title: Novel Compliance Index derived from digital volume pulse associated with risk factors and exercise capacity in patients undergoing treadmill exercise tests.
abstract: OBJECTIVE
  Although large-artery stiffness is a well-known independent factor for cardiovascular risk, the importance of small-artery stiffness is not well elucidated. We have developed a novel Compliance Index as a marker of small-artery stiffness. This study aimed to determine the clinical significance of this index by evaluating 140 patients without left ventricular dysfunction referred for treadmill exercise tests.
  
  
  METHODS
  Immediately after a 10-min rest period before the test, the pulse wave velocity and Compliance Index were measured. The patients were then given a symptom-limited treadmill test using Bruce's protocol. Our dual-channel photoplethysmography system automatically measured the area under the curve of each digital volume pulse, which represented the volume change in the finger with each heart beat. The Compliance Index was calculated by dividing the area under the curve of finger digital volume pulse by pulse pressure.
  
  
  RESULTS
  The Compliance Index was significantly correlated with pulse wave velocity (r=-0.254, P=0.002), systolic blood pressure (r=-0.606, P<0.001), and diastolic blood pressure (r=-0.323, P<0.001). It was lower in males (3.3+/-1.4 versus 4.8+/-2.4 units, P<0.001), in hypertensive patients (3.2+/-1.5 versus 4.4+/-2.2 units, P<0.001), and in smokers (3.0+/-1.5 versus 4.1+/-2.1 units, P=0.006).
  
  
  CONCLUSIONS
  The Compliance Index was lower in patients with risk factors and was associated with poor exercise capacity. This index may be clinically useful for evaluating arterial stiffness.
authors.affiliation: Division of Cardiology, Department of Internal Medicine, National Cheng Kung University Hospital, Tainan, Taiwan.
authors.forename: Ju-Yi
authors.initials: JY
authors.lastname: Chen
authors.forename: Wei-Chuan
authors.initials: WC
authors.lastname: Tsai
authors.forename: Ming-Sheng
authors.initials: MS
authors.lastname: Wu
authors.forename: Chih-Hsin
authors.initials: CH
authors.lastname: Hsu
authors.forename: Chih-Chan
authors.initials: CC
authors.lastname: Lin
authors.forename: Hsien-Tsai
authors.initials: HT
authors.lastname: Wu
authors.forename: Li-Jen
authors.initials: LJ
authors.lastname: Lin
authors.forename: Jyh-Hong
authors.initials: JH
authors.lastname: Chen
mesh_terms: D000368:Aged; D003187:Compliance; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010991:Plethysmography / Q000379:methods