FIGURE 1: VELOCITY AND FLOW EQUATIONS
a) Velocity Equation:
_ graph area (cm) _
v(cm/sec) = graph length (cm) X recorder sensitivity (cps/cm) X
_ c(m/sec) x 100(cm/m) x K3 _
2Ft(cps) x cos O x 6(Hz/MHz)
10
_a(cm)_ ___1550(m/sec) x 100 (cm/m) x 1.724___
v = l(cm) X 1000cps X 2 x 9.221(MHz) x cos 45 x 6 (Hz/MHZ)
10
_a(cm)_
v = l(cm) X 20.49
where: v = velocity of blood
c = speed of sound in tissue
K3 = correction factor for zero-crossover processing
Ft = doppler transmitted frequency
O = incident angle (probe to surface)
A = vessel cross-sectional area
FIGURE 1 (Continued)
b) Flow Equation:
Q(ml/min) = v(cm/sec) X A(cm2) X 60(sec/min)
substituting for v (velocity):
_a(cm)_ _ 1550(m/sec) x 100(cm/m) x 1.724_
Q(ml/min) = l(cm) X 1000cps X 2 x 9.221MHz x cos45 x 6(Hz/MHz)
10
X A(cm2) X 60(sec/min)
_a(cm)_
Q(ml/min) = l(cm) X 1229.50 X A
__a___
Thus: for popliteal a.: Q = l X 1229.5 X 0.196
_a_
or Q = l X 241.4
For posterior tibial a.:
_a_
Q = l X 1229.50 X 0.031416
_a_
or Q = l X 38.63
For dorsalis pedis a.:
_a_
Q = l X 1229.50 X 0.031416
_a_
or Q = l X 38.63
FIGURE 2: DOPPLER GRAPH FOR THE EXAMPLE OF
COMPENSATED ANTIBIOTIC DOSAGE
Dorsalis Pedis A., Right Posterior Tibial A., Right
Dorsalis Pedis A., Left Posterior Tibial A., Left
FIGURE 3: WHOLE BLOOD VISCOSITY
FIGURE 3.: Viscosity of heparinized normal human blood relative to
hematocrit, expressed in relation to viscosity of normal saline solution.
Adapted from Williams, W.J., et al. Hematology, McGraw Hill, 1983 P.
61.
FIGURE 4: SUMMARY OF CALCULATIONS
Velocity = Height of Curve (in cm) X 20.49 (Constant) Recorder
Gain
Adjustment for 20.49 X _( )MHz_ if < 9.221 MHz
Frequency Change: 9.221 MHz
20.49 X _9.221 MHz _ if > 9.221 MHz
( )MHz
Flow = Height of X Pop= 241.4 Recorder =100 - _( )_ = % Increase
Curve (cm) Gain 0.089 in Dosage
PT= 38.63 = 100 - _( )_
0.068
DP= 38.63 = 100 - _( )_
0.099
Resistance = K-A Distance X Popliteal= 0.53 X _0.040 poise
Viscosity x 8 ii
Cross-Sectional Area
PT= 0.81 Popliteal= 0.196
DP= 0.87 DP or PT = 0.0314
FIGURE 4: SUMMARY OF CALCULATIONS
1. Height of curve = instantaneous blood velocity at any given time.
The peak velocity is measured (height in cm), corresponding with
the peak frequency shift.
2. Velocity = wave period length X factor (standardized measurement
parameters).
3. Flow = velocity X averaged vessel parameters ^ recorder gain
4. Flow and velocity are calibrated to the practitioner's frequency
used and recorder gain.
5. Vessel length is factored for vessel knee-ankle distance.
6. Resistance = (factored vessel length X viscosity X constants) ^
the square of averaged vessel parameters.
PHOTOGRAPHS
Photo 1:
One of the earliest signs of circulatory inadequacy is intermittent
claudication. Historically, this has been measured in the number of
blocks walked or the number of steps climbed before the onset of pain.
Photo 2:
Angiogram of partial obstruction of the femoral profunda artery. Note
multiple athrosclerotic areas, and how collateral circulation attempts to
comprimise to supply blood distally.
Angiogram courtesy of Roanoke Memorial Hospitals.
Photo 3:
Angiogram of the foot, which is normal for this patient, but doppler
measurements show decreased blood flow. Although blood supply is
patent distally, proximal collateral circulation is responsible for
circulatory adequacy of this limb. The calibrated doppler measurement
of these arteries enable closer monitoring of a more proximal
pathological obstruction.
Angiogram courtesy of Roanoke Memorial Hospitals.
Photo 4:
The Podiatric Physician may be consulted to monitor cases involving
vascular trauma should the foot become a high risk of loss. Note
circulatory embarrassment of the Popliteal Artery as it rides over the
crest of a fractured tibial epiphysis. Calibrated blood flow measurement
provides early non-invasive measurement of circulation deficiency as
fracture healing continues. Bone callus formation in this area could
gradually constrict flow to the distal leg and foot.
Angiogram courtesy of Roanoke Memorial Hospitals.
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