuous measurement of aortic blood velocity,after cardiac surgery,by means of an extractable doppler ultrasound probe

A new method has been developed for the continuous measurement of aortic blood velocity in patients following cardiac surgery. Using an extractable Doppler ultrasound probe placed on the ascending aorta, the changes in aortic velocity were recorded up to 24 h postoperatively, in 14 patients undergoing coronary bypass surgery. Volume flow rate is calculated from the mean velocity, the diameter of the aorta and the angle between the ultrasound beam and the direction of the blood flow, by means of an analogue flow calculator. Estimation of aortic flow showed a correlation of r = 0.79 with cardiac output measured by a thermodilution technique. The main advantage of the system is that it allows continuous monitoring of cardiac output, as well as short and long-term trend analyses, during the early postoperative period.     

Capillary blood perfusion during postischemic reperfusion in striated muscle.

Monitoring of nutritive blood flow in muscle is of particular importance to reconstructive surgeons, since ischemia/reperfusion in striated muscle is known to result in postischemic microvascular perfusion failure. Laser Doppler flowmetry has recently been introduced as an easy-to-use, noninvasive technique for continuous monitoring of microvascular tissue perfusion. Despite its popularity, there exists a great deal of controversy as to what actually generates the laser Doppler signal recorded from a given tissue. Intravital microscopy is a technique for direct visualization of the nutritional circulation in tissue. By using intravital microscopy, direct measurements of blood perfusion in individual segments of the nutritional microcirculation can be made. In 22 Syrian golden hamsters we performed laser Doppler flowmetry and intravital microscopy measurements in muscle tissue prior to and during reperfusion after 4 hours of tourniquet ischemia using the dorsal skinfold chamber model. Intravital microscopy (n = 10) revealed a heterogeneous capillary perfusion during the early reperfusion phase with a decrease (p less than 0.01) in functional capillary density to 49.4 +/- 17.0 percent of control. No recovery was observed after 24 hours of reperfusion. Laser Doppler flowmetry (n = 12) showed a parallel reduction of capillary red blood cell flux during the early perfusion phase to 43.9 +/- 22.6 percent of control values (p less than 0.01), and no recovery was observed after 24 hours of reperfusion. However, the laser Doppler flowmetry technique was not able to detect the capillary perfusion inhomogeneities shown by intravital microscopy. Postischemic reperfusion in striated muscle is characterized by a decrease in functional capillary density and a heterogeneous capillary perfusion. Laser Doppler flowmetry is a useful tool for monitoring microvascular tissue perfusion, although in striated muscle of the hamster it must be considered that accurate nutritional "capillary" flow readings can be grossly overestimated if larger vessels, such as arterioles and collecting venules, are contained in the measuring field of the laser Doppler probe.     

Noninvasive ultrasonic measurement of arterial wall motion in mice

Despite the extensive use of genetically altered mice to study cardiovascular physiology and pathology, it remains difficult to quantify arterial function noninvasively in vivo. We have developed a noninvasive Doppler method for quantifying vessel wall motion in anesthetized mice. A 20-MHz probe was held by an alligator clip and positioned over the carotid arteries of 16 mice, including six 3- to 5-mo-old wild-type (WT), four 30-mo-old senescent (old), two apolipoprotein E null (ApoE), and four alpha-smooth muscle actin null (alpha-SMA) mice. Doppler signals were obtained simultaneously from both vessel walls and from blood flow. The calculated displacement signals from the near and far walls were subtracted to generate a diameter signal from which the excursion and an augmentation index were calculated. The excursion ranged between 13 microm (in ApoE) and 95 microm (in alpha-SMA). The augmentation index was lowest in the WT mice (0.06) and highest in the old mice (0.29). We conclude that Doppler signal processing may be used to measure vessel wall motion in mice with high spatial and temporal resolution and that diameter signals can replace pressure signals for calculating the augmentation index. This noninvasive method is able to identify and confirm characteristic changes in arterial properties previously associated with age, atherosclerosis, and the absence of vascular tone.     

Measurement of mucosal blood flow in the canine intestine with laser doppler velocimetry

Laser Doppler velocimetry is a technique for continuous estimation of changing blood flow in the surface of a tissue and does not require invasion of the circulation. This technique is based upon the Doppler principle that a shift in the frequency of an electromagnetic wave emitted or reflected from a moving object is proportional to the velocity of the object. The capacity of Laser Doppler velocimetry to estimate changes in intestinal mucosal blood flow was tested in a canine free flow preparation. In anesthetized dogs in which a segment of ileum was isolated, simultaneous measurements of instantaneous changes in total blood flow (measured with the electromagnetic blood flow meter) and instantaneous changes in presumed mucosal blood flow (using laser Doppler velocimetry) were obtained. Determinations were made during conditions of rest, prostacyclin induced vasodilation and norepinephrine induced vasoconstriction. Changes in laser Doppler velocimeter readings were qualitatively similar to and temporally related to changes in total blood flow to the gut segment during administration of the vasoactive drugs. The magnitude and direction of changes with the two measurements were significantly correlated. Stabilizing the laser probe on the mucosal surface to ensure reproducible readings proved technically difficult. Pharmacologically induced changes in laser Doppler velocimeter estimated changes in flow were more readily correlated with changes in electromagnetic flow meter readings than were control values obtained with the two methods.     

Molecular probe for enzymatic activity with dual output

A novel molecular probe for enzymatic activity with a dual output detection-mode has been developed. The probe effectively detected the presence of the bacterial protease penicillin-G-amidase; a single cleavage by the enzyme initiated the fragmentation of a self immolative dendritic platform to release two reporter units. The signals of the free reporters were detected by two different spectroscopic techniques, fluorescence and UV-vis. This is the first reported molecular probe with two different chromogenic reporter units activated by a specific stimulus.     

Difficulties in noninvasive cardiac stroke volume determination in "small" blood circulation systems]

Pulsewave velocity analysis is an option for the noninvasive determination of cardiac output and the evaluation of additional haemodynamic parameters. An algorithm we developed ourselves has been established as a method for the measurement of cardiac output in rabbits. The effectiveness of this program was investigated by monitoring controlled hypoxia-induced alterations in the circulatory system. Calculated values were compared with direct measurements of cardiac output with a Doppler flow probe placed in the ascending aorta. Within the physiological framework of blood gas analysis, a good correlation was found between the two methods. In the case of hypoxia-induced depression, however, the two methods showed diverging results, presumably due to arrhythmia-induced wave reflections within the arterial vascular tree. This makes an extension of the algorithm necessary to take account for these case.     

Focal extraction of surface-bound DNA from a microchip using photo-thermal denaturation

High-throughput, selective extraction of a particular DNA fragment from a mixture of DNA before PCR amplification is becoming increasingly important in the DNA analysis field. Although the latest microchip technology has enabled real-time DNA expression analysis using hybridization between surface-bound probe DNA and sample DNA, the potential of this technology in purification of a small amount of DNA has not been demonstrated. We report here a method for area-selective release and collection of specific DNA, in which an IR laser beam is focused onto surface-bound sample DNA at the target-spotted area to denature hybridized DNA. First, sample DNA labeled with a fluorescent dye was hybridized to a probe DNA immobilized on a chromium-coated chip. A 1053-nm IR laser beam with an intensity of 10-100 mW was then focused on the target area with a spatial resolution of 10 microns, causing the release of the fluorophore-labeled sample DNA as a result of photo-thermal denaturation. Confirmation of the amount of eluted DNA by PCR amplification after collection indicated that more than 10(-20) mol DNA/micron 2 area was eluted from the microchip, representing more than 70% of the chip-bound sample DNA. These results indicate that this method can be applied to the highly sensitive purification of DNA in microchip technology.     

The thyroglobulin gene resides on chromosome 8 in man and on chromosome 7 in the rat

Human chromosomes were separated by a dual laser FACS sorter and their DNA hybridized with a thyroglobulin gene probe. A strong hybridization signal was obtained with DNA from chromosome 8. A panel of mouse-rat cell hybrids was used to determine the chromosomal localization of the rat thyroglobulin gene by the Southern blotting method. Comparison of the cytogenetic data with the hybridization signals obtained with the rat thyroglobulin probe allowed assignment of this gene to rat chromosome 7. It is concluded that the synteny relationship between the thyroglobulin gene and the c-myc oncogene has been conserved in rat and man.