CONTROLLED INTERMITTENT MANDATORY VENTILATION MODE
When controlled IMV is selected, gas flows from the inlet manifold to the Mark-2
servo, low pressure alarm, nebulizer, inspiratory-interrupter cartridge, and compound-
lockout cartridge. With the servo off, gas flow is stopped inside. As the servo cycles to
the inspiratory phase, gas flows from the outlet.
a. During the inspiratory phase (figure 1-14), the approximately 15- to 18-psi gas
flow applies pressure against the diaphragm in the inspiratory-interrupter switch, closing
it and interrupting the flow of gas to the compound-lockout cartridge through the duckbill-
check valve. This pressure is also applied to the inspiratory-venturi switch, which is
open due to the gas trapped between the diaphragms of the compound-lockout
cartridge, and to the reset button, holding it closed. From the venturi switch, gas flows
through the inspiratory relief pressure control through the spoiler assembly to the top of
the outflow-valve diaphragm. As the diaphragm is pressurized, peak inspiratory
pressure limiting is maintained by the outflow valve.
b. The trapped gas between the diaphragms of the compound-lockout cartridge
escapes to the atmosphere through the inspiratory time-limit control outlet port and
pneumatic bleed down begins. If the inspiratory time limit set on the Mark 2 exceeds the
inspiratory bleed-down time, the inspiratory phase is terminated and an audible alarm
c. Inspiratory lockout occurs when the trapped gas has bled off completely. As
the diaphragms relax, the inspiratory-venturi switch closes and no more gas is supplied
to the outflow-valve diaphragm.
d. When the diaphragms of the compound-lockout cartridge are depressurized,
the following two events occur simultaneously.
(1) Gas flow to the inspiratory venturi and the spoiler assembly is
interrupted, ending the inspiratory phase.
(2) The inspiratory time-limit alarm is activated by the flow through the
lockout-alarm switch of the compound-lockout cartridge, notifying the operator that the
ventilator has automatically switched over to spontaneous breathing.