Diseño de un circuito de estimulación eléctrica del nervio frénico para activación del diafragma, orientado a asistencia respiratoria

Abstract

Conditions such as diaphragmatic dysfunction, cervical spinal cord injuries, or autonomic control disorders can lead to critical dependence on mechanical ventilation, affecting the patient's quality of life. This paper describes the design and development of a prototype pulse generator intended to stimulate the phrenic nerve for diaphragm activation. The system uses a PIC16F628A microcontroller to generate PWM signals processed by a power stage with an L293D bridge, which allows for a safe symmetrical biphasic output. Stimulation parameters were established based on physiological and anatomical research of the structures and tissues involved, defining a frequency of 20 Hz to achieve muscle tetanization and a pulse width of 150 µs based on the chronaxie of the phrenic nerve. To verify the accuracy of the system, a mathematical model of the ideal signal was developed in MATLAB, which was compared with the experimental results obtained through physical validation of the prototype and its output displayed on an oscilloscope. The correlation obtained confirmed the stability of the frequency, validating the design from a practical and theoretical perspective. Finally, a mechanical validation was performed, in which a signal conditioning stage was implemented that reduced the 12 V potential of the main circuit to logic levels compatible with an Arduino Uno microcontroller to ensure the integrity of the processing. The developed algorithm allowed the translation of these electrical signals into mechanical movement using a servomotor actuator, achieving a physical representation of the diaphragmatic respiratory cycle synchronized with the signal generator. A wireless on/off system was also integrated using an ESP32 module and a mobile application developed in MIT App Inventor, incorporating wireless activation protocols required in implantable devices after surgery.