Blood Pressure Evaluation

Blood pressure measurement in both arms and legs is indicated in every young person with hypertension of unknown cause. It is mandated in our patient by the findings of both hypertension in the right arm and decreased femoral arterial pulsations. The likely cause for these observations is coarctation of the aorta, a congenital abnormality that produces an obstruction in the aorta, usually just distal to the origin of the left subclavian artery.

Systolic blood pressure in both legs in our patient measured 90 mmHg by Doppler technique. Blood pressure in the left arm measured 170/100 mmHg.

Evaluation of coarctation of the aorta by determination of blood pressure in the arms and legs requires an experienced examiner and proper equipment. Blood pressure cuffs in several sizes must be available. Choose a cuff whose width is at least two thirds of the length of the limb portion - upper arm or calf - being examined. Cuff bladder should cover approximately three quarters of the limb circumference. An electronic flow detection system, such as a Doppler probe, facilitates measurement of systolic blood pressure in the leg. Manual methods controlled by the examiner are preferable to automatic equipment.

The patient should be supine and at rest. Measure blood pressure in the right arm in the usual manner. Using the electronic detection system, repeat measurement of systolic pressure in the right arm, as this method may result in a slightly higher value. Place a proper size cuff in the calf - usually a size larger than the arm cuff - and measure systolic pressure in both legs, either at the ankle (over the posterior tibial artery) or at the foot (over the dorsalis pedis artery). Finally, measure blood pressure in the left arm.

Interpretation of blood pressure in the legs requires awareness that measured systolic blood pressure increases as the measurement site moves further from the heart, particularly at smaller arteries such as those in the foot. This phenomenon is due to the artifact that distal pulse wave amplification. As the pulse wave generated by each systolic cardiac contraction moves distally within the arterial system, decreasing diameter of the arteries compresses the pulse wave, thereby, amplifying it, so that systolic pressure appears higher and diastolic pressure appears slightly lower.

For example, in a normal adult male whose pressure in the ascending aorta is 110/70 mmHg, blood pressure measured by cuff at the brachial artery might be 115/68 mmHg, and at the posterior tibial artery 120/65 mmHg. Magnitude of the artifact is directly related to the true pulse pressure. In an individual with wide aortic pulse pressure, as from aortic regurgitation, systolic blood pressure measured in the foot appears substantially higher than that measured in the arm. This artifact does not affect mean arterial pressure.