Article Figures & Data
Figures
- FIGURE 1.
Diagram of the travel of breathing gases in the standard ventilator. The inhalation produced by the bellows passes via the safety relief valve into the patient circle. (A) The safety relief valve modified by attachment of 2 new ducts. The first duct is a custom-made L-shaped pipe that reroutes gases from the bellows straight into the TDU. The gas returning from the TDU enters the safety valve via the second new connector and passes through the valve into the patient circle, retaining the safety function of the valve. (B) The original configuration, which can easily be restored by interconnecting the 2 new ducts with silicone hose, thus bypassing the TDU.
- FIGURE 2.
The new TDU, enclosed in spare pneumatic casing. The production line of tracer gases is attached to the tracer delivery route selector. This selector directs the tracer gas either into the short normal breathing loop (for continuous administration) or into the scissor valve controlled reservoir (for collecting the tracer gas bolus). The pressure in the reservoir is displayed on the manometer, and a pressure regulator valve maintains the pressure at a level below the working pressure of the ventilator.
- FIGURE 3.
(A) During standard VC or PS ventilation, the breathing gases from the bellows are directed via an open scissor valve S1 back to the ventilator. Steady-state inhalation of C15O does not affect the ventilation. In 15O2 bolus studies, collection does not affect ventilation. (B) For delivery of the 15O2 bolus during VC or PS ventilation, the unit is manually triggered into the bolus delivery mode, causing the next inhalation to pass through the reservoir into the ventilated subject.
- FIGURE 4.
The control electronics of the TDU are connected to serial port N28 of the ventilator. The remote trigger switches the TDU into bolus delivery mode. If the expiration-phase signal is present in pin 17, the relays RL1–3 change the open/closed status of the pull-magnet valves S1–S3, redirecting the next inspiration through the reservoir. If the ventilator is performing VC type ventilation, the tidal volume setting (pins 19 and 20) is increased (by the resistor) and the inspiratory pause (pin 18) is activated until the trigger is released.
- FIGURE 5.
Comparison of detected counting rates after tracer delivery using 3 different dosing methods: spontaneous inhalation from bag (left column, n = 10), ventilator-assisted spontaneous inhalation using the TDU (middle column, n = 8), and involuntary inhalation in mechanically ventilated, anesthetized, or paralyzed subjects using the TDU (right column, n = 8). Counting rates after 15O2 bolus are seen in the top (continuous individual rates, corrected for dead time and randoms) and middle rows (group mean ± SD for total and random counting rates in each frame). The bottom row shows individual mean rates of total and random counts during the single 240-s time frame after 2 min of C15O inhalation.
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