title: Modified gorlin equation for the diagnosis of mixed aortic valve pathology.
abstract: OBJECTIVE
  The accuracy of the Gorlin equation when applied to mixed valve pathology has not been investigated. An in-vitro study was performed to determine how a range of valve regurgitations and stenoses affects the Gorlin aortic valve area.
  
  
  METHODS
  Various combinations of stenosis and regurgitation were simulated by placement of constricting orifices and minimal blockage reflux tubes within a 29-mm prosthetic pericardial valve. The orifice areas ranged from 0.7 cm2 to 1.75 cm2, and regurgitant fraction (RF) ranged from 0 to 0.35. Twenty-eight tests were performed at 70 beats/min, cardiac output of 5 l/min and systole 33-36% of the cycle. The mean pressure drops across the valve were adjusted to a value appropriate to blood density. Peripheral resistance was set to give a mean value of 1,537 dyn.s.cm(-5).
  
  
  RESULTS
  The Gorlin area varied up to 0.55 cm2 from the geometric orifice area over the range of regurgitant fractions and stenoses. To improve the Gorlin equation, an amended mean volumetric forward flow rate was obtained by multiplying the cardiac output in the equation by the factor (1 - RF)(-1), to reconcile the equation for valvular regurgitation. The area predicted by the modified equation differed by <0.15 cm2 from the non-regurgitant valve geometric orifice area over the range of regurgitation and stenoses simulated.
  
  
  CONCLUSIONS
  The study supports the validity of the Gorlin equation predicting pure aortic valve stenosis (areas <1.3 cm2); however, the equation overestimates the severity of stenoses when regurgitation is present. A modified equation is proposed, which includes regurgitant fraction. The new equation improves the calculation of valve geometric area in the presence of regurgitation and may be useful in cardiac catheterization laboratories where mixed aortic valve pathology is being evaluated.
authors.affiliation: Vivitro Systems Inc, Victoria, BC, Canada.
authors.forename: Lawrence N
authors.initials: LN
authors.lastname: Scotten
authors.forename: David K
authors.initials: DK
authors.lastname: Walker
authors.forename: James W
authors.initials: JW
authors.lastname: Dutton
mesh_terms: D001021:Aortic Valve / Q000473:pathology* / Q000503:physiopathology; D001022:Aortic Valve Insufficiency / Q000150:complications* / Q000175:diagnosis* / Q000503:physiopathology; D001024:Aortic Valve Stenosis / Q000150:complications* / Q000175:diagnosis* / Q000503:physiopathology; D003971:Diastole / Q000502:physiology; D006801:Humans; D008962:Models, Theoretical; D011237:Predictive Value of Tests; D012720:Severity of Illness Index; D013318:Stroke Volume / Q000502:physiology; D013599:Systole / Q000502:physiology; D017725:Ventricular Pressure / Q000502:physiology