2.7
THEORY
of
OPERATION
2.7.1 GENERAL
The theory of operation of the ventilator in the volume limited and
pressure limited modes will be discussed in this section. We shall
study the path of gas flow from the mixer to the main flow outputs. We
shall consider various conditions that affect or change the flow path.
The inspiratory time, respiratory rate,
F102 and the amount of flow will
not be considered since these do not affect the flow path. They will
only determine the quantity, quality and duration of the flow. An
understanding of the switching of the solenoids and valves is
important in tracing the flow of gas and the outputs in the
Newport
Breeze.
2.7.2 VOLUME LIMITED MODES
The flow path in the three modes
(A)
Assist Control
+
sigh (NC
+
sigh)
(B) Assist Control
(NC)
(C) Synchronized
l
ntermittent Mandatory Ventilation (SIMV)
is different only in the pattern in which it is delivered. The difference
between
A/C and
A/C
+
Sigh is that in A/C
+
Sigh the first breath has
an inspiratory time 1.5 times that of the setting and thereafter every
100th breath is equal to 1.5 times the inspiratory time setting. The
difference between
A/C and SlMV is in the timing of the delivered
breath. In SlMV the timing of the synchronized breaths is set by the
respiratory rate.
EXAMPLE:
If the respiratory rate is set at 6 BPM then the
Synchronized Timing Period
=
60
/
6
=
10 seconds. The
10
sec. is divided into a 75% and 25% window. A breath
can not be initiated during the 75% window. The
machine watches for the patient effort during the
25%
window and will deliver a breath when a patient effort is
sensed. If no patient effort is sensed the machine will
deliver a breath at the end of the
25%
window.
In the
A/C mode a breath is delivered each time an inspiratory patient
effort is sensed regardless of the respiratory rate setting, while the
SlMV breaths are delivered only at the respiratory rate setting.
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