(2) Inspiratory tube. The inspiratory breathing tube connects to the front
port. The bottom port connects to a large green tube from the water trap. To prevent
possible misalignment of components, the master tee, shuttle valve (item 2, figure 1-8),
and nebulizer mounting tee are permanently fused together. Inspiratory gases are
conducted from the nebulizer mounting tee to a Bird water trap (item 5, figure 1-8) to
collect condensate and reduce mechanical resistance in the inspiratory side of the
breathing circuit. From the water trap, a smaller green tube transports the gas to the
airway "Y" junction (item 6, figure 1-8).
(3) Expiratory breathing circuit. The expiratory side of the breathing circuit
begins at the "Y" junction with a small red tube extending to the expiratory water trap,
which is connected by larger red tubing to the expiratory shuttle valve. Exhaled gases
leave the shuttle valve through the expiratory venturi, flow through the master tee, over
the top of the airBird valve diaphragm to the outflow valve and vent to atmosphere.
Pressurized lines provide pneumatic control over the dynamic breathing circuit. The first
of these, a large green tube of the quick-disconnect type, is attached at socket A and
provides inspiratory gases to the top of the outflow valve diaphragm.
(4) Proximal airway pressure gauge. From socket B, a line extends to the
nebulizer jet, providing constant flow of medication to the nebulizer. A line from the
mechanical airway junction extends through socket C to feed airway pressure to the
proximal airway pressure (PAP) gauge, which measures actual physiological airway
(5) Gas flow lines. Pressurized gas is directed from socket D to the
expiratory venturi jet in the shuttle valve. Respiratory gases are delivered to an
accessory port in the top of the 500cc nebulizer/humidifier from the auxiliary flow
socket E. Inflow gases are delivered into the inspiratory side of the breathing circuit
through the ports of the nebulizer from two outlet power sources, but both flows are
totalled at the flowrate gauge in liters per minute. Take care to avoid confusing the
nebulizer jet and auxiliary flow connections on the top of the nebulizer.
The tall socket is the nebulizer jet socket.
(6) Outflow valve. The outflow valve (figure 1-9) helps regulate pressure in
the breathing circuit. Exhaled gases enter the outflow valve through an unrestricted
orifice controlled by a red lever which may be moved through a 180-degree arc, having a
stop on either side.
(a) The expiratory resistance from the orifice is controlled by a molded
elastomer seat on the bottom of the diaphragm. The diaphragm assembly is held
together by a stainless steel screw through the top of the valve seat. A vented piston
attached to the diaphragm acts as an anti-chatter device. It also provides a seat for
alignment between the orifice and the hard plastic seat. The outflow valve allows the
operator to select a constant positive pressure within the breathing circuit. Constant
positive pressures from 0 to 20mmHg can be developed.