Red Cross

Reflex Hammer 2.0

03. 03. 2014

Besides the stethoscope, a reflex hammer is one of the best known symbols of the doctor. From time out of mind, reflex hammers have been used to test reflexes. A doctor will tap with the hammer and observe how the limb reacts to stimulation of the receptors. Reflex hammers are used to record the time between the tap and the body’s reaction, and thus help doctors detect possible injury to neural pathways.

A delayed or weak reaction suggests a nervous system disorder. Before the occurrence of modern technologies, doctors had to solely rely on their own experience to evaluate the length of this response.

Pyramidal hippocampal neuron 40x

How do reflex hammers look today?

Over the years, medicine has made considerable progress and today reflex hammers are equipped with electronic means of detection. Electronic detection determines contact with the body far more precisely: reaction time is measured from that very moment. This moment of contact can be detected using several principles, e.g. activating a microsensor upon the moment of contact, using an acceleration (or deceleration) sensor or the electrical contact produced by touching the skin. These solution do have some disadvantages however, such as inaccuracy, the occurrence of false signals or risk of patient injury.

Precise and quick solution from Brno University of Technology

Touch is detected based on changes in the membrane of a miniature microphone placed inside the hammer head. Upon the hammer’s impact, the microphone records the impulse (deformation by impact of the microphone membrane upon sudden deceleration of the hammer and the sound wave of the impact). Deflection of the microphone membrane is converted by amplifier into an electric signal. The signal is the trigger to start sensing from leads attached to patient. Once the start of measurement has been determined, reading the reaction time on the lead is easy. An integrated signalling device lights up an LED light at the moment the signal is created. A special time filter silences the microphone for a certain period so that no false additional signals can occur. The impact surface is made of rubber or foam so the examination is not painful to the patient. The effectiveness of the system has been demonstrated using comparative tests.

The inventor of this protected (patent and utility model) solution is Doc. Ing. Milan Chmelař, CSc. of the Institute of Biomedical Engineering at the Faculty of Electrical Engineering and Communication Technologies, Brno University of Technology. Biomedical Engineering applies technical knowledge in medicine and biology. This branch is particularly adept at designing medical devices, medical instruments and diagnostic equipment and for producing artificial organs.

The introductory Red Cross image is licensed under Public Domain CC0.
The image of the neuron is licensed under CC-BY-SA.

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