EFFECTS OF ULTRASOUND ON EMBRYONIC HEART STRUCTURE AND FUNCTION.

Chick embryos at a critical stage of cardiogenesis were removed from their shells intact, placed in a 37. 7 degree C chick Ringer's bath, and exposed to either pulsed-wave (PW) or continuous-wave (CW) ultrasound for 5 or 30 min at intensities of 0 (sham), 50, 500, or 1000 mW/cm**2 SATA (spatial-average temporal-average) at 1 MHz. Heart rate (HR) and shortening fraction (SF) were calculated using cinephotoanalysis. Additional embryos were fixed in glutaraldehyde immediately after exposure and after 24-h recovery from exposure for ultrastructural examination. Cardiac contractility, as measured by SF, showed no significant changes from baseline for any of the intensities. HR measurements after exposure were not significantly different from baseline but embryos exposed to 1000 mW/cm**2 showed a difference in HR response when compared to embryos exposed to 50 and 500 mW/cm**2. Electron micrographs (EM) revealed intracellular damage which increased in magnitude with higher intensities and duration. Cell edema, margination and loss of nuclear chromatin, swelling of mitochondria, vacuole formation, and hemorrhage formation were noted in both CW and PW exposures but were not present in the shams.