Falsely raised ankle/brachial pressure index: a method to determine tibial artery compressibility

The ankle/brachial index (abPI) may be falsely raised, notably in diabetes, due to the relative incompressibility of the tibial artery. This paper presents a method of determining tibial artery compressibility by deriving abPIs with the patient supine and with legs raised in increments up to 0.55 m (ankle to heart). The effective negative hydrostatic pressure superimposed on the blood pressure at the ankle was converted to mmHg, normalised with respect to the brachial systolic pressure and then expressed as a hydrostatic pressure index (hPI). abPI was regressed on hPI and the gradient of the regression line calculated. If the arterial wall offers no significant resistance to compression the measured pressure will equal intraluminal pressure. In this case regression of the changing arterial pressure with the applied hydrostatic pressure would be expected to produce a gradient of -1. With resistance to compression the measured pressure is greater than the intraluminal pressure and a steeper gradient would be expected. The method was tested using age and sex matched groups, (A) controls (16 arteries), (B) patients with PVD and no diabetes (17 arteries), and (C) diabetics with PVD (34 arteries). There was no significant difference between the regression line gradients of groups A and B but both differ significantly from group C. The difference between the medians of groups B and C was 0.46, the 95% confidence interval for the difference being 0.66 to 0.02. Twelve of the diabetic arteries had a gradient steeper than -1.8 compared with one from group (B) and none from group (C).(ABSTRACT TRUNCATED AT 250 WORDS)