Blood pressure reflects the force of blood pushing against the walls of your arteries as your heart pumps. It is expressed as two numbers: systolic pressure, the top number, measures the force when your heart beats, and diastolic pressure, the bottom number, indicates the pressure when your heart rests between beats. These measurements offer insights into blood circulation and cardiovascular well-being.
Reasons for Taking Leg Blood Pressure
Sometimes, obtaining an accurate blood pressure measurement from the arm is not feasible or advisable. This can occur if an individual has an arm injury, intravenous lines, or medical devices like dialysis shunts. People who have undergone a mastectomy might also be at risk for lymphedema, making arm measurements in the affected limb ill-advised. In these situations, leg blood pressure provides an alternative.
Healthcare providers also intentionally measure blood pressure in the lower extremities as a proactive diagnostic step. This approach allows for a direct assessment of blood flow to the legs and feet. This evaluation can reveal issues in the circulatory system below the waist that might not be apparent from arm readings.
The Leg Blood Pressure Procedure
The procedure for taking blood pressure on the leg begins with the individual lying flat on their back for several minutes. This resting period allows the body’s blood pressure to stabilize before the measurement is taken. A blood pressure cuff, larger than an arm cuff, is then placed around the thigh or just above the ankle.
A healthcare professional uses a Doppler ultrasound to locate and amplify the pulse sound in the artery. The cuff is inflated until blood flow is temporarily stopped, then slowly deflated. As the cuff deflates, the professional listens for the distinct sounds of blood flow returning, which indicate the systolic and diastolic pressures.
Interpreting Leg Blood Pressure Readings
When measured at the ankle, systolic blood pressure is slightly higher than in the arm. This difference is a typical physiological variation.
To standardize the comparison between arm and leg readings, healthcare professionals calculate the Ankle-Brachial Index (ABI). The ABI is a ratio determined by dividing the systolic blood pressure measured at the ankle by the higher systolic blood pressure measured in either arm.
A normal ABI value ranges from 1.0 to 1.4. This range indicates healthy and unobstructed blood flow to the lower limbs.
Conditions Indicated by Leg Blood Pressure Differences
An abnormal Ankle-Brachial Index signals underlying vascular issues, with Peripheral Artery Disease (PAD) being a common concern. PAD involves the narrowing of arteries, which significantly reduces blood flow to the limbs, most commonly the legs. This condition can lead to pain, numbness, or other complications in the affected extremities.
A low ABI value, specifically below 0.9, indicates the presence of PAD. Values between 0.90 and 0.70 indicate mild PAD, while readings from 0.70 to 0.40 point to moderate disease severity. An ABI below 0.40 suggests severe PAD, indicating significantly restricted blood flow that may require immediate attention.
A high ABI, exceeding 1.4, can also be problematic, despite seeming counterintuitive. This elevated reading may suggest that the arteries in the legs are rigid or calcified, preventing accurate compression by the blood pressure cuff. This arterial stiffness is more commonly observed in older patients or individuals with long-standing diabetes, and it can also indicate increased cardiovascular risk.