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At least 19 recordsLinked to original sources
PubMed1999

Pharmacological evaluation of a new laser blood flowmeter for measuring coronary blood flow, assessed in the canine isolated, blood-perfused ventricular tissue preparation in comparison with an electromagnetic flowmeter.

A new portable-type laser blood flowmeter was recently developed for measuring the blood flow in vessels. The sensitivity and specificity of the laser flowmeter was assessed in comparison with the well-established electromagnetic flowmeter using a canine isolated, blood-perfused ventricular tissue preparation. The laser flowmeter can record the phasic pattern of the coronary blood flow like the electromagnetic flowmeter. The extent of the changes after intracoronary administration of ACh and angiotensin II as well as coronary occlusion was almost identical between these two methods. These results suggest that the new laser flowmeter may possess potential utilities in both basic experimental and clinical practices.

Acetylcholine↗
PubMed2003

Ultrasonic flowmeters: temperature gradients and transducer geometry effects.

Ultrasonic flowmeter performance is addressed for the case of cylindrically shaped flowmeters employing two reciprocal ultrasonic transducers A and B so as to measure time-of-flight differences between signals transmitted from transducer A towards B followed by an equivalent signal transmitted from transducer B towards A. In the case where a liquid flows through the flowmeter's measuring section ("spoolpiece"), the arrival times of the two signals differ by an amount related to the flow passing between the two transducers. Firstly, a detailed study of flow measurement errors with mean flow in the laminar flow regime is carried out as a function of the mode index and the transducer diameter/cylinder diameter ratio in the case where no temperature gradients are present in the flowmeter sensor. It is shown that all modes except the fundamental mode overestimate the mean flow by a factor of 33.33% while excitation of the fundamental mode solely give error-free measurements. The immediate consequences are that the flowmeter error decreases as the transducer diameter/cylinder diameter ratio approaches 1 from 0 reflecting the fact that the excitation level of the fundamental mode increases from almost 0 to 1 as this ratio approaches 1 from 0. Secondly, the effect on flowmeter performance due to flow-induced temperature gradients is examined. It is shown that the presence of temperature gradients leads to flowmeter errors at the higher-flow values even in the case where the fundamental mode is the only mode excited. It is also deduced that flowmeter errors in general depend on the distance between transducers A and B whether temperature gradients exist or not. This conclusion is not reflected in the usual definition of flowmeter errors given by the so-called mode-dependent deviation of measurement introduced in earlier works.

Journal Article↗
PubMed1999

Effects of xenon on the performance of various respiratory flowmeters.

BACKGROUND: The anesthetic gas xenon has distinctly different physical properties compared with air, nitrous oxide, or oxygen. This led us to predict that xenon would affect the performance of commercially available flowmeters. METHODS: Flow was generated by an anesthesia ventilator connected to a lung simulator via a semiclosed breathing circuit. With the system filled with air or with various concentrations of xenon or nitrous oxide in a balance of oxygen, the tidal volume was measured with two rotating vanes, a Pitot tube, a variable-orifice flowmeter, and two constant-temperature hot-wire flowmeters. RESULTS: Although xenon minimally affected both rotating vane flowmeters, it caused the Pitot tube and the variable-orifice flowmeters to overread in proportion to the square root of the density of the gas mixture used (xenon is 4.6 times more dense than air). In contrast, the hot-wire anemometers underread with xenon; for example, their readings in the presence of 45% and 70% xenon were less than 10% of those displayed when air was used. Nitrous oxide minimally affected all the flowmeters except the variable-orifice device. The Pitot flowmeter was also affected, but only when its gas analyzer port was open to the ambient air so that it no longer corrected its readings for changes in gas composition. In these cases, nitrous oxide produced overreadings in the same manner as did xenon. CONCLUSION: Among the four types of flowmeters studied, only the rotating-vane type is sufficiently accurate for use during anesthesia with xenon.

Anesthetics, Inhalation↗
PubMed1984

Clinical use of blood flowmeters.

The concept of an electromagnetic flowmeter was first described by Kolin in 1936. He demonstrated that with the flowmeter which required surgical exposure of the blood vessel for probe contact but not requiring cannulation, it was possible to follow rapid flow changes and that the deflection bore a linear relationship to flow. Twenty years later a greatly improved circuitry and design was described by Denison and Spencer. Soon thereafter, a number of investigators, notably Schenk and his colleagues utilizing the square wave electromagnetic flowmeter and Cannon and his colleagues with the sine wave electromagnetic flowmeter reported on a number of experimental and clinical studies on blood flow measurements. My introduction to blood flow measurements was through Ferguson who had had a flowmeter and flowmeter probes constructed according to the design of Denison and Spencer. Our first report on flow measurements in patients with peripheral arterial disease was made in 1960. Electromagnetic flowmeters and probes available today are a vast improvement in ease of use, reliability and accuracy, thus the pertinent question is whether or not the information that can be obtained with it would warrant its routine clinical use. We started with a flowmeter constructed by following a schematic diagram and hand winding our own probes, then to the purchase of Medicon 2000, then Medicon 4000, and to our present unit, the SP2204. The advancement in instrumentation has been truly remarkable. All intraoperative blood pressure measurements are made with direct arterial puncture with 23 size needle with the hub removed and needle tip fitted to polyethylene tube connected to a strain gauge.(ABSTRACT TRUNCATED AT 250 WORDS)

Aorta↗
PubMed1992

Evaluation of accuracy and reproducibility of peak flowmeters at 1,400 m.

Peak flow meters provide physicians and patients with objective measures about changes in pulmonary obstruction. We evaluated eight models of peak flowmeters and measured their accuracy and reproducibility with methods recently recommended by the National Asthma Education Program (NAEP). Waveforms from the American Thoracic Society's spirometer testing set were used to drive a computer-controlled syringe. Testing was done at Salt Lake City at an altitude 1,400 m. It appears that the original Wright peak flowmeter has been used as the "de facto" standard. We found that the original Wright peak flowmeter overestimated flows in its midrange; and, as a consequence, most of the other peak flowmeters also overestimated peak flows. The overestimation of peak flows may have been understated because of the 1,400-m altitude testing site. To the credit of the instrument manufacturers, we were pleasantly surprised with the quality, accuracy, and reproducibility of presently available peak flowmeters; however, as a result of our testing, we suspect that with little effort, manufacturers of peak flowmeters could improve the accuracy of their devices. Standardized testing methods and equipment should make the task of peak flowmeter design, manufacture, and testing even easier. We trust that manufacturers of peak flowmeters will respond appropriately and improve their instruments.

Adult↗
PubMed1998

The effect of physiologic and mechanical aging on the performance of peak flowmeters.

PURPOSE: To investigate the effects of physiologic and mechanical aging on peak flowmeters. MATERIALS AND METHODS: Eight each of MiniWright (MW; Clement Clark; Harlow, UK), Personal-Best (PB; HealthScan Products; Cedar Grove, NJ), Vitalograph (V; Vitalograph Ltd; Buckingham, UK), and Breath-Taker (BT; Medical Development Australia; Melbourne, Australia) peak flowmeters were assessed for accuracy and repeatability before and after aging using a computer-driven syringe to deliver peak flows from 100 to 700 L/min. Four of each type of flowmeter were physiologically aged by normal subjects performing up to six peak flows daily for 1 year. The remaining four of each flowmeter were mechanically aged using an accelerated aging device to deliver 2,000 exponential waveforms with a peak flow of 600 L/min over a period of 3 h. RESULTS: The V and BT flowmeters were linear and accurate over the range 100 to 700 L/min, while the PB overread at high flows. The MW was alinear throughout. The SD of the difference between readings before and after aging ranged from 8.6 to 40.6 L/min (mean, 9.2). Comparing the slopes of the relationship of actual against reference peak expiratory flow (PEF) showed that 16 flowmeters--5 BTs, 6 MWs, 4 PBs, and 1 V had no significant change in slope after aging. Mechanical aging caused a consistent underreading in PEF at high flow rates. Physiologic aging showed a more variable pattern both within and between flowmeter types. The MW was the most affected by physiologic aging, producing overestimates of PEF by as much as 100 L/min at 500 L/min. CONCLUSIONS: We conclude that the effects of physiologic and mechanical aging are different, and that while mechanical aging may provide a guide to the effects of aging, studies using physiologic aging would be more appropriate.

Equipment Failure↗
PubMed1999

Quantitative assessment of chronic aortic regurgitation with 3-dimensional echocardiographic reconstruction: comparison with electromagnetic flowmeter measurements.

Two-dimensional echocardiography and color Doppler are useful in the qualitative assessment of aortic regurgitation. However, color Doppler planar methods are not accurate in quantifying regurgitant flow, in part because of the complex geometry of aortic regurgitant flow events. Three-dimensional echocardiographic reconstruction is a new technique that provides dynamic 3-dimensional images of intracardiac color flow jets. We sought to determine whether the measurement of aortic regurgitant jet volume by 3-dimensional echocardiography correlated with the true regurgitant volume, measured by electromagnetic flowmeter in vivo, to accurately reflect the severity of aortic regurgitation. We performed volume-rendered 3-dimensional echocardiography in 6 sheep with surgically induced chronic eccentric aortic regurgitation. We obtained a total of 22 aortic regurgitation states by altering loading conditions. Instantaneous regurgitant flow rates were obtained by aortic and pulmonary electromagnetic flowmeters. The maximum aortic regurgitant jet volume by 3-dimensional echocardiography and the maximum jet area by 2-dimensional echocardiography were measured and compared with electromagnetic flowmeter data. By electromagnetic flowmeter, aortic regurgitant flow rate varied from 0.14 to 3.1 L/min (mean 1. 25 +/- 0.78); aortic regurgitant stroke volume varied from 1 to 34 mL/beat (mean 12 +/- 8), and regurgitant fraction varied from 3% to 42% (mean 25% +/- 12%). The maximum jet volume by 3-dimensional echocardiography correlated very well with the aortic regurgitant stroke volume (r = 0.92; P <.0001), with the mean regurgitant flow rate (r = 0.87; P <.0001), and with the regurgitant fraction (r = 0. 87; P <.0001) derived from electromagnetic flowmeter. Both intraobserver and interobserver variability on the measurement of the jet volume by 3-dimensional echocardiography were excellent (r = 0.98; P <.0001 and r = 0.90; P <.001, respectively). The maximum jet area by 2-dimensional echocardiography did not correlate with the aortic regurgitant stroke volume (r = 0.41; P = not significant) and related poorly with the regurgitant fraction (r = 0.52; P <.05) by electromagnetic flowmeter. Dynamic 3-dimensional echocardiography can allow better determination of the geometry of the aortic regurgitant jet and may assist of quantifying the severity of aortic regurgitation.

Animals↗
PubMed1980

Accuracy of new gas flowmeters.

The accuracy of five new oxygen and nitrous oxide flowmeter units was investigated using the bubble meter method. The results were compared with those previously found in flowmeters withdrawn from clinical use. New oxygen flowmeters demonstrated less inaccuracies than old flowmeters. No differences were found between the nitrous oxide flowmeters. Unacceptable errors were demonstrated at oxygen presettings less than 1 litre min-1, suggesting the grading within this range to be of no value. Marked deviations which exceeded the limits stated by the manufacturer could still be shown at presettings greater than 1 litre min-1. If an exact FIO2 is required, continuous monitoring with a high accuracy oxygen analyser is essential, even using new flowmeters.

Anesthesia, Inhalation↗
PubMed1994

Evaluation of a symmetrically disposed Pitot tube flowmeter for measuring gas flow during exercise.

We evaluated the effect of airflow and gas composition on the linearity of measurement of airflow by a new disposable flowmeter. The flowmeter is based on the principle of differential pressure measurement across two symmetrically disposed Pitot tubes. Nonlinearities arising from the pressure-to-airflow relationship and sensitivity to changes in gas density were linearized with appropriate software and monitoring of the gas composition. With room air used as the respired gas, the measured tidal volume from a piston pump assembly was consistently within 1-2% of the target tidal volume for each of five flowmeters tested across physiological ranges of flow. Changing gas densities by varying concentrations of O2, CO2, and N2 led to errors in tidal volume measurement that ranged up to 6-8%. However, because the errors were predictable, they were corrected by software to within 0.6% of the target volume. Measurement of minute ventilation during exercise was within 1-2% of that determined from bag collections. We conclude that this type of flowmeter can accurately measure exercise minute ventilation and has advantages over some other flowmeters because of its ruggedness, reproducibility, and ease of sterilization or replacement compared with other flowmeters.

Equipment Design↗
PubMed1998

Elevation of peak expiratory flow by a "spitting" maneuver: measured with five peak flowmeters.

STUDY OBJECTIVE: To determine if peak expiratory flow (PEF) is higher using incorrect technique versus correct technique with five marketed peak flowmeters. DESIGN: Randomized, nonblinded study. SETTING: University pulmonary medicine clinic. PATIENTS: Twenty adults with clinically stable asthma. INTERVENTIONS: After inhaling 2 puffs of albuterol via a valved aerosol holding chamber (Aerochamber), patients were instructed over the next 15 min in correct and incorrect (a "spitting" action) technique when using peak flowmeters. Order of use of five peak flowmeters and correct vs incorrect technique was random. MEASUREMENTS AND RESULTS: PEF (percentage of personal best) was recorded for best of three attempts with correct and incorrect technique. Each peak flowmeter had a statistically significant elevation in PEF with incorrect technique. The range for elevation in PEF using incorrect technique was 12.4 to 68.2% above the PEF with the subject using correct technique. CONCLUSION: Each of the five marketed peak flowmeters had a significant elevation in PEF when a "spitting action" was used. Clinicians need to instruct patients carefully regarding correct technique when using peak flowmeters.

Adult↗
PubMedDate not supplied

Comparison of ocular hemodynamics measured by a new retinal blood flowmeter and color Doppler imaging.

BACKGROUND AND OBJECTIVE: To compare measurements of a new retinal blood flow device with central retinal artery blood velocity. MATERIALS AND METHODS: One randomly selected eye from each of 13 subjects was examined. Blood flow was measured by laser blood flowmeter and velocity by color Doppler imaging. The correlation between measurements was analyzed using regression analysis where a P value of less than .05 and coefficient of regression values of greater than .5 were considered significant. RESULTS: The laser blood flowmeter produced vessel diameter measurements of 90.1 +/- 18.7 microm (mean +/- standard deviation), velocity of 19.7 +/- 8.06 mm/sec, and flow measurements of 4.24 +/- 2.41 microL/min. Central retinal artery peak systolic velocity, end diastolic velocity, and mean velocity correlated significantly with laser blood flowmeter velocity (P = .01, r = .66; P < .01, r = .77; and P = .003, r = .76, respectively) and flow (P = .01, r = .71; P = .03, r = .6; and P = .01, r = .69, respectively). CONCLUSIONS: The laser blood flowmeter produces retinal artery flow and velocity measurements that correlate with central retinal artery peak systolic velocity end diastolic velocity, and mean velocity measurements. Further validation of the laser blood flowmeter's accuracy in measuring real flow warranted and likely requires more invasive in vivo studies (in animal models). However, this study supports the ability of the laser blood flowmeter to measure retinal blood flow.

Adult↗
PubMed1986

A Doppler flowmeter for use in theatre.

We have developed a Doppler flowmeter based on a 10 MHz pencil probe and mean frequency estimator which overcomes many of the limitations of existing electromagnetic and ultrasonic flowmeters. The output of the flowmeter, which is proportional to the first moment of the Doppler power spectrum and hence mean blood velocity is linear from 1.3 to over 50 cm s-1 for pulsatile flow. Variation in vessel diameter and angle of insonation, which are the common sources of error in Doppler flowmetry, are minimised by constraining the vessel in a plastic cuff which fixes the probe angle at 50 degrees. A simple gauge is used to compress the vessel flat, before the cuff is applied, to measure the wall thickness to within 0.25 mm. The vessel internal diameter and hence blood flow can then be calculated using an experimentally determined calibration factor to compensate for non-even insonation. A range of sterilizable cuffs from 3-12 mm diameter have been built and the flowmeter is now being used routinely during all arterial reconstructive surgery. The accuracy and reproducibility of the system was tested for range of different sized silastic tubes on a hydraulic model and found to be less than 12% for vessels greater than 2 mm internal diameter. Satisfactory signals were easily obtained from all prosthetic materials with the exception of PTFE. The instantaneous output was compared to an electromagnetic flowmeter using a fast Fourier transform algorithm; the moduli of the harmonics were virtually identical but the Doppler system produced a smaller phase shift with increasing harmonics.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMedDate not supplied

Numerically based design of an orifice plate flowmetering system for human respiratory flow monitoring.

During certain medical procedures, it is important to continuously measure the respiratory flow of a patient, as lack of proper ventilation can cause brain damage and ultimately death. The monitoring of the ventilatory condition of a patient is usually performed with the aid of flowmeters. However, water and other secretions present in the expired air can build up and ultimately block a traditional, restriction-based flowmeter; by using an orifice plate flowmeter, such blockages are minimized. This paper describes the design of an orifice plate flowmetering system including, especially, a description of the numerical and computational techniques adopted in order to simulate human respiratory and sinusoidal air flow across various possible designs for the orifice plate flowmeter device. Parallel computation and multigrid techniques were employed in order to reduce execution time. The simulated orifice plate was later built and tested under unsteady sinusoidal flows. Experimental tests show reasonable agreement with the numerical simulation, thereby reinforcing the general hypothesis that computational exploration of the design space is sufficiently accurate to allow designers of such systems to use this in preference to the more traditional, mechanical prototyping techniques.

Biomedical Engineering↗
PubMed1982

A rapid technique for dynamic calibration of electromagnetic flowmeters.

A new technique for the dynamic calibration of electromagnetic flowmeters has been developed that uses a simple transistor circuit and is suitable for both sine- and square-wave flowmeters. The magnet current is amplitude modulated using a square wave at a frequency of 1 Hz to provide a suitable input to the flowmeter. This input simulates the input that would have been generated is a square-wave oscillatory flow had been passed through a flow probe. The modulating square wave together with the square wave from the flowmeter output are sampled using a digital computer, and comparison of the Fourier transforms of the two waveforms yields a calibration of amplitude attentuation and phase lag for frequencies up to 50 Hz. The technique is very fast and thus allows multiple determinations of the calibration, which in turn lead to a more accurate calibration that has been achieved by other methods. The calibration of a Statham SP2202 flowmeter is presented providing an example of the technique.

Calibration↗
PubMed1987

Turbine flowmeter vs. Fleisch pneumotachometer: a comparative study for exercise testing.

The purpose of this study was to investigate the characteristics of a newly developed turbine flowmeter (Alpha Technologies, model VMM-2) for use in an exercise testing system by comparing its measurement of expiratory flow (VE), O2 uptake (VO2), and CO2 output (VCO2) with the Fleisch pneumotachometer. An IBM PC/AT-based breath-by-breath system was developed, with turbine flowmeter and dual-Fleisch pneumotachometers connected in series. A normal subject was tested twice at rest, 100-W, and 175-W of exercise. Expired gas of 24-32 breaths was collected in a Douglas bag. VE was within 4% accuracy for both flowmeter systems. The Fleisch pneumotachometer system had 5% accuracy for VO2 and VCO2 at rest and exercise. The turbine flowmeter system had up to 20% error for VO2 and VCO2 at rest. Errors decreased as work load increased. Visual observations of the flow curves revealed the turbine signal always lagged the Fleisch signal at the beginning of inspiration or expiration. At the end of inspiration or expiration, the turbine signal continued after the Fleisch signal had returned to zero. The "lag-before-start" and "spin-after-stop" effects of the turbine flowmeter resulted in larger than acceptable error for the VO2 and VCO2 measurements at low flow rates.

Carbon Dioxide↗
PubMed1996

Effect of altitude on hand-held peak flowmeters.

OBJECTIVE: To quantify the effect of altitude on the operational characteristics of hand-held peak flowmeters. DESIGN: Altitude simulation within a hypobaric chamber combined with five constant simulated peak flows delivered from a computerized pump were used to test commercially available peak flowmeters. SETTING: F.G. Hall Hyperbaric/Hypobaric facilities located at Duke University School of Medicine. MEASUREMENTS: Two each of nine models of commercially available hand-held peak flowmeters and a volume spirometer were tested at six simulated altitudes (100, 500, 1,000, 1,500, 2,000, and 3,000 m) using five target peak flows. Each peak flow was injected into each meter twice. Forward stepwise regression was used to check for nonlinear relationships between altitude and peak expiratory flowmeter readings. Linear regression equations were fit to the data at each target flow across altitude. Effect of absolute peak flow was tested by analysis of covariance. RESULTS: For these altitudes, linear relationships were found between altitude and measured peak flow. For all meters tested, the average decrease in peak flow ranged from -8.7% at the lowest target flow (123 L/min) to -6.5% at the highest target flow (702 L/min) for each 100 mm Hg decrease in barometric pressure (PB). Individual meters ranged from -12.3% at the lowest target flow to -4.4% at the highest target flow for 100 mm Hg decrease in PB. The spirometer had no significant changes associated with changes in PB. In all cases, the magnitude of the altitude effect, measured by percent change, decreased with increasing peak flow. CONCLUSIONS: Peak expiratory flowmeters underread PEF as a function of both increasing altitude and increasing target peak flow.

Altitude↗