Citations

The present series of experiments was undertaken in an effort to delineate those aspects of ultrasonic irradiation that might be destructive to malignant tumors of bone. The experiments were performed on rabbits having Vx-2 carcinoma implanted within the tibias. In preliminary, experiments, it was shown that the destructive effect of ultrasound on normal bone and on the circulation through normal bone was probably primarily due to heat. In the current series of experiments, it was shown that the heating of the bone was critically dependent on the exact location of the focus of the ultrasonic transducer within the rabbit leg. Our experiments suggested that (1) exposure of Vx-2 carcinoma to a temperature of 50°C for at least 10 min is sufficient to destroy the transmissible characteristics of this tumor, (2) exposure of Vx-2 carcinoma to ultrasonic fields with intense cavitation (applied in the absence of heat) has an effect that is far less than that of heating to 50°C for 10 min, and (3) controlled ultrasonic heating can increase the temperature of a bone to levels sufficient to destroy tumor growth within the bone.

Direct measurements were made of the displacement of the guinea-pig eardrum when acted upon by acoustic pressures (200–6000 cps). The mechanical nonlinearities of the ear were studied by introducing a static pressure (0 to ±3000 dyn/cm2) in the middle-ear cavity. Below 1000 cps, the ratio of the tympanum displacement to the sound pressure was frequency-independent, with a value of about 4×10−7 cm3/dyn. Above 1000 cps, this ratio exhibited a series of maxima and minima. A static-pressure difference across the tympanum changed the frequency at which the maximum occurred and generally decreased the displacement/pressure ratio. It was concluded (1) for low frequencies, the lumped-parameter description of the ear as a cavity was valid; (2) the tympanum acts as a flexible, conical plate under slight tension; (3) the measurements were best explained in terms of two nonlinearities: hysteresis and a nonlinearity of the elastic properties of the ear.

Many therapeutic procedures have been introduced into the art and science of medical practice empirically by a method of trial and error. Such a method has marked limitations and may produce unfavorable consequences. The facilities available in experimental medicine permit a thorough and extensive investigation of biological effects of many therapeutic agents or procedures before any clinical application is made. Optimal doses of the therapeutic agent can be approximated and a comparative study of various technics designed for clinical application can be made. Unfortunately ultrasound was used clinically by certain enthusiastic therapeutists before a thorough study of its biologic effects was completed. These therapeutists regarded the major biologic effect of ultrasonic energy to be mechanical. They were aware of a heating effect, but considered that it played a minor role. Experimental measurements have shown clearly that the major effect of ultrasound on living tissues is thermal when an intensity suitable for therapy is employed. The heating of bone by ultrasound is spectacular. No other heating agent used in therapy can raise the temperature of bone to such high levels so quickly. The application of ultrasound for diagnostic purposes and also for instrumentation will be described.

Experimental investigations indicate that ultrasound may prove useful for therapy, for diagnosis, and for biologic measurement. Ultrasound, although it may be dangerous in unskilled hands, is an excellent agent for the structural heating of living tissues. The term “structural heating” is used to denote heating at abrupt interfaces.The living organism presents numerous abrupt interfaces. Ultrasound promises to become a reliable diagnostic tool. Either the transmitted or the reflected ultrasonic energy can be used in this application. Tumors, gallstones, kidney stones, stones in the salivary glands, foreign bodies, and abnormal collections of fluid have been located accurately. Preliminary observations on the use of ultrasound for certain biologic measurements are encouraging. Instrumentation for biologic measurement includes ultrasonic flowmeters, devices for measuring thickness of some tissue structures, and equipment for measuring the viscosity of blood.

Experiments have been carried out to investigate ultrasound as a possible therapeutic agent. These show that selective heating occurs in nerves and bones treated in situ. Effects of direct heat on nerves are strikingly similar to the effects of ultrasound. Blocking of nerves by sound or heat with present techniques seems impractical because the margin of safety is too narrow.

As early as 1932 Freundlich, Sollner, and Rogowski proposed the use of ultrasonics in medicine for diathermy. They were able to demonstrate that bone marrow could be heated. The results of their study indicated clearly that further experiments needed to be done to extend these preliminary observations. We have completed a study of the temperatures produced by ultrasonics in bone marrow, bone, and adjacent tissues in the extremities of the dog. The frequency used in these studies was 800 kilocycles per second. The maximum output of the ultrasonic generator was approximately 15 watts. High temperatures can be produced in bone marrow and bone with relatively low outputs of ultrasonic energy. The adjacent tissues are heated only moderately. Ultrasonics must be used with caution in the proximity of bones because the temperatures produced in bone and bone marrow may rise to dangerous levels within a very few minutes.

Dilute suspensions of canine erythrocytes were exposed to 1 Mc focused ultrasonic fields with maximum acoustic pressures estimated at 10 atm. In standing wave patterns in which circulation was inhibited, the cells clumped rapidly at the nodes and no changes were found. With a free surface, fountaining and stirring occurred. Exposure at 1 atm ambient pressure then resulted in rapid lysis. Erythrocytes exposed briefly in isotonic Rous-Turner mixture and controls were both diluted with sodium chloride solutions of varying concentration. The optical density at 650 mμ was plotted as a function of salt concentration. The exposed samples showed a greater fractional decrease in optical density at low sodium chloride concentrations than did the controls. Other samples exposed in hypotonic solutions showed both the greater sensitivity to low sodium chloride concentrations and a smaller change in optical density as the sodium chloride was varied from isotonic to 70% isotonic. It has not been possible to demonstrate that any factor other than cavitation was responsible for the observed changes in osmotic fragility.

By use of a high-power, corona type loudspeaker we have been able to demonstrate behavioral and endocrine responses of laboratory rodents to measured high sound-pressure levels at the frequencies at which their hearing is most sensitive, namely, 10 to 40 kc. The corona type loudspeaker behaves in the fashion predicted by the theoretical analysis reviewed in this paper. It is limited by extremely low efficiency (2.5%) and high production of ozone. At high frequencies it is limited by the volume of the corona, and at low frequencies by the failure of the quasi-adiabatic condition within the corona. Despite these limitations its performance has not been equaled by other types of loudspeakers; it is a unique tool for studying the responses of laboratory rodents to sound fields.

AbstractGenetic counseling students were surveyed about their backgrounds, application process to genetic counseling programs, and career motivations and plans. Program directors from 27 accredited programs were asked to distribute 362 surveys to students. Fifty‐two survey items assess demographics; sources of support for pursuing a genetic counseling career (information about genetic counseling, encouragement/discouragement from others); career motivations (reasons for applying and for becoming a genetic counselor); and career certainty. Two hundred and thirty‐five usable surveys were returned (64.9% usable return rate). Most respondents were Caucasian females (mean age = 25.4 years). About 13% identified as ethnic minorities, and about one‐third reported family histories of a genetic condition(s). Most respondents learned about the field in classes, and most were strongly encouraged by family and friends to pursue genetic counseling. Reasons rated as most important for becoming a genetic counselor included helping others and intellectual stimulation. Recruitment, training, and research recommendations are given.