Hot-Film Anemometer Velocity Measurements of Arterial …circres.ahajournals.org/content/circresaha/34/2/193.full.pdf · Hot-Film Anemometer Velocity Measurements of Arterial Blood

Hot-Film Anemometer Velocity Measurements of Arterial Blood Flowin Horses

By Robert M. Nerem, John A. Rumberger, Jr., David R. Gross, Robert L. Hamlin, and Gary L. Geiger

ABSTRACTBlood velocity measurements were carried out using a constant-temperature hot-film

anemometer system in both anesthetized and conscious horses. Catheter probes wereused to measure velocity wave forms in conscious horses and L-shaped needle probes in-serted by direct vessel puncture were used to measure the profiles in regions ofthe thoracic and abdominal aorta of anesthetized, open-chest horses. Both catheter andL-shaped probes were used for coronary velocity wave-form measurements. The flowconditions were characterized by peak Reynolds numbers of 200-10,000 and unsteadi-ness parameter of 2-30. These measurements indicate that in the thoracic aorta the flowat peak systole is largely inviscid with a thin-wall boundary layer; in the abdominal aortathe flow is more fully developed but skewed due to branching effects. Highly disturbedflows were observed in the thoracic aorta of both anesthetized and conscious horses, butnot in the abdominal aortic region or in the coronary arteries. The results of this study in-dicate that the flow in the arterial system, although in many cases laminar and distur-bance free, is extremely varied in character. It may be asymmetric and certainly is notrepresentative of fully developed, Poiseuille flow.

KEY WORDS aortic blood flow hemodynamicsReynolds numbers laminar flow disturbed flow

velocity profile

• Fluid mechanical factors influence the locationof sites which show preferential development ofarterial disease. For example, both Caro et al. (1)and Fry (2) have identified arterial wall shearingstresses as potentially important factors in the de-velopment of atheroma. Although there is somequestion about the exact role of these fluid me-chanical factors (e.g., is it an effect of wall shear onthe fluid mass transport or on the properties of thearterial wall), the possible importance of suchphenomena requires that more detailed knowledgeof the properties of arterial blood flow begathered.

Recently, point velocity and shear stressmeasurements within the arterial system havebecome possible with constant-temperature hot-film anemometer systems. Reports on the use ofsuch systems in the aorta (3-9) agree on the factthat in the ascending and upper descending por-tions of the aorta a clearly defined aortic wallvelocity boundary layer exists. Furthermore, for

From the Physiological Fluid Mechanics Croup, The OhioState University Bio-Medical Engineering Center, Columbus,Ohio 43210.

This investigation was supported by the National ScienceFoundation under Grant CK-31026 and by the Central OhioHeart Association.

Received July 2, 1973. Accepted for publication November26, 1973.

Circulation Research, VoL XXXIV, February 1974

certain conditions, observations of highly disturbedvelocity wave forms have been reported and at-tributed to the presence of fluid mechanical tur-bulence in the flow (10).

These in vivo studies have been carried outlargely in animals smaller than humans, e.g., dogsand pigs. Limitations on the size of instrumentationhave precluded the resolution of certain importantflow details in studies on these animals. Thus, thereis little, if any, quantitative experimental evidenceabout the detailed nature of the flow in the aortic-wall boundary layer, in the region of branching,and downstream from such branch points. Further-more, with animals such as dogs and pigs, the ob-served values of the important flow similarity pa-rameters, e.g., Reynolds number Re = uDIv and theunsteadiness parameter a = R(a>/j/)% (u is meanvelocity, R is vessel radius, w is fundamental fre-quency of the flow pulsations, D is vessel diameter,and v is kinematic viscosity), differ from those asso-ciated with the human arterial system (11).

The limiting factor in making measurements ofthis kind is instrument resolution vs. vessel size.Large horses have aortic diameters in the range of5 cm, brachiocephalic artery diameters near 3 cm,intercostal and coronary artery diameters of ap-proximately 1 cm, and iliac artery diameters in therange of 1-2 cm. The large size of these vessels

193

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194 NEREM, RUMBERQER, GROSS, HAMLIN, QEIQER

offers the opportunity of making detailed measure-ments in numerous vessels with a degree of instru-ment resolution not possible in smaller species.

MethodsMeasurements of velocity wave forms in horses which

varied in weight from 136 to 410 kg were made using aconstant-temperature hot-film anemometer system withthe film held at a temperature approximately 5°C higherthan that of the blood. The system used the Disa 55DO1anemometer and the Disa 55D10 linearizer. The princi-ple of operation of hot-film anemometer systems andsome of the problems encountered in their use in bloodvelocity measurements have been discussed in the liter-ature (3).

Catheter probes and L-shaped probes were insertedby direct puncture through the vessel wall. The L-shaped probes were Disa A-87 probes or probesmanufactured in our own laboratory (Fig. 1). The cathe-ter probe was also manufactured in our laboratory (Fig.1). The velocity probes were calibrated during each ex-periment using blood from the horse. At the start of each

Wire Leads

Thin Platinum Film

L-Shape Hot Film Probe

Thin Platinum Film

-Wire Leads EE

10

7 Cottieter

Catheter Hot Film Probe

FIGURE 1

Hot-film velocity probes used in this investigation.

experiment, a 200-ml sample of blood was taken, hepa-rin was added to prevent coagulation, and the samplewas placed in the calibration turntable channel (12).Here it was maintained at a temperature of 38°C with athermostatically controlled water heater-circulatorsystem. The probe was immersed in the blood, and bycontrolling the speed of the turntable channel the probewas calibrated at various known constant velocities.

Output signals were passed through the linearizer,which was adjusted to provide a linear outputvoltage-velocity relationship. Although only a steady-state flow calibration was performed, there have beenprevious evaluations of the performance of hot-filmanemometer systems under unsteady flow conditions.The L-shaped probes manufactured in our laboratoryare physically similar to those used by Seed and Wood •(3) and thus should have the same frequency responsecharacteristics. For the catheter probes, similar perfor-mance characteristics exist for forward flow, i.e., flowcoming in over the tip of the catheter; however, for re-verse flow the catheter probes are rather unresponsive.The same is true of the Disa A-87 L-shaped probe. Noneof the probes used in the present series of experimentshad a direction capability.

As noted earlier, L-shaped probes were inserted bydirect vessel puncture in anesthetized, open-chesthorses. Anesthesia was induced with a bolus injection ofsodium pentobarbital administered via a catheter pre-viously inserted in the jugular vein. More sodium pen-tobarbital was administered as indicated. Fluids wereadministered throughout the experiment in an attemptto inhibit the effects of circulatory shock. For thoracicmeasurements, the thorax was opened via a left or rightthoracotomy with resection of four to six ribs, dependingon the exposure required. Abdominal measurementswere made via a laparotomy incision from the paralum-bar fossa ventral to the midline and cranial to thexiphoid cartilage.

After insertion, the probe was aligned as nearly aspossible on a diameter normal to the vessel wall. Amicrometer device, which was attached to the probeafter puncture of the vessel wall, allowed for graduatedchanges in probe position. The internal diameter of thevessel at each site was measured by traversing the probefrom the near wall to the far wall and adding on theprobe width. The probe was then traversed across thevessel in approximately 1-mm steps. Velocity waveforms were thus recorded at a series of positions acrossthe vessel. By keying on the electrocardiogram, the in-stantaneous velocity profile could then be re-constructed. It should be noted that velocity waveforms were measured repeatedly at the center-line sta-tion to check for changes in flow conditions and forprobe fouling due to fibrin deposition. If a drift in probeoutput was noted, the film was wiped gently against thevessel wall to remove any deposition on the sensor sur-face. In addition, the film cold resistance was repeatedlychecked to ensure the repeatability of the velocity

Circulation flweerrfi, VoL XXXIV, Ftbnuny 1974



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HORSE ARTERIAL VELOCITY MEASUREMENTS 195

probe measurements.Catheter probes were used to measure coronary ar-

tery flow and aortic flow (in conscious animals). For cor-onary artery flow measurements, the heart was exposedand the pericardial sac opened. The catheter was theninserted in the coronary vessel distal to the region of in-terest. Prior to insertion of the catheter, the vessel wasoccluded; it was released by digital manipulation proxi-mal to the area of catheterization periodically over a5-10-minute period. This procedure was designed toproduce some level of tolerance of the myocardium toischemia. Without this procedure, ligation of the vesseland the sudden onset of ischemia caused cardiac arrestin some animals.

Once inserted, the catheter probe could be easilymoved upstream to any position desired. To determinethe actual position of the probe at each recording sta-tion, a record of how far the probe had been movedfrom the point of initial insertion was kept. The finalprobe position was always at the inlet of the coronaryvessel within the sinus of Valsalva. After the horse waskilled, the probe was kept in position and the heart wasexcised; visual observation of the final probe positionand of the vessel geometry allowed retracing of theother probe positions.

Measurements of velocity wave forms with L-shapedprobes were also carried out in coronary arteries. Thesemeasurements used the earlier described direct vesselpuncture procedure; however, due to the limited vesselsize, the only velocity measurements possible were atthe approximate midstream of the vessel.

As noted above, catheter measurements of aorticflows in conscious horses were also conducted. Thehorses were tranquilized with Acepromazine maleate (2mg/100 lb body weight). The area of the jugular furrowwas then instilled with lidocaine HC1 2%, and the jugu-lar vein and the carotid artery were dissected and iso-lated. The hot-film catheter was taped to a Pieperpressure transducer (13); the tip of the hot-film catheteralways extended at least 0.5 inches beyond the pressurecatheter. The two catheters were then passed down thecarotid artery through the ascending aorta and the aor-tic valve into the left ventricle. The various positionswere verified by typical pressure wave forms. The cath-eter was then withdrawn and, at selected positions,velocity wave forms were recorded. In all cathetermeasurements, recordings at various positions wererepeated to guard against undetected probe fouling.

Results

The present investigation involved four series ofvelocity wave-form measurements. (1) Cathetermeasurements were made in conscious horses atselected sites obtained by progressively moving thecatheter from an initial position inside the leftventricle in a distal direction to its final position inthe carotid artery. (2) Thoracic aorta velocity


profile measurements were obtained in anesthe-tized horses using L-shaped probes inserted bydirect vessel puncture. (3) Velocity profilemeasurements were obtained using L-shapedprobes inserted into the abdominal aorta and itsbranch vessels. Finally, (4) velocity wave-formmeasurements of coronary flow were made usingboth catheter and L-shaped probes.

In the first series, aortic flow measurementswere carried out in conscious horses. These experi-ments are summarized in Table 1. Although thecatheter was not rigidly positioned in the vesselcross section because of the flatness of the profile(see Figs. 3 and 4), it was felt that the recordedmeasurements were representative. Included inTable 1 (as well as in subsequent tables) are boththe peak center-line velocity (u) and the meancenter-line velocity (u). It is possible to obtain udirectly from the measurement. However, u is anaverage calculated from the center-line velocitywave form. The probes used were not directionsensitive, and, although a correction for reverseflow was made for those positions at which it wasfelt to be appropriate, the values of 0 must be con-sidered to be only approximate.

Peak aortic center-line flow velocities of nearly100 cm/sec were obtained in this series of measure-ments. The corresponding peak Reynolds numberRe was on the order of 10,000, and the range ofvalues for the unsteadiness parameter a was 10 to30. The estimated ratio of peak velocity to meanvelocity at the center line ranged from 3.5 to 7. Theobserved degree of aortic flow disturbance is notedin Table 1. In this table, the flow has been charac-terized as undisturbed (U), disturbed (D), or highlydisturbed (HD) following the definitions in thepaper by Nerem and Seed (10). As may be seen,disturbed flows were frequently encountered.Figure 2 shows disturbed flow in a series ofmeasured velocity wave forms for three positions:the left ventricle, just distal to the aortic valve, andthe carotid artery. Also shown are the measuredpressure wave forms. It should be emphasized thatthese pressure measurements were uncalibratedand that the crude wave form obtained was onlyused to determine the catheter location. However,the mean arterial blood pressure was estimated tobe between 85 and 105 torr. It should also be notedthat the tip of the hot-film catheter was located 2inches proximal to the tip of the pressuretransducer.

The measured velocity in the left ventricle (Fig.2) must be considered qualitative, since the orien-



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196 NEREM, RUMBERGER, GROSS, HAMLIN, GEIGER

TABLE 1

Aortic Flow Measurements in Conscious Horses

Horse no. Position

1 Left ventricleAscending aorta just distal to aor-

tic valveAscending aorta 2 inches distal to

aortic valveArch of aorta 6 inches distal to

aortic valve near carotid ar-tery inlet

Carotid artery 9 inches distal toaortic valve

Carotid artery 11 inches distal toaortic valve

2 Left ventricleAt aortic valveAscending aortaArch of aorta near inlet to carotid

arteryCarotid artery near incision

3 Left ventricleAt aortic valve6 inches distal to aortic valve near

inlet to carotid arteryCarotid artery

HR(min-1)

7678

83

85

93

79

67334140

42403838

38

2R(cm)

3.8

3.6

3.0

2.1

1.8

3.02.62.5

1.4

3.52.7

1.7

0(cm/sec)

4887

62

33

16

8.5

50935328

5.0708718

7

u / u

3.8

3.4

4.0

3.7

2.8

6.65.95.6

3.4

7.26.0

6.3

a

29.0

28.4

23.9

17.5

13.8

14.814.413.7

7.8

18.614.4

9.06

Re

9460

6380

2830

960

437

713034902000

200

87001388

340

Character of flow

HDHD

D

D

U

U

HDHD

DD

UHDHD

U

uHR = heart rate, R = radius, u= peak center-line velocity, u =• mean center-line velocity, a = unsteadiness parameter, Re •» peak

Reynolds number, HD -highly disturbed flow, D -disturbed flow, and U -undisturbed flow.

Catheter within Ventricle

15-

o-

Catheter I" Distal to Aortic Valve Catheter in Carotid Artery

FIGURE 2

Hot-film catheter velocity probe recordings in a conscious horse(no. 1) as the catheter is withdrawn from the left ventricle outinto tlie carotid artery. P — pressure wave form, V - velocitywave form, T = time marks.

tation of the probe to the flow and thus the calibra-tion are unknown. However, the presence and theassociated intensity of the high-frequency fluctua-tions are striking. These fluctuations are associatedwith the filling process of the left ventricle. At aposition 1 inch distal to the aortic valve, the flow inthe aorta is still highly disturbed; however, in thecarotid artery the flow appears to be smooth andundisturbed, and the peak velocity is considerablylower, being on the order of 20 cm/sec.

The experiments in which thoracic aortavelocity measurements were obtained using L-shaped probes are summarized in Table 2. As notedabove, these measurements were performed inopen-chest, anesthetized horses in which the probewas inserted by direct vessel puncture. Both theDisa A-87 and the probes manufactured in ourlaboratory were used. The location of each of themeasurements is indicated in Table 2. Because-ofaccess limitations, the measurements were carriedout in a plane extending through the center of thevessel and perpendicular to the plane of curvatureof the aorta. In this series of measurements, peakaortic flow velocities of 90 cm/sec were seen with a

Circulation Research, Vol. XXXIV, February 1974



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TABLE 2Flow Measurements in the Thoracic Aorta of Anesthetized Horses

Horse no. Probe PositionHR 2R u

(mlrr1) (cm) (cm/sec) u /u Re Character of flow

4

5

6'

Disa A-87

Disa A-87

Catheter

L-shaped

L-shaped

L-shaped

96

70

45

51

Descending aorta 7 inchesdistal to aortic arch



Descending aorta 11 in-ches distal to aorticarch

Descending aorta 15 in- 59ches distal to aorticarch

Descending thoracic aorta4 inches distal to aorticarch



45

80

51

3.05

2.69

2.41

2.08

1.40

22

33

22

70

96

A A

5.3

4.0

3.0

2.8

25.8

19.4

13.9

12.8

9.29

1920

2536

1514

4160

3840

D

D

D

D

D

2.5

2.6

2.5

33

23

33

3.8

2.4

3.5

14.5 2357

20.1 1709

15.44 2357 D

See Table 1 for abbreviations."Horse was in shock.

corresponding Reynolds number of 4,000 based ondiameter. The range of values of the unsteadinessparameter was from 10 to 25. The estimated ratioof peak velocity to mean velocity ranged from 2.5to 5.5. This finding is reasonably consistent with themeasurements in Table 1 and with measurementsin dogs (14).

In selected horses complete velocity profileswere obtained as a function of temporal position inthe cardiac cycle. Representative measurements ofsuch a series of velocity profiles in the thoracic aor-ta are shown in Figures 3 and 4. These profiles arebased on averaging over ten cardiac cycles at eachstation across the vessel lumen. As the probe ismoved sequentially across the vessel, the time of ameasured velocity during the cardiac cycle is ob-tained by keying on the peak of the R wave in theelectrocardiogram. The finite width of the probeprevented any measurements in the immediateregion of the near wall. As a result, it was not al-ways possible to obtain measurements in the near-wall boundary layer. In Figure 3 only measure-ments in the far-wall boundary layer are included.Thus, in this figure the apparent asymmetry is dueto the absence of any near-wall boundary layermeasurements. In Figure 4, portions of both the

Circulation Research. Vol. XXXIV, February 1974

near- and far-wall boundary layers are evident, andno noticeable skewing is present. These measure-ments were made distal to the aortic arch and not

TimeA

cm /sec

30Time B

30JL»

2 0

16 0.8 0.8

TimeC

cm/sec

30

2 0

I 0

16 0.8 O 0.8Distance from <£_ cm

16

Time16 0.8 0 0.8 16

Distance from ^ cm

FIGURE 3Thoracic aorta velocity profile in an anesthetized horse (no. 5)at various times during the cardiac cycle as indicated. Measure-ments were performed in the plane orthogonal to that of aorticcurvature.



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cm/sec

29

• * • • •«

TimeB

cm/sec

• * •

1.0 0.6 0.2 0.2 0.6 1.0 1.0 0.6 0.2 02 0.6 10

TimeC

cm/sec

30Time

acm/sec

4°2 0

Time

10 0.6 02 0.2 06 10 10 0.6 "02 02 06 To

Distance from £ cm

FIGURE 4Thoracic aorta velocity profile in an anesthetized horse (no. 7)at various times during the cardiac cycle as indicated. Measure-ments were performed in the plane orthogonal to that of aorticcurvature.

in the plane of curvature. Thus the absence of anyskewing of the profile was not unexpected.

The third series of measurements was carried outin the region of the abdominal aorta using L-shaped velocity probes inserted by direct vesselpuncture. These measurements are summarized inTable 3. Velocity profiles were obtained in the ab-dominal aorta proximal to the mesenteric artery,between the mesenteric and renal arteries, and dis-tal to the point at which the renal artery branchesoff. Profiles were also measured in the terminal aor-ta and the internal "and external iliac arteries. In thehorses used, the distal aorta usually gave off pairedexternal iliac arteries which bifurcated within 1-3cm into the internal iliac arteries. In addition,limited velocity wave-form measurements wereobtained in the mesenteric and renal arteries them-selves.

Profile measurements in the abdominal aortawere also obtained by sequentially moving thevelocity probe across the vessel, keying on theelectrocardiogram to reconstruct the velocityprofile. Velocity profiles measured in this mannerare shown in Figures 5-8. It should be emphasizedthat many more profiles were measured and thatFigures 5-8 have only been selected as representa-tive examples. Included in each figure is a center-line velocity wave form; the time corresponding tothe associated velocity profiles is indicated on eachwave form. As is obvious, these profiles aredifferent in character with respect to each otherand to the thoracic aorta profiles of Figures 3 and 4.

K X > .

TimeB

cm

i

/sec[50

ioo

50

1 1 1

0.2 0 0.2 0.4 04 0.2 0 0.2 0.4

Time0

Timec •

•

• 1 1

cm

J

/sec

Too•

L50

I

•

I I

Time

04 02 0 02 0.4 04 0.2 0 0.2 04

Distance from <f_ cm

FIGURES

Abdominal aorta velocity profile in an anesthetized horse (no.14) at various times during the cardiac cycle as indicated.Measurements were performed proximal to the branching of themesenteric artery in the plane orthogonal to the plane ofbranching.

These differences will be discussed in the next sec-tion; however, it is obvious that the flow is in manycases complex and certainly not indicative of fullydeveloped Poiseuille flow. From the center-linevelocity wave form, the peak Reynolds number Re(based on the peak center-line velocity u), the ratioof peak center-line velocity to mean center-line

2 0

Cross - Sectional ViewAbdominal Aorta

TimeB

T)4 0 04

cm/sec

• 60

2 0

TimeC

Time

6 0

2 0

0.4

TimeD

t 1

0

cm

6

4

• •

20

sec

g

0

• •

i

0 4

» •

1

Distance from C cm

FIGURE 8

Abdominal aorta velocity profile in an anesthetized horse (no.10) at various times during the cardiac cycle as indicated.Measurements were performed distal to the branching of therenal artery and proximal to the iliac bifurcation in the planeindicated.




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TABLESFlow Measurements in the Abdominal Aorta and Its Branching Vessels in Anestlietized Horses

Horse no. PositionHR

(min-i)2R u

(cm) (cm/sec) u / u Re Character of flow

10 Abdominal aorta proximal to iliactrifurcation

11 Internal iliac distal to flow dividerAbdominal aorta 1 inch distal to

renal arteryAbdominal aorta proximal to

renal inlet12° External iliac distal to flow

dividerTerminal aorta distal to flow

divider13 Internal iliac distal to flow divider

Abdominal aorta 2 inches distalto renal inlet

Abdominal aorta 1 inch proximalto renal artery inlet

Renal artery14 External iliac distal to flow

dividerAbdominal aorta distal to renal

arteryMesenteric artery just off aortaAbdominal aorta proximal to

mesenteric artery15 External iliac distal to flow

dividerTerminal aorta distal to flow

dividerAbdominal aorta distal to renal

arteryAbdominal aorta proximal to

renal artery

92 1.25 63 1.8 10.4 2250 U

4763

68

115

115

4140

40

7772

81

84.587

54.5

53.5

51

50

0.781.30

1.20

1.7

1.74

0.791.42

1.54

0.30.78

0.91

0.40.8

0.4

0.53

0.79

1.4

5315.4

23

16

1.6

923

26

12010.8

30

188118

29

14

3

15.2

7.14.5

4.5

3.0

4.2

1.42.0

1.254.9

5.0

3.14.2

4.7

3.0

4.0

3.9

4.628.92

8.55

15.8

16.1

4.377.76

8.42

2.275.7

7.08

3.176.45

2.55

3.35

4.84

8.55

1181572

788

111

79.5

202925

1140

1028240

780

21482697

331

212

67.2

608

UU

U

U

U

U

u

u

uu

u

uu

u

u

u

u

See Table 1 for abbreviations.'Animal was anoxic throughout experiment.

velocity u/u, and the unsteadiness parameter a canbe calculated. This information is included in Table3; however, compared with those for the thoracicaorta, the peak Reynolds numbers are lower, theunsteadiness parameter values are smaller, and thevalue of u/u is in some cases considerably less.

The final series of measurements was carried outin the right and left coronary arteries with both thecatheter and the L-shaped probe. These measure-ments are summarized in Table 4, and typical waveforms are shown in Figure 9. The apparentdifference in wave forms may be partially ex-plained by the difference in heart rate and the con-dition of the preparation at the time of measure-ment. Maximum peak velocities of 50-60 cm/secwere measured. The corresponding maximum


value of the peak Reynolds number was approxi-mately 1,500, and the range of values for theunsteadiness parameter was 1.5 to 4.0. The esti-mated ratio of peak velocity to mean velocityranged from 1.5 to 3.

In Figure 9a a double wave form per cardiac cy-cle is apparent; it is believed that both wave formscorrespond to forward flow (the catheter probe isnot direction sensitive). The first hump is associatedwith systole and the second with diastole. Assumingthat both humps correspond to forward flow, then amean velocity can be calculated. The resultingvalues are indicated in Table 4. Of course, thesemeasurements must only be considered as repre-sentative, since the exact position of the probe inthe vessel cross section was not known.



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cm/sec

60cm /sec

60Time

B

0 3 0.2 01 0 OJ 02 03 03 02 OJ 0.1 0.2 03

cm/secS|0

TimeC

.. t t

Time

03 02 0.1 01 0.2 03

Distance from <t , cm

FIGURE 7

External iliac artery velocity profile in an anesthetized horse(no. 11) at various times during the cardiac cycle as indicated.Measurements were performed in the plane orthogonal to theplane of branching.

Discussion

From the measurements performed in this seriesof in vivo experiments in horses, a more completepicture of the general nature of the blood flow inthe aorta and the larger arteries is available. Thispicture obviously is partially due to the results ofprevious investigations. However, as noted in theintroduction, the large size of the vessels of a horse

TimeA

•

4

cm/sec6

4

2•

cm/sec6

TimeB

0.8 04 0 0.4 0.8 3.8 0.4 04 08

TimeC

cm/sec6|

Time

08 0.4 0 0.4 0 8

Distance from £ , cm

FIGURE 8

Terminal aorta velocity profile in an anesthetized horse (no. 12)at various times during the cardiac cycle as indicated. Measure-ments were performed in the plane orthogonal to the plane ofbranching.

O

a>

Eo

in

u<oin

EoOJIO 1 AJ

^Velocity

^A^^EKG

( b )FIGURE 9

Recordings of coronary artery velocity wave forms inanesthetized horses, a: Catheter probe in right main coronaryartery, b: L-shaped probe in left anterior descending coronaryartery.

provided an access and a resolution not afforded bythe use of smaller animals, and thus the presentmeasurements provide some unique results whichin some cases are a verification of what beforecould only be suspected.

Starting with the left ventricle and its filling pro-cess, it is clear from Figure 2 that the flow in thischamber has a reasonably high velocity and con-siderable high-frequency content. As noted in theprevious section, the orientation of the catheterprobe and the flow within the ventricle is notknown in these measurements in conscious horses.Since differences in probe orientation can cause achange in the calibration characteristics of as muchas a factor of two, the peak velocities measuredmay range from a low of 30 cm/sec to the indicatedvalue in Figure 2 of approximately 60 cm/sec.

The high-frequency content is of interest,Circulation Research, Vol. XXXIV, February 1974



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TABLE 4

Coronary Flow Measurements in Anesthetized Horses

Horse no.

16

17

12

13

15

Probe

Catheter

Catheter

L-shaped

L-shaped

L-shaped

Position

Descending branch ofright main coronary ar-tery

Upstream of descendingbranch of right maincoronary artery

0.5 inches within rightmain coronary arterydownstream of sinus ofValsalva

3 inches distal to sinus inright main coronary ar-tery

8 inches distal to sinus indescending branch ofright main coronary ar-tery near incision"

Left anterior descendingcoronary artery



HR(min-1)

52

50

67

79

8262

157

117

42

54.5

2R(cm)

0.70

0.80

0.90

0.90

0.700.700.70

0.6

0.5

0.4

u(cm/sec)

53

60

52

65

171164

32

63

45

u/u

1.4

1.8

2.6

2.0

3.1

2.4

3.0

1.6

a

4.36

4.89

6.36

6.91

5.484.767.58

5.6

2.80

2.55

Re

1060

1371

1337

1671

340220

1280

548

900

512

Character of flow

U

U

u

u

uuu

u

u

u

See Table 1 for abbreviations."Drugs administered to produce three different flow conditions.

because these disturbances are undoubtedly con-vected into the aorta itself and are thus importantto an understanding of the nature of and the condi-tions necessary for the presence of highly disturbedaortic flows. Observations of such flows have beenreported by several investigators (4-6) and havebeen considered in detail (10). They have also beenobserved in the present study, as is illustrated inFigure 2 by the velocity wave-form measurement 1inch distal to the aortic valve.

In addition to this possible presence of high-fre-quency disturbances, the most striking feature ofthe flow in the thoracic aorta is the flatness of theprofile in the center region of the vessel. Such aprofile is illustrated for the aortic arch in Figures 3and 4, where the flow can be seen to be charac-terized by an inviscid core and a thin-wall bound-ary layer region to which viscous effects are by inlarge confined. Based on steady-state pipe flowdata and for the Reynolds numbers characterizingthe mean aortic flow (15), the entrance length, i.e.,the distance required for a fully developed viscousflow to be attained, would be approximately 30-40tube diameters. The thoracic aorta measurementsCirculation Retearch, VoL XXXIV. February 1974

of Figures 3 and 4 were performed within 15 cm ofthe aortic valve (3-5 tube diameters), and thus thepresence of an inviscid core and a thin-wall bound-ary layer was not surprising. The nature of theboundary layer, of course, must be a combination ofthe properties due to a steady-state mean flow andto the unsteady, pulsatile flow. In terms of unsteadyeffects, for pulsatile flow in an infinite cylindricaltube, the viscous effects in the limit of a becominglarge are confined to a thin-wall boundary layer(16). Thus, this effect also would suggest that thevelocity profile should appear as it is shown inFigures 3 and 4. This finding also has been sug-gested by the measurements in dogs (4-6).

As noted in the previous section, the measure-ments in Figures 3 and 4 were not performed in theplane of aortic arch curvature, and thus no skewingdue to a curvature effect, such as found by Seedand Wood (6), was anticipated. It should also benoted that, although the peak velocities in Figures3 and 4 may appear low, this fact is undoubtedlydue to the condition of the horse, e.g., the effects ofanesthesia and trauma. As may be seen in Table 2,varying peak center-line velocities were recorded.



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By comparing with Table 1, it can be seen that thehigher values correspond to the conditions in con-scious horses. It is felt, however, that, in terms ofthe profiles shown in Figures 4 and-5 and in subse-quent figures, the important thing is the qualitativenature of the velocity profiles and not the exactquantitative value of the velocity.

A similar flat profile to that in the thoracic aortaregion is seen in Figure 5 for the flow just proximalto the point at which the mesenteric arterybranches off of the abdominal aorta. The highvelocity at this point is in marked contrast with thatobserved in the aorta of the same horse distal to thepoint at which the renal artery branches off. In thisparticular animal (horse 13), the mesenteric andrenal arteries branched almost immediately adja-cent to one another; the large diversion of bloodinto these branches thus resulted in low velocitiesat distal points in the abdominal aorta and also inthe iliac arteries. Although the velocity profile inthe mesenteric artery could not be resolvedbecause of the small vessel size, an approximatemidstream velocity wave form was recorded; thiswave form is compared in Figure 10 with center-line wave forms for the aorta, both proximal to themesenteric artery and distal to the renal artery,and for the external iliac artery. As is evident, thehigher velocities are observed proximal to thepoint at which the mesenteric artery branches offand in the mesenteric artery itself.

It has already been noted that distal to the pointat which the renal artery branches off thevelocities are sharply reduced from those furtherupstream in the aorta. However, of more interest isthe fact that the profiles in this region are no longernecessarily flat but demonstrate a more fully devel-oped viscous flow character. In addition, there is askewing of the profile which is illustrated in Figure6 and is believed to be associated with the effectsof the branching off of the mesenteric and renal ar-teries. The profile shown in Figure 6 was obtainedin a plane such that the near wall was closer to theside from which the renal artery branched oft thanit was to the far wall side, and the skewing isbelieved to be associated with the development ofa new boundary layer distal to the renal arterybranch point. Thus, though the velocities arerelatively low in this region, there appear to bemarked profile characteristics associated withbranching effects.

Within 10-20 cm (depending on the size of thehorse) of the point at which the renal arterybranches off, the abdominal aorta then branches

120

o

190

oo

30

io

o

Abdominal AortaProximal to MesentericArtery

Mesenteric Artery

Abdominal AortaDistal to RenalArtery

External Iliac Artery

TimeFIGURE 10

Recordings of center-line velocity wave forms at various posi-tions along the abdominal aorta and in the branching vessels foran anesthetized horse (no. 14).

into the iliac arteries. As illustrated in Figures 7 and8, the profiles in the external iliac artery and in theterminal aorta just prior to the branching off of theinternal iliac arteries are characterized by the samelow velocities seen in the abdominal aorta justproximal and by profiles indicative of a somewhatfully developed viscous flow. The terminal aortaprofile is of particular interest because the velocityon the center line is much lower than that in theregion further out near either wall. This finding wasobserved in several horses, but it was most notice-able in horse 11 in which, because of the high heartrate, the velocities and thus the Reynolds numberswere reduced. Comparing the terminal aortaprofile measured in horse 12 with that measured inhorse 11 (Fig. 8), it appeared that in the former thedip in the profile in the center was not as marked.Horse 11 also had higher Reynolds numbers, andthe suggestion of a decrease in the center-line dipwith increasing Reynolds number and the generalshape of these profiles is in agreement with pre-viously reported measurements in branching airflows (17).




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It was noted previously that disturbed flowswere observed in a number of experiments. Theseobservations were in the thoracic aorta of bothconscious and anesthetized horses. High-frequencydisturbances were not observed in the coronary ar-teries or the abdominal aorta and its branch vessels.However, no measurements in conscious horseswere performed in these vessels, and thus nodefinite conclusions can be stated. Low-frequencydisturbances on the order of 5-10 Hz were ob-served in the abdominal aorta distal to the renal ar-tery branch point in certain horses. This flow ap-pears to be laminar with a low-frequency oscilla-tion which may be the result of complexities associ-ated with the bifurcation at the renal artery branchpoint, e.g., a shed vortex, and thus not indicative offluid mechanical turbulence.

As is apparent from the data in Tables 1-4, theflow conditions corresponding to the presentmeasurements cover a wide range. Considering thetwo basic fluid mechanical parameters —peakReynolds number Re and unsteadiness parametera —the range of conditions encountered in thepresent experiments includes peak Reynolds num-bers ranging from 200 to 10,000 and unsteadinessparameter values ranging from 2 to 30. Associatedwith these widely different conditions weremarkedly different velocity wave forms, velocityprofiles, and flow disturbance characteristics. It isobvious from these results that the flow in the ar-terial system, although in many cases laminar anddisturbance free, is extremely complex incharacter. Further studies will provide additionalinsight into the details of these fluid mechanicalcharacteristics, and it appears that the horse,because of the size of its vessels, offers itself as anexcellent experimental animal for such studies.

ReferencesCARO, C.G., FITZ-GERALD, J.M., AND SCHROTER, R.C..

Atheroma and arterial wall shear: Observation, correla-tion and proposal of a shear dependent mass transfer

mechanism for atherogenesis. Proc R Soc Lond [Biol]117:109-159,1971.

2. FRY, D.L.: Acute vascular endothelial changes associatedwith increased blood velocity gradients. Circ Res22:165-197, 1968.

3. SEED. W.A., AND WOOD. N.B.: Development and evaluationof a hot-film velocity probe for cardiovascular studies.Cardiovasc Res 4:253-263, 1970.

4. SCHULTZ, D.L., TUNSTALL-PEDOE, D.S., LEE, G.DEJ., GUN-NING. A.J., AND BELLHOUSE, B.J.: Velocity distribution andtransition in the arterial system. In Circulatory andRespiratory Mass Transport CIBA Foundation Sym-posium, edited by G.E.W. Wolstenholme and J. Knight.London, Churchill, 1969, pp 172-199.

5. LINC, S.C., ATABEK. H.B., FRY. D.L., PATEL, D.J., AND JANICKI.J.S.: Application of heated film velocity and shearprobes to hemodynamic studies. Circ Res 23:789-801,1968.

6. SEED, W.A., AND WOOD. N.B.: Velocity patterns in the aorta.Cardiovasc Res 5:319-330, 1971.

7. SEED. W.A., AND WOOD, N.B.: Use of a hot-film probe forcardiovascular studies. J Sci Instr 3:377-384, 1970.

8. TUNSTALL-PEDOE, D.S.: Velocity distribution of blood flowin major arteries of animal and man. Ph.D. Thesis,University of Oxford, 1970.

9. REUBEN, S.R., SWADUNG, J.P., AND LEE, G.DEJ.: Velocityprofiles in the main pulmonary artery of dogs and manmeasured with a thin film resistance anemometer. CircRes 27:995-1001, 1970.

10. NEREM.R.M., AND SEED. W.A.: In vivo study of the nature ofaortic flow disturbances. Cardiovasc Res 6:1-14, 1972.

11. MCDONALD, D.A.: Blood Flow in Arteries. London, Arnold,1960, pp 53-90.

12. SEED, W.A., AND WOOD. N.B.: Apparatus for calibratingvelocity probes in liquids. J Sci Instr 2:896-898, 1969.

13. PlEPER, H.: Catheter-tip manometer for measuring bloodpressure during G-changes. J AppI Physiol 22:352-353,1967.

14. FALSETTI, H.L., KISER. K.M., FRANCIS. G.P., AND BEL-MORE.E.R.: Sequential velocity development in the ascendingand descending aorta of the dog. Circ Res 21:328-338,1972.

15. GOLDSTEIN, S.: Modern Developments in Fluid Dynamics,vol. 1. Oxford, Clarendon, 1938, p 301.

16. NEHEM. R.M.: Fluid mechanical aspects of blood flow. InProceedings of the 8th International Symposium onSpace Technology and Science, Tokyo, Japan, 1969, pp1201-1216.

17. SCHROTEB, R.C., AND SUDLOW, M.F.: Flow patterns inmodels of the human bronchial airways. Respir Physiol7:341-355, 1969.

Ctrcuiatim RtttcnK VoL XXXIV, February 1974



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and GARY L. GEIGERROBERT M. NEREM, JOHN A. RUMBERGER, Jr., DAVID R. GROSS, ROBERT L. HAMLIN

Hot-Film Anemometer Velocity Measurements of Arterial Blood Flow in Horses

Print ISSN: 0009-7330. Online ISSN: 1524-4571 Copyright © 1974 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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