Analysis of the dynamic properties of a hot-film anemometer system for blood velocity measurements in humans

Increasing emphasis has been put on the occurrence of turbulent blood flow in the great arteries in humans and on the possible role of this phenomenon in various pathological vascular conditions. The hot-film anemometer has been widely used to register fluid velocity (and turbulence—if any). In the present paper the dynamic properties of a commercially available hot-film anemometer system are determined. Simulating a turbulent velocity component, a conical 1 mm needle probe was vibrated with a frequency from 10–2000 Hz in rotating steady state human heparinised whole blood, varying the laminar velocity from 5 to 150 cm s⁻¹. Both the sine sweep test and the random noise test were used for frequency response determinations. No significant difference was found between the results from the tests. The cut-off frequency (−3 dB) increased with increasing laminar velocity as a second order function (e.g. 200, 500 and 1500 Hz at laminar velocities of 25, 50 and 100 cm s⁻¹). The cut-off frequency decreased to a minor degree with increasing amplitude of the turbulent velocity component. It is concluded that the hot-film anemometer system with the used conical quartz coated blood velocity probe is well suited for in vivo turbulence analysis on the arterial side.     

Nasal airflow measurement using a compensated thermistor anemometer

A nasal anemometer is a useful tool for speech therapists in their assessment of treatment effectiveness. This work is the second part of a research scheme which describes how the system is compatible with the use of an IBM PC-AT microcomputer using a suitable analogue-to-digital convertor. This enables the system to perform signal processing and to display, draw, and calculate a numerical ‘figure of merit’ using Kendall's tau nonparametric correlation.     

Microprocessor-based time-of-flight respirometer

The paper describes a microprocessor-based pulsed-wire time-of-flight anemometer for use with neonatal ventilation. A short pulse of electric current is passed through an upstream ‘pulsed’ wire causing it to emit a burst of heat which is carried downstream and changes the resistance of a second ‘sensor’ wire. The time-of-flight of the heat pulse is measured and the microprocessor calculates the flow velocity. We consider the thermodynamic theory of the transfer of heat from the pulsed wire to the gas flow and the subsequent warming of the sensor wire. The meter introduces minimal dead space or pressure drop and is small and light enough to fit into the endotracheal tube.     

Evaluation of a constant-temperature hot-wire anemometer for respiratory-gas-flow measurements

The performance of a constant-temperature hot-wire anemometer for respiratory-gas-flow measurement has bee investigated. It is shown that the anemometer satisfies common demands with respect to accuracy, response time and to insensitivity to humidity and temperature variations. A calibration method is suggested that permits correction for variation of the flowmeter signal caused by changes of the gas composition. Finally, a procedure for linearisation of the flowmeter signal as a function of flow rate is presented.     

Hot-wire anemometer for spirography

The use of a constant temperature hot-wire anemometer flow sensor for spirography is reported. The construction, operating principles and calibration procedure of the apparatus are described, and temperature compensation method is discussed. Frequency response is studied. It is shown that this hot-wire flow transducer satisfies common demands with respect to accuracy, response time and temperature variations.     

A test system for the biological safety cabinet

A simple, cheap and readily available test system for biological safety cabinets is described. It depends on the containment of an aerosol of Bacillus subtilis spores generated in a BIRD micronebulizer and the measurement of air flows with an anemometer. The system was set up to survey new equipment but equally valuable results have been obtained from tests during use. New units were often badly installed and used equipment was poorly maintained. It is suggested that any department which has a need for a biological safety cabinet must be in a position to test its function.     

An Electromechanical Breathing Device for Minimal Particle Loss While Inhaling Aerosols

The design of an electromechanical breathing mask that minimizes particle loss during inhalation of aerosols from a Provocation box is described. The device measures air flow by means of an anemometer. A provocation example is depicted and the possibility of measuring the provocalion dose is discussed. The breathing device here described has been shown lo be easy to use and to give reliable results.     

The spirodynamometer

Summary To investigate the normal and the maximal forced exhalation the use of cup anemometer is suggested. The instrument is attached at a definite distance from the tube through which the a ir is exhaled.Presented by Active Member AMN SSSR V. V. Parin Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 52, No. 11, pp. 121–122, November, 1961     

An experimental evaluation of the use of an ensemble average for the calculation of turbulence in pulsatile flow

A comparison was made between turbulence calculated by subtracting an ensemble average from the instantaneous velocity and calculations made with a high pass digital filter. Velocity was measured with a laser Doppler anemometer in vitro in the region of a normal porcine aortic valve and in patients with a hot film anemometer in the region of normal aortic valves. From the velocity obtained in patients, the absolute turbulence intensity calculated using an ensemble average of 50 beats was nearly twice the turbulence intensity calculated using a digital filter. Individual beats sometimes showed differences of 150% compared to calculations based upon the use of a digital filter. Inspection showed that the ensemble average varied widely from the actual nonfluctuating velocity. Studies in vitro showed less beat to beat variation than occurred in patients. The absolute turbulence intensity measured in vitro, when calculated using an ensemble average, was only 20% greater than calculations using a digital filter. The differences were due primarily to beat-to-beat variations of the nonfluctuating velocity, but these beat-to-beat variations were less prominent than occurred in patients. These observations suggest that ensemble averaging may not be appropriate for the calculation of turbulence, particularly in patients.     

Laser-doppler anemometer to study velocity fields in the vicinity of prosthetic heart valves

Laser-Doppler anemometry is relatively new technique which is used for measuring velocity fields. It has major applications in the field ofin vitro biofluid mechanics. The laser-Doppler anemometers have many advantages compared with the traditional hot-wire or hot-film anemometers which are still mainly used in studies of biofluid mechanics. A laser-Doppler anemometer (I.d.a) system which can be used to measurein vitro velocity and shear-stress profiles in the vicinity of prosthetic heart valves is described. Accurate velocity measurements in the vicinity of prosthetic heart valves are very scarce, and the use of I.d.a systems will facilitate acquisition of these data.     

Design considerations for the omniscience pivoting disc cardiac valve prosthesis

Parametric studies are conducted in an effort to determine the optimum curvature and eccentricity for concave-convex pivoting disc prosthetic heart valves. Steady-state pressure measurements with prototype valves and laser-Doppler anemometer measurements of the velocity field with a two-dimensional model are presented. These results suggest that an optimum curvature exists and that the minimum eccentricity that promotes full opening should be used. Estimates of the shear stress distribution in the wake of the valve are computed. The maximum shear stress for both the major and minor outflow areas appear to be: 1) fairly evenly distributed, 2) well below the level for damage to the formed elements of blood as they pass through the valve, and 3) above the level required for the formation of a stable thrombus.     

Micropatterned surfaces of PDMS as growth templates for HEK 293 cells

In this paper the easy and reliable preparation of precise micropatterns on PDMS surfaces is described and the growth of HEK 293 cells on those patterns during culture over several days is examined. The first patterning approach described is based on soft-lithography and polyelectrolyte multilayer deposition. Two different soft-lithographic techniques are employed for creating surface patterns of PAH, PSS, untreated and oxidized PDMS. The growth behavior of HEK 293 cells is investigated on all the dual combinations of the four surfaces, and decreasing preference of the cells for the surfaces in the order PAH (–NH₂) > ox-PDMS (–OH) >> PSS (–SO₃ ⁻) > PDMS (–CH₃) is revealed. As the second patterning approach a method is introduced, which allows the deposition of gel droplets in a microarray format utilizing differences in the surface wettability. This concept is new and expected to be very useful for various applications. Finally, a speculative explanation for the different cell spreading behavior is provided considering the interplay between individual cell–surface interactions and a permanent cell tractional force.     

A method for evaluation of volatile sulfur-containing substances in preparations for intravenous infusions

Gas chromatographic method for measuring volatile sulfur compounds in solutions for intravenous infusions is proposed. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 142, No. 12, pp. 701–703, December, 2006     

Performance of two commercial blood IFN-γ release assays for the detection of Mycobacterium tuberculosis infection in patient candidates for anti-TNF-α treatment

The reactivation of latent tuberculosis (TB) is a major complication of tumor necrosis factor (TNF)-α inhibitors. Screening for TB infection is recommended before anti-TNF therapy is initiated; however, the use of tuberculin skin testing (TST) is controversial, due to the high rate of false-negative results in patients receiving immunosuppressive treatment. To compare the performance of two commercial interferon (IFN)-γ release assays (IGRA), T-SPOT.TB (TS-TB) and QuantiFERON-TB Gold “In-tube” (QFT-GIT), with TST for the detection of TB infection in patients due to start anti-TNF therapy, 69 human immunodeficiency virus (HIV)-negative Italian patients (mean age: 45.2 ± 12.6 years; male=39) were enrolled between September 2005 to August 2006. Patients affected by rheumatoid arthritis (n = 18), psoriatic arthritis (n = 26), ulcerous rectocolitis (n = 6), and Crohn’s disease (n = 19) were tested simultaneously with TST, TS-TB, and QFT-GIT. Overall, 26% of patients were positive by TST, 30.4% by TS-TB, and 31.8% by QFT-GIT. Agreement with TST was similar (κ = 0.21, p = 0.0002 and κ = 0.26, p < 0.001, respectively). In 11 TST-negative cases, IFN-γ release assays were positive. In addition, in seven Mantoux-positive cases with no TB risk factors, TST result agreement was achieved with at least one blood test. Indeterminate results were detected in 5.8% and 2.8% of cases, respectively, with TS-TB and with QFT-GIT (p = not significant [ns]). In conclusion, our results suggest that IGRAs may be helpful for screening purposes in patient candidates for anti-TNF therapy to confirm positive TST results and in selected cases when false-negative results are suspected. The utility of blood tests in patients with low or no TB risk remains to be assessed.     

Parameters influencing antigen-specific immunotherapy for type 1 diabetes

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease in which the insulin producing β cells are destroyed. Antigen-based immunotherapy provides an approach to selectively tolerize pathogenic β cell-specific T cells, while leaving the remainder of the immune system intact. In this chapter, we discuss our group’s experience in defining the parameters that impact the efficacy of β cell antigen “vaccination” for the prevention and treatment of T1D.     

Comparison of Techniques for Correction of Magnification of Pelvic X-rays for Hip Surgery Planning

The aim of this study was to develop an accurate method for correction of magnification of pelvic x-rays to enhance accuracy of hip surgery planning. All investigated methods aim at estimating the anteroposterior location of the hip joint in supine position to correctly position a reference object for correction of magnification. An existing method—which is currently being used in clinical practice in our clinics—is based on estimating the position of the hip joint by palpation of the greater trochanter. It is only moderately accurate and difficult to execute reliably in clinical practice. To develop a new method, 99 patients who already had a hip implant in situ were included; this enabled determining the true location of the hip joint deducted from the magnification of the prosthesis. Physical examination was used to obtain predictor variables possibly associated with the height of the hip joint. This included a simple dynamic hip joint examination to estimate the position of the center of rotation. Prediction equations were then constructed using regression analysis. The performance of these prediction equations was compared with the performance of the existing protocol. The mean absolute error in predicting the height of the hip joint center using the old method was 20 mm (range −79 mm to +46 mm). This was 11 mm for the new method (−32 mm to +39 mm). The prediction equation is: height (mm) = 34 + 1/2 abdominal circumference (cm). The newly developed prediction equation is a superior method for predicting the height of the hip joint center for correction of magnification of pelvic x-rays. We recommend its implementation in the departments of radiology and orthopedic surgery.     

Improved accuracy and extended flow range for a Fleisch pneumotachograph

A large linear flow range and a small instrumental dead space volume are incompatible properties for a pneumotachometer (PTM). The linearity of a Fleisch number 2 PTM is studied for flows up to 6 litre s⁻¹ (nominal range 0–2 litre s⁻¹) with various up- and downstream geometries. It is hypothesised that using an array of calibration factors (conductance; flow/pressure), instead of a single calibration factor over the entire flow range, could improve accuracy and also extend the applicable flow range. The conductance against pressure characteristics are calculated with a previously described weighted averaging technique based on multiple strokes from a precision syringe. A single conductance value gives stroke volume errors in the range of −5 to 3% (0–2 litre s⁻¹) and −6 to 11% (0–6 litre s⁻¹) for validation using the same geometry as for calibration. The pressure dependent conductance improves accuracy to within −3% and 1% independent of flow range. However, for validation using a different geometry than for calibration, errors range from −5% to +8%. The degree of non-linearity varies between the geometries (range 3–15%) and is highest when using a one-directional valve upstream of the PTM and a Y-shaped connector. In conclusion, a pressure-dependent conductance improves accuracy and can also be used to extend the applicable flow range up to at least three times the nominal flow range.     

Silicon-based microelectrodes for neurophysiology, micromachined from silicon-on-insulator wafers

A process is described for the fabrication of silicon-based microelectrodes for neurophysiology using bonded and etched-back silicon-on-insulator (BESOI) wafers. The probe shapes are defined without high levels of boron doping in the silicon; this is considered as a step towards producing probes with active electronics integrated directly beneath the electrodes. Gold electrodes, of 4μm by 4μm to 50μm by 50μm are fabricated on shanks (cantilever beams) 6μm thick and which taper to an area approximately 100μm wide and 200μm long, which are inserted into the tissue under investigation. The passive probes fabricated have been successfully employed to make acute recordings from locust peripheral nerve.     

Three-dimensional ray tracing through curvilinear interfaces with application to laser Doppler anemometry in a blood analogue fluid

Prediction of the effects of refractive index (RI) mismatch on laser Doppler anemometer (LDA) measurements within a curvilinear cavity (an artificial ventricle) was achieved by developing a general technique for modelling the paths of the convergent beams of the LDA system using 3D vector geometry. Validated by ray tracing through CAD drawings, the predicted maximum tolerance in RI between the solid model and the working fluid was ± 0.0005, equivalent to focusing errors commensurate with the geometric and alignment uncertainties associated with the flow model and the LDA arrangement. This technique supports predictions of the effects of refraction within a complex geometry. Where the RI mismatch is unavoidable but known, it is possible not only to calculate the true position of the measuring volume (using the probe location and model geometry), but also to estimate degradation in signal quality arising from differential displacement and refraction of the laser beams.     

A Unifying Model for the Substitutional Genetic Load

In this paper, a general deterministic model for gene substitutionat all segregating loci is derived. The results of a rigorousmathematical analysis of the equations are stated and foundto be consistent with results derived by making typical simplifyingassumptions. All previous deterministic calculations of possiblerates of gene substitution and the ‘substitutional geneticload’ are shown to be special cases of the model. Newexpressions for the substitutional genetic load and rate ofsubstitution in hard selection with cth-order epistasis aregiven. In addition, the concept of ‘threshold selection’is generalized to less extreme ‘rank selection", and formulaefor the relationship between the substitution rate and the selectioncoefficient are given. The ‘load argument’ for theneutral theory is reviewed in light of the new findings andstrongly rejected. Several other areas of disagreement, suchas the effect of population dynamics and competition on thesubstitutional genetic load, are sorted out using the model.Some remarks regarding experimental input are made.