PHYSIOLOGICAL, HISTOLOGIC, AND NEUROLOGIC RESPONSES TO SIMULTANEOUS BILATERAL CEREBRAL VESSEL DOPPLER IMAGING AT HIGH BEAM INTENSITY

This study evaluates physiological fluid heating during continuous bil ateral insonation at 530 mW/cm(2) for 8 h in a bench simulation. It al so examines the physiologic, histopathologic, and neurologic effects o f bilateral Doppler imaging of middle cerebral artery (MCA) blood flow velocity using ultrasonic beams with 530 mW/cm(2) intensity in a cani ne model immediately after and 2 weeks after insonation. In saline-fil led containers, instrumented with opposing Doppler probes angled 10 de grees off axis, temperature was recorded at 15-min intervals for appro ximately 8 h at the intersection of the Doppler probe axes. Three cond itions were tested: 1) an ambient control, 2) continuous bilateral ins onation at 530 mW/cm(2) per channel with the thermistor in position, a nd 3) intermittent thermistor insertion. In one group of canines, phys iopathologic responses during continuous bilateral insonation of the M CAs for 8 h at 2 MHz and 530 mW/cm(2) were studied. Brains were prepar ed for histologic examination immediately after insonation. Cerebral t emperature; arterial, venous, pulmonary artery, and capillary wedge pr essures; electrocardiogram; cardiac output; MCA velocity; and arterial blood gases were monitored. In a second group of canines, a neurologi c evaluation was performed before and after insonation and again after 2 weeks. Brain tissue was evaluated histologically after the last neu rologic examination. Light microscopic study was used for all histolog ic evaluations. In the bench experiments, a net temperature rise in th e fluid of the simulation amounted to 0.0075 degrees C/h in the overla p region after correction for ambient temperature effects and artifact thermistor heating. In canines, brain temperature (after correction f or core body temperature changes and artifact heating of the thermisto r) rose a mean of 0.2 degrees C (p < 0.05) by the first hour, thereaft er unchanging. No significant changes in the physiologic, neurologic, or histologic evaluations were observed in either of the experimental groups.