Measurement of systolic blood pressure in both arms is indicated in this patient at high risk for atherosclerotic cardiovascular disease (ASCVD) who likely has upper extremity peripheral arterial disease (PAD) as the cause of his symptoms. His extremity symptoms are consistent with impaired arterial blood flow with exertion causing claudication in the left arm, and his associated neurologic symptoms suggest the subclavian steal syndrome. In subclavian steal, a stenosis in the left subclavian artery proximal to the take-off of the vertebral artery results in retrograde blood flow from the central nervous system to the arm, resulting in neurologic symptoms. A hallmark feature of upper extremity PAD on physical examination is a difference in systolic blood pressures between the arms, with a differential of greater than 15 mm Hg being typical. Differences in the distal pulses (upstroke and duration) may also be noted when comparing the upper extremities, and a bruit detected over the subclavian artery may be present. Noninvasive vascular testing with Doppler ultrasonography may be confirmatory. Upper extremity PAD, whether symptomatic or asymptomatic, is a marker for significant ASCVD and is associated with an increased risk for future cardiovascular disease. Therefore, primary treatment is aggressive therapy for ASCVD, including antiplatelet therapy. Treatment for clinically symptomatic upper extremity PAD, as in this patient, may include angioplasty with stenting or surgical bypass.

The ankle-brachial index is used to assess for lower extremity PAD and might be abnormal in this patient with likely ASCVD, although this test would not be helpful in evaluating his upper extremity symptoms.

Pulsus paradoxus is an exaggerated drop in systolic blood pressure (>10 mm Hg) during inspiration and may be present in patients with severe pericardial disease (tamponade and occasionally constrictive pericarditis), asthma, and COPD. This patient, however, does not have a history suggestive of these disorders, and evaluation for pulsus paradoxus would not be diagnostically helpful.

Thoracic outlet maneuvers are used to evaluate for neurovascular impingement at the point where the upper extremity neurovascular bundle exits the thoracic cavity. Although thoracic outlet syndrome could be responsible for his vascular symptoms, the obstruction occurring with this syndrome is distal to the vertebral artery and would not explain his accompanying neurologic symptoms.