Maintenance File of the
LEGENDAIR
®CH1-8
−CPU block (piloting printed circuit board + turbine control board)
−Structure and User-Machine Interfaces (housings + display + keypad +
communication ports)
3.2 OPERATION OF THE DEVICE
The
LEGENDAIR
®
ventilator is composed on one hand of an airflow generator
capable of supplying a sufficient range of flow rates and pressures and on the other
hand of a three-way valve enabling piloting of the expiration valve.
The flow generator is a low-inertia micro-turbine driven by a brushless electric motor:
the valve is a proportional piezo valve.
These two actuators are controlled according to specific piloting laws by a computer
receiving information from the pressure and flow sensors built into the apparatus.
The operation of the device is based on a self-adapting drive system of the speed of
the flow generator, in a closed loop.
The speed of the flow generator (turbine) is servo-controlled to the patient pressure
signal or the inspired flow signal.
The laws for piloting turbine speed are based on equations and vary according to the
ventilation modes, settings and the ventilatory cycle phases. Thus, fixing the pressure
flow ramp or flow rise time has an influence on the level of turbine acceleration at the
start of insufflation. The transition between the insufflation and expiration phase is itself
controlled by a deceleration or braking proportional to the difference in pressure
between the two phases.
The expiration valve is pressure-piloted during the inspiratory phase and as the main
regulation part during the expiratory phase. The speed of the turbine is thus adapted to
the expiratory pressure level during the entire expiratory phase in order to compensate
for "parasite" leaks in the circuit beyond the leak regulated by the valve. This rinsing
flow is as small as possible in order to limit the patient expiratory brake phenomenon
without however cancelling it in order to prevent turbine overheating and expired
gasses re-aspiration phenomena. A system of non-return valve and spontaneous
ventilation are used to facilitate the threshold of balance.