An Electromagnetic Catheter-Flowmetercircres.ahajournals.org/content/circresaha/21/6/889.full.pdf · An Electromagnetic Catheter-Flowmeter By Alexander Kolin, ... The transducer thus

An Electromagnetic Catheter-Flowmeter

By Alexander Kolin, Ph.D., James D. Archer, and Gordon Ross, B.Sc,

M.B.B.S. (London), M.R.C.P. (London)

ABSTRACTAn electromagnetic flowmeter incorporated into a catheter is described. The

catheter is introduced into the aorta via the femoral artery. The flow sensoris located some distance below the catheter tip and is sensitive to flow at rightangles to the catheter. A crater-like elevation at one end of the transducerlumen permits funnel-like connection of the transducer to the ostium of anaortic branch. The transducer thus measures the blood flow through a selectedbranch of the aorta. It is pressed against the branch artery by arching thecatheter by means of a pull-wire. A reliable and readily reproducible zero-flowbaseline is obtained by slightly withdrawing the lumen of the transducer fromthe branch ostium, thus closing the lumen by the aortic wall. Records of phasicblood flow in the left renal and superior mesenteric arteries of a dog arepresented. The calibration was accomplished by comparison with a calibratednoncannulating electromagnetic flow transducer. Reliable calibration can alsobe performed in vitro.

ADDITIONAL KEY WORDSrenal arterial flow dog

superior mesenteric artery flow

• Several attempts have been made in thepast to measure blood flow in the major ar-teries by means of a flow sensor attached tothe tip of a catheter. Pieper (1) succeeded inobtaining blood flow recordings by means ofa differential transformer transducer at thetip of a catheter centered in the aorta bymeans of an "umbrella skeleton" device. Healso succeeded in obtaining coronary flowrecords with a similar transducer monitoringthe flow through a hollow catheter tip in-serted into the opening of the main coronaryartery (2). Blood flow records have also beenobtained with catheter-mounted thermistorflow sensors (3). Mills attempted to accom-plish the same thing by means of an electro-magnetic flowmeter attached to a cathetertip intended for use at the center of a majorvessel (4). His flow sensor was unconvention-al in that the magnet was enclosed in a plastic

From the Department of Biophysics, University ofCalifornia Los Angeles School of Medicine, Los An-geles, California 90024.

This work was supported in part by U. S. PublicHealth Service Grant 1 SOL FR 05354, AEC Gen-12Contract, and the Office of Naval Research.

Accepted for publication November 1, 1967.

cylinder capped by hemispheres at both ends.It was oriented parallel to the flow axis, andthe electrodes were located on the peripheryof the cylinder along a line transverse tothe magnetic field. This configuration is ex-tremely unfavorable since the short-circuitingeffect of the fluid surrounding the electrodesgreatly lowers the sensitivity as compared tothe conventional configuration at equal inter-electrode distance and magnetic field intensi-ty where the electrode tips are insulated fromthe surrounding fluid by a plastic sleeve.The paper did not give any data on experi-mental calibration and presented no flow rec-ords.

In a preliminary paper (5), one of us hasshown how an electromagnetic catheter-flow-meter can be used for quantitative determina-tion and recording of the volume rate ofarterial flow in branches of the aorta. Theobjective of this publication is to describe animproved modification of the device and toshow that it has some advantages over theconventional electromagnetic flow transducerapplied externally to intact arteries. The elec-tronic system we use in connection with thecatheter transducer is identical with the 400-

Circulation Research, Vol. XXI, December 1967 889

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Circulation Research, Vol. XXI, December 1967



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ELECTROMAGNETIC CATHETER-FLOWMETER 891

cps gated sine-wave system employed withconventional flow transducers as previouslydescribed (6).

The approach to the solution of our ob-jective deviates from the conventional modeof application of catheter flow-velocity trans-ducers. The flow-sensing element is not lo-cated at the catheter tip, and instead of beingsensitive to flow parallel to the catheter axis,the transducer is sensitive to flow perpendicu-lar to the catheter axis. It thus displays zerosensitivity to the axial flow in the aortic trunkwhen placed along the aortic axis. To measurethe flow through an artery branching off theaorta, the transverse opening of the flow trans-ducer near the tip of the catheter is pressedagainst the periphery of the aorta at the pointof origin of the selected branch artery as de-scribed below.

The Flow Sensor

The application of the flow sensor in funnel-like fashion to the ostium of a branch of theaorta is equivalent to measuring the branchflow with a cannulating flowmeter (i.e., with-out an intervening blood vessel wall separat-ing the blood from the electrodes). Any con-ventional cannulating flow transducer would,in principle, be suitable for this purpose. Ac-tually, however, the introduction of the trans-ducer through the lumen of an artery, such asthe femoral or the carotid, imposes limita-tions upon the cross-sectional area of the flow

FIGURE 1

Flow sensor of the catheter-flowmeter. Clt C2 = mag-net coils; I,, L, = permalloy cores; Ej, E, =.exposedareas of the electrode; P l ; P2 = electrode plates; Wc =wire connecting coils in series; Wa, Wb = magnetleads; Wj, W2 = electrode leads; B = wire braid;Fj, F2 = epoxy frames; L = transducer lumen; S =seal. At top left is an end-on view of transducerlumen. At top right a side view of the transducershows the crater on the left-hand side of the lumen.Diagram at bottom shows the transducer with awasher that permits application to artery ostia withdiameters greater than the transducer diameter. W =silicone rubber washer; CP = cemented area; C —catheter; L = transducer lumen.


sensor. It must be at least slightly larger indiameter than the ostium of the internal ar-tery in which the flow is to be measured butno larger than the diameter of the slightlystretched peripheral artery through which itis introduced with the attached catheter. Wehave chosen a design (5) that permits re-ducing the cross section of the transducer toa minimum and made modifications, de-scribed below, that further reduce its diam-eter without reducing its mechanical strengthor sensitivity.

Figure 1, upper left, is a cross-sectional viewof the flow transducer looking into the lumen,L, which is approximately square. Its sidewalls are platinum sheets, P] and P2, /•* mmthick, insulated with a layer of Epoxylite 1/3mm thick. The insulation is removed insidethe lumen over an approximately circulararea % mm in diameter to create the two re-cessed electrode spots, Ei and E2, contactingthe blood. The electrode plates, Pt and P2,are cemented with Hysol epoxy to the Hysolepoxy frames, Fi and F2, to form a rigidstructure that supports and centers the cylin-drical permalloy cores, Ix and I2, which fit intocylindrical depressions in the frames, Fx andF2. Coils, Ci and C2, are wound about thecores, i! and 12 (1.25 mm in diameter, 5 mmlong), with 75 turns of 32-gauge Gripezeinsulated copper wire. A magnetic field of170 gauss is generated at the center of thelumen, L, at the normal operating current of0.8 amp.

The electrode wires, Wj and W2, are sol-dered to the plates, Px and P2, and are guidedsymmetrically toward the catheter, C, with atight twist along the surface of coil Ca asshown. Just beyond coil Co wires Wi andW2 enter the grounded metal braid, B, whichserves as a shield.

The coils, Ci and Co, are connected inseries by wire Wc. Wires Wa and Wb (Teflon-insulated copper wire, gauge 7/40) conveythe 400-cps current energizing the magnetcoils. They are twisted and run parallel towires Wt and W2 through the catheter toward



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the plug which is attached to the oppositeend of the catheter. The radiopaque catheter(United States Catheter Co. 5264-8F) ismade of a nylon tube reinforced with wovendacron coated on the outside with a radio-paque resin. It is cemented with Hysol epoxyto the transducer body which is completelyencapsulated in Hysol epoxy (C9-4206) bydipping and subsequent exposure to infraredradiation. A layer of Silastic silicone rubber(General Electric, RTV-112) is coated overthe epoxy seal at S for added protectionagainst leakage.

The transducer body is not symmetricalin side view (Fig. 1, upper right). Its lumen(indicated by horizontal dashed lines) ter-minates in a crater-like protrusion on the leftside. This protrusion facilitates applicationof the transducer lumen to the ostium of thearterial branch, making the protrusion "snap"into the arterial lumen in press-buttonfashion.

When the diameter of the ostium of theartery to which the flow-sensing catheter isto be applied exceeds the diameter of theflow sensor, leakage of blood around the

FIGURE 2

Catheter flowmeter. At left, catheter is unarched; at right, it is arched by tension appliedto wire, W, to make the crater on the left side of the flow transducer snap into the ostium ofartery branch, B. The center drawing shows the device for application of wire tension. C z=catheter; B = branch of the aorta; T = tail portion of the catheter cemented to the transducer;L =: transducer lumen; W := pull wire; S = emergence point of the pull wire; t = stainlesssteel tubing harboring the pull wire; H = hole for attachment of pidl wire; LO = end wireloop; P = stainless steel tubing for intra-arterial injection; ST]; ST2 = syringe needle hafts;PL = transducer plug; SL = slide; A = spring actuator; SS = set screw; Sp =: spring; SC =scale; I = index; W = pull wire; b = aluminum body; N = nipple.




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flow sensor could occur, and the transducerwould thus measure a fraction of the flowpassing through the artery branch. Such flowleakage can be prevented by the slight mod-ification shown in Figure 1, lower left. Asilicone rubber washer, W, 0.25 mm thickand perforated at the center by an openingequal in diameter to the diagonal of thelumen, L, is cemented by Silastic to the bodyof the probe, allowing the crater1 to protrude.The cemented area is indicated by the shadedarea, CP, which surrounds the opening, L,and extends beyond the ends of the verticaldiameter of the washer, W. If we allow thevertical washer to wrap itself once around

'In view of the tendency of a hard epoxy crater toinjure the aortic intima as it is moved in and out ofthe branch ostium to secure a zero flow base line,we recommend that the crater edge be covered withRTV-112 Silastic, which reduces or eliminates thishazard. At the same time, the fibrin film, which tendsto form on an epoxy crater, is avoided.

the transducer (which happens when thetransducer is introduced through a narrowartery into the aorta), we can use a washerapproximately 9 mm in diameter for a trans-ducer 3 mm in diameter. Usually, the di-ameter of the artery ostium will not surpassthe diameter of the transducer by such alarge factor. Consequently, a washer with aconsiderably smaller diameter will suffice formost practical purposes.

The use of a square transducer lumen per-mits reduction of the outer transducer dimen-sions to a minimum, since the electrodes nowalso serve the structural function of sidewalls, which, being made of metal, are strongthough very thin. Suitability of rectangularlumens for electromagnetic flow transducershas been pointed out by Shercliff (7). Thesensitivity and linearity of this transducer arecomparable to the performance of a trans-ducer with a circular lumen of correspondingdimensions.

FIGURE 3

Left, frontal mew of the catheter-flowmeter depicting the lumen of the transducer and thecatheter sections adjacent to it. The catheter is unarched in the abdominal aorta of a dog.Right, lateral view of the catheter flow transducer (lumen not shown). The catheter is archedin the abdominal aorta of a dog and is positioned to measure the blood flow in the leftrenal artery running from the transducer to the kidney. The renal artery (between whitearrows), ureters, and kidneys have been opacified by the injection of contrast material througha small catheter introduced -percutaneously into the aorta. The black arrow points to the tipof this catheter, from which a stream of radiopaque material passing downward obscures thelower section of the catheter-flowmeter.




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Flow-Sensing CatheterFigure 2 shows the incorporation of the

flow transducer into the catheter flow sensoras well as some details omitted in Figure 1.For pharmacological studies, it is convenientto have a means of injecting drugs into theartery through which the blood flow is beingrecorded. For this purpose, 26-gauge hypo-dermic tubing is run through the catheter. Itemerges at point P and is bent to inject intothe transducer lumen, L.

In principle, radiopaque material could beinjected in the same fashion to visualize theartery by x-rays and to delineate the distribu-tion of the blood passing through it. Actually,however, the high viscosity of the contrastmaterial does not permit sufficient influx. Forbest results, a radiopaque catheter is intro-duced percutaneously into the aorta via thecontralateral femoral artery. By intermittenthand injection of contrast material, the de-sired artery can be readily located, permittingthe catheter flow sensor to be positionedquickly and easily. Figure 3, left, is a roent-genogram of the catheter with the transducerlumen facing the observer, before injectionof the contrast material. The roentgenogramon the right shows the catheter with the trans-ducer lumen oriented coaxially with the en-trance section of the renal artery after injec-tion of the contrast material. The kidney,ureters, and left renal artery are clearlydepicted.

For proper operation of the transducer tomeasure the entire blood flow entering a givenartery from the aorta, the left opening of thelumen, L, must be pressed against the pointfrom which the artery branches off, as shownin the right-hand diagram of Figure 2.

Application and Performance of theCatheter-Flowmeter in the

Living AnimalThe flow sensor, perforated by the lumen,

L, is located between two sections of thecatheter, which can be arched into the shapeof a bow between points H and S, as shownin the right-hand diagram of Figure 2. Thisis accomplished by application of tension to

the wire, W, which is attached to the cathetertip at point H and dives into the catheterinterior at point S. This point is a terminalof a 26-gauge stainless steel tube, t (left-handdiagram, Fig. 2), which traverses the cathe-ter to emerge about 100 mm from the plug,PL, which supplies the power to the transducerelectromagnet and conveys the flow signalfrom the electrodes to the amplifier. Figure 2shows the catheter in the straight positionbefore application of tension to the wire, W(left diagram), and in the arched position(right-hand diagram). Figure 3 shows thetwo positions of the catheter in anesthetizeddogs. In Figure 3 (left) the transducer isoriented to show its lumen. On the right,the catheter is suitably arched and the trans-ducer is properly positioned for recordingleft renal artery flow.

It is hazardous to apply tension to thewire, W, directly by hand. It can be over-stressed and broken. To avoid this, the pullis transmitted to the wire by means of aspring, SP (Fig. 2), which is housed in ahollow cylindrical spring "actuator," A, whichcan be pulled upward, thus shortening thespring and exerting a pull on the wire, W,which enters the tubing, t, through the sy-ringe needle haft, STj. The actuator slidesin an outer hollow cylindrical body, b, andcan be fixed in position relative to it by a setscrew, SS, thus securing action of a constantspring tension upon the wire, W, and conse-quently providing a constant force pressingthe crater of the transducer lumen into theostium of the artery under investigation. Com-pression of the spring, by pressing the slide,SL, inward, diminishes the tension of thewire and allows a temporary complete orpartial relaxation of the spring and a conse-quent straightening of the catheter. This isdone to facilitate frequent in-and-out move-ment of the catheter in the aorta.

We have tested the performance of thecatheter-flowmeter in several branches of theabdominal aorta of large dogs (18-28 kg).After anesthesia with pentobarbital sodium(30 mg/kg), we performed a femoral ar-teriotomy. After intravenous injection of




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heparin (500 U.S.P. units/kg), we intro-duced the instrument into the femoral arteryand advanced it into the abdominal aorta,with the spring, SP (Fig. 2), deactivated (i.e.,no tension on wire, W). It proved possibleto measure renal arterial flow without ancil-lary aids by searching for the ostium of therenal artery by adjusting the position of thecatheter until the characteristic renal flowsignal with its high ratio of diastolic to systolic

flow was obtained. The catheter end was thenarched as described above and further fineadjustments in its position were made to max-imize the flow signal. Although, in favorablecases, correct placement of the instrumentfor renal flow measurement can be achievedin this way within 3 minutes of insertion intothe femoral artery, the procedure is greatlyfacilitated by fluoroscopy (Fig. 3).

Renal arterial flow signals obtained from

150

FIGURE 4

Comparison between velocity pulses in the renal artery obtained by the electromagneticcatheter-flowmeter (bottom tracing) and a noncanniilating iron-core electromagnetic transducerexternally applied to the renal artery (middle trace). The top trace shows systemic arterialpressure. The slight differences in the wave forms recorded from the two transducers areascribed to their separation by an elastic conduit (2 cm of the renal artery).

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FIGURE 5

Zero flow reference obtained by withdrawing the transducer lumen from the ostium of therenal artery to press it against the aortic wall and thus stop the flow of blood in it. The endsection of the catheter is kept arched during this operation. The record shows that the trans-ducer can be returned to the flow-sensing position within 1 second.

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the catheter-flowmeter are shown in Figure4 to be almost identical with those obtainedfrom a 2.5-mm lumen split-pole noncannu-lating electromagnetic transducer (8) simul-taneously recording from the same artery. Thezero flow reference was obtained repeatedlyby slightly withdrawing the catheter main-tained in the arched position so as to pressthe lumen of the transducer against the aorticwall. This zero reference can be obtainedand the probe returned to the flow-sensingposition in less than 1 second (Fig. 5). Thezero base line is remarkably stable and isidentical to that obtained by occluding therenal artery (Fig. 6). The artery is occludedat B, yielding a pulsating base line in bothflow records. At A, the crater of the catheteris pressed against the aortic wall and a smoothbase line, shown at A, is obtained. The zero-flow base line can thus be obtained for thisdevice by stopping flow through the sensorwithout interruption of blood flow throughthe aorta or renal artery.

Figure 7 illustrates the use of the catheter-flowmeter to determine the effect of intra-venous norepinephrine on average renal bloodflow.

Figure 8 illustrates measurement of bloodflow in the superior mesenteric artery, a flowpattern different from that in the renal artery.

CalibrationIn work with conventional electromagnetic

flowmeters, one commonly considers as mostreliable that method of calibration which iscarried out under conditions closely approxi-mating those of the physiological measure-ments. A calibration in vivo can be performedconveniently in animals by applying thecatheter-flowmeter to the ostium of an arterythrough which the blood flow is recorded bymeans of a calibrated conventional noncannu-lating electromagnetic flow transducer. How-ever, it is desirable to be able to calibrateflow in vitro. This requires a special device,which can be made of Lucite, to feed the flow

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FIGURE 6

Reproducibility of catheter-flowmeter zero reference. The bottom trace depicts phasic leftrenal arterial flow determined by the electromagnetic catheter-flowmeter. The middle traceshows the same flow determined by a noncannulating, iron-core electromagnetic transducerapplied externally to the left renal artery. The catheter was repeatedly withdrawn from, andsubsequently replaced in, the renal artery orifice to obtain the baselines, A. At B the renalartery was occluded by a snare distal to the conventional transducer. Note the agreementbetween the zero A and the zero B. Small flow pulsations are recorded by both transducers atB because of pulsatile volume changes of the arterial segment upstream from the point ofocclusion. At the arrow the crater of the transducer lumen was withdrawn from the renal arteryorifice and pressed against the aortic wall; pulsations are no longer recorded by the catheter-flowmeter.




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Effect of 1 ng/kg of intravenous norepinephrine onmean blood flow in the left renal artery determinedby the electromagnetic catheter-flowmeler. Uppertrace = systemic arterial pressure; lower trace = renalarterial blood flow.

to the catheter flow transducer. We found thefollowing scheme convenient. A tube approx-imately 3 cm i.d. and 6 cm long is closed atboth ends by circular end plates about 1 mmthick. At the center of one end plate, a tube(about 5 mm i.d.) is cemented coaxially withthe large tube. At the opposite end of theaxis of the two tubes, a 3-mm hole is drilledcentrally into the second end plate. A thick,soft, silicone rubber square perforated byan opening of the same diameter as thetransducer lumen is cemented over the end-plate hole superposing the two openings. ALucite plate carrying a similar perforatedsilicone rubber square over a hole 3 mm indiameter facing the opening in the end platecan be pressed by means of two screws

against the perforated end plate so that theholes in the two silicone rubber squares aresuperimposed precisely. The Lucite plate andthe tub end plate are then separated byloosening the screws. The flow transducer issandwiched between them and aligned so thatthe perforated silicone rubber gaskets fittightly around the transducer lumen afterthe screws are tightened. Blood or salinecan then be fed into the nipple of the firstend plate. The fluid fills the large tube andescapes through the opening in the terminalLucite plate after passing through the lumenof the flow probe. The rate of flow againstwhich the catheter transducer is to be cali-brated can be measured by measuring thefluid escaping through the calibrating set-upor by a second flow probe placed in serieswith the input nipple of the calibrating device.

Table 1 illustrates the effectiveness of thiscalibration procedure. Fifteen rates of flowof physiological saline were selected: fivevalues of constant flow, five of pulsatingflow (approximately 1 cps frequency) re-corded on the phasic flow setting of theelectronic channel, and five of pulsating flowrecorded on the average flow setting of theelectronic channel (time constant 0.36 sec-onds). The average flow values for the pul-sating flow curves were determined by plani-metry. In all there was a concurrent volu-metric determination of the average rate offlow. Figure 9 shows a plot of the points

150

FIGURE 8

Blood flow in the superior mesenteric artery determined by the electromagnetic catheter-flow-meter. Upper trace == systemic arterial pressure; lower trace = superior mesenteric arterial flow.

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TABLE 1

Catheter Calibration with Constant and Pulsating Flows on "Average" and "Phasic" Instrument Settings

Volumetricflow

determination(ml/min)

Constant flow,instrument deflectionon "average" setting

(time constant 0.36 sec)(mm)

Pulsating flow,average deflection(by integration)

on "phasic" setting(mm)

Pulsating flow,average deflection(by integration)

on "average" flow setting(time constant 0.36 sec)

(mm)

350 ± 5340 ± 5270 ± 5210 ± 5154 ± 2195 ± 5190 ± 5190 ± 5190 ± 5170 ± 2170 ± 2122 ± 2128 ± 2104+197 ± 1

33 ± 0.331.5 ± 0.325 ±0.320 ± 0.314.5 ± 0.3

18.4 ± 0.3

17.3 ± 0.3

16.2 ± 0.3

11.6 ±0.39.7 ± 0.3

17.1 ± 0.317.1 ± 0.3

15.5 ± 0.3

10.4 ± 0.3

9.0 ± 0.3

50 100 150 300 250 300 330 400

VOLUMETRICALLY DETERMINED FLOW RATE IN ml/min

FIGURE 9

Calibration of the catheter-flowmeter with constant and pubating flows. + = constant flow(instrument on "average" setting). & = pulsating flow (instrument on "phasic" setting). O =pulsating flow (instrument on "average" setting).

obtained from Table 1. They lie on the samestraight line as that expected for a typicalelectromagnetic flowmeter within the limitsof experimental error (4%).

To ascertain to what extent the replace-ment of the blood vessel walls by the materialsof the calibrating device could affect thecalibration if the in-vitro technique were used




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instead of the in-vivo method, a comparisonwas made between two drastically differentmaterials serving as walls of artificial modelsof the aorta with a side branch. One modelwas made of Lucite, whose conductivity ismany orders of magnitude below that of theartery wall, and a second one of copper,whose conductivity surpasses that of theaorta by several orders of magnitude. Thecalibrations proved to be identical within thelimits of experimental error (about 4%). Thusthe material of the conduit does not percep-tibly affect the calibration, and it can becarried out in vitro with adequate reliability.

When blood is used for calibration, changesin hematocrit do not affect the sensitivity.Blood plasma and whole blood yield thesame calibration within the limits of experi-mental error (about 4%).

Discussion

The electromagnetic catheter-flowmeter hasseveral advantages over the conventional elec-tromagnetic transducer. It obviates the needfor major surgical procedures to expose adeep-seated blood vessel. The hazard ofstripping the arterial adventitia and possibleinterference with nerve supply is eliminated.Drugs are easily injected intra-arterially with-out puncturing the artery. Blood flow canbe measured successively in several vascularbeds using only one transducer; and, finally,the zero-flow reference level is very stableand can be readily and reliably obtainedwithout interfering with the blood flowthrough the organ under investigation.2

At the moment, the method has limitations.Flow can be measured quantitatively onlywhen the catheter is correctly positioned andno blood enters the artery ostium by flowingaround the sides of the transducer. Further-more, there are organs supplied by arterieswhich do not directly branch off the aorta,such as the hepatic, gastric, and splenic ar-teries. We believe, however, that some of these

2Electromagnetic catheter-flowmeters of this typewill be obtainable from the MICRON InstrumentCompany, 1519 Pontius Ave., Los Angeles, Calif.90025.


present limitations can be overcome by tech-nical and methodological developments suchas the use of a silicone rubber washer.

Our experience suggests that this device,sterilized by ethylene oxide, might be usedwith appropriate caution to provide contin-uous recording of instantaneous and averageregional blood flow in conscious humanbeings. Such observations would probably beof value in the diagnosis and treatment oforganic disease. As with all catheterizationsof human subjects, there is a hazard of dam-aging the internal coat of the vessels throughwhich the catheter passes. The presence ofa rigid section with a slight protrusion maymake the present catheter somewhat morehazardous than standard catheters. Also, thenecessity of giving the patient heparin toincrease clotting time would constitute anadded risk.

AcknowledgmentsWe gratefully acknowledge the cooperation of

Dr. William Hanafee of the Department of Radiologyin developing the roentgenographic procedures andin placing the facilities of his department at our dis-posal.

References1. PIEPEB, H. P.: Registration of phasic changes of

blood flow by means of a catheter-type flow-meter. Rev. Sci. Instr. 29: 965, 1958.

2. PIEPEB, H. P.: Catheter-tip flowmeter for cor-onary arterial flow in closed-chest dogs. J.Appl. Physiol. 19: 1199, 1964.

3. AFONSO, S.: A thermodilution flowmeter. J.Appl. Physiol. 21: 1883, 1966.

4. MILLS, C. J.: A catheter tip electromagneticvelocity probe. Phys. Med. Biol. 11: 323,1966.

5. KOLIN, A.: An electromagnetic intravascularblood-flow sensor. Proc. Nat. Acad. Sci. U.S.57: 1331, 1967.

6. KOLIN, A., AND KADO, R. T.: Miniaturization ofthe electromagnetic blood flow meter and itsuse for the recording of circulatory responsesof conscious animals to sensory stimuli. Proc.Nat. Acad. Sci. U. S. 45: 1312, 1959.

7. SHEHCLIFF, J. A.: Theory of ElectromagneticFlow Measurements. New York, CambridgeUniversity Press, 1962, pp. 16, 31.

8. KOLIN, A., AND VANYO, J.: New design of mini-ature electromagnetic blood flow transducerssuitable for semi-automatic fabrication. Car-diovascular Res. 1: 274, 1967.



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ALEXANDER KOLIN, JAMES D. ARCHER and GORDON ROSSAn Electromagnetic Catheter-Flowmeter

Print ISSN: 0009-7330. Online ISSN: 1524-4571 Copyright © 1967 American Heart Association, Inc. All rights reserved.is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231Circulation Research

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An Electromagnetic Catheter-Flowmetercircres.ahajournals.org/content/circresaha/21/6/889.full.pdf · An Electromagnetic Catheter-Flowmeter By Alexander Kolin, ... The transducer thus