Electromagnetic Flow Measurements Research Articles

Stem compensation of loop sensors for electromagnetic blood flow and vascular diameter measurement

Accuracy of electromagnetic blood flow--and vascular diameter--measurements by means of intravascular loop probes in an extracorporeal alternating magnetic field can be impaired by an error signal induced in the probe stem. The standard method of removing this artifact by twisting the lead wires is difficult to implement in this case because the wires are bifilar and are made of highly resilient metals. The solution described here makes use of a hair pin loop incorporated within the probe stem in which an e.m.f. is induced that can be used to cancel the unwanted e.m.f. induced in the lead wires of the loop of the sensor. This scheme is applicable to simple loop probes as well as to orthogonal double-loop sensors.

Flow Measurements and Simultaneously Performed Angiography of Aorto-coronary Bypass Grafts during Bypass Surgery

The function of aorto-coronary bypass grafts is usually assessed by the run-off, determined from postoperatively performed cineangiograms. The reliability of this method was tested by comparing the electromagnetically measured graft flow with the run-off, qualitatively estimated from cineangiograms. The electromagnetic flow measurements and cineangiography were performed simultaneously during bypass surgery. The run-off was classified by three independent observers into three classes (poor, moderate, and good). The average mean flow rates corresponding to the three classes were: poor: Q = (43 +/- 11)ml/min; moderate: Q = (48 +/- 14)ml/min; good; Q = (63 +/- 22)ml/min. Although the differences between the flow rates of the three classes were found significant (except between poor and moderate run-off), there was a wide range of overlapping. Especially in grafts with low flow rates (Q less than 70 ml/min) there were pronounced disagreements between the qualitative estimation of flow and the electromagnetically measured flow. Using videodensitometric flow measurements as a check test, the uncertainties in classification proved to be caused by the lack of reliability of the observer. The flow rates in aorto-coronary bypass grafts can be determined reliably only by means of quantitative methods, e.g., electromagnetic or videodensitometric flow measurements.

The effects of changes in the carotid sinus baroreceptor activity on splanchnic blood flow in anesthetized man.

In 9 patients being subjected to abdominal surgery, electromagnetic blood flow measurements were obtained from the hepatic, mesenteric and iliac beds while the carotid sinus baroreceptors were stimulated by carotid sinus massage. Carotid sinus stimulation produced an average maximum decrease in mean arterial pressure of 21%. Hepatic and mesenteric blood flows decreased by 15% and calculated vascular resistances were not significantly changed in these vascular beds. Iliac blood flow, on the other hand, showed a slight increase and iliac vascular resistance was decreased by 29%. It is concluded that the splanchnic vascular bed is of less importance in the carotid sinus baroreflex control of systemic arterial pressure in anesthetized man.

Experimental validation of methods for the measurement of coronary sinus blood flow in man.

The measurement accuracy of clinically applicable methods for blood flow measurement in coronary sinus -- continuous local thermodilution (LTD), differential pressure (DP), ultrasonic Doppler (US) and the electromagnetic flow measurement method (EMF) -- was examined in 15 anaesthetized closed chest dogs with left ventricle weights between 150 and 200 g. The LTD, DP, US and the EMF were examined in each experiment in the two following arrangements. 1. In coronary sinus -- left jugular vein by-pass: This arrangement allowed four reference methods for measurement of coronary sinus blood flow (CBF). 2. In "clinical" position, without by-pass, which allowed two reference methods for CBF measurements. The results on the measurement accuracy of the LTD, DP and US are, depending on the measurement arrangement, contradictory. In the by-pass arrangement 1 there was observed a good agreement of the LTD, DP and US CBF values with the reference values. In the "clinical" position, without by-pass 2 the measurement accuracy of LTD was not sufficient for exact measurement of CBF and derived parameters. The examined velocity tip flow probes (US, DP) gave no correlation with the reference methods. US and DP are even for semiquantitative estimation of CBF unsuitable. The EMF tip flow probe was for the CBF measurement unsuitable, because of disturbance by the electrical activity of myocardium.

Effect of synthetic substance P on internal carotid artery blood flow in man

Internal carotid artery blood flow was studied by peroperative electromagnetic blood flow measurement in 7 patients following 9 intravenous infusions of synthetic Substance P, 2 ng.kg-1.min-1. The blood flow responses varied interindividually. No significant blood flow changes were observed for the whole group. The arterial mean blood pressure decreased significantly.

The profunda femoris-popliteal artery bypass.

The profunda femoris artery can be used for the origin of a femoropopliteal bypass in cases of previous aorto femoral bypass graft, short saphenous vein, and other less common conditions that render the common femoral artery unsuitable for proximal anastomosis. Fourteen profunda-popliteal bypass procedures were performed in 12 patients between 1973 and 1976. The indications for surgery were incapacitating claudication in seven, and rest pain or tissue necrosis in five patients. Electromagnetic flow measurements at operation in ten patients indicated a mean graft blood flow of 146 +/- 51 ml/min. The mean Doppler ankle/wrist pressure ratio improved from 0.48 +/- 0.11 preoperatively to 0.87 +/- 0.14 postoperatively, while the plethysmographic mean pulse volume increased from 1.1 +/- 0.6 microliter to 2.4 +/- 0.4 microliter. Thirteen of the 14 grafts remain patient at one to three years' follow-up. The profunda-popiteal bypass is an effective alternative to standard femoropopliteal bypass in cases where the common femoral artery is not available for proximal graft anastomosis.

Determination of lower leg blood flow in man by thermodilution.

A thermodilution method for measuring distal femoral vein flow in man is presented. The catheter is introduced percutaneously in central direction into the popliteal vein. Tests for accuracy in vitro (r = 0.999, range of true flow 63–2600 ml/min) and in dog experiments (r = 0.994, range of electromagnetic flow measurements 110–780 ml/min) are presented and discussed in relation to the anatomical (dissections on corpses) and functional conditions in the popliteal/distal femoral vein of man. A group of normal persons [7] and of patients suffering from ischaemic lower limb disease [17] were studied at rest and during exercise on an ergometer in supine and sitting positions. In all but two, reliable measurements were obtained. In the normals, a mean resting flow of 114 ml/min (range 82–140 ml/min) was found. The individual coefficient of correlation between load and flow measurements in the normals varied from 0.80 to 0.94 during stepwise increasing load exercise. No serious complications occurred. The method...

Microvascular bypass surgery. Part 2: physiological studies.

Intraoperative electromagnetic blood flow measurements were recorded in 15 patients undergoing extracranial-intracranial arterial bypass surgery. The initial average blood flow of 28.2 cc/min supplies 8.4% of the expected flow from one internal carotid artery. Blood flow probably increases postoperatively, as evidenced by angiographic enlargement of the bypass and its recipient cortical arteries.

Extracorporeal magnet perivascular electromagnetic flow meters.

The "interrupted resonance" circuit proved effective in combination with an extracorporeal magnet in permitting electromagnetic blood flow measurements to be made in branch arteries of dogs by application of perivascular cuffs equipped with pick-up electrodes contacting the vessel wall. A four-turn coil, acting as a transformer secondary measures the amplitude of the magnetic field component which is effective in inducing the flow signal and thus permits calibrations for arbitrary orientations of the perivascular cuff relative to the magnetic field of the extracorporeal magnet. Recordings of mean and phasic blood flow in dogs' arteries provide illustrations of effectiveness in pharmacological studies and exhibit the reliability of the non-occlusive zero-flow base line obtained by de-energizing the magnet.

Intra-Aortic Balloon Pumping in the Treatment of Cardiogenic Shock Following Open-Heart Surgery

Intra-aortic balloon pumping (IABP) was used in the treatment of 29 patients in cardiogenic shock refractory to pressor drugs subsequent to open-heart surgery. Nineteen patients recovered from the shock primarily, but four died later in hospital. The remaining 15 were discharged alive. Peroperative electromagnetic flow measurements in one patient showed a 23% increase in aortic flow and a 26% increase in aortocoronary bypass flow when pumping was started.

Influence of electrical stimulation of the posterior hypothalamus on musculocutaneous and renal circulation in anesthetized dogs.

Hypertension and tachycardia were consistently induced by electrical stimulation of the median posterior hypothalamus in dogs under chloralose anesthesia, curarized and artificially ventilated. When renal and femoral vascular beds were perfused at a constant blood flow, the renal perfusion pressure markedly increased, whereas only minor variations of the femoral perfusion pressure occurred. When the renal and femoral vessels were perfused by the heart at the prevailing blood pressure, peri-arterial electromagnetic flow measurements revealed that renal flow decreased and that femoral flow increased during hypothalamic hypertension, both before and after vagotomy. In the same animals, no significant changes of renal or femoral flow occurred during reflexogenic hypertension induced by carotid occlusion. These marked hemodynamic differences between the reflexogenic and the hypothalamic type of hypertension were consistently and repeatedly observed. The indications that baroreflex counter-regulation and ganglionic inhibition due to elevated catecholaminemia contribute to the relative lack of femoral vasoconstriction during hypothalamic hypertension, are discussed.

Vasopressin and Hepatic Artery

Electromagnetic flow measurement study was performed in 20 anesthetized dogs to evaluate the effect of selective celiac infusion of vasopressin on the hepatic arterial vasculature. Teh hepatic arterial flow showed a biphasic response with an initial decrease followed by a substantial increase in spite of a continued infusion. The left gastric, splenic, and superior mesentric arteries showed a monophasic response with persistent decrease of flow during the whole infusion. The biphasic response of the hepatic arterial flow is thought to be due to autoregulatory dilative action of the liver to a decrease of the portal flow. The results and previous clinical experience suggest that the selective infusions of vasopressin into arteries supplying the liver can be used for short-term vasoconstrictive therapy of acute gastrointestinal bleeding in patients without liver damage. Further experience is necessary to evaluate the safety of prolonged hepatic infusions in patients with liver damage.

A Simple Method for Determining Cardiac Output During Cardiac Surgery

A simple method for estimating cardiac output following cardiopulmonary bypass is described. The results of this method were compared with electromagnetic flow measurements in 16 patients. Changes in cardiac output of 700 ml. per minute or more could be accurately measured by our new method. This simple modification of the Fick method for measuring cardiac output is very useful in evaluating prosthetic valve and myocardial function in the period immediately following perfusion.

Compression of arteries via an esophagostoma as an aid to electromagnetic blood flow measurement

To obtain the zero flow signal in chronic electromagnetic blood flow measurements in the internal mammary artery (I.M.A.) of the dog, digital occlusion of the blood vessel via a low cervical esophagostoma is used. By this method implantation of an occluding device and resulting injury to the vessel can be avoided. The technique of the esophagostomy and the postoperative care of the animals are described. The I.M.A. as well as a number of other arteries in the upper part of the thorax can be easily compressed by this method. It is suggested that compression of arteries via the digestive tract is a method also applicable to other parts of the body.

A miniaturized occluder for electromagnetic blood flow measurements

A miniaturized occluder for electromagnetic blood flow measurements

Fluid network response characteristics under pulsating flow conditions

The strong analogies between electrical and fluid system can be used to effect in modeling behaviour under pulsating flow conditions. This paper discusses the model of a simple pipe network experiencing pulsating flow as a result of valve movement. Experimental results are presented, indicating that care needs to be taken in modeling the valve behaviour as analogous to thermionic valve. One of the major problems in modeling fluid networks of this type is the lack of information regarding the characteristics of active components such as the valve. Developments in the field of Electro-magnetic and Ultrasonic flow measurement are helping to improve this situation.

Theory of induced voltage electromagnetic flowmeasurement

The contribution of each part of the flow to a meter signal is expressed in terms of a weight vector <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> and the velocity ν, with the signal <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\propto \int \nu \cdot W dr</tex> over the flowmeter volume. <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> depends on the magnetic field <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</tex> and a vector defined entirely by the electrode and flowmeter geometry. A meter is called "ideal" if the signal is proportional to the flow rate and independent of the flow pattern. The condition on <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> for this is given and an experimental ideal meter mentioned. Since meters with small (point) electrodes cannot be ideal, weaker conditions on <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> for flows of different types are reviewed. A technique for designing short meters suitable for rectilinear flow with an unknown axisymmetric velocity profile is briefly described. The behavior of different shapes of electrodes, including electrodes of finite and variable conductivity, is discussed. Finally the problems of pulsating flow, magnetic field specification, and nonuniform and anisotropic blood conductivity are discussed.

THE MEASUREMENT OF TIDAL WATER TRANSPORT IN CHANNELS

For the electromagnetic flow measurement in straits, channels etc use is made of the electric potential difference between two points m the bottom, near the moving water. The potential difference can be put down to natural causes the water is an electric conductor and moves m the magnetic field of the earth There are a number of quantities and variables that are of importance for the measured signal Beside this, the measurement is above all a matter of eliminating some disturbances Information about the two measuring systems as applied m The Netherlands is given m this article.

Mesure du débit des eaux usées ou fortement chargées en matières solides en vue de déterminer les flux de pollution

The quantity of pollution due to industrial or urban effluent over a given time T is given by P = S T 0 q c dt, where q and c are instantaneous polluant discharge and concentration respectively. Where continous concentration measurement is impracticable, the only theoretically correct procedure is by taking a sample at a discharge proportional to that of the effluent. A common alternative is to take a set number of samples at constant discharge and to multiply the average concentration found for each by the volume flow during the smapling time. The aim in every case is to record discharge. No special methods are available for polluted water discharge measurement. Standard methods are applied, there fore, and are briefly discussed from the point of view of possible effects of pollution or of how the instrumentation is installed on measurement accuracy and sensitivity. Vane-type water meters or discharge measurement orifice plates or nozzles are hardly suitable for pipes containing highly sediment-laden or corrosive water. Dilution methods and electro-magnetic flow measurement instruments are less sensitive to effluent quality, and acoustic instruments seem to hold great promise. Finally, pump running time measurement should not be disregarded altogether, in spite of its not particularly accurate results. Measurements by electro-magnetic pickup are preferable to current meters for free-surface flow. Broad-crested weirs or Venturi flumes producing a hydraulic jump are preferable to sharp-crested weirs, but are more difficult to set up. Dilution methods call for precautions in the choice of a suitable tracer, and it is not always easy to achieve the right mixture. The use of radio-active tracers enables discharge to be recorded. With chemical tracers, the present trend is towards constant-rate injection and the constitution of average samples from which both flow volume and pollution concentration can be established. There is a systematic error with this method which, however, remains within acceptable limits if the discharge does not vary too much. Present research subjects include the use of electro-magnetic pickups and the behaviour of various tracers in polluted water. It is proposed to design special equipment for the use of radio-active tracers.

An improved hydraulic vascular occluder for chronic electromagnetic blood flow measurements.

ARTICLESAn improved hydraulic vascular occluder for chronic electromagnetic blood flow measurementsW. L. Henry, C. Ploeg, S. L. Kountz, and D. C. HarrisonW. L. Henry, C. Ploeg, S. L. Kountz, and D. C. HarrisonPublished Online:01 Dec 1968https://doi.org/10.1152/jappl.1968.25.6.790MoreSectionsPDF (531 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByVelocity and flow measurements by electromagnetic techniquesThe American Journal of Cardiology, Vol. 29, No. 3Use of Active Notch Filtration With Electrically Induced Cardiac Asystole To Establish Zero Blood Flow for in Vivo Flowmeter Calibration2 July 2016 | Angiology, Vol. 22, No. 5 More from this issue > Volume 25Issue 6December 1968Pages 790-792 Copyright & PermissionsCopyright © 1968 the American Physiological Societyhttps://doi.org/10.1152/jappl.1968.25.6.790PubMed5727211History Published online 1 December 1968 Published in print 1 December 1968 Metrics