Theoretical and practical differences between the Gorlin formula and the continuity equation for calculating aortic and mitral valve areas

Am J Cardiol. 1991 Jun 1;67(15):1268-72. doi: 10.1016/0002-9149(91)90939-i.


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.

Publication types

  • Comparative Study

MeSH terms

  • Aortic Valve / anatomy & histology*
  • Bioprosthesis
  • Heart Valve Prosthesis
  • Hemodynamics / physiology*
  • Humans
  • Mathematics
  • Mitral Valve / anatomy & histology*