Accuracy of tha ankle brachial pressure measurement by physical therapists and physical therapy students

Cardiopulmonary Physical Therapy Journal, Sep 2000 by Augustine, Michael J, Eagleton, Kash J, Graham, David H, Story, Stephen B, Et al

Lower extremity claudication pain can be differentiated between neurogenic and vascular causes by comparing systolic blood pressures of the upper and lower extremities with the ankle brachial index (ABI) test. The ABI is a measure of identifying peripheral vascular disease (PVD) in the population. Limited research has assessed the reliability of various health care professionals in performing this measurement. Purpose: The purpose of this study was to determine the measurement accuracy of the ABI between an expert vascular technician, 3 practicing physical therapists, and 4 inexperienced physical therapy students. Methods: Forty healthy adults volunteered to participate. Following a rest period, each of the above testers measured systolic blood pressures on upper and lower extremities using calibrated mercury sphygmomanometer and a handheld pocket Doppler Ultrasound (8.0-9.2 MHz sound head). The highest upper extremity measurement was then used to calculate a right and left ABI for each subject. Data analysis consisted of a dependent t-test at the N=0.05 level and calculations using an intraclass correlation coefficient (2,1). Results: Data analysis revealed no significant differences between the means of inexperienced vs. expert and the experienced vs. expert. Results also revealed low ICC values (all below 0.40), thus a weak correlation within the groups of raters indicating poor reliability. The weak correlation values were attributed to the subjects being comprised of a small homogenous group that allowed for little variance between individual ABI values. The accuracy ( /- 0.15 as used clinically) of the inexperienced physical therapy students was 78.2/o on the right and 78.8% on the left as compared to the expert, while the practicing physical therapists were 86.7% on the right and 88.2% on the left compared to the expert. Conclusion: The results of this study showed poor reliability due to the small variation within the subjects but good accuracy for the inexperienced student therapists and practicing physical therapists. The results suggest that with one hour of training, inexperienced students, as well as practicing physical therapists, are capable of performing accurate ABI measurements.

Key Words: ankle brachial index, reliability; peripheral vascular disease

Each year within the United States, there are several million vascular related medical conditions affecting various age ranges of the population.1 Of these conditions, approximately 1.5 million are myocardial infarctions, 400,000 are strokes, 100,000 are amputations, and 600,000 are surgeries related to peripheral vascular disease.1 These and other vascular related pathologies lead to impairments that can lead to functional limitations and disabilities that interfere with an individual's independence, emotional stability, as well as daily living. Peripheral vascular arterial disease (PVD) occurs due to atherosclerosis, a disease in which artery walls become filled with fibrous fatty plaques that can eventually occlude the vessel lumen. Intermittent claudication, pain at rest, and ischemic ulceration or gangrene can result from an increase in the severity of the atherosclerotic process.2 Intermittent claudication is brought on by lower extremity activity and is described as a cramp-- like tightening in the calf, and occasionally in the foot, thigh, or buttock. It is often the result of increased activity by the lower extremity musculature when the oxygen demand cannot be met by the impaired arterial circulation. Claudication is often relieved by stopping the lower extremity activity, thus allowing adequate oxygen supply to the musculature. An estimation for the prevalence of claudication in the population showed 1.8% for those under age 60, 3.7% for those between ages 60 and 70, and 5.2% for those over age 70.2

The ankle brachial pressure index (ABI) is a noninvasive diagnostic test readily used in the clinic by an array of medical professionals to assess PVD. The ABI compares the systolic blood pressure in the ankle to the systolic blood pressure in the brachial artery while the subject is supine. The ABI is useful in determining the severity of peripheral arterial occlusive disease and the severity of lower limb arterial ischemia. Lower extremities are considerably more susceptible to atherosclerosis secondary to the likelihood that the abdominal aorta and iliac arteries will be the primary arteries affected by this disease process. These arteries become primarily involved due to the increased pressures found in these vessels. According to Kloth et al,3 the following ABI values correspond to the severity of atherosclerosis: 1.0 or above is normal, 0.9 or 0.8 correlates with symptoms of intermittent claudication, 0.7 to 0.5 is correlated with lower extremity pain at rest, 0.4 or less indicates tissue necrosis. This test also has been found to be useful in assessing the progression of the atherosclerotic disease process, and in determining the effectiveness of treatment intervention for this disease.4,5 Results of other research has shown that a cut off point for ABI ratios of 0.9 is approximately 95% sensitive in detecting positive disease using angiogram measurements. There is usually greater than 60% occlusion within the vessel lumen before clinical symptoms present themselves. Likewise, the ABI has been found to be nearly 100% specific in distinguishing healthy subjects from those with pathology.6 However, a study by McLafferty et al,7compared ABI verses imaging studies in determination of the progression of lower-extremity arterial occlusive disease. The study looked at 193 extremities in 114 patients with a prior lower extremity revascularization. The superficial femoral and popliteal arteries of the extremities were classified into less than 50% stenosis, 50% to 99% stenosis, or occluded. Their results showed that the ABI had a 41% sensitivity, 84% specificity, 59% positive predictive value, 71% negative predictive value, and 68% accuracy for determining the progression of lower extremity arterial occlusive disease, as defined by a decrease in the ABI of 0.15 or greater.7 Although the ABI is an accurate test for determining the occlusion of a vessel, the most accurate test for atherosclerosis remains imaging technology (duplex-ultrasonography).