Non-Invasive Laboratory Evaluation in PAD
Clifford J. Buckley, MD, FACS
Professor of Surgery
Diabetic Foot Update 2011
San Antonio
Central Texas Veterans Health Care System
Disclosure
I have no relevant financial relationships with
proprietary entities producing health care goods or
services related to the content of this presentation.
I am a consultant for Endologix and participate in
research for Endologix, Medtronic and Gore
Content may not reflect position of US Government
PURPOSE OF NONINVASIVE
VASCULAR EXAMINATION
• Define presence/absence of PVD
• Define severity of PVD
• Define location of PVD
• No substitute for thorough H&P
NONINVASIVE VASCULAR EXAMINATION
ADVANTAGES
• Noninvasive
• Reproducible
• Provided physiologic & anatomic information
Standard Non-Invasive Arterial
Studies
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Segmental Systolic Pressure Measurements
Doppler Wave Form Evaluation
Segmental Plethysmography
Exercise Testing
Color Flow Duplex Ultrasound Imaging
Niche Evaluation Techniques
• Transcutaneous Oxygen Tension (TcpO2)
• Laser Doppler Flowmetry
When To Test
• If pulses not easily palpable or significant neuropathy
present – need baseline vascular testing evaluation
• Segmental systolic pressure measurements
• Segmental plethysmography with/without exercise
testing
When To Test
• Necessary for Predicting
• Wound healing potential
• Level of amputation
• Need for revascularization
Segmental Systolic Pressure
Measurements
• Made at multiple levels in an extremity
• Complete exam includes high thigh, low thigh, calf, ankle
and sometimes digital pressure measurements
• Ankle-brachial index (ABI) – leg systolic pressure/arm
systolic pressure
• Normal ABI – > 0.95
• 0.5 – 0.9 = intermittent claudication
• < 0.4 = severe lower extremity ischemia
• Rest pain
• Non-healing soft tissue lesions
• Threatened viability
Segmental Systolic Pressure
Measurements
• ABI usually inaccurate in diabetics d/t
abnormal arterial stiffness (medial
calcification)
• Toe pressure measurements may be
useful
• Cost
• $25 – simple ABI
• $125 - $300 – full study
Doppler Wave Form Evaluation
• Usually obtained
• Common femoral
• Superficial femoral
• Popliteal
• Posterior tibial
• Anterior tibial
• Peroneal
Doppler Wave Form Evaluation
• Advantages
• More sensitive to milder forms of
occlusive disease
• More vessel specific
• Cost - $200 for standard resting multilevel wave form study
Doppler Wave Form Evaluation
• Disadvantages
• Extremely operator dependent
• Must be held at approximate 60º angle
• Too much pressure – vessel compressed
simulating stenosis or occlusion
• Wave form difficult to evaluate in obese
patients and post surgical patients d/t
scarring
• Distorted wave forms seen in patients with
advance diffuse arterial occlusive disease
Segmental Plethysmography
• Pulse-volume recordings obtained
• High thigh
• Low thigh
• Calf
• Ankle
• Transmetatarsal
• Digital
• Uses air-filled cuffs
• Inflated to 65mm Hg for limbs
• Represents arterial inflow during systole
• Inflated to 35-40mm Hg for digits
Segmental Plethysmography
• Advantages
• More sensitive than segmental systolic
pressure measurements
• Not particularly operator dependent
• Detect occlusive disease in heavily calcified
vessels
• Not dependent on compressibility of
calcified vessels
• Serial patient evaluations
• Easily identifies disease
progression/intervention improvement
Segmental Plethysmography
• Disadvantages
• Sensitive to changes in cardiac output
• Data qualitative and not quantative
• PVR recorders moderately expensive $25,000 - $30,000
• Cost
• $175 - $400 for individual test
• Always includes segmental systolic
pressure measurements
Exercise Testing
• Accomplished by
• Foot pump (heel-toe)
• Used for patients limited by advanced
cardiac or pulmonary disease or soft
tissue wounds on feet/toes
• Exercise duration usually 2 minutes
Exercise Testing
• Motorized treadmill
• Two programs
• Low speed program
• 5 minutes of ambulation
• 1.5 – 1.7 mph fixed grade 10% - 12%
• High speed program
• Used for claudicants
• 5 minutes of ambulation
• 2.25 – 2.5 mph fixed grade 10% - 12%
Exercise Testing
• Useful for
• Evaluating complaints of claudication
• Documenting reproducibility of symptoms
• Defining exercise tolerance
• Limitations
• Tests vary from laboratory to laboratory
• Additional $35 - $100 cost
Color Flow Duplex Ultrasound
Imaging
• Localize arterial occlusive lesions identified by
other non-invasive testing
• Surveillance of previously constructed LE
bypass grafts
• Evaluate greater/lesser saphenous vein for
bypass conduits
• Describes artery evaluated as
• Patent w/o significant stenosis
• Patent with stenosis > 50%
• Segmentally occluded
• Characterizes plaque morphology
Color Flow Duplex Ultrasound
Imaging
Cost
• $125,000 - $200,000 high quality imaging unit
• $50,000 - $60,000 per year salary for
experienced tech
• $250 - $300 exam cost for localizing lesion
• $850 - $1,000 exam cost for full lower extremity
mapping
Transcutaneous Oxygen Tension
• Reflects metabolic state of target tissues
• Relates primarily to metabolic state of
skin when used for assessment of lower
extremity arterial perfusion
Transcutaneous Oxygen Tension
Measurement affected by
• Cutaneous blood flow
• Abnormal venous pressure
• Metabolic activity
• Oxyhemoglobin dissociation
• Oxygen diffusion through tissue
Transcutaneous Oxygen Tension
Transcutaneous Oximeter
• Uses large Clark polarographic electrode
• Modified to contain heating element & thermister
• Heating element maintains preset temperature of
42-450C
• Temperature continuously monitored by thermister
• Attached to skin by adhesive fixation
Transcutaneous Oxygen Tension
Mechanism of Action
• Heat transfer beneath electrode
• Dilates capillaries
• Opens skin pores
• Decreases 02 solubility
• Shifts the oxyhemoglobin curve to the right –
ready release of 02
• Skin surface 02 tension approximates arterial 02
tension
Transcutaneous Oxygen Tension
Normal Tissue Oxygen Tension
• 1 atm abs
• 55 - 70 mm Hg on room air
• 250 – 450 mm Hg on oxygen
Transcutaneous Oxygen Tension
Predictor of Wound Healing
• Diabetics with Tcp02 > 40 mm Hg
• Sufficient tissue oxygenation to heal
with
• Standard wound care
• Grafting
• Application of growth factor products
Transcutaneous Oxygen
Tension
Predictor of Wound Healing
• Diabetics with Tcp02 < 40 mm Hg
• Moderate to severe tissue hypoxia
• HBO candidate
• Aggressive wound management
• Revascularization
Laser Doppler Flowmetry
• Non-invasive method of using light laser to
detect blood movement in a small tissue sample
• Two basic types
• Laser Doppler Perfusion Monitoring (LDPM)
• Requires contact with skin through fiber
optic probe
• Laser Doppler Perfusion Imaging (LDPI)
• Laser beam scans tissue and gives 2-D
perfusion picture
Laser Doppler Flowmetry
• Uses Doppler effect to assess blood movement
within microvasculature of the skin
• Two optic fiber probe contains
• Transmitter
• Emits light beam of specific wavelength
that enters the tissue and scatters
• Receiver
• Photo detector converts scatters to
electrical signals
• Blood perfusion
• Blood cell concentration
• Velocity
Laser Doppler Flowmetry
Depth of Measurement
• Identifies total blood perfusion in the measured
volume
• Capillaries
• Arterioles
• Venules
• Shunts
• Measured volume
• Region under probe to which laser light is
transmitted and returned
Laser Doppler Flowmetry
Evaluation of Skin Perfusion
• Laser Doppler velocimeter serves as blood flow
sensor placed under pneumatic cuff
• Needs provocative test
• Occlusion
• Heat
• Posturing (elevating or lowering limb)
• Difficult to use as predictor of wound healing
without provocative test
Laser Doppler
Laser Doppler
Laser Doppler Flowmetry
Measurement Values – plantar skin of great
toe/foot
• Normal
• 75mm Hg + 10mm Hg
• Claudicants
• 50 – 70mm Hg
• Rest pain or non-healing soft tissue wounds
• 10 – 40mm Hg
Laser Doppler Flowmetry
Occlusion as Provocative Test
• Toe pressure in diabetics more reliable
than ankle pressure
• Toe pressure < 30mm Hg suggests critical
limb ischemia
• Toe pressure < 60 – 70mm Hg associated
with poor wound healing
Laser Doppler Flowmetry
LDF In Combination With Tcp02
• LDF values most useful when Tcp02
values falsely low due to inflammation or
acute edema
Minimally Invasive Arterial
Examination Modalities
• Require administration of some form of IV
contrast material to opacify arterial system
• Types
• Magnetic Resonance Angiography
• Spiral CT Angiography
Minimally Invasive Arterial
Examination Modalities
• Magnetic Resonance Angiography
• Graphic picture of arterial anatomy
• Limitations
• Venous contamination especially below
knee
• No assessment of vessel wall
calcification
Minimally Invasive Arterial
Examination Modalities
• Spiral CT Angiography
• Accurate picture of arterial anatomy to
knee – variable reliability below knee
• 3D reconstruction extremely helpful when
available
Future Improvements
• Segmental plethysmography is being refined
to measure segmental perfusion in terms of
cc/per minute of arterial flow
• This device will be in trial in 2012
Thank You