COMPARISON OF THE BIOMEDICAL EFFECTS OF THE EXPOSURE OF HUMAN TISSUES TO LOW AND HIGH ENERGY LASERS *

For the investigation of the effect of the laser on tissues of man, a variety of instrumentation and exposure conditions was The instrumentation used included pulsed ruby lasers, exit energies from 0.5 joule to 450 joules; a neodymium laser, 40 to 50 joules exit energy; a helium-neon gas laser, 1 milliwatt; lasers attached to microscopes and Q-switched and repetitive lasers. For exposure of animal tissues, pulsed ruby lasers of reported exit energy of 1500 joules were used. The wide range of instrumentation permitted the use not only of different wavelengths of radiation but also of different energy densities (TABLE 1). The exposures of tissues were done in living subjects, excised fresh tissues of various organs, blood, cytologic materials from the skin, mucous membrane, and various types of tissues. In addition, a separate study was done on enzymes. This has been reported by Igelman, Rotte, Schechter, and B l a n e ~ . ~ A detailed study of the effect of the laser on blood is being done by Mauer and ForristaP of our group. Additional studies of our group are in the field of cytogenetics and teratology with Warkany' and in the use of fiber optics with Long8 Work is also being done in cardiovascular dynamics with Kaplans and Stockert.'" A detailed study on the impact of the laser on teeth is also under way. The development of the laser presented us with a problem of studying the ionization changes by wavelengths with which we were not familiar and with energy densities, in tissue, which we had not experienced before. As an aid to the understanding of these complex problems of investigation the medical laser laboratory" was established in which the interest was in laser instrumentation design and development and personnel protection. This was accomplished through the cooperative research of physicians, biologists, physicists, and engineers. In this product of biomedical engineering, it was felt that progress could be made. It has been emphasized repeatedly that because of the hysterical type of publicity and the hectic development and expense of laser research, the work should be left to the highly specialized laboratories with their extensive instrumentation and with their great responsibilities for laser research and development, One difficulty in current biomedical research has been the impatience to design and to develop applied instrumentation rather than to expend time to study the much less dramatic phase of basic research. To some extent, then, many experiments were of a loose, multiple probing nature, rather than exhaustive, detailed, and controlled studies. The three basic qualities of the laser that have been emphasized repeatedly" because of their applications to the biomedical aspects are directionality, selectivty, and high energy density. Currently available instrumentation allows studies of energy densities from low exit energies to high energies. The various optical