Lehmann Jf

Therapeutic applications of electromagnetic power

The use of electromagnetic (EM) power for therapeutic applications has existed since EM sources have been available to man. Physical medicine has been a major user of both shortwave (27.33 MHz) and microwave (2450 MHz) diathermy over the decades in which the EM power has been used to heat deep tissues for stimulating various medically beneficial physiologic responses in the relief of certain pathological conditions. Experimental and clinical research indicates that these responses will occur as a result of elevating the tissue temperatures in the range 41° to 45°C requiring absorbed power densities from 50 to 170 W/kg in the deep tissues where treatment is desired. The combination of pain responses and a large reserve of blood cooling capacity seems to be sufficient for limiting the heating to safe, but therapeutic levels in vasculated and innervated tissue. Recent research has shown that the use of the industrial, scientific, and medical (ISM) frequency of 915 MHz is more efficient than the currently used 2450-MHz microwave frequency in terms of maximum power transfer to deep tissues. The results also show that in addition to thermal applications, microwave energy can be used for the controlled transcutaneous stimulation of nerve action potentials via implanted miniature microwave diodes.

Comprehensive analysis of dynamic elastic response feet: Seattle ankle/lite foot versus SACH foot

This study evaluated biomechanical and metabolic performance differences between two prosthetic foot designs in light of their mechanical properties. Ten unilateral below-knee amputee subjects, at least 1 year after amputation, capable of walking and running, were studied. Differences in heel and forefoot compliance explained differences in gait events and alignment. Increased efficiency of pushoff in the Seattle Ankle/Lite Foot exists as evidenced by the decrease loading on the opposite limb during double support and a less shortened step length on the sound side compared to the SACH foot. The natural frequency of oscillation for the prosthetic feet was determined to be too high to provide energy storage and release synchronized with kinematic requirements because neither metabolic cost savings nor differences in metabolic efficiency were found. Comfortable walking speed and the nadir of metabolic rate and efficiency are not different. Via accelerometer measurement, it was found that the more compliant and lossy SACH foot heel was less likely to transmit high frequency vibration.

Footwear And Posture: Compensatory Strategies for Heel Height

The belief that wearing high-heeled shoes increases lumbar lordosis is firmly ingrained in clinical folklore. Proponents of negative heel footwear argue that because high positive heels increase the lumbar lordosis, negative heels will decrease the lumbar lordosis. Quantitative documentation of the assumption regarding high heels is not to be found in the literature, although sporadic attempts to prove this assumption have been made throughout the 20th Century. Although other effects, such as decreased gait speed and step length, and increased knee flexion at heel strike have been found in more than one study, no increase in lumbar lordosis has been found. Where an actual decrease in lordosis has been found, authors tend to explain it away as inconsistent with what every clinician feels that he or she has observed. We felt it appropriate, then, to conduct both a static and a dynamic study to assess the effects of heel height on lumbar spine and lower limb joint kinematics in the sagittal plane, as well as other strategies to compensate for heel height. The results indicate that the greatest compensation is at the ankle and knee. Where a significant effect occurred in the lumbar spine (males, dynamic study), high heels decreased the lumbar lordosis, i.e., resulted in less swayback rather than more.

Microwave Heating of Simulated Human Limbs by Aperture Sources

Microwave heating of phantom models of human limbs by aperture sources is investigated theoretically and experimentally. These phantom models consist of triple-layered circular lossy dielectric cylinders. The three layers of dielectric materials simulate human tissues of fat, muscle, and bone. In the theoretical investigation, apertures operating in the frequency range of 433 to 2450 MHz are used as microwave sources for heating the dielectric materials. The theoretical investigation makes use of the technique of summation of cylindrical waves. A high-speed computer is used to calculate the numerical results. For the experimental investigation, an aperture is designed and built to operate at the frequency of 918 MHz. The resulting temperature patterns in the phantom models are detected by the use of a thermograph camera. The theoretical results are shown to be in agreement with the experimental results. The technique and results of this investigation may be applied towards the design of applicators for therapeutic heating of human tissues.

Development of a 915-MHz Direct-Contact Applicator for Therapeutic Heating of Tissues

The design of a 915-MHz diathermy dielectric-loaded applicator with a TE/sub 10/-mode aperture field distribution is described. The lightweight porous dielectric used for loading the applicator allows for the transmission of refrigerated air through the cavity to provide surface cooling so therapeutic temperature can be produced in deep tissues without excessive heating of surface tissues. The design is based on theoretical calculations previously developed by the authors which predict optimal size of the aperture and field distribution that would provide the best heating patterns in deep layers of tissue. Experimental evaluations of the heating of tissues of models and human beings are discussed.

The stretch reflex response in the normal and spastic ankle: Effect of ankle position

OBJECTIVE The influence of stretch of the gastrocnemiussoleus muscle on the stretch reflex activity was studied, by varying the ankle angle in steps from 10 degrees of plantarflexion (PF) to 5 degrees of dorsiflexion (DF). DESIGN Nonrandomized control trial. SETTING Department of Rehabilitation Medicine of a university medical center. PATIENTS Sixteen subjects with and 16 subjects without spasticity. MAIN OUTCOME MEASURES The passive elastic stiffness and active reflex response, expressed by the total and elastic path lengths, were determined at each ankle angle as a sinusoidal displacement of 5 degrees was applied to the joint at frequencies from 3 to 12 Hz. RESULTS The elastic stiffness showed no difference between the spastic and normal subjects for all ankle angles (p > .05). The elastic stiffness increased linearly similarly in both groups when the ankle was dorsiflexed. The reflex response was significantly greater in the spastic group for all positions (p < or = .01). The total and elastic path lengths showed a linear increase in both groups when the ankle angle was varied from PF to DF. The spastic group, however, had a significantly faster increase (p < or = .005). Between-group comparison showed a significant quadratic trend in the elastic path length for the spastic group (p < or = .05), with a maximum at 2.5 degrees of DF. CONCLUSIONS This study showed that the stretch reflex activity varies with the ankle position. This must be considered when performing spasticity tests subsequent to an intervention that has changed the available range of motion and when comparing subjects measured at different ankle positions.

Evaluation of a Therapeutic Direct-Contact 915-MHz Microwave Applicator for Effective Deep-Tissue Heating in Humans

A 13-cm square direct-contact microwave applicator which operates at 915 MHz was evaluated in tissue models and human volunteers to determine its therapeutic effectiveness. It was found that the applicator with radome- and forced-air cooling selectively elevates temperatures in muscles (1-2 cm) to 43-45/spl deg/C. At this higher range of temperature, certain physiologic responses such as an increase in blood flow are produced. The applicator may also be used to heat malignant tumors of muscle.

On the Determination of an Optimum Microwave Diathermy Frequency for a Direct Contact Applicator

An approximate theoretical analysis is presented for determining the relative heating in a two layer fat-muscle medium due to a dielectric loaded dipole-corner reflector applicator in direct contact with the finite fat layer. The results indicate that convenient applicator sizes, equivalent to those now used at 2450 Mc/s, operating at a frequency in the neighborhood of 750 Mc/s provide the maximum ratio of relative heat per unit volume in the muscle as compared to that in the fat. Experimental data taken with the aid of an electrical model of the fat-muscle layers shows reasonable agreement with the results of the approximate analysis.

Ankle-foot orthoses: Effect on gait abnormalities in tibial nerve paralysis

To study the biomechanical effects of gastrocnemius-soleus dysfunction and its potential remediation, the gait patterns of six able-bodied young adults were analyzed before and after induced temporary tibial nerve paralysis. Ambulation with the tibial nerve block was performed with and without the assistance of an ankle-foot orthosis (AFO) with a rigid anterior stop adjusted to either 5 degrees plantarflexion or 5 degrees dorsiflexion. The gait abnormalities resulting from tibial nerve paralysis include delayed advancement of the center of pressure, delayed ipsilateral heeloff and early contralateral heelstrike, decreased steplength, decreased ankle dorsiflexion moment, and increased knee flexion moment. This study provides quantitative information on the degree to which these abnormalities were corrected by appropriately adjusted AFOs. When using an AFO with an anterior stop, subjects with tibial nerve paralysis had improved advancement of the center of pressure (p less than 0.01). The bodys ground reactive force line moved forward more normally, pivoting over the metatarsal head area and raising the heel earlier than observed with uncorrected tibial nerve paralysis, thus approximating the normal ankle dorsiflexion moment, normal timing of gait events, normal advancement of the hip, and normal steplength. The AFO with the anterior stop set at 5 degrees plantarflexion was more effective in restoring the values to normal than the AFO with the anterior stop set at 5 degrees dorsiflexion, but still did not consistently achieve the normal values. Only by using the AFO with the anterior stop set at 5 degrees plantarflexion was the increased knee flexion moment observed during the block reduced to normal levels (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Calculation by the Method of Finite Differences of the Temperature Distribution in Layered Tissues

A numerical approach to obtain the temperature distribution in layered tissues with thermal source and cooling inside the tissues is presented in this paper. This approach can be applied to problems with a distributed internal thermal source produced by external radiation such as microwave, ultrasound, and shortwave, or by internal increase of metabolic rate in live subjects. The exact mechanism of cooling is not discussed here, but it is assumed to be due to blood flow in vivo. The calculation of the temperature distribution in layered tissues is based on a linear model of the tissues that consists of several layers of different kinds of tissues separated by parallel boundaries. Some simple mathematical forms of the cooling functions are also assumed in this paper. The results obtained agree well with six available experiments.