Mechanical Ventilator spontaneous breathing detection tested by robot SIMVENT

Abstract

Mechanical Ventilators (MV) are only tested at the manufacturer's facilities in their ability to detect spontaneous breathing so as to trigger concomitant support. A robot patient was developed (called SIMVENT) to test MVs after repair or to compare MVs in hospitals. SIMVENT is a complete active patient simulator, as opposed to rubber bag simulation. SIMVENT implements lung equations under given user selected parameters of ventilatory mechanics to simulate different respiratory conditions. By producing spontaneous breathing (SB) pressure drops (1-10 cm H2O) at random times or phase-locked to ventilation cycles, SIMVENT tests the capacity of MVs to sense spontaneous ventilation. SIMVENT also calculates basic mechanical parameters (frequency, airway pressure, esophageal pressure, resistance and compliance). SIMVENT was designed with a step-motor powered piston moving in a 2-litre cylinder, a second cylinder mimicking residual volume, pressure sensors, a variable resistance tube, a microcontroller and a computer interface. A normalized spontaneous breathing detection graph was constructed for two MVs: one behaved well and the other could be harmful if ventilating a patient during weaning, because SBs were not sensed at the set pressure-drop value.