Functional Description; Operating Modes - BIO-MED DEVICES IC-2A Service Manual

II.

FUNCTIONAL DESCRIPTION

INTRODUCTION
Figure 2-1 presents a schematic view of the IC-2A Ventilator. Figure 2-2 presents the
logic system. Refer to the list of symbols and abbreviations at the front of the manual.

OPERATING MODES

Intermittent Positive Pressure Ventilation (IPPV)
In the IPPV mode the IC-2A Ventilator acts as a controller or assist/controller. The
following control switch settings are required:
A pilot valve, operated by the timing signal from the fluid logic, opens for the time set by
the INSPIRATORY TIME control. This allows the gas to flow at a rate set by the FLOW
RATE control. The exhalation valve pressurizes, closing the exhalation port and thus
ensuring that all gas is directed to the patient.
Since the gas supply is a high pressure source and the pressure reached in the patient
is relatively low, the flow rate remains constant and independent of changes in patient
pressure.
a. Volume Limited. The pressure developed in the system depends on the total
compliance and the column of gas delivered. If the adjustable pressure limit
is set higher than the pressure that is reached, then no gas is dumped to
atmosphere and the ventilator is volume limited. In this mode the tidal volume
(V ) is the product of inspiratory time (T
T
In this mode the pressure limit is normally set to 10cm H
It then acts as an upper-level fail-safe. If patient resistance or compliance causes a
significant increase in pressure, the pressure will be limited at the preset level. When
this occurs the ventilator is no longer volume limited since some gas is dumped to
atmosphere and therefore the tidal volume is unknown.
b. Pressure Limited. Whenever the pressure reached within the patient circuit is
equal to the maximum pressure limit established using the MAX PRESSURE
control on the rear panel, the excess gas is dumped to atmosphere and the
unit is operating in a pressure-limited mode. The Ventilator may be used
continuously in the pressure-limited mode by setting the maximum pressure
and adjusting the inspiratory time and flow rate to give a large enough volume
of gas per breath to ensure that the preset pressure level is reached on each
cycle. When the pressure limit is reached, it is held until the end of
inspiration, thus producing a plateau-type pressure waveform.
Switch
CYCLE/MANUAL
CPAP
NORMAL/SIMV
Setting
CYCLE
NORMAL
) and flow rate (V
I
V =T X V
T I I
O above the pressure attained.
2
),
I
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