Validation of a Correction Factor for Measurement of an Accurate Ankle-Brachial Index in the Seated Position

Peripheral arterial disease (PAD) is a highly prevalent medical condition. Patients with PAD are usually diagnosed on the basis of a simple diagnostic procedure know as the ankle-brachial index (ABI). The ABI is the ratio of ankle pressure to arm pressure after measurement of blood pressures in the arms and legs using a hand-held Doppler device. In order for the ABI measurement to be accurate, the test is conducted with the patient in the supine position. This eliminates the influence of hydrostatic pressure on the ankle and toes which can lead to a falsely elevated reading. Unfortunately, many patients are unable to lie supine for ABI measurement, including: the wheel-chair bound, patients with degenerative disease of the spine or arthritis with chronic back pain, and patients with advanced cardiopulmonary disease and orthopnea.

Given the importance of detecting PAD across a broad spectrum of patients, there is a need to identify a mechanism for reliable measurement of the ABI for patients who cannot lie supine. The purpose of this study is to test a correction factor for the effects of hydrostatic pressure on the lower extremities to allow for accurate ABI calculation in the seated position.

100 Subjects with suspected arterial disease in the vascular lab will be enrolled. Arm, ankle, and toe pressure measurements will be made in the supine and seated positions. The seated ankle pressures will be corrected for hydrostatic pressure using a mechanical formula. The ABI and toe brachial index (TBI) will be calculated.

Inclusion criteria

• Patient at least 60 years of age
• Ambulatory outpatient
• Referred to non-invasive Vascular Laboratory for evaluation of suspected arterial disease.

Exclusion criteria

• Unable to give informed consent
• Unable to lie supine for at least 15 minutes