aorta

aorta

cvc

oa

iia

dca

uboaua

bua

eia

ipa

ubvava

ov(uov)

cvc

ov(uov)

uboa

oa

eiauma

ua

bua

ubva va

uma

iia

aorta

aorta

cvc

oa

iia

dca

uboaua

bua

eia

ipa

ubvava

ov(uov)

cvc

ov(uov)

uboa

oa

eiauma

ua

bua

ubva va

uma

iia

MARE

HEIFER

13Circulatory System

18 Chapter 1

Hemodynamics

Parabola

Plug flow

disturbed flow

Plug flow

Plug flow

Laminar flow

Turbulent flow

with eddies

Entrance length

Laminae

Laminar flow

Natural

1-11

Blood flow patterns. The drawing depicts alterations in blood-flow velocitiesas blood progresses from a large artery (aorta) to increasingly smaller branches.The crudely depicted flow patterns are plug flow, natural disturbed flow, turbulentflow with eddies, and laminar flow (for reviews see 30, 108, 115, 145).

20 Chapter 1

Pulsatile arterial flow. The patterns of arterial flow, described above, are asthough arterial blood flow is steady, but with varying velocities across the lumen.In reality, arterial flow to the reproductive tract is pulsatile in response to heart-beats or pulsations of the left ventricle. The red line in the illustration shows rela-tive velocity or pressure changes during systole and diastole of a cardiac cycle orarterial pulse in a major artery. The time required for a cardiac cycle (heartbeat) isdepicted as a timeline. In cattle and horses, the length of the timeline for a cardiaccycle is about 1 and 2 seconds, respectively; that is, the depicted velocity changesoccur rapidly. The vessels on the images are approximately transverse sections ofan external iliac artery and the associated vein (blue) in a horse. The images depictthe effects of the velocity changes on the color-flow mode of Doppler ultrasonog-raphy. These color-flow images are intended to serve as an illustration of thechanging velocities depicted by the red line on the graph for a single arterial pulseand, at the same time, introduce the technology that will be discussed in Chapter

Velocityestimates

1. Mean2. Variance

Autocorrelator

Transmitter

AP PRF

Colordata for

each pixelTransducer

Artery

Scan lines

B-mode

Color mode

3/6

Amplifieddata from:

Redcells

Stationaryreflectors

Redcells

Stationaryreflectors

Clutter

Clutter

Clutter

Echosources

Redcells

Redcells

Removedsignals from

stationaryreflectors

Removedclutter

Stationaryecho

canceler

Receiver

+Color gain

Filter

1

2

3

4

5

Averagephase shift

Consecutivephase shiftsper packet

45Color Flow

46 Chapter 3

Power-flow imaging. These sonograms compare conventional color-flow(A,C) and power-flow displays (B,D). The sonograms are from double equine cor-pora lutea (A,B) and the aorta of a 110-day equine fetus (C,D). The power-flowmode is more sensitive to flow and more signals are detected (B,D). Also, power-flow mode is independent of the angle of insonation and direction of flow (pg 47);power-flow mode shows only red signals (pg 47), whereas color-flow mode showsboth red and blue signals (pg 52).

Power-flow or energy-mode imaging is a more recent innovation for color-flow imaging and display of the processed Doppler signals (7). The power functiondisplays blood flow on the B-mode image in a graduated range for a single colorregardless of direction of flow. The intensities of the color vary, according topower of the Doppler signal. The power refers to the number of reflectors (redcells) moving at a given velocity (153, 158). For power-Doppler imaging, the inten-sity of a color is generated by processing the power of the Doppler signal, ratherthan the Doppler-shift frequency. Power Doppler increases the sensitivity for dis-

Power Flow

Velocity display.In this example, theoperator has placedan angle cursor intoan artery on thecolor-flow image torepresent the angleof insonation at theintersection of theultrasound beamsand the arterial flow.The vertical row oflarge green dots rep-resents the path ofthe beams at the cur-sor gate. The gate isrotated by the instru-ment automaticallyso that the gate

direction is compatible with the direction of the beams. A selected cardiac cycle of the resulting spectral graph has been delineated by

the vertical broken green lines, and a tracing of the maximal velocity values overtime (selected spectrum) is shown; the trace is sometimes called the envelope.Some instruments automatically trace the outline of the designated cardiac cycle,using built-in algorithms, and in some instruments the cycle is traced manually.However, automatic traces may be compromised by extraneous signals (clutter)and may need fine-tuning manually. The maximum point along the length of thetraced outline represents the peak systolic velocity (PSV) or maximum Doppler-shift frequency. Similarly, the maximum value at the low point just before the nextsystolic increase represents the end diastolic velocity (EDV), and an average of themaximum velocity values (upper surface of spectrum) over the time of a cardiaccycle is called the time-averaged maximum velocity (TAMV). The spectral loca-tions used for computation of PSV, EDV, and TAMV (broken blue line) are shown.The computed velocities for these locations are numerically displayed on thescreen of most instruments. The computed pulsatility index (PI) and resistanceindex (RI) are also automatically displayed on the screen. An explanation for some

70 Chapter 4

95Follicle Blood Flow

Color-flow signals and anechoic band. This image depicts the spatial relation-ship among granulosa (gl), anechoic band (ab), and color-flow signals (cfs) in anequine preovulatory follicle. The color-flow signals at 10 o’clock extend beyondthe anechoic band and even involve the granulosa. This may be, at least in part, anartifact, wherein the signal extends beyond the vessel walls (pg 57). Considering that the blood vessels are expected to be in the theca externaand that the anechoic band is in close apposition to the granulosa, it is likely thatthe anechoic band involves both the theca externa and theca interna.

Histologically, the fluid between cells in the follicle wall is enclosed by bothvascular capillaries and terminal lymphatics and likely accounts at least partiallyfor the anechoic band. In this regard, the capillary and lymphatic systems originatein a network of terminal sacs (38), and considerable dilation of capillaries in thetheca has been described as ovulation approaches in mares (103) and women (92). Inaddition, the ovulatory process has been described as an inflammatory reaction(47), including hyperemia, congestion, increased vascular permeability, and edema(103). On this basis, the fluid of the anechoic band also could be attributed to edemaor an excessive accumulation of fluid in the intercellular spaces (102). However, theanechoic band increases in prominence (53) long before the inflammatory edemaassociated with ovulation in mares (103). The color-Doppler signals of blood floware dispersed within the anechoic band, indicating that the band includes the fluidof blood vessels, presumably venules as well as arterioles.

106 Chapter 5

Blood-flow signals in follicle wall. Morphologic studies in cattle have demon-strated an extensive vascular network in the thecal layers surrounding the avascu-lar basement membranes and granulosa in cattle (4). These images were obtainedin color-flow or power-flow mode as indicated by the color bars. Diameter aver-aged for two dimensions is shown for the follicle of each image. The periphery ofthe ovary (arrows) and location of the mesovarium (mo) are shown in the upper-right panel. The smallest follicle (4 mm, arrow) in this series shows color signals;the large colored areas (lower-right of image) are from external iliac vessels. Thelower tier of images is from different heifers and shows extensive vascularizationof follicles and vessels in the mesovarium on the day before ovulation.

Color-Doppler ultrasound has been used extensively in women to evaluate arte-rial blood flow in the wall of the preovulatory follicle. Doppler color-flow map-

Summary of preovulatory follicle. Cattle. In an initial study, data were normal-ized to the beginning of the LH surge. The area with blood-flow signals was lim-ited to the follicle base before the increase in LH. The first increase in blood-flowarea occurred during the 6 hours before the onset of the LH surge and was tempo-rally associated with a plasma estradiol increase. However, time-averaged maxi-mum velocity did not increase until 6 hours after onset of the LH surge.

Color-flow images of CL. Horses. Images on this page and images on thefacing page are from a single estrous cycle (Day 0 = ovulation) for each page.Plasma progesterone concentrations (P4) are shown for each day. The color-flowsignals are primarily at the periphery and outer portion of the CL. The colorsignals also involve the internal structure, especially during high progesteroneproduction (Days 8 and 12). The percentage of CL area with color-flow signals in

118 Chapter 6

193Fetal Stage

ao = aorta hv = hepatic veinca = carotid artery jv = jugular veindv = ductus venosus uc = umbilical cordfet = fetus uma = umbilical arteryfl = front limb umv = umbilical veinht = heart vc = vena cava

Images of the spermatic cord. Bulls. A function of the scanner was used thatdisplayed the same image in B-mode (left) and color-Doppler mode (right). Thecolor modes were for color-flow (A) and power flow (B,C). The anechoicstructures in B-mode are sections of the highly convoluted testicular artery as itintertwines among the network of veins of the pampiniform plexus. Some of theanechoic structures are rounded with prominent specular reflections (Bk1-66, 65),indicating a smooth surface (arterial wall) perpendicular to the direction of theultrasound beams. Often, these anechoic areas are devoid of color signals, alsoindicating a 90º angle of insonation (pgs 36, 54).

220 Chapter 9