Figure 1-6. Inspiratory-interrupter switch(A), inspiratory time-limit control (B),
and reset button (C).
(6) Inspiratory time-limit control. Gas flows from the inspiratory-interrupter
switch through the duckbill-check valve to the inspiratory time-limit control (B in figure 1-
6), an unrestricted needle valve. The needle valve provides a means of interrupting the
inspiratory phase after the preset inspiratory- time interval has elapsed. This allows the
compound-lockout cartridge to drain. Flow through the needle valve from the
inspiratory-interrupter switch is constant during spontaneous breathing and occurs
during the expiratory phase of IMV. Gas also flows from the inspiratory-interrupter
switch to the expiratory flow gradient control, which controls the expiratory venturi in the
shuttle valve to assist in exhalation. During the spontaneous breathing mode, the
expiratory flow gradient control can be used to precisely control pressure within the
breathing circuit. This is done by using the expiratory venturi passively, to overcome
mechanical resistance caused by gas flow through the breathing circuit.
(7) Reset button. Gas pressure trapped by the venturi jet side of the
compound-lockout cartridge and held behind the inspiratory-interrupter switch diaphragm
(holding it closed) can be dumped to atmosphere by pressing the reset button (C in
figure 1-6). This allows the compound-lockout cartridge to refill after lockout occurs.