Destructive, nonclassical "beating" of acoustic waves and electric field generation in lased heart muscle.

Increased use of the laser in heart research warranted examination of the physical effects of the laser on the heart muscle. Laser action on the heart muscle was found to induce nonclassical (nonlinear) properties in the muscle such as low-frequency harmonics of acoustic transients. This "beating" effect resulted in a destructive thermal-wave propagation within the tissue. The nonlinear effects found in lased heart muscle had not been previously observed and occurred at laser intensities two or three orders of magnitude lower than those which occur in nonbiological media. One possible explanation of this nonlinear behavior at lower intensities was the finding that the laser induced an electric field in heart muscle which interfered with cell-membrane resting potential, and conduction. Temperatures above 300 degrees C were recorded. These are very high, considering that cells are 80-90% water, and that the boiling point of water is 100 degrees C. The laser crater profile exhibited a two-stage effect which was atypical according to conventional thermal theory. Electron micrographs demonstrated an unexpected capillary growth which had occurred postmortem in the lased heart muscle.