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Outcomes measures in cardiopulmonary physical therapy: focus on the Ankle Brachial Index (ABI).

INTRODUCTION

Peripheral vascular disease causes a progressive destruction of the wall of the arteries and veins in the vascular system. When this destruction targets the arterial system, decreased oxygenated blood flow to the extremities results. (1,2) A decline in oxygenated blood to the tissues can result in complications such as wound formation and occurs because the metabolic demands of skin and muscles cannot be met. In addition, this ischemia, when manifested in the lower extremities, is often accompanied by lower extremity claudication, which can significantly impair functional mobility. (3-5) If deprivation of oxygen to the skin and muscle is extreme, the tissue may become necrotic. At this point, even restoration of blood flow to the extremity may not result in restoring the viability of the tissue and often results in amputation of the involved extremity. (1)

The complications of peripheral vascular disease, such as critical leg ischemia, are preventable when appropriate screening tools and prophylactic treatment are provided for patients at risk. Those at high risk for complications from peripheral vascular disease often present with co-morbid diagnoses that impact the cardiovascular system, such as diabetes, atherosclerosis, arteriosclerosis or thrombophlebitis. A substantial number of patients who present for physical therapy intervention may exhibit signs and symptoms of peripheral vascular disease or are at high risk for the development of the complications associated with peripheral vascular disease. Research also indicates, though, that patients with peripheral vascular disease may be asymptomatic, but still show signs of lower extremity ischemia with appropriate vascular screening. (6) Peripheral vascular disease affects nearly 30% of the elderly population above the age of 65 and accounts for 95% of arterial occlusive diseases. (2) In individuals with critical limb ischemia, 30% will undergo amputations with a mortality rate of 20% within 6 months. (7) Other than exhibiting an increased risk of lower extremity amputation, individuals who present with peripheral vascular disease have poorer functional status with regards to mobility and ambulation secondary to decreased oxygenated blood flow to the lower extremities. (3)

Although many different options exist for screening and preventing complications, especially among the elderly, many cases of peripheral vascular disease remain unrecognized, untreated, or mismanaged by clinicians. For example, several studies have reported that asymptomatic peripheral vascular disease often goes undetected and untreated due to a lack of screening by health care practitioners. 8,9 In addition, a lack of appropriate screening can contribute to an increased prevalence in complications such as wounds, claudication, and amputation. Physical therapists should familiarize themselves with the screening tests available to assist in the prevention, intervention, and appropriate referral of those individuals who may be at the highest level of risk for developing the above mentioned complications.

There are several noninvasive measures for determining the vascular status of an individual. These noninvasive measures include the Ankle-Brachial Index (ABI), Edinburgh Claudication Questionnaire, the World Health Organization/Rose questionnaire on intermittent claudication, segmental limb pressures, or pulse volume recordings. 4,10 Each of these measures is inexpensive and easily performed by the primary care practitioner, which includes physicians, nurses, or physical and occupational therapists. The ABI is a noninvasive test that can detect not only symptomatic and asymptomatic peripheral vascular disease, but it is a clear predictor of function and cardiovascular status. (4) The use and characteristics of the ABI will be the focus of discussion for this article.

ADMINISTRATION

The ABI is an inexpensive and relatively easy test to administer in any physical therapy setting. The ABI measurement involves comparing systolic blood pressures of the upper extremity brachial artery with systolic blood pressures of the lower extremity, including the anterior or posterior tibial artery or the dorsal pedis artery. The patient should be placed in the supine position for the assessment of the systolic blood pressures. The ABI is a ratio calculated by comparing the highest systolic pressure found in the lower extremity to the highest systolic pressure found in the brachial artery of either upper extremity. To ensure accuracy of the measurement, many practitioners will take the mean of 3 systolic measures in the upper extremity and the mean of 3 systolic measurements taken in the lower extremity. (14)

Although a standard stethoscope can be used to assess pressures in the arteries of the upper and lower extremities, a Doppler ultrasound device is recommended for accuracy in blood pressure measurements. The standard Doppler ultrasound unit used for measurement of the ABI is a hand held unit that can vary in frequency from 6-9 MHz in strength and still obtain accurate systolic readings. A pulse should be located at the brachial artery in the upper extremity and the anterior/posterior tibial or dorsal pedis artery of the lower extremity. A standard blood pressure cuff or sphygmomanometer should be placed as high as possible on the limb being investigated and then should be inflated to a level 20-30 mmHg greater than that pressure that allows a pulse to be heard. The cuff should be deflated at a rate of 2-4 mm Hg/second until the pulse sound returns. The first pulse sound, or the systolic pressure, should be recorded for use in calculation of the ABI.

Once systolic pressures are recorded for both of the upper extremities and lower extremities, the higher of the mean systolic pressure from each leg (if multiple arteries are assessed) should be compared to the higher mean systolic pressure from the brachial artery (regardless of side used for assessment). For example, if a mean systolic brachial pressure of 130 mm Hg was found in the right upper extremity and a mean systolic brachial pressure of 125 was found in the left upper extremity, the right sided brachial pressure should be used for calculation of the ABI. In addition, if a mean systolic pressure of 125 mm Hg was found in the right dorsal pedis artery, but a mean systolic pressure of 130 mm Hg was found in the right posterior tibial artery, the posterior tibial mean systolic pressure should be used when using the following ratio to calculate ABI. (15)

The ABI = mean of 3 systolic pressures at the lower extremity/ mean of 3 systolic pressures taken at the brachial artery

INTERPRETATION

There are slight variations in the literature regarding appropriate guidelines to determine severity of illness as indicated by the ABI measurement. Although many published guidelines in research studies use an ABI < 0.90 as an indication of lower extremity ischemia, according to published guidelines of the Standards Division of the Society of Interventional Radiology, the following measurements are the gold standard for interpretation of the ABI. A measurement of ABI > 1.10 is considered normal; abnormal values are considered an ABI measurement of < 1.0. The majority of patients with claudication have ABIs ranging from 0.30 to 0.90. Rest pain or severe occlusive disease typically occurs with an ABI lower than 0.50. Indices lower than 0.20 are associated with severely ischemic or gangrenous extremities. Because individuals with critical limb ischemia can present without the above mentioned symptoms of claudication or rest pain, it is important to be aware of the ranges of ABI that indicate limb ischemia, especially at the critical values of < 0.50 that indicate ischemia and critical limb ischemia so that correct referral and intervention can be made (16) (Table 1).

RELIABILITY

Although the inter- and intra-rater reliability of the ABI are influenced by training, experience and practice, several studies support the fact that the variability of the test in trained observers ranges from approximately 7% to 15%. (6,18,19) A study by Ray et al (20) also supports the reproducibility and reliability of the ankle brachial index, but also stresses the need for repeat measurements and training. Participants in both the Atherosclerosis Risk in Communities study and the NHLBI Family Heart Study had repeat ABIs taken within 1 year, using the methodology described in this paper. According to these studies, the estimated reliability coefficient for the ankle systolic blood pressure was 0.68 and 0.74 for the brachial systolic blood pressure. (21,22) The reliability for the ABI based on single ankle and arm systolic blood pressures was 0.61 and the reliability of the ABI computed as the ratio of the average of 2 ankle systolic blood pressures to 2 arm systolic blood pressures was 0.70 as estimated from simulated data. (21,22)

Validity

The ABI, is predictive of both functional status and cardiovascular mortality. (4,8,10-13) For example, Leng et al (13) determined that individuals with an ABI of < 0.90 have an increased risk of nonfatal myocardial infarction, stroke, and all-cause cardiovascular mortality after adjusting for pertinent co-morbidities, such as age, sex, coronary heart disease, and diabetes, while Lee et al (11) determined that by using the ABI, prediction of fatal myocardial infarction is more accurate. Furthermore, McDermott (4) found a strong correlation between the ABI and lower extremity function and physical activity. Patients in this study were assessed with the 6 minute walk test, the 4 meter walking velocity test, the summary performance score, Caltrac accelerometry, and repeated chair rises. According to their findings, individuals with lower ABI measurements had to stop more frequently during the 6 minute walk test, experienced lower accelerometer measured activity over 7 days, poorer standing balance, slower walking pace velocity, and lower summary performance score.

The sensitivity and specificity of the ABI remains very high as determined across multiple studies. A review paper by Ouriel et al,17 determined that the sensitivity of the ABI measurement can be as high as 90%, while the specificity has been reported in the range of 98%. In addition, a meta-analysis of data from 28 studies examined 679 individuals across 7 population based cohort studies and evaluated the sensitivity and specificity of the ABI to predict cardiovascular events. (12) The results indicated high specificity (92.2%-97.7%) for predicting stroke incidence, variable sensitivity of 31.2%-85.0% and a specificity of 30.1-88.9% for all cause mortality across various studies evaluated in the meta-analysis. And finally, in another study evaluating the relationship between veno-arteriolar response and ABI, the test was 100% sensitive and 80% specific for detecting patients with the presence of peripheral vascular disease as correlated with the measurement of ABI < 0.90. (13)

Ankle brachial index is predictive of both functional status and cardiovascular mortality. (4,8,10-14) For example, Leng et al14 found that individuals with an ABI of < 0.90 experienced an increased risk of nonfatal myocardial infarction, stroke, and all-cause cardiovascular mortality after adjusting for pertinent co-morbidities, such as age, sex, coronary heart disease, and diabetes. Lee et al (11) determined that by using ABI, fatal myocardial infarction could more accurately be identified. Furthermore, McDermott et al (23) found a strong correlation between ABI and lower extremity function and physical activity. Patients in this study were assessed with the 6 minute walk test, the 4 meter walking velocity test, the summary performance score, Caltrac accelerometry, and repeated chair rises. According to their findings, individuals with lower ABI measurements had to stop more frequently during the 6 minute walk test, experienced lower accelerometer measured activity over 7 days, poorer standing balance, slower walking pace velocity, and lower summary performance score.

CONCLUSION

Vascular damage, which can lead to eventual amputation, as a result of peripheral vascular disease is both preventable and treatable. Patient education, as part of the Legs for Life National Screening and Awareness Program for Peripheral Vascular Disease, was found to be highly successful in increasing individual's knowledge of prevention and awareness. (22) Addressing risk factors, such as smoking and diet, also has a direct impact on vascular health. (23) Pharmacologic treatments, such as statins, have been found to reverse lower extremity pain and improve functioning in patients with peripheral vascular disease. (23) Daily exercise and interventions with a physical therapist can improve ankle brachial measurements of lower extremity circulation. (24,25) And invasive interventions, such as angioplasty, stenting, and bypass are successful in limb preservation in the individual with peripheral vascular disease. (25,26)

Physical therapists can play a vital role in assessment, screening, and prevention of the complications of peripheral vascular disease with specific training and use of the ABI. In addition, due to the sensitivity and specificity of the tool, therapists can be confident in the values recorded as a result of testing patients during their cardiopulmonary assessments. As a primary care practitioner, therapists should use the ABI on a regular basis to address the status of lower extremity ischemia of any individual at risk for possible complications of peripheral vascular disease, thus contributing to the prescription of appropriate therapeutic intervention and the limitation of progression of disease.

REFERENCES

(1.) Fowkes FG, Housley E, Cawood EH, Macintyre CC, Ruckley CV, Prescott RJ. Edinburgh Artery Study: prevalence of asymptomatic and symptomatic peripheral arterial disease in the general population. Int J Epidemiol. 1991;20:384-392.

(2.) Goodman CC, Fuller KS, Boissonnault WG. Pathology: Implications for the Physical Therapist. 2nd ed. Philadelphia, Pa: Saunders; 2003.

(3.) Dolan N, Liu K, Criqui M, et al. Peripheral artery disease, diabetes and reduced lower extremity functioning. Diabetes Care. 2002;25:113-120.

(4.) McDermott MM, Greenland P, Liu K, et al. The ankle brachial index is associated with leg function and physical activity: the walking and leg circulation study. Ann Intern Med. 2002;136:873-883.

(5.) McDermott MM, Guralnik JM, Greenland P, et al. Statin use and leg functioning in patients with and without lower-extremity peripheral arterial disease. Circulation. 2006;107:757-761.

(6.) Matzke S, Lepantalo M. Claudication does not always precede critical leg ischemia. Vasc Med. 2001;6:77-80.

(7.) Mitka M. Diabetes group warns vascular complication is underdiagnosed and undertreated. JAMA. 2004;291:809-810.

(8.) Khan NA, Rahim SA, Anand SS, Simel DL, Panju A. Does the clinical examination predict lower extremity peripheral arterial disease? JAMA. 2006;295:537-546.

(9.) Lange S, Diehm C, Darius H, et al. High prevalence of peripheral arterial disease and low treatment rates in elderly primary care patients with diabetes. Exp Clin Endocrinol Diabetes. 2004;112:566-573.

(10.) Brevetti G, Silvestro A, Schiano V, Chiariello M. Endothelial dysfunction and cardiovascular risk prediction in peripheral arterial disease: additive value of flowmediated dilation to ankle-brachial pressure index. Circulation. 2003;108:2093-2098.

(11.) Lee AJ, Price JF, Russell MJ, Smith FB, van Wijk MC, Fowkes FG. Improved prediction of fatal myocardial infarction using the ankle brachial index in addition to conventional risk factors: the Edinburgh Artery Study. Circulation. 2004;110:3075-3080.

(12.) Doobay AV, Anand SS. Sensitivity and specificity of the ankle-brachial index to predict future cardiovascular outcomes: a systematic review. Arterioscler Thromb Vasc Biol. 2005;25:1463-1469.

(13.) Otah KE, Otah E, Clark LT, Salifu M. Relationship of lower extremity skin blood flow to the ankle brachial index in patients with peripheral arterial disease and normal volunteers. Int J Cardiol.2005;103:41-46.

(14.) Leng GC, Fowkes FGR, Lee AJ, Dunbar J, Housley E, Ruckley CV. Use of the ankle brachial pressure index to predict cardiovascular events and death: a cohort study. Br Med J. 1996;313:1440-1444.

(15.) Raines JK, Farrar J, Noicely K, et al. Ankle/brachial index in the primary care setting. Vasc Endovascular Surg. 2004;38:131-136.

(16.) Rice KL. How to measure ankle/brachial index. Nursing. 2005;35:56-57.

(17.) Sacks D, Bakal CW, Beatty PT, et al. Position statement on the use of the ankle brachial index in the evaluation of patients with peripheral vascular disease. A consensus statement developed by the Standards Division of the Society of Interventional Radiology. J Vasc Interv Radiol. 2003;14(9 Pt 2):S389.

(18.) Ouriel K, McDonnell AE, Metz CE, Zarins CK. Critical evaluation of stress testing in the diagnosis of peripheral vascular disease. Surgery. 1982;91:686-693.

(19.) Kaiser V, Kester AD, Stofers HE, et al. The influence of experience on the reproducibility of the ankle-brachial systolic pressure ratio in peripheral arterial occlusive disease. Eur J Vasc Endovasc Surg. 1999;18:25-29.

(20.) Ray SA, Srodon PD, Taylor RS, et al. Reliability of ankle: brachial pressure index measurement by junior doctors. Br J Surg. 1994;81:188-190.

(21.) Weatherley BD, Chambless LE, Heiss G, et al. The reliability of the ankle-brachial in index in the Atherosclerosis Risk in Communities (ARIC) study and the NHLBI family heart study (FHS). BMC Cardiovasc Disord. 2006;6:7.

(22.) Johnsen MC, Landow WJ, Sonnefeld J, McClenny TE, Beatty PT, Raabe RD. Evaluation of Legs For Life National Screening and Awareness Program for Peripheral Vascular Disease: results of a follow-up survey of screening participants. J Vasc Interv Radiol. 2002;13:25-35.

(23.) McDermott MM, Guralnik JM, Greenland P, et al. Statin use and leg functioning in patients with and without lower-extremity peripheral arterial disease. Circulation. 2003;107:757-761.

(24.) Perkins JM, Collin J, Creasy TS, Fletcher EW, Morris PJ. Exercise training versus angioplasty for stable claudication. Long and medium term results of a prospective, randomised trial. Eur J Vasc Endovasc Surg. 1996;11:409-413.

(25.) Burns P, Gough S, Bradbury AW. Management of peripheral arterial disease in primary care. Br Med J. 2003;326:584-588.

(26.) Bradbury AW. Bypass versus angioplasty in severe ischaemia of the leg (BASIL): multicentre, randomised controlled trial. Lancet. 2005;366:1925-1934.

Kristin M. Lefebvre, MPT Institute for Physical Therapy Education, Widener University, Chester, PA

Address correspondence to: Kristin Lefebvre, Institute for Physical Therapy Education, One University Place, 111 Cottee Hall, Chester, PA 19013 (kmlefebvre@widener.edu).
Table 1. Interpretation of Ankle Brachial Index Measurements

ABI Measurement Possible Symptoms Clinical Presentation

> 1.10 None Normal Limb
0.50 - 1.00 Claudication Pain in calf with
 ambulation
0.20 - .50 Critical Limb Ischemia Atrophic changes/rest
 pain/wounds
< .20 Severe Ischemia Gangrene/severe necrosis
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Title Annotation:Research Corner
Author:Lefebvre, Kristin M.
Publication:Cardiopulmonary Physical Therapy Journal
Geographic Code:1USA
Date:Dec 1, 2006
Words:2947
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