title: Measurement of regional elastic properties of the human aorta. A new application of transesophageal echocardiography with automated border detection and calibrated subclavian pulse tracings.
abstract: BACKGROUND
  Evaluation of regional aortic elastic properties in humans has been hampered by the need for invasive techniques to access instantaneous aortic pressure, wall thickness, and cross-sectional area or diameter. In this study, a new noninvasive method is presented for quantification of regional aortic elastic properties.
  
  
  RESULTS
  Twenty-five patients were studied during transesophageal echocardiographic procedures. Measurements of instantaneous aortic cross-sectional area were obtained with an automated border detection algorithm applied to short-axis transesophageal two-dimensional echocardiographic images of the proximal descending thoracic aorta. Instantaneous aortic wall thickness was derived from combined two-dimensional targeted M-mode end-diastolic wall thickness and instantaneous aortic area measurements. Instantaneous aortic pressures were estimated from calibrated subclavian pulse tracings recorded simultaneously. Data were digitized to generate aortic area-pressure loops. Regional aortic mechanical properties were quantified in terms of compliance per unit length (C is the slope of the area-pressure regression), aortic midwall radius (Rm), and incremental elastic modulus of the aortic wall (Einc). To assess the independent effect of age, Rm and Einc values were compared at a common level of aortic midwall stress (0.666 x 10(6) dynes/cm2). Mean values (+/- SD) for C, Rm, and Einc were 0.01 +/- 0.004 cm2/mm Hg, 1.14 +/- 0.17 cm, and 7.059 +/- 4.091 x 10(6) dynes/cm2, respectively. An inverse linear correlation was found between aortic compliance per unit length and age (r = -.68, P < .0007). Incremental elastic modulus was related to age (r = +.80, P < .00003) in a nonlinear fashion such that it increased sharply after the age of 60 years. Finally, midwall radius was less tightly correlated with age (r = +.45, P < .05). Values for C, Rm, and Einc as well as the age dependency of these properties are similar to those reported previously when invasive techniques were used.
  
  
  CONCLUSIONS
  This methodology constitutes a new tool to improve the clinical evaluation of regional aortic elastic properties in multiple disease states.
authors.affiliation: University of Chicago Hospitals, Department of Medicine, Ill.
authors.forename: R M
authors.initials: RM
authors.lastname: Lang
authors.forename: B P
authors.initials: BP
authors.lastname: Cholley
authors.forename: C
authors.initials: C
authors.lastname: Korcarz
authors.forename: R H
authors.initials: RH
authors.lastname: Marcus
authors.forename: S G
authors.initials: SG
authors.lastname: Shroff
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology; D000465:Algorithms; D001011:Aorta / Q000000981:diagnostic imaging* / Q000502:physiology*; D001794:Blood Pressure; D002138:Calibration; D003187:Compliance; D017548:Echocardiography, Transesophageal; D004548:Elasticity; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D011674:Pulse; D013348:Subclavian Artery / Q000000981:diagnostic imaging*