Tecme NEUMOVENT - Equation of Motion; Criteria for Determining the Control Variable

TECHNICAL AND MAINTENANCE MANUAL
Graph VENTILATOR
Review : 04
Date:
09/05/06
2
In the course of an inspiration and expiration, there is a change of pressure, volume
and flow. A mathematical model called Equation of the Motion of the breathing
system describes this change.
Equation of Motion
Muscle Pressure + Ventilator Pressure = Volume
+ Resistance x Flow
Compliance
Muscle pressure: Forces generated by the breathing muscles during the inspiration.
Ventilator Pressure: Transrespiratory Pressure generated by the ventilator during the
inspiration (e.g.: pressure of the airway less pressure of the surface of the body).
The combined muscle and ventilator pressure cause volume and flow to be delivered to the
patient. Pressure, volume and flow change with time and hence are variables. The
compliance and the resistance are the constants maintained by the respiratory system.
If the patient’s ventilatory muscles are not functioning, the ventilator must generate all the
pressure required to deliver the tidal volume and the inspiratory flow rate. In this case, it will
control the ventilation.
The NEUMOVENT Graph Ventilator is able to control the pressure waveforms like the flow
waveforms. This control also can be doing in a single inspiration.
2. Control Circuit
The NEUMOVENT Graph Ventilator uses an electronic circuit to perform, control and monitor
the ventilation. The critical components of this system include a microprocessor, pressure
sensors and servo proportional valves.
3. Control Variables
As it was mentioned, the control variables of the NEUMOVENT Graph Ventilator are the
Pressure and the Flow.
The equation of motion establishes that if the Pressure is selected as the control variable,
then the ventilator is a pressure controller. Therefore, the left side of the equation will be
Criteria for determining the control variable
The ventilator is a
Time
Controller
NEUMOVENT Graph
The ventilator is a
Volume
Controller
The ventilator is a
Fow
Controller
Observation
and
previous
knowledge
The ventilator is a
Pressure
Controller
Does pressure waveform
change when patient
resistance and compliance
change?
Does volume waveform
change when patient
resistance and compliance
change?
Is volume measured directly
(by volumetric displacement
rather than by flow
transducer)?
no yes yes
yes
no
no
(modify from. Chatburn )
(9)