title: The ankle brachial index independently predicts walking velocity and walking endurance in peripheral arterial disease.
abstract: OBJECTIVE
  Maintaining function among older men and women is an important public health goal as the population lives longer with chronic disease. We report the relationships between lower extremity peripheral arterial disease (PAD), PAD severity, and PAD-related symptoms with walking velocity and endurance among men and women aged 55 and older.
  
  
  METHODS
  A cross-sectional design.
  
  
  METHODS
  An academic medical center.
  
  
  METHODS
  Participants with PAD were men and women aged 55 and older identified from a blood flow laboratory or a general medicine practice (n = 158). Randomly selected controls without PAD were identified from the general medicine practice (n = 70).
  
  
  METHODS
  PAD was diagnosed and quantified using the ankle brachial index (ABI). Subjects were categorized according to whether they had severe PAD (ABI <0.40), mild to moderate PAD (ABI 0.40 to <0.90), or no PAD (ABI 0.90 to <1.50). Walking endurance was assessed with the 6-minute walk. Usual walking velocity and maximal walking velocity were assessed with "usual" and "maximal" paced 4-meter walks, respectively.
  
  
  RESULTS
  Average distances achieved in the 6-minute walk were 1569+/-390 feet for subjects with ABI 0.90-1.50, 1192+/-368 feet for subjects with ABI 0.40 to <0.90, and 942+/-334 feet for subjects with ABI < 0.40 (trend P value < .001). Walking velocities for both the usual and maximal paced 4-meter walks were slowest among subjects with ABI < 0.40 and fastest among subjects with ABI 0.90 to <1.50. Subjects with PAD who had pain at rest had slower walking velocity and poorer walking endurance than other subjects with PAD. In multiple linear regression analyses that included subjects with PAD only, ABI level was an independent predictor of 6-minute walk performance (regression coefficient = 159 ft/0.40 ABI units, P = .011), usual paced 4-meter walk (regression coefficient = .095 meters/sec/0.40 ABI units, P = .031), and maximal paced 4-meter walk (regression coefficient = .120 meters/sec/0.40 ABI units, P = .050) adjusting for age, sex, race, leg symptoms, and comorbid diseases known to affect functioning. Pain at rest was associated independently with the maximally paced 4-meter walk (-0.201 meters/sec, P = .024), but not with the other walks.
  
  
  CONCLUSIONS
  ABI level has a measurable and independent association with walking endurance and both usual and maximal walking velocity. These data suggest that PAD may impair lower extremity function by diminishing function of both Type I ("slow twitch") and Type II ("fast twitch") muscle fibers. Because walking velocity has important prognostic implications for functioning, these data also suggest that ABI may be used to identify patients at increased risk of mobility loss.
authors.affiliation: Department of Medicine, Northwestern University Medical School, Chicago, Illinois 60611, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: McDermott
authors.forename: K
authors.initials: K
authors.lastname: Liu
authors.forename: J M
authors.initials: JM
authors.lastname: Guralnik
authors.forename: S
authors.initials: S
authors.lastname: Mehta
authors.forename: M H
authors.initials: MH
authors.lastname: Criqui
authors.forename: G J
authors.initials: GJ
authors.lastname: Martin
authors.forename: P
authors.initials: P
authors.lastname: Greenland
mesh_terms: D000368:Aged; D000842:Ankle / Q000098:blood supply*; D001783:Blood Flow Velocity; D001916:Brachial Artery / Q000000981:diagnostic imaging*; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D005080:Exercise Test; D005260:Female; D006801:Humans; D007383:Intermittent Claudication / Q000209:etiology; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D016491:Peripheral Vascular Diseases / Q000175:diagnosis* / Q000000981:diagnostic imaging* / Q000503:physiopathology; D010807:Physical Endurance; D011237:Predictive Value of Tests; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D014463:Ultrasonography; D016138:Walking