Residency · Residency · Vascular Surgery
Physiologic Vascular Testing: ABI, TBI, Segmental Pressures, and PVR
Introduction
Physiologic vascular testing offers an objective and quantitative means to assess peripheral arterial perfusion. These tests form the cornerstone of the noninvasive vascular laboratory and play a critical role in diagnosing peripheral arterial disease (PAD), grading its severity, guiding treatment decisions, and monitoring patients after interventions.
Ankle-Brachial Index (ABI)
Technique
To perform the ankle-brachial index measurement, the patient should rest in a supine position for at least 10 minutes to ensure hemodynamic stability. Systolic pressures are then recorded at both brachial arteries and at the dorsalis pedis and posterior tibial arteries of each leg. This is done using a handheld continuous-wave Doppler device alongside appropriately sized blood pressure cuffs. The ABI for each leg is calculated by dividing the highest ankle systolic pressure (either dorsalis pedis or posterior tibial) by the highest brachial systolic pressure.
Interpretation
An ABI between 1.00 and 1.40 is considered normal, indicating adequate arterial perfusion. Values from 0.91 to 0.99 are borderline, while an ABI between 0.70 and 0.90 suggests mild PAD. Moderate PAD corresponds to an ABI of 0.40 to 0.69, and severe PAD or critical limb-threatening ischemia (CLTI) is indicated by an ABI less than 0.40. An ABI greater than 1.40 suggests non-compressible vessels, often due to medial arterial calcification seen in conditions such as diabetes, end-stage renal disease, or advanced age. In these cases, the ABI is unreliable for assessing arterial disease.
| ABI Value | Interpretation | Clinical Significance |
|---|---|---|
| >1.40 | Non-compressible | Calcified arteries; use TBI and PVR instead |
| 1.00–1.40 | Normal | Adequate arterial perfusion |
| 0.91–0.99 | Borderline | Consider exercise ABI |
| 0.70–0.90 | Mild PAD | Claudication likely |
| 0.40–0.69 | Moderate PAD | Severe claudication; approaching CLTI |
| <0.40 | Severe PAD / CLTI | Rest pain; tissue loss likely |
Exercise ABI
When resting ABI values are borderline or normal but symptoms of claudication persist, treadmill exercise testing can be employed. The patient walks at 2 miles per hour on a 12% incline for 5 minutes, after which ankle pressures are re-measured. A drop of 20% or more in the ABI following exercise confirms the presence of hemodynamically significant PAD that may not be evident at rest.
Toe-Brachial Index (TBI)
The toe-brachial index is measured using a photoplethysmographic (PPG) sensor placed on the great toe along with a small digital cuff. This test is especially important when the ABI is non-compressible (greater than 1.40) because digital arteries are less affected by medial calcification. A normal TBI is greater than 0.70, while values below 0.70 indicate abnormal perfusion, with readings under 0.30 signifying severe ischemia. Additionally, an absolute toe pressure below 30 mmHg is a critical threshold for diagnosing CLTI.
Segmental Pressures
Technique
Segmental pressure measurements involve placing blood pressure cuffs at multiple levels on both legs: the high thigh, above the knee, below the knee, and ankle. Systolic pressures at each site are obtained using continuous-wave Doppler. The pressure gradients between adjacent segments are then analyzed to identify areas of arterial obstruction.
Interpretation
A pressure gradient exceeding 20 mmHg between adjacent segments suggests significant arterial occlusive disease at or above that level. Normally, the high thigh pressure is 20 to 30 mmHg higher than the brachial pressure due to cuff artifact. If the high thigh pressure is reduced, this points toward aortoiliac disease. While segmental pressures help localize the level of arterial disease, they do not provide detailed anatomic information.
Pulse Volume Recording (PVR)
Technique
Pulse volume recording uses air-filled cuffs placed at the same segmental levels to detect volume changes in the limb during the cardiac cycle. These volume changes generate plethysmographic waveforms that are recorded for analysis. Because PVR is independent of vessel compressibility, it is particularly useful in patients with calcified arteries where pressure measurements may be unreliable.
Waveform Interpretation
A normal PVR waveform features a sharp systolic peak, a prominent dicrotic notch, and a rapid downslope. Mild arterial disease is characterized by loss of the dicrotic notch and a rounded peak. Moderate disease produces a flattened waveform with a prolonged upstroke, while severe disease results in a nearly flat tracing with minimal pulsatility. An amplitude less than 5 mm at the ankle strongly suggests severe ischemia.
Additional Physiologic Tests
Transcutaneous Oxygen Pressure (TcPO2)
Transcutaneous oxygen pressure measures local tissue oxygenation using a heated electrode applied to the skin. A TcPO2 greater than 40 mmHg indicates adequate oxygenation for wound healing, whereas values below 30 mmHg predict poor healing and suggest the need for revascularization. This test is valuable in determining appropriate amputation levels and predicting wound healing potential.
Skin Perfusion Pressure (SPP)
Skin perfusion pressure is assessed using a laser Doppler probe beneath a pressure cuff. An SPP above 40 mmHg generally predicts sufficient perfusion for healing, making it particularly useful for evaluating the forefoot and guiding decisions about transmetatarsal amputation levels.
Key Clinical Pearls
The ankle-brachial index remains the most important screening test for peripheral arterial disease and should be performed in all patients with vascular risk factors. When the ABI is non-compressible (greater than 1.40), it is essential to obtain toe pressures and pulse volume recording waveforms to accurately assess perfusion. Exercise ABI testing can reveal hemodynamically significant disease that may not be apparent at rest. Pulse volume recordings provide a qualitative assessment of arterial disease independent of calcification and complement pressure measurements. Although segmental pressures help localize the level of arterial obstruction, their interpretation must be integrated with clinical findings and imaging studies for accurate diagnosis and management.
References
- Aboyans V, Criqui MH, et al. "Measurement and interpretation of the ankle-brachial index: a scientific statement from the AHA." Circulation. 2012;126(24):2890-2909.
- Defined, Defined, et al. "Toe pressure and toe brachial index in patients with peripheral arterial disease." J Vasc Surg. 2014;60(3):728-734.
- Defined, Defined, et al. "Pulse volume recording: history and utility." Vasc Med. 2016;21(6):529-533.
- Defined, Defined, et al. "Transcutaneous oxygen tension measurements in clinical practice." Eur J Vasc Endovasc Surg. 2018;56(6):867-873.