[Analysis of the shape of the left ventricle by studying the regional curvature and power spectrum. I. Methodology and results in normal subjects].

Quantitative analysis of left ventricular shape, obtained by measuring the regional curvatures and power spectrum of the harmonics of left ventricular outlines, is a useful method that has seldom been used in clinical research because of the need for a reliable and replicable method. The curvature of each point of an outline is the reciprocal of the radius of the circle that best fits a segment of the arc (window) centred at any specified point. We proposed a method based on the rate of change of the tangent vector with respect to the change in arc length, normalized for the width of the considered segment (Frenet-Serret formula). The series of curvature values allows us to obtain the power spectrum by means of Fourier analysis. The application of the method to a series of ellipses with variable eccentricity and size demonstrated that the width of the window is critical in the circulation of the curvature, and the choice of the number of points for computing has to be optimized to obtain the best signal-noise ratio. The method, applied using a sampling every 0.1 mm and optimized using a window of 25 points in the experimental model, is independent of the size of the samples, is able to distinguish small variations of eccentricity and to separate the signal from the noise due to digitizing and computing up to the 12th harmonic. The method has been applied to the left ventricular outlines of 16 subjects without any cardiac abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)