动脉和静脉疾病ABC of Arterial and Venous Disease

ABC of Arterial and Venous Disease

waveform flattens; in critical limb ischaemia it may be
undetectable.
Examination of an arterial stenosis shows an increase in
blood velocity through the area of narrowing. The site(s) of any
stenotic lesions can be identified by serial placement of the
Doppler probe along the extremities. The criteria used to define
a stenosis vary between laboratories, but a twofold increase in
peak systolic velocity compared with the velocity in an adjacent
segment of the artery usually signifies a stenosis of 50% or
more.
By combining the pulsed Doppler system with real time B
mode ultrasound imaging of vessels, it is possible to examine
Doppler flow patterns in a precisely defined area within the
vessel lumen. This combination of real time B mode sound
imaging with pulsed Doppler ultrasonography is called duplex
scanning. The addition of colour frequency mapping (so called
colour duplex or triplex scanners) makes the identification of
arterial stenoses even easier and reduces the scanning time.
Investigations of arterial disease
Ankle brachial pressure index
Under normal conditions, systolic blood pressure in the legs is
equal to or slightly greater than the systolic pressure in the
upper limbs. In the presence of an arterial stenosis, a reduction
in pressure occurs distal to the lesion. The ankle brachial
pressure index, which is calculated from the ratio of ankle to
brachial systolic pressure, is a sensitive marker of arterial
insufficiency.
The highest pressure measured in any ankle artery is used
as the numerator in the calculation of the index; a value >1.0 is
normal and a value < 0.9 is abnormal. Patients with
claudication tend to have ankle brachial pressure indexes in the
range 0.5
0.9, whereas those with critical ischaemia usually have
an index of < 0.5. The index also has prognostic significance
because of the association with arterial disease elsewhere,
especially coronary heart disease.
Diabetic limbs
Systolic blood pressure in the lower limbs cannot be measured
reliably when the vessels are calcified and incompressible—for
example, in patients with diabetes—as this can result in falsely
high ankle pressures. An alternative approach is to use either
the pole test or measurement of toe pressures. Normal toe
systolic pressure ranges from 90
100 mm Hg and is 80
90% of
brachial systolic pressure. A toe systolic pressure < 30 mm Hg
indicates critical ischaemia.
Spectral analysis of blood velocity in a stenosis, and
unaffected area of proximal superficial femoral artery. The
velocity increases from 150 to 300 m/s across the stenosis
Colour duplex scanning of blood flow through stenosis of superficial
femoral artery. Colour assignment (red or blue) depends on direction of
blood flow and colour saturation reflects velocity of blood flow. Less
saturation indicates regions of higher blood flow and deeper colours
indicate slower flow; the absence of flow is coded as black
Years
Patient survival (%)
0 2 4 6 8 10
20
60
800
100
ABPI < 0.4 ABPI 0.4-0.85 ABPI > 0.85
40
Patient survival according to measurements of ankle brachial pressure index
(adapted from McKenna et al, Atherosclerosis 1991;87:11928)
Pole test for measurement of ankle pressures in patients with calcified
vessels: the Doppler probe is placed over a patent pedal artery and the foot
raised against a pole that is calibrated in mm Hg. The point at which the
pedal signal disappears is taken as the ankle pressure
Relation between increased blood velocity and degree of
stenosis
Diameter of
stenosis (%)
Peak sytolic
velocity* (m/s)
Peak diastolic
velocity* (m/s)
Internal: common
carotid artery
velocity ratio&#8224;
0
39 < 1.1 < 0.45 < 1.8
4
59 1.1
1.49 < 0.45 < 1.8
60
79 1.5
2.49 0.45
1.4 1.8
3.7
80
99 2.5
6.1 > 1.4 > 3.7
> 99 (critical) Extremely low NA NA
*Measured in lower part of internal carotid artery
&#8224;Ratio of peak systolic velocity in internal carotid artery stenosis
relative to proximal measurement in common carotid artery

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