title: Effect of cardiac output on mitral valve area in patients with mitral stenosis: validation and pitfalls of the pressure half-time method.
abstract: OBJECTIVE
  The non-invasive evaluation of mitral valve area is often used in the assessment of patients with mitral stenosis. The pressure half-time method is commonly used to calculate valve area, but is inaccurate in many clinical scenarios. We sought to quantify the effects of changing cardiac output on the accuracy of mitral valve area determination.
  
  
  METHODS
  Thirteen patients with mitral stenosis underwent routine stress echocardiography with resting and peak exercise results compared. A previously described and clinically validated mathematical model of the cardiovascular system was used to validate the clinical results. Seven different loading conditions for each of four different stenotic valve areas were modeled.
  
  
  RESULTS
  In patients, with increasing cardiac output, pressure half-time decreased (-30.6+/-35.3 ms/l/min) and calculated valve area increased by 0.25+/-0.30 cm2/l/min. By continuity, it appeared that approximately half of this increase was due to actual valve orifice stretching, the remainder reflecting fundamental changes in the relationship between half-time and valve area. Mathematical modeling resulted in similar changes in pressure half-time and calculated valve area (0.06 to 0.12 cm2/l/min, p = 0.20 versus clinical results).
  
  
  CONCLUSIONS
  Changes in cardiac output result in predictable changes in pressure half-time, and should be considered when performing serial examinations in patients with mitral stenosis.
authors.affiliation: Cardiovascular Imaging Center in the Department of Cardiology, The Cleveland Clinic Foundation, Ohio 44195, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Firstenberg
authors.forename: D L
authors.initials: DL
authors.lastname: Prior
authors.forename: N L
authors.initials: NL
authors.lastname: Greenberg
authors.forename: S
authors.initials: S
authors.lastname: Wahi
authors.forename: A
authors.initials: A
authors.lastname: Pasquet
authors.forename: M J
authors.initials: MJ
authors.lastname: Garcia
authors.forename: J D
authors.initials: JD
authors.lastname: Thomas
mesh_terms: D000328:Adult; D000368:Aged; D001794:Blood Pressure / Q000502:physiology*; D002302:Cardiac Output / Q000502:physiology*; D003198:Computer Simulation; D003971:Diastole / Q000502:physiology; D004452:Echocardiography; D015150:Echocardiography, Doppler; D005080:Exercise Test; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D008943:Mitral Valve / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008946:Mitral Valve Stenosis / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008962:Models, Theoretical; D013318:Stroke Volume / Q000502:physiology; D013599:Systole / Q000502:physiology; D016277:Ventricular Function, Left / Q000502:physiology