Validation of a method for determination of the ankle-brachial index in the seated position

Objective: To validate a method for determination of the ankle-brachial index (ABI) in the seated position.

Background: Peripheral arterial disease (PAD) is a prevalent disorder that is associated with quality of life impairment and increased risk of a major cardiovascular event. The ABI is the initial test for screening and diagnosis of PAD. To prevent error due hydrostatic pressure, accurate measurement of the ABI requires supine patient positioning. Access to ABI measurement is limited for patients who are immobilized or unable to lie flat.

Methods: Patients presenting to a vascular laboratory for suspected arterial disease were enrolled. Arm and ankle blood pressures were measured in the supine and seated positions. Seated ankle pressures were corrected by the following physiology-based formula: Corrected ankle pressure = Measured ankle pressure - D*(.078), where D = the vertical distance between the arm and ankle cuffs (mm). This formula equates to a correction factor of 78 mm Hg per meter distance between the arm and ankle cuffs. Corrected ankle pressure measurements were used for seated ABI calculation.

Results: Complete data were available for 100 patients. Mean ABI was 0.97, and 31% of patients had an ABI < or =0.9. There was excellent correlation between supine and corrected seated ankle pressure measurements (r = 0.884-0.936, P < .001). The difference between measurements was negligible (<5 mm Hg). Similarly, there was excellent correlation between supine and seated ABI measures (r = 0.936, P < .001). There was no significant difference between the supine and seated ABI measures.

Conclusion: We have developed and validated a method for determination of the ABI in the seated position which can be used to broaden availability of PAD testing. This method could also be incorporated into new technologies for ABI determination in the seated position.