Abstract
A portable electronic device has been developed for controlling the limb load exerted by a patient in a partial-weight-bearing walking exercise. The device consists of three units: 1) a capacitive load transducer and a pre-amplifier that detect limb load; 2) a main electronic unit which converts the output of the pre-amplifier into avoltage signal and generates feedback tones; and 3) a meter used to adjust the voltage gain and threshold levels. The capacitive transducer is shaped like an insole and can be attached to the sole of the shoe from outside by elastic bands and Velcro straps. The transducer is divided into a front unit and a rear unit; thus the load exerted on the front part of the foot and the rear part of the foot can be separately measured. The transducer is thin (3.5mm), light (130g) and flexible, so it does not hinder the natural gait pattern. The main electronic unit converts the change in capacitance of the front and rear units into voltage signals and adds them to generate a voltage signal corresponding to the total load exerted on the foot. The main electronic unit measures 160×110×35mm and weighs about 430g and is fastened at the waist of the patient. The device has two basic operating modes: load-amplitude mode and stance-duration mode. In the load-amplitude mode, the load is compared with two presettable thresholds and two audible feedback tones are generated. A low-frequency tone is emitted when the load falls in the desired range, i.e., between the lower and upper thresholds, and a high-frequency tone is activated when the load exceeds the upper threshold. Thus, the patient is asked to walk so that he/she hears only the low tone in each step of the affected limb. In the stance-duration mode, the load is compared with the lower threshold, and the low frequency tone is generated if the load is maintained above this threshold for a period longer than a presettable stance duration time. This mode is used primarily for the purpose of encouraging the patient to exert the load on the affected limb for a longer period. In both modes, the load compared with the threshold(s) is the total load in usual application, but the load exerted only on the front foot or the rear foot may be used if so required. The feedback tone is transmitted to the patient via an earphone, and is simultaneously transmitted via commercial FM frequency so that an accompaning PT can monitor the tone by FM radio. To evaluate the effectiveness of the feedback tones in controlling the limb load in the loadamplitude mode, an experiment was made. Forty-two normal subjects and 17 patients with lower limb fracture were asked to walk at prescribed load ranges. These load ranges were 15-25kgf, 25-35kgf and 35-45kgf in normal subjects. In the case of patients, the upper threshold was set at the maximum load level allowed at the time of the experiment and the lower threshold was set 5 to 10kgf below this level. Each subject walked on a 15-m straight level floor with two crutches, and 50 steps were selected for data analysis. When the feedback tones were not trasmitted to the subjects, the peak load fell into the prescribed load range in less than 50% of the steps in normal subjects, and the peak load exceeded the upper threshold in more than 50% of the steps in the patients. When the feedback tones were transmitted, the peak load was maintained in the prescribed range in more than 80% of the steps both in the normal subjects and patients. The variation of the peak load decreased in the majority of the subjects when the feedback tones were heard. These results demonstrate that the feedback tones are very effective in controlling the limb load and to reduce the mental tension of patients during exercise.
