Circulatory System MARE HEIFER. aorta cvc. iia eia ipa. aorta. dca. (uov) oa. uboa. uma. ubva va. bua. iia. uma. ubva. eia. ua bua. cvc.

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1 Circulatory System 13 MARE aorta cvc ov (uov) oa dca uboa iia eia ipa ua uma bua ubva va HEIFER iia aorta cvc eia oa uma ua bua ubva va ov (uov) uboa

2 18 Chapter 1 Hemodynamics Plug flow Natural disturbed flow Plug flow Turbulent flow with eddies Laminar flow Plug flow Entrance length Laminae Laminar flow Parabola Blood flow patterns. The drawing depicts alterations in blood-flow velocities as blood progresses from a large artery (aorta) to increasingly smaller branches. The crudely depicted flow patterns are plug flow, natural disturbed flow, turbulent flow with eddies, and laminar flow (for reviews see 30, 108, 115, 145).

3 20 Chapter 1 Pulsatile arterial flow. The patterns of arterial flow, described above, are as though 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 heartbeats or pulsations of the left ventricle. The red line in the illustration shows relative velocity or pressure changes during systole and diastole of a cardiac cycle or arterial pulse in a major artery. The time required for a cardiac cycle (heartbeat) is depicted as a timeline. In cattle and horses, the length of the timeline for a cardiac cycle is about 1 and 2 seconds, respectively; that is, the depicted velocity changes occur rapidly. The vessels on the images are approximately transverse sections of an external iliac artery and the associated vein (blue) in a horse. The images depict the effects of the velocity changes on the color-flow mode of Doppler ultrasonography. These color-flow images are intended to serve as an illustration of the changing velocities depicted by the red line on the graph for a single arterial pulse and, at the same time, introduce the technology that will be discussed in Chapter

4 Color Flow 45 Autocorrelator AP Transmitter PRF Consecutive phase shifts per packet Average phase shift Transducer Color data for each pixel Velocity estimates 1. Mean 2. Variance Scan lines B-mode Color mode Echo sources Artery Red cells Clutter Stationary reflectors Removed clutter Red cells Receiver Amplified data from: Stationary echo canceler Removed signals from stationary reflectors Filter Color gain Red cells Clutter Stationary reflectors Red cells Clutter 3 4 5

5 46 Chapter 3 Power Flow Power-flow imaging. These sonograms compare conventional color-flow (A,C) and power-flow displays (B,D). The sonograms are from double equine corpora lutea (A,B) and the aorta of a 110-day equine fetus (C,D). The power-flow mode is more sensitive to flow and more signals are detected (B,D). Also, powerflow 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 shows both red and blue signals (pg 52). Power-flow or energy-mode imaging is a more recent innovation for colorflow imaging and display of the processed Doppler signals (7). The power function displays blood flow on the B-mode image in a graduated range for a single color regardless of direction of flow. The intensities of the color vary, according to power of the Doppler signal. The power refers to the number of reflectors (red cells) moving at a given velocity (153, 158). For power-doppler imaging, the intensity of a color is generated by processing the power of the Doppler signal, rather than the Doppler-shift frequency. Power Doppler increases the sensitivity for dis-

6 70 Chapter 4 Velocity display. In this example, the operator has placed an angle cursor into an artery on the color-flow image to represent the angle of insonation at the intersection of the ultrasound beams and the arterial flow. The vertical row of large green dots represents the path of the beams at the cursor gate. The gate is rotated by the instrument automatically so 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 over time (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 the traced outline represents the peak systolic velocity (PSV) or maximum Dopplershift frequency. Similarly, the maximum value at the low point just before the next systolic increase represents the end diastolic velocity (EDV), and an average of the maximum velocity values (upper surface of spectrum) over the time of a cardiac cycle is called the time-averaged maximum velocity (TAMV). The spectral locations used for computation of PSV, EDV, and TAMV (broken blue line) are shown. The computed velocities for these locations are numerically displayed on the screen of most instruments. The computed pulsatility index (PI) and resistance index (RI) are also automatically displayed on the screen. An explanation for some

7 Follicle Blood Flow 95 Histologically, the fluid between cells in the follicle wall is enclosed by both vascular capillaries and terminal lymphatics and likely accounts at least partially for the anechoic band. In this regard, the capillary and lymphatic systems originate in a network of terminal sacs (38), and considerable dilation of capillaries in the theca has been described as ovulation approaches in mares (103) and women (92). In addition, 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 edema or an excessive accumulation of fluid in the intercellular spaces (102). However, the anechoic band increases in prominence (53) long before the inflammatory edema associated with ovulation in mares (103). The color-doppler signals of blood flow are dispersed within the anechoic band, indicating that the band includes the fluid of blood vessels, presumably venules as well as arterioles. Color-flow signals and anechoic band. This image depicts the spatial relationship among granulosa (gl), anechoic band (ab), and color-flow signals (cfs) in an equine preovulatory follicle. The color-flow signals at 10 o clock extend beyond the anechoic band and even involve the granulosa. This may be, at least in part, an artifact, wherein the signal extends beyond the vessel walls (pg 57). Considering that the blood vessels are expected to be in the theca externa and that the anechoic band is in close apposition to the granulosa, it is likely that the anechoic band involves both the theca externa and theca interna.

8 106 Chapter 5 Blood-flow signals in follicle wall. Morphologic studies in cattle have demonstrated an extensive vascular network in the thecal layers surrounding the avascular basement membranes and granulosa in cattle (4). These images were obtained in color-flow or power-flow mode as indicated by the color bars. Diameter averaged for two dimensions is shown for the follicle of each image. The periphery of the ovary (arrows) and location of the mesovarium (mo) are shown in the upperright 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. The lower tier of images is from different heifers and shows extensive vascularization of follicles and vessels in the mesovarium on the day before ovulation. Color-Doppler ultrasound has been used extensively in women to evaluate arterial blood flow in the wall of the preovulatory follicle. Doppler color-flow map- Summary of preovulatory follicle. Cattle. In an initial study, data were normalized to the beginning of the LH surge. The area with blood-flow signals was limited to the follicle base before the increase in LH. The first increase in blood-flow area occurred during the 6 hours before the onset of the LH surge and was temporally associated with a plasma estradiol increase. However, time-averaged maximum velocity did not increase until 6 hours after onset of the LH surge.

9 118 Chapter 6 Color-flow images of CL. Horses. Images on this page and images on the facing page are from a single estrous cycle (Day 0 = ovulation) for each page. Plasma progesterone concentrations (P4) are shown for each day. The color-flow signals are primarily at the periphery and outer portion of the CL. The color signals also involve the internal structure, especially during high progesterone production (Days 8 and 12). The percentage of CL area with color-flow signals in

10 Fetal Stage 193 ao = aorta ca = carotid artery dv = ductus venosus fet = fetus fl = front limb ht = heart hv = hepatic vein jv = jugular vein uc = umbilical cord uma = umbilical artery umv = umbilical vein vc = vena cava

11 220 Chapter 9 Images of the spermatic cord. Bulls. A function of the scanner was used that displayed the same image in B-mode (left) and color-doppler mode (right). The color modes were for color-flow (A) and power flow (B,C). The anechoic structures in B-mode are sections of the highly convoluted testicular artery as it intertwines among the network of veins of the pampiniform plexus. Some of the anechoic structures are rounded with prominent specular reflections (Bk1-66, 65), indicating a smooth surface (arterial wall) perpendicular to the direction of the ultrasound beams. Often, these anechoic areas are devoid of color signals, also indicating a 90º angle of insonation (pgs 36, 54).