title: Theoretical and practical differences between the Gorlin formula and the continuity equation for calculating aortic and mitral valve areas.
abstract: Although the Gorlin formula and the continuity equation are both used to calculate valvular areas in the clinical situation, there have been few comparisons of the 2 methods. Mathematically, it can be shown that both formulas are derived from similar hydrodynamic principles which basically give a measure of the physiologic or effective area occupied by flow. However, the Gorlin formula contains errors in formulation and incorporates a constant that purports to give a measure of the anatomic rather than of the effective area of the valve. If both formulas are applied to the same hemodynamic data from aortic and mitral bioprostheses studied in a pulse duplicator system, the Gorlin formula constantly yields results 1 to 2% higher than the continuity equation for aortic valves and 12 to 13% higher for mitral valves. For any given type and size of prosthesis, the areas calculated by either formula increase linearly in relation to increasing pressure and flow (up to 20% for aortic valves and up to 35% for mitral valves). It is concluded that the Gorlin formula and the continuity equation are both pressure- and flow-dependent and are primarily related to the effective area occupied by flow rather than to the anatomic area of the valve. The 2 methods yield consistently different results due to differences in mathematical formulation. Such factors are important to consider when interpreting valve area calculations clinically.
authors.affiliation: Québec Heart Institute, Laval University, Canada.
authors.forename: J G
authors.initials: JG
authors.lastname: Dumesnil
authors.forename: A P
authors.initials: AP
authors.lastname: Yoganathan
mesh_terms: D001021:Aortic Valve / Q000033:anatomy & histology*; D001705:Bioprosthesis; D006350:Heart Valve Prosthesis; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008433:Mathematics; D008943:Mitral Valve / Q000033:anatomy & histology*