DIAGNOSTIC DOPPLER BASICS
With PPG and PNEUMO
Excellence in Human Service and Technology
HAYASHI DENKI CO., LTD.
Contents
Ultrasound Doppler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1. Doppler effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. What can be measured using ultrasound Doppler? . . . . . . . . . 2
3. Probe selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Ultrasonic gel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. How to use the probe in measurement . . . . . . . . . . . . . . . . . 4
6. What is Doppler sound like? . . . . . . . . . . . . . . . . . . . . . . . 6
7. Blood pressure measurement . . . . . . . . . . . . . . . . . . . . . . . . 6
8. Analysis of waveform patterns . . . . . . . . . . . . . . . . . . . . . . . 9
9. Fetal heartbeat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Photoplethysmography (PPG) . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Pneumoplethysmography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
HADECO Doppler Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
ULTRASOUND DOPPLER
1. Doppler effect
Doppler effect is the apparent change in frequency by movement. This effect is exemplified most commonly by the sound frequency change in a train whistle as the train moves away from a stationary listener.
Doppler instruments are based on the properties of the piezoelectric crystal. Generated ultrasonic waves penetrate the tissue and are backscatterd by moving red blood calls. The Doppler shift in frequency between the transmitted and the reflected sound is proportional to the blood velocity.
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2. What can be measured using ultrasound Doppler?
Hemodynamics of blood flow in the vessel, stenosis and occlusion can be evaluated by measuring blood velocity.
Using Doppler instead of stethoscope in the auscultation method, systolic blood pressure also can be measured.
RADIAL A. FEMORAL A. DORSAL ARTERY OF FOOT POSTERIOR TIBIAL A. POPLITEAL A. ULNAR A. BRACHIAL A. COMMON CAROTID A. SUPERFICIAL TEMPORAL A.
The arterial sites of the human body generally measured using Doppler
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3. Probe selection
Probe frequency, focal depth and site
Probe frequency Focal depth Site
2 MHz 100 mm Fetal
4 MHz 20 mm Middle or deep vessels
5 MHz 15 mm Middle or deep vessels
8 MHz 10 mm Peripheral extremity vessels
10 MHz 5 mm Superficial vessels
Probe type and use
Probe type Use
Standard type (Fat) Clinic
Pencil type Intra-op
Flat type Monitoring
QFM type Volumetric blood flow
and vessel wall motion
Laparoscopic type Laparoscopic surgery
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4. Ultrasonic gel
Ultrasonic sound is attenuated greater when transmitting in the air, because its frequency is so high. The measurement using Doppler will be hardly done if the air exists between the probe and the skin. Ultrasonic gel should be used to fill in the gap for the ultrasonic sound transmission.
5. How to use the probe in measurement
Apply ultrasonic gel to the probe tip or the skin surface.
Put the probe on the measurement area and move it slowly to locate the point where the Doppler sounds are at the maximum.
The probe should be placed at an angle of approximately 45° to 60° to the vessel. Please note the best sound is the best angle.
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For monitoring measurement, a flat fixing type probe in which the beam angle is fixed to 60 ° to the skin surface, is more suitable.
KEY TO TRANSDUCERS DIAMETER A : A-mode VELOCITY Ra: Receiving (Doppler) Rb: Receiving T : Transmitting SIDE VIEW TOP VIEW
Further, a QFM type probe which is designed to be angle independent probe is most suitable for accurate measurement values. (This model will also calculate volume flow in ml/min.)
SKIN SURFACE
BLOOD FLOW
FIGURE 1. Cross-sectional diagram of transducers and blood vessels. A-mode transducer is used to measure the diameter of the vessel shown left; remaining three square-shaped transducers are for the Doppler study. The crystal in the center is for the transmitting transducer, and one on each side of T is for the receiving transducer (Ra and Rb). Vb: velocity.
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6. What is Doppler sound like?
Artery
The arterial Doppler sound is rhythmic and synchronized with the heartbeat. Sounds are loud and sharp.
At the site of a stenosis, faint higher frequency sounds mixed with a loud low frequency sounds are common.
Vein
The venous sound is a low-pitched, almost harsh tone that is similar to the sound of a windstorm. It is synchronized with respiration and body movement.
7. Blood pressure measurement
By using Doppler instead of stethoscope in the auscultation method, the systolic blood pressure can be measured.
Systolic blood pressure
After localizing the vessel, inflate a proximal blood pressure cuff rapidly to a point above the expected systolic blood pressure value (or to where no flow is heard). Then hold the probe in place over vessel, and gradually deflate the cuff. The first sound coming through as the cuff is deflated is the systolic blood pressure level.
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Ankle/brachial index (ABI)
The ankle/brachial index (ABI) is the single most valuable noninvasive test available for assessing the arterial circulation in the lower limbs.
Procedure
a) Apply blood pressure cuffs of appropriate width on the arm above the elbow and around each ankle.
b) Place the probe over the brachial artery just inside the elbow, or the radial artery at the wrist, and inflate the cuff to a pressure 20 to 30 mmHg above the point where Doppler sounds cease.
c) Deflate the cuff at moderate bleed rate until the first Doppler sound is heard. The pressure at the instant the first Doppler sound is heard is the brachial systolic pressure.
d) Place the probe over the posterior tibial artery, just behind the ankle bone on the inside of the leg, or the dorsalis pedis artery, which run across the top of the foot. Measure the ankle pressure in the same way as the brachial pressure.
e) Divide the ankle pressure by the brachial pressure.
ABI = ankle pressure / brachial pressure
Interpretation
Normal ABI =/> 1.0
Suggestion of the possibility of occlusive conditions ABI < 0.89
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Segmental blood pressures
Segmental pressure studies localize lower extremity arterial disease.
Procedure
a) Apply pneumatic cuffs on each arm above the elbow and four levels on the leg, using cuffs of the appropriate width. The four levels, as shown in the diagram below, are High Thigh (HT), Above Knee (AK), Below Knee (BK), and Ankle.
b) Following the same procedure as discussed above for measurement of ankle pressure, apply the Doppler probe over the brachial (or radial) artery and over the posterior tibial (or dorsalis pedis) artery and obtain the pressure at each level sequentially.
Interpretation
Any pressure difference between two adjacent levels of less than 20mmHg is considered normal. If the pressure difference is greater than 30mmHg, there is a probability of an occlusive lesion in the segment where the drop occurs.
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8. Analysis of waveform patterns
Lower extremity artery
The contour shows prolongation of both the upstroke and the downstroke and diminished waveform amplitude (flattening). Doppler sounds are heard during systole and continuing through all or most of diastole. II The contour demonstrates a strong but diminished systolic component and loss of reverse flow. The width of systolic pulse is broadened. The Doppler sounds are diminished very little as compared to the type "0" pattern. I The contour exhibits a steeply rising upslope at the onset of systole, rapid systolic downslope, and reverse flow (below baseline). Doppler sounds are loud and sharp. Normal peak forward velocity = 30 +/- 10 cm/sec at the dorsalis pedis artery 0 FINDINGS TYPICAL WAVEFORM TYPE
The Doppler arterial waveforms obtained from the lower extremity may be classified into six categories as an aid in interpretation.
The amplitude of the waveform is extremely reduced. The contour is hardly recognizable as an arterial blood flow waveform. The Doppler sounds are very faint. V The amplitude of the waveform and the Doppler sounds is greatly reduced. IV The contour exhibits slowly rising velocity during systole, and the amplitude of the waveform is reduced. Doppler sounds are not sharp even during systole. III
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9. Fetal heartbeat
In the early stages of pregnancy, the search for fetal heart sound should be concentrated directly above the symphysis pubis.
Doppler fetal heartbeat detector is mainly used in following applications:
• Detect fetal life as early as 10 weeks from the last menstrual period.
• Assess fetal cardiac function throughout the pregnancy.
• Localize the placenta as a possible indication of placenta praevia.
• Monitor fetal heart beat during labor.
• Diagnose multiple pregnancy.
• Provide audible evidence of fetal life and, by the disappearance of detectable heart action, evidence of fetal death.
Positive Ratio of Fetus Detection Ultrasonic Doppler Method
Apply ultrasonic gel to the probe or patient skin, and slowly move the probe to locate the point where Doppler sounds are maximum.
Fetal Doppler sounds
Two very distinguishable sounds can readily be detected from the pregnant uterus.
a) The fetal heart beat is a mechanical "plop-plop" sound which varies somewhat according to the gestational age and the orientation of the fetal heart in relation to the sound beam from the transmitter.
b) The cord signal is a "swishing" type of sound that resembles the sound from other large arteries. The cord signal pulsates at the fetal heart rate.
- Consciousness of Fetal Movement Fetal PCG Fetal ECG Weeks after Conception
PHOTOPLETHYSMOGRAPHY (PPG)
Arterial pulse studies
Arterial PPG provides a waveform analogous to an arterial blood pressure waveform in appearance. Arterial PPG is an indicator of perfusion. It is not quantifiable but the waveform patterns are useful in diagnosing poor perfusion.
Procedure
a) Affix probe to the finger with double side scotch tape.
b) Observe the LED bar graph, and depress the RUN button to record waveforms.
Interpretation
Normal Abnormal
Arterial Pressures
PPG is used as a sensor for systolic blood pressures. Its purpose is to determine adequacy of flow in digits and vasculogenic impotence.
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Venous reflux study
Chronic venous insufficiency is related to the superficial and or the deep veins of the leg. The basic principle of venous reflux testing is to measure the recovery times following calf emptying exercises. The PPG sensor monitors the calf emptying and refilling sequence.
a) Have patient sit on the exam table.
b) Attach the PPG probe, emitter side down adjacent to the medal malleolus.
c) Depress the MODE key to select AC mode.
d) Activate printer.
e) Ask patient to flex the foot 3-5 times in succession. After flexing ask the patient to relax the foot and not move.
f) Test is complete when the baseline returns to pretest level.
Interpretation
Normal: Venous refill time (return to baseline) > 20 seconds.
Incompetent valves: (Venous reflux) < 20 seconds.
Normal
VENOUS REFLUX
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PNEUMOPLETHYSMOGRAPHY
Arterial studies
Pneumoplethysmography is useful in detecting arterial occlusive conditions in the lower limbs through analysis of waveform patterns. It is especially useful where arterial calcification prevents Doppler signal processing for waveform analysis and segmental blood pressures.
Procedure
a) Patient is in supine position with leg and hip externally rotated.
b) Wrap cuffs of appropriate width around the thigh at the groin, above the knee, below the knee, and at the ankle on both limbs.
c) Connect a 3-way stopcock, tubing, cuff, and sphygmomanometer as shown in the diagram below.
d) Turn the stopcock so that air is routed from the sphygmomanometer to the cuff.
e) Inflate the cuff 60 mmHg and turn the stopcock so that it blocks the sphyg and opens up to the PV interface unit or main unit.
f) The motion of the waveform is shown on the LED bar graph, and waveform patterns are recorded by depressing the RUN button to activate the printer.
g) Repeat the test by disconnecting the air hose from the first cuff and inserting it into the calf cuff.
Interpretation
Normal pneumo waveforms have sharp upstrokes and downstrokes with the presence of the dicrotic notch. The overall waveform shape is analogous to an in - line arterial pressure waveform in appearance.
Abnormal pneumo waveforms have amplitude degradation and loss of dicrotic notch. The downslope is also shallow or more gradual.
TYPICAL NORMAL WAVEFORM TYPICAL ABNORMAL WAVEFORM
ANKLE BELOW KNEE THIGH BRACHIAL Downslope curves Dicrotic notch Sharp upstroke
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Maximum venous outflow (MVO) studies
The Purpose of venous out flow testing is to diagnose occlusion of the deep venous system of the thigh. It is used in conjunction with venous Doppler compression studies. The former is used primarily for venous calf occlusion. The latter is for the deep veins in the thigh.
Procedure
The patient is supine and the limb to be tested is externally rotated and elevated above the heart. Two cuffs are used. A sensing cuff is placed on the calf and a pressure cuff at the thigh. The thigh cuff is inflated to 60 mmHg which is sufficient pressure to occlude venous return. The sensing cuff will begin to sense an increase in calf volume. M.V.O. studies are performed in the DC mode which has a longer time constant. The printer records a gradual rise from the baseline. In principle it takes about 3 seconds for the return of the waveform to baseline after dumping the occlusive thigh cuff.
Interpretation
NORMAL: Return of venous flow to original baseline within 3 seconds.
ABNORMAL: Venous flow will take longer.
3 sec Outflow Cuff deflated Venous Capacitance Cuff inflated
Normal
Venous Capacitance
Abnormal
Cuff deflated 3 sec Outflow Cuff inflated
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HADECO DOPPLER PRODUCTS
* Classification
A: Ultrasound blood flow detector (unidirectional): Pocket or pencil type without printer
B: Ultrasound blood flow meter (unidirectional): Handheld type with printer
C: Ultrasound blood flow detector (bidirectional): Pocket or handheld type without printer
D: Ultrasound blood flow meter (bidirectional): Portable type with printer
E: Ultrasound blood flow meter (bidirectional): Desktop type with printer
F: Ultrasound Fetal heartbeat detector: Fetal use
Q: Quantitative ultrasound blood flow meter: Volumetric blood flow, angle independent
* RS model has an interface for computer connection.