Peripheral Arterial Disease (PAD): Evaluating Blood Flow with Doppler Ultrasound

Dr. Segnini
Dec 29, 2025
3 min read

When the Legs Don't Receive Enough Blood arterial Doppler ultrasound

Peripheral Arterial Disease (PAD) is a chronic condition in which the arteries that carry blood to the extremities, primarily the legs, narrow or become blocked due to atherosclerosis (plaque buildup). This reduces blood flow, causing symptoms such as calf pain when walking (intermittent claudication) , coldness, numbness, slow-healing wounds, and, in severe cases, a risk of gangrene. Arterial Doppler ultrasound is a non-invasive, dynamic, and essential diagnostic tool for detecting, locating, and quantifying the severity of PAD.

Why is Doppler Ultrasound Essential in PAD?

Unlike conventional ultrasound, which shows the structure, Doppler analyzes movement, in this case, of the blood. For PAD, it is the first-line technique because:

Evaluates Anatomy and Function: Combines imaging (B-mode ultrasound) to view arteries, with flow assessment ( Doppler ).
It is non-invasive and does not use radiation: Far superior to conventional angiography for initial diagnosis.
It is dynamic and functional: It allows measuring velocities before and after a stenosis (narrowing), evaluating the flow response to compression, and studying the effect of postures.
Guide the Treatment: It is crucial for planning interventions (angioplasty, bypass surgery) and for post-treatment follow-up.

Key Ultrasound Findings: The Signature of a Diseased Artery

The examination is performed sequentially, from the abdominal aorta to the arteries in the feet, comparing both sides.

1. In B-mode (Structural Ultrasound):

Atheroma or Plaque: This appears as a lesion in the arterial wall that protrudes into the lumen (the inside of the vessel). It can be:
- Hypoechoic (soft): Lipid plaque, more dangerous.
- Hyperechoic (hard): Calcified plaque, with acoustic shadowing.
Intima-Media Thickening (IMT): An early marker of atherosclerosis, measured in the common carotid artery, but reflecting systemic risk.
Arterial Remodeling: Changes in the diameter of the artery.

2. In Spectral Doppler (The Heart of Diagnosis):

Doppler generates a velocity-time graph that is the fingerprint of the flow. Changes in its shape indicate the severity of the obstruction.

Normal Flow Pattern in Leg Arteries: It is triphasic or biphasic , with a rapid forward component in systole (high systolic peak), a brief reverse flow at the beginning of diastole (due to arterial elasticity), and sometimes a small forward flow in late diastole.
Abnormal Flow Pattern (Indicative of PAD):
1. Focal Increase in Systolic Velocity: The most direct sign. At the point of a stenosis, blood must accelerate to pass through. An increase in Peak Systolic Velocity (PSV) > 2 times (ratio >2) compared to the immediately preceding healthy segment is considered significant.
2. Color Doppler Aliasing: In the narrow area, the color map "breaks up" or shows a chaotic mixture, indicating high-speed turbulent flow .
3. Change in Spectrum Morphology (Distal to Stenosis):
  - Moderate Phase: The flow becomes monophasic (loses the reverse component) and "late pulsatile" ( tardus-parvus ) , meaning it takes longer to rise and has a low amplitude. This indicates a significant obstruction further upstream.
  - Severe Phase/Occlusion: The spectrum flattens even further, almost like venous flow, a sign of critical obstruction.

3. Calculated Hemodynamic Indices:

Ankle-Brachial Index (ABI) Doppler : This is a fundamental test . Systolic blood pressure is measured at the ankle (using Doppler ) and in the arm. An ABI < 0.90 is diagnostic of peripheral arterial disease (PAD). Ultrasound allows localization of the obstruction causing a low ABI.
Resistance Index (RI): Measures resistance to distal flow. It increases proximal to an obstruction and decreases distally.

Exploration and Classification Protocol

Anatomical Examination (B-Mode): The arteries are identified and measured (common femoral, superficial femoral, popliteal, tibial).
Segmental Spectral Doppler : Flow samples are taken in each key arterial segment.
Calculation of Velocity Ratios: The VSP in suspicious areas are compared to healthy areas.
Severity Classification: The findings are integrated into a classification (e.g., based on velocity ratios or ABI) that defines the degree of stenosis:
- Normal / < 50%
- Stenosis 50-69%
- Stenosis 70-99%
- Total Occlusion

Differential Diagnosis and Limitations

Doppler ultrasound also helps differentiate PAD from other causes of leg pain, such as lumbar spinal stenosis, deep vein thrombosis, or orthopedic problems. Its limitations include difficulty in obese patients or those with heavily calcified vessels (which block the ultrasound), and the fact that it requires a skilled operator and can be a lengthy examination.

Conclusion: The Blood Flow Map

Doppler ultrasound for PAD is much more than an imaging test. It is a comprehensive physiological study that creates a detailed map of the vascular health of the extremities. It provides quantitative and qualitative information that allows for:

accurately diagnose and grade PAD.
To pinpoint the exact location of the obstructive lesions.
Establish a personalized treatment plan (medical, endovascular , or surgical).
disease

progression or the success of an intervention is an indispensable tool in angiology, vascular surgery, and internal medicine consultations, improving patients' prognosis and quality of life.