An IC-based controllable stimulator for in vivo experiments

International audienceHigh-cervical spinal cord injury can lead to respiratory deficiency due to paralysis of inspiratory muscles. Functional electrical stimulation has been applied to restore ventilatory function in individuals with respiratory deficiency as an alternative to mechanical ventilation. In our approach, stimulation is applied through intramuscular electrodes in the diaphragm causing contraction to increase lung volume. The developed respiratory pacing system requires 2 or 4 stimulation channels, not necessarily synchronized, with both open-loop and closed-loop capabilities. A multi-channel, multi-application electronic stimulation system has been developed, compliant with respiratory pacing experiments. The stimulator is built around a full-custom high voltage integrated circuit (IC). Each of the 8 available stimulation channels provides fully configurable biphasic current waveforms, with up to 1mA amplitude current (set as multiples of 4µA) and over-second pulse width (20µs steps). Different stimulation modes can be utilized, such as bursts mode and continuous stimulation. The stimulator can be used in standalone application or controlled by a wide range of devices, such as computers or FPGAs, through USB or UART. A user friendly GUI and a python based Application Programming Interface allows to fully control each parameter of the stimulator during the experiment (maximum delay 50µs). We present in-vivo experimental results in an uninjured rat model (n=2), using the stimulation system, in open-loop and closed-loop configurations. In the latter, a software-based adaptive controller modulates the amplitude of stimulation pulses delivered to the diaphragm with breath volume as feedback. Results show successful modulation of breath volume to a desired value via stimulation