Vyaire VELA, Service Manual

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2-1
33373-001 Version A
Chapter 2: Theory of Operation
2.1 General Device Description
The VELA Ventilator uses a revolutionary turbine gas delivery system with sophisticated
microprocessor control. Its Graphical User Interface provides support for pediatric to adult patients.
The VELA can deliver clinically advanced modes of ventilation like Pressure Support, APRV, NPPV
and PRVC, and can be powered with an internal battery or AC power for a more extensive patient
range.
2.2 Pneumatic System Overview
The VELA ventilator pneumatic system is electromechanical and comprises four major subsystems,
each containing several components. These systems are the flow delivery system, the exhalation
system, the safety system and the inspiratory hold valve. Individual subsystems are discussed in
detail below
.
2.2.1 Flow Delivery System
This electromechanical system controls all inspiratory flow to the patient. The system delivers flow
to satisfy criteria for many breath types, including volume controlled, pressure controlled, pressure
supported, APRV, NPPV and PRVC. The system comprises a turbine, differential pressure
transducer, 2 auto-zero valves
, and an optical encoder speed transducer. When a breath is
initiated, the microprocessor controls the speed of the turbine to achieve the required flow rate.
The speed and differential pressure transducer signals function as control inputs to ensure that the
proper flow rate is delivered even when backpressure varies. Periodically, the auto zero valves
activate to reference both sides of the differential pressure transducer to ambient pressure. The
offset is recorded by the microprocessor, and is used as a correction for future pressure
measurements. This compensates for long term and temperature drift. Materials exposed to patient
gases include compatible plastics, aluminum, and plated steel.
2.2.2 Exhalation System
The exhalation system controls the flow of gas from
the patient’s lungs during the exhalation phase
of a breath. This electromechanical subsystem is made up of an exhalation valve, a flow
transducer, a differential pressure transducer, an airway pressure transducer, and three auto zero
solenoid valves. During exhalation, the outflow of gases is regulated by the exhalation valve to
achieve the set PEEP. The exhalation valve is comprised of an electromagnetic linear actuator
operating against a mechanical poppet/seat. The gas flow travels through the flow transducer. The
flow transducer is a variable orifice type and creates a differential pressure proportional to flow.
This differential pressure is transmitted to the differential pressure transducer, which converts the
pressure signal to an electrical signal. The microprocessor uses this signal for flow triggering and
to monitor exhaled tidal volume. The airway pressure transducer reads pressure in the exhalation
leg of the patient circuit. This signal is used as a feedback signal for controlling PEEP, pressure
control, pressure support, and various pressure monitors. Periodically, the auto zero valves activate
to reference the differential and airway pressure transducers to ambient pressure. The offset is
recorded by the microprocessor, and is used as an offset for future pressure measurements. This
compensates for long term and temperature drift. Materials exposed to patient gases include
compatible plastics, aluminum, and stainless steel.