5.1 Physiologic Exams (12%) Overview

5.1 Physiologic Exams (12%) Overview

Physiologic testing (also called indirect testing) measures the hemodynamic consequences of vascular disease rather than imaging the vessel. On the ARDMS Registered Vascular Technologist (RVT) Vascular Technology examination, this domain is about 12% of an exam of roughly 170 multiple-choice and hotspot items delivered in a 3-hour appointment; passing requires a scaled score of 555 on the 300-700 ARDMS scale. Expect calculation items (compute an ABI), interpretation items (grade severity), and protocol items (which cuff, which position).

The five indirect tools

ABI calculation and interpretation

The ABI is the higher ankle pressure (dorsalis pedis or posterior tibial) for that limb divided by the higher of the two brachial pressures. Example: right dorsalis pedis 112 mmHg, posterior tibial 104 mmHg, brachials 140 and 138 mmHg. Use 112 / 140 = 0.80, a mild-to-moderate result. Memorize the bands:

• 1.00-1.40 normal
• 0.91-0.99 borderline
• 0.41-0.90 mild-to-moderate disease (claudication range)
• ≤ 0.40 severe disease / critical limb ischemia
• > 1.40 non-compressible (medial calcinosis) — ABI is invalid, obtain a toe-brachial index (TBI)

Physiology behind the numbers

Understanding why the thresholds exist makes them stick. Blood pressure should be nearly equal at every level of a healthy arterial tree because large arteries offer little resistance; a measurable systolic gradient between adjacent segments means an obstruction has converted pressure energy into turbulence and heat. A stenosis becomes hemodynamically significant when it narrows the lumen enough to drop distal pressure or flow, generally around a 50% diameter reduction (roughly 75% cross-sectional area).

Below that, collateral vessels and the pressure reserve keep resting distal pressure normal, which is exactly why a resting ABI can be normal in early disease and only falls when exercise raises demand. The post-exercise drop reflects vasodilation of muscle beds downstream: blood is shunted across a fixed proximal lesion, the pressure gradient grows, and the ankle pressure plummets until rest restores it. Holding this model lets you predict, not just memorize, what each test will show.

Why indirect testing still matters

Duplex imaging shows anatomy, but a single B-mode image cannot prove a stenosis is hemodynamically significant. Physiologic tests answer “is flow actually reduced, and where?” A normal ankle pressure but absent palpable pulse is reassuring; a 30 mmHg drop between thigh and calf localizes disease to the superficial femoral or popliteal segment regardless of how the artery looks. The exam rewards candidates who pair the number with the clinical action: a resting ABI of 0.95 in a patient with classic calf claudication is not normal enough — it warrants exercise testing to expose a post-exercise drop.

Continuous-wave Doppler waveforms

Many physiologic stations pair pressures with a continuous-wave (CW) Doppler velocity waveform recorded with a 4-8 MHz pencil probe over the ankle arteries. The normal peripheral arterial signal is triphasic: a sharp forward systolic peak, a brief early-diastolic flow reversal (from high peripheral resistance), and a small late forward component. As disease develops the reverse component disappears, leaving a biphasic then monophasic signal. A monophasic, low-amplitude, broadened waveform distal to a lesion is the audible and visual signature of significant inflow obstruction.

The exam may ask you to match a waveform description to severity, so memorize the triphasic → biphasic → monophasic progression and that loss of the reverse flow component is the first sign of proximal disease.

Indications and reporting

Indirect studies are ordered for claudication, rest pain, non-healing wounds or ulcers, suspected critical limb ischemia, pre-amputation level assessment, vasospastic disorders, and graft or bypass surveillance. A complete report states the resting ABI for each limb, the segmental pressures and gradients, waveform morphology at each level, and any toe pressure or exercise data. Because Medicare and accreditation bodies (the IAC, Intersocietal Accreditation Commission) require objective documentation, the exam favors answers that record the measured values and the artery sampled rather than a bare impression.

A study that finds a normal resting ABI in a symptomatic patient is incomplete until exercise testing is performed or explicitly contraindicated.

Test-day mindset

Read each stem for three things: which measurement is described, which level or digit it represents, and which threshold decides the answer. Many distractors are real findings placed at the wrong segment or the wrong cutoff. Anchor every choice to a memorized threshold (20-30 mmHg segmental gradient, 0.15 post-exercise ABI drop, TBI 0.70, venous refill time 20 seconds) so a familiar-sounding option cannot pull you off the correct number. When a question gives raw pressures, do the arithmetic before reading the options — the distractors are usually the values you get by selecting the lower ankle or lower brachial pressure.