• patients with suspected or known acute deep venous thrombosis (DVT) or superficial thrombophlebitis;
• those who have had recent surgery, ulcers, casts or bandages that cannot or should not be compressed by pressure cuffs;
• patients with incompressible arteries due to medial calcification;
• patients who have had an interventional procedure (i.e., stent placement, arterial bypass graft); and
• patients who have had a lower extremity (ankle level) interventional procedure (i.e., ankle level arterial bypass graft).
When PVR And SPP Testing Can Have An Impact
With these caveats in mind, patients with combination disease require tests that are not subject to the same limitations as ABI but that are also conducive to outpatient, clinic-based vascular testing. Two tests that meet these criteria include air or volume plethysmography (also called pulse volume recording or PVR) and the skin perfusion pressure (SPP) test, which measures reactive hyperemia.
The PVR test requires the use of pressure cuffs that one can place at various levels. With each cardiac cycle, blood pumps throughout arteries. The PVR test uses a partially inflated pressure cuff to apply slight pressure to the limb. The impact of blood passing through the limb transfers to the pressure cuff where the cuff measures the impact as small changes in cuff pressure. The changes display as a PVR waveform. The amplitude and shape (pulse contour) of these waves provide an indication of blood volume in the limb arteries. The normal pulse volume recording is composed of a systolic upstroke with a sharp systolic peak followed by a downstroke that contains a prominent dicrotic notch. Changes in the pulse volume contour such as disappearance of the dicrotic notch and loss of a sharp systolic peak indicate proximal arterial obstruction and are due to the dissipated energy that occurs due to arterial narrowing. These changes can be a sign of PAD. One must perform bilateral PVRs in order to compare them to each other since disease can be different in both legs.15
Skin perfusion pressure, a provocative functional test of the capillaries, is a measurement of reactive hyperemia. For the SPP test, the clinician inflates a circumferential cuff to a known pressure and holds it at that pressure for a specified period of time. This subjects the capillaries to a brief period of pressure-induced ischemia. When one deflates the pressure cuff under an automated release protocol, reactive hyperemia occurs. The cuff pressure (mmHg) when the capillary bed reperfuses (hyperemia) is the skin perfusion pressure.
A simple way to think of skin perfusion pressure is capillary blood pressure. To perform the test, one would place a laser Doppler probe on the patient. Light from the laser enters the tissue and interacts with tissue and capillaries. The probe assesses light that returns through the laser to the instrument for the Doppler signal. The probe processes this signal and translates it into the cuff pressure at which flow was able to return to the capillary beds. In normal, healthy adults, skin perfusion pressure ranges are 70 to 110 mmHg.16-18 Perfusion pressures associated with PAD are typically in the range of 30 to 60 mmHg while critical limb ischemia is defined as perfusion pressures below 30 mmHg.
Outside of PAD detection and management, SPP/PVR/ABI testing also provides valuable vascular information to guide many of the common treatment decisions facing the podiatrist regarding the diabetic foot. Not only is adequate tissue perfusion required to heal a diabetic foot ulcer but in cases of elective, prophylactic or curative surgery, one should assess perfusion in order to predict wound healing.
Myth: ‘An ABI Is An ABI’
In October 2012, the American Heart Association (AHA) published a scientific statement regarding the measurement and interpretation of ABI.19 The AHA Writing Committee’s review of the literature found multiple variations in technique for measuring and interpreting ABI, including different positions for the patient during measurement, different sizes of the arm and leg cuffs, different locations of the cuff on the extremity, and different methods of pulse detection.