Is there a change in myocardial nonlinearity during the cardiac cycle?

The distortion of a sound wave during propagation results in progressive tr ansfer of the energy from fundamental to higher harmonics, and is dependent on the nonlinearity of the medium, We studied if relative changes in acous tical nonlinearity occur in healthy myocardium during the cardiac cycle. Ra diofrequency data were acquired from transthoracic echocardiography (2.5 an d 3.5 MHz), parasternal long axis view, from five dogs and nine healthy vol unteers. Integrated backscatter was calculated after filtering for fundamen tal (FIB) and second harmonic frequencies (SHIB), from a region in the post erior myocardial wall. The results suggest that there is little difference between the SHIB and FIB, although there mere large variations between indi viduals. The maximal changes in nonlinearity, as estimated by SHIB/FIB rati o, mostly occurred during systole, SHIB presented similar cyclic variation with FIB (p = NS), Further studies are necessary to separate the role of my ocardial nonlinearity, attenuation, propagating distance, or acoustical pro perties of the blood. The results are important in further tissue character ization studies employing second harmonic data. (C) 2001 World Federation f or Ultrasound in Medicine & Biology.