Physiologic Testing Modalities

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Physiologic Testing Modalities

• Segmental Limb Pressure

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Pressure Assessment

• Continuous-wave Doppler
• Doppler derived systolic blood pressure
• Generally utilized to acquire all segmental limb
  pressures except for digits
• Photoplethysmography
• Generally utilized for digit pressures
• May be utilized to acquire segmental pressures

• Positives
• Bilateral capability
• Convenient
• Requires less skill

• Negatives
• Ambient light interference
• No audible pulse
• Not good for severe disease

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Segmental Pressure Principle

• In a normal individual in a supine position,
  ankle systolic pressure is brachial systolic
  pressure.
• The pressure obtained is the pressure in the
  vessel immediately under the pressure cuff.
• Not the pressure at the site of sampling, e.g.
  high thigh pressure acquisition while listening
  at the ankle.
• Patient should be in a basal state prior to
  pressure acquisition.
• Patient should not have had activity for at least
  15-20 minutes before testing is started.

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Limitations of SLP Acquisition

• Media sclerosis, medial calcinosis, arterial
  calcification
• Esp. occurs in patients with diabetes, end-stage
  renal disease and patients on chronic steroid
  therapy.
• Falsely elevates segmental limb pressures making
  them nondiagnostic
• Digit pressures and digit/brachial indices are
  more useful in these patients as the digit
  vessels are generally not affected by medial
  calcinosis
• Hypertension low cardiac output
• Hypertension can falsely elevate pressure
  gradients between adjacent cuff levels
• Low cardiac output can falsely lower pressure
  gradients between adjacent cuff levels

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Limitations of SLP Acquisition

• Multilevel arterial occlusive disease
• May make interpretation difficult.
• ABIs, however, will still indicate the severity
  of disease and high thigh pressure/pressure
  indices will generally still be diagnostic of
  inflow vs. outflow disease.
• Measurement of pressure postexercise
• Postexercise pressures must be obtained quickly
  and accurately. Otherwise the full extent of a
  exercise induced pressure drop may not be
  recognized.
• Edema
• Limb edema, esp. lipedema, may make arterial
  compression difficult, falsely elevating pressure
  values.

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Limitations of SLP Acquisition

• Uncompensated congestive heart failure (CHF)
• May cause an abnormally decreased ABI
  postexercise which may not be due to arterial
  occlusive disease
• Stenosis vs. occlusion disease level isolation
• Cannot differentiate stenosis, esp. severe
  stenosis from vessel occlusion
• Cannot distinguish disease in the CFA from
  disease in the iliac vessels because the high
  thigh pressure cuff is below the CFA .
• Resting period
• Appropriate rest intervals must be observed
  before resting pressure acquisition.
• It may take patients with severe arterial
  occlusive disease more than the generally
  accepted 15-20 minute rest interval to recover to
  their normal resting baseline.

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Limitations of SLP Acquisition

• Deflation errors
• Pressure cuff deflation should be maintained
  between 2-4 mmHg per second.
• Too fast a deflation rate will cause erroneously
  low pressure values to be measured.
• Arm-leg measurement intervals
• SLPs must be obtained without a long acquisition
  interval.
• Obtain all pressures quickly and accurately to
  avoid false pressure gradients and pressure
  indices from being obtained.
• Subclavian stenosis or occlusion
• This situation can lead to calculating falsely
  high pressure indices which may not be indicative
  of the severity of arterial occlusive disease
• Due to decreased arm pressures

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Limitations in SLP Acquisition

• Flow velocity in the arteries measured
• Low flow velocities, lt6 cm/s, are below the
  threshold of a CW Doppler to recognize
• Generally occurs in patients with very
  significant arterial occlusive disease
• Effect of limb girth
• Cuff artifact
• Falsely elevated pressures due to too small a
  pressure cuff for the limb girth
• Occurs most often at the high thigh
• Too large a cuff for the limb girth may cause a
  falsely low limb pressure

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Limitations of SLP Acquisition

• Effect of vasomotor tone changes
• Vessel dilatation, decreased vascular tone, due
  to heating, exercise or reactive hyperemia, with
  concomitant vascular disease can lead to
  abnormally low pressures being obtained.
• Stenosis or occlusion in parallel vessels
• Will not be recognized, esp. if other vessels
  present under the pressure cuff have a
  higher pressure.

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Advantages

• There is substantial clinical validation of SLP
  acquisition and pressure indices
• Relatively easy to perform
• Quantitative information of limb perfusion

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Pressure Cuffs

• Cuff Size
• Pressure cuff is too small (width is lt50 of limb
  diameter) ? artifactually high pressure
• Pressure cuff is too large ? artifactually low
  pressure
• Rules
• Pressure cuff width should be 20 wider than the
  diameter of the limb
• Pressure cuff width should be at least 40 of the
  limb girth
• Placement Rules
• Place snugly
• Do not place over bony prominences
• Place straight, not at an angle
• When obtaining blood pressures, the inferior edge
  of the cuff should be at least one inch above the
  point being evaluated

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Doppler Pressure Sampling Sites
Lower Extremity
Essential not to drift off vessel !

• Dorsalis Pedis
• Dorsum of foot
• Easily compressed
• Posterior Tibial
• Posterior to medial malleolus

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Segmental Limb Pressure

• Useful in identifying region(s) of disease
• Pressure gradients between two adjacent cuff
  levels or at the same level horizontally between
  limbs in the contralateral extremity do not
  generally exceed 20 mmHg.
• Comparison of adjacent levels in a limb
• 30 mmHg gradient is suggests significant
  arterial obstruction between or beneath the cuffs
• Compare to the same segment horizontally
• 20 mmHg gradient suggests significant arterial
  obstruction in the limb with the lower pressure
• Compare to brachial pressure
• All pressures are compared to the highest of the
  two brachial systolic pressures
• Digit pressures are useful, esp. in presence of
  medial calcinosis due to diabetes and/or renal
  disease

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Lower Extremity - 3 Cuff Method
3 cuff method (17 cm thigh cuff) If abnormal,
cannot differentiate aorto-iliac disease from SFA
disease
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Lower Extremity - 4 Cuff Method

• Upper thigh cuff pressure artifact (20 mmHg)
• Helps to differentiate aortoiliac disease from
  SFA disease

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Segmental Limb Pressure Levels

• High thigh
• Above knee
• Calf
• Ankle/Foot PTA, DPA
• Ankle Peroneal (optional)
• Metatarsal (optional)
• Digit

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The Ankle/Brachial Index (ABI)

• Used to determine severity of disease
• Bilateral ankle pressures divided by the higher
  brachial pressure
• Highest ankle pressure value is used for reported
  ABI

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ABIs
ABI Relationship to Peripheral Arterial Disease
ABIs exceeding 1.3, some authors suggest 1.4,
are highly suggestive of arterial calcification
and falsely elevated ankle pressures and
therefore ABIs making the ABI nondiagnostic for
the severity of arterial occlusive disease.
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ABI Technical Considerations

• ABI lt1.00 is suggestive of arterial disease
• ABI of 0.92 - 1.00 should be viewed with caution
• ABI lt1.00 but gt0.80 - Suspect claudication
• ABI 0.50 0.70 - Typical range of claudication
• ABI gt0.50 - indicative of single level disease
• ABI lt0.50 - indicative of multi-level disease
• ABI lt0.30
• Arterial ischemic rest pain, ischemic ulceration,
  gangrene
• Generally multi-level arterial occlusive disease
• ABI lt0.20
• Limb threatening, tissue necrosis

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Absolute Ankle Pressures
Absolute Ankle Pressure
Calf systolic pressures which are gt65-70 mmHg are
typically sufficient to heal below knee
amputations
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Digit/Brachial Index (DBI)

• Digit/Brachial Index
• Normal gt0.75
• Abnormal lt0.66

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Toe Brachial Index (TBI)

• Recommended for all patients but esp. patients
  with diabetes or renal disease as the tibial
  arteries may become incompressible with ankle
  pressures being gt 300 mmHg.
• Digital vessels are rarely significantly affected
  by calcification.
• Normal TBI is 0.80 but is not considered abnormal
  until reduced to lt0.65.

TBI Relationship to Peripheral Arterial Disease

• Toe pressures of lt30 mmHg, diabetic and
  non-diabetic, suggest wound healing will not be
  successful.

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Thigh Pressures Pressure Index

• Thigh pressures when utilizing a 12 cm cuff will
  generally exceed the highest brachial pressure by
  20 producing a high thigh/brachial pressure
  index of 1.2.
• High thigh/brachial pressure index of lt1.2 is
  suggestive of aortoiliac arterial occlusive
  disease, esp. if the ABI is abnormally reduced.
• High thigh/brachial pressure index of lt1.0 is
  indicative of aortoiliac arterial occlusive
  disease

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Segmental Limb PressuresUpper Extremity - LEVELS
Forearm Obtain pressures while sampling the
radial ulnar arteries at the wrist Arm Obtain
pressure while sampling the artery with the
greatest pressure at the wrist
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Segmental Limb PressuresUpper Extremities

• Some labs add a wrist cuff, 7 cm, same as during
  PVR assessment and obtain
• Two wrist pressures radial ulnar
• One forearm pressure
• One arm pressure

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Upper Extremity

• Pressure gradients between two adjacent cuff
  levels, or at the same level of the contralateral
  extremity generally do not exceed 20 mmHg.
• Pressure gradients of gt 30 mmHg suggests
  significant arterial obstruction between the
  cuffs or beneath the cuff.
• A significant brachial artery gradient suggests
  disease proximal to the point of sampling in the
  arm with the lower pressure with a possible
  resultant subclavian steal in the ipsilateral
  arm.

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Upper Extremity Pressure Sampling Sites
Radial Artery - Wrist
Ulnar Artery - Wrist
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Arm Pressure Utilizing Radial Site
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Digit Pressure TestingPhotoplethysmography
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Finger Pressure DBI

• Normal upper extremity digit pressure is gt80 of
  the (normal) ipsilateral brachial systolic
  pressure, i.e. a digit brachial index (DBI)
  gt0.80.
• Systolic finger pressure of lt70 mmHg and
  brachial-finger pressure gradients of gt35 mmHg
  are suggestive of proximal arterial obstruction,
  i.e. between the brachial and digit levels.
• When comparing digit pressures to a normal
  ipsilateral wrist pressure, a pressure gradient
  (wrist-to-finger) of gt30 mmHg or a
  finger-to-finger pressure gradient of gt15 mmHg is
  suggestive of distal digit ischemia.