1. 1. Standard hydrokinetic orifice formulas have been applied to stenotic mitral, pulmonic, tricuspid, and aortic valves, patent ductus arteriosus, and atrial and ventricular septal defects. These formulas were considered applicatble because of the high kinetic energy losses through small orifices or in the presence of high volume flow. 2. 2. In its general form, the formula is as follows: A = F C 2gh where A = cross-sectional area in cm.2of the orifice F = flow rate in c.c. per second C = empirical constant g = gravity acceleration h = pressure gradient across the orifice in mm. Hg. 3. 3. Cross-sectional valve areas have been calculated in twenty-one patients with mitral stenosis. Calculated and measured areas have checked within 0.2 cm.2in six post-mortem examinations and in five patients at the time of operation. Repeated calculations from different sets of data in the same patient have checked well in all instances. Valve area showed a good correlation with severity of pulmonary symptoms. Changes in valve area following finger fracture valvuloplasty were observed in two patients. The exponential relation of pressure to flow and valve area is briefly discussed. 4. 4. The stenotic cross-sectional area has been calculated in ten patients with pulmonic stenosis with one post-mortem observation and in two patients with patent ductus arteriosus with operative correlations. 5. 5. Calculations have likewise been made but without post-mortem confirmation in tricuspid stenosis, atrial septal defect, and ventricular septal defect. Formulas are presented for calculation of the size of the aortic orifice in aortic stenosis. In these groups, the empirical constant, C, has not as yet been determined and must await the collection of post-mortem data. 6. 6. In each case an attempt has been made to assess the sources of error as well as the degree of accuracy involved in the particular formula. 7. 7. The chief value of these formulas is that they present an objective evaluation of surgical procedures designed to widen stenotic orifices or to abolish abnormal shunts. Furthermore, a theoretical prediction of the benefit to be derived from surgical widening of stenotic valves may be made. © 1951.
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