The Emerson 3 PV ventilator is a time-cycled, rotary-drive piston, non-constant flow generator. The one we have in lab is a controller. There is an optional assist mechanism that can be added. Once upon a time it had a big green spirometer for measuring exhaled tidal volume. The spirometer was mounted on the bar that sticks up over the ventilator.

Looking inside the ventilator, air enters the " trombone sectionduring the downstroke of rotary drive piston. is filled with copper wool which serves as a bacteriocidal air filter. There small tube connected to top this where oxygen can be bled in. formula for determining liter flow O2 LPM = [VE(FIO2 - 0.2)] / 0.8

During the upstroke of the piston, gas is pushed out of the piston, through the pass-over humidifier, past the pressure relief, out to the circuit and the patient. Also during the inspiratory phase, gas pressure closes the exhalation valve. During the downstroke of the piston, the exhalation valve is no longer pressurized. The positive pressure in the airway pushes the diaphragm in the exhalation valve back, allowing exhalation. Tubing can be connected from the outlet of the exhalation valve to the water-weighted diaphragm type of PEEP valve that we have attached next to the exhalaton valve. The level of PEEP is determined by the height of the water column. Five centimeters of water would provide 5 cm H20 PEEP. The airway pressure manometer tees into the circuit just past the pressure relief valve.

Rotary drive refers to the wheel that moves the piston rod. The attachment point is adjustable. As the piston rod is moved closer toward the center of the wheel, the upward movement of the piston is less, and less volume is delivered. If the attachment point is moved out toward the edge of the wheel, the piston displacement is greater for larger tidal volume delivery.

The rotary drive also creates the sine flow wave pattern. As the piston starts the upstroke (moves to the right), the piston rod moves around with the wheel from the A to the B position. Since there is more vertical than lateral motion, the piston moves slowly and a short distance. As the attachment point on the wheel rotates from B to C, there is more lateral than vertical movement of the piston rod. The piston moves faster, increasing the delivered flow rate. The last third of inspiration repeats the slower speed of the first third since the piston rod in now moving from C to D. Exhalation occurs during the time the piston rod moves from D to A, causing the downstroke of the piston. During the downstroke (as the piston moves to the left), fresh gas is drawn into the piston chamber.

Sighs are provided by a blower. The sigh circuit tees into the main circuit just above the humidifier inlet. A set screw adjusts the width of a notch which triggers the start and stop of the sigh period. A wider notch will allow more sighs to be given. A control knob on the blower determines the sigh volume.

IMV could be given with our ventilator by adding an H-valve to the inspiratory limb of the patient's circuit.