PNF ELECTRICAL STIMULATOR

Marko Munih ^*, Pavla Obreza ^#, Erik Ott ^*, Helika Benko ^#

^* Faculty of Electrical Engineering, University of Ljubljana, ^# Institute for Rehablitation of Republic of Slovenia

^* Tržaška 25, 1000 Ljubljana, Slovenia, ^# Linhartova 51, 1000 Ljubljana, Slovenia

ABSTRACT

The aim of Proprioceptive Neuromuscular Facilitation (PNF) is to promote functional movement of paralyzed limb through facilitation, inhibition, strengthening, and relaxation of muscle groups. The muscle contractions are carried out by the handicapped person, combined with a properly graded resistance being fitted to the patient’s needs by a physiotherapist. PNF is used in intact person training and in rehabilitation as a set of specific movement patterns. New addition introduced here, is the assistance of surface functional electrical stimulation during some movement patterns of the leg (e.g. flexion-adduction-external rotation). Highly adaptable: pulse width, frequency and amplitude adjustable electrical stimulator was mounted inside a leg pedal housing, enabling precise control of stimulation amplitude.

INTRODUCTION

The PNF approach, first appearing during the late 1940s, was developed primarily as a method to treat patients with neurological dysfunction. The desired motor response in general, being smooth, coordinated and optimal muscle pattern, is consisting of both isometric and isotonic contractions. In PNF there are used assistance, resistance, traction, approximation, quick stretch, verbal and visual stimuli by a physiotherapist to produce the required patterns of facilitation. The common denominator is always the patient’s voluntary mediated, complex activity in several joints resulting (most frequently) in limb movement. In the cases with severe neuromuscular dysfunction, the range of motion or desired performance is not adequate if compared to the patient intention, desire or psychical effort during the exercise. At such a point the Functional Electrical Stimulation seems to be a valuable addition to achieve: (i) instant improvement of motor response, (ii) steady and marked progress of the health condition, (iii) last, however very important the help to the physiotherapist. Prior to the session, the physiotherapist adjusts the maximal desired amplitude. During the training, while is the physiotherapist still being involved with the patient, additionally controls the stimulator amplitude with the leg pedal up to the previously adjusted 100 % level. In such a way the physiotherapist supervises timing and the “degree of help”.

METHODS

Developed was simple microprocessor based stimulator for surface electrodes. Minimum required maintenance, easiness of use and the compliance with EC requirements were among design goals. To enhance versatility and accommodate the device to individual needs, the stimulator adjustable stimulation parameters: pulse width, stimulation frequency and amplitude can be set by the clinician via PC computer or a simple external module in advance or during stimulation if necessary. External module enables communication with the user via two pushbuttons and LED bar display. The frequency may be preset at [15 20 25 30 40 50 70 100] Hz, pulse width at [150 200 250 300 350 400 500 600 700] ms and amplitude from 0 up to 135 V. A potentiometer, mounted aside of the housing, is used to set the overall maximum stimulation amplitude, being present when the pedal is fully pressed down. The second potentiometer mounted on the pedal plate is adjusting stimulation amplitude from 0 up to the maximal level adjusted before. Amplitude is low when the pedal is in upward position. In upward position is the DC/DC converter switched off automatically via hidden contact-less reed relay. Such operation regime is significantly extending battery life. The use of device is very simple for the physiotherapist; additional controls, not mentioned before, include only ON/OFF switch and connector for electrodes. External module, if needed, can be connected via DB9 connector. The unit usually stays on the floor and is operated during a session with a foot only. Low battery situation is indicated with a beep signal.

Figure 1 PNF stimulator

RESULTS

Fulfilled were the design goals: to have simple for operation, robust, adjustable parameters and energy efficient unit. To make it as simple as possible, the number of controls was reduced to a minimal possible number. Commercially designed housing makes it robust and cosmetic. The energy efficiency was tested at 50% duty cycle, which is way above the normal use. Two Nickel-Metal-Hydride AA sized cells having capacity of 1500 mA proved to be sufficient for 20 hours of operation at maximal amplitude. However, at used few percent duty cycles the operation extends to several months if not used more than few hours per day.

REFERENCES

1. S. Adler, PNF in practice : an illustrated guide, Springer, Berlin, 1993.

2. E. Ott, M. Munih, A. Kralj, Voluntary controlled peroneal stimulator, Int. Conf. IEEE Engineering in Medicine and Biology, Atlanta, Georgia, 1999.

3. E. Ott, A. Kralj, Wireless-controlled portable peroneal stimulator, IEEE Int. Symph. on Industrial Electronics, Bled, Slovenia, 1999.