Design of Microcontroller-Based Electrical Stimulator as a Replacement of Reflex Hammer

Stretch reflex is usually assessed by using a hammer, tapped at the tendon to yield reflex response. The strength of the reflex response is classified to a particular scale as an indication of a neurological condition. According to the practitioners, reflex test nowadays still has some drawbacks. Despite the fact that the use of hammer reflex has been incorporated in clinical practice for decades, the strength of the stimulus elicited on the tendon is not quantified. Tapping the tendon depends on the skill of the clinicians. Improper technique will lead to erroneous interpretation. This study aims to develop an alternative instrument to replace the reflex hammer in eliciting stimulus on the patellar tendon. The device is a microcontroller-based electrical stimulator designed to generate spike voltage stimulating the tendon. A controllable amplitude of spike voltage allows the clinician to quantify the stimulus given to the patient. In turn, it yields a more accurate and quantitative value of stretch reflex. By Using a voltage divider, the stimulus delivered through the electrodes is divided into eight accurate levels of spike voltage, ranging from 70 to 260 V, with 20 μs of the pulse width. This electrical stimulator is evaluated with two methods. The first method evaluates the output voltage quality, including amplitude accuracy and stability. Meanwhile, the second method assesses the performance of the stimulator in quantifying the stimulus given to the patient. The test shows that the output voltage accuracy is 99,592%, while its output stability is 99,533%. Under stringent supervision from an expert, the stimulator was tested to elicit stimulus on the patellar tendon of eight patients. Five of them are considered normal as they do not have any neuromuscular issues. At the same time, the rest patients are areflexia. The test results indicate that the voltage of 200-240 V is able to elicit muscular contraction in normal people. In contrast, people who suffer from areflexia do not respond to the stimulus even though the amplitude is set to 260V.