Local muscle blood flow and temperature responses to 915MHz diathermy as simultaneously measured and numerically predicted.

The therapeutic benefits of diathermy are tied to the relationship thought to exist between tissue temperature and augmented blood flow (BF). To further define this relationship, simultaneous measurements of thigh muscle blood flow (MBF) and temperature have been made in 15 human subjects during 915MHz, direct-contact microwave diathermy (MWD) with simultaneous skin cooling. Tissue temperatures were measured invasively by special thermistor probes designed to minimize MW-induced artifacts, and the local rates of MBF were measured by monitoring the radioactive washout of injected Xenon133 (Xe133). The experimental results have shown that the initial MBF response is characterized by a "critical temperature" behavior such that rapid increases in MBF occur for tissues above approximately 42C when diathermy power is sufficient. A proportionality between tissue temperature and MBF has not been found. To provide more useful descriptions of the temperature fields and diathermic BF responses, two-dimensional numerical thermal simulations of six of the subjects' treatments were constructed and recorded. An average peak simulated MBF of 48ml/min-100g was found for these subjects, a level in excess of previous estimates for maximum perfusion during diathermy.

Determination of perfusion field during local hyperthermia with the aid of finite element thermal models.

Two-dimensional transient thermal models of human thighs undergoing microwave diathermy are developed with the aid of experimental data to shed light on the blood flow response occurring during local hyperthermia in muscle. The experimental data were taken from tests on six human subjects treated with a 915-Mz, direct-contact microwave diathermy device which incorporated a system for simultaneously cooling the skin surface with a cold air stream. The numerically calculated perfusion fields were determined by systematically varying a model's blood flow response to the temperature stimulus until good agreement between the experimental and model temperature fields were achieved. The model blood flow values were then checked against those measured in the human experiments via xenon 133 washout and good agreement here was also found. The future use of models of this type in clinical diagnosis and hyperthermic treatment is proposed.

Acute microwave irradiation and cataract formation in rabbits and monkeys.

Rabbits and monkeys were irradiated in the near field of a cavity-backed 2450 MHz resonant slot radiator, to determine the cataractogenic threshold. Rabbits developed cataracts at incident "apparent" power densities of 180 mW/cm2 (E2/120 pi, where E=rms/electric field strength). Monkeys sustained facial burns, but no lens damage, even at incident "apparent" power densities of 500 mW/cm2. These results were substantiated by computer thermal models.

The ocular effects of microwaves on hypothermic rabbits: a study of microwave cataractogenic mechanisms.

Rabbits, irradiated by known cataractogenic levels of 2.45 GHz radiation at 5 cm, did not develop cataracts if kept under general hypothermia. Radiation-induced temperature elevation appears to be essential for the cataractogenic effect of microwaves.