What type of drive mechanism would produce the pressure, volume, ...

[Sufayan.ah]

What type of drive mechanism would produce the pressure, volume, and flow waveforms illustrated below?
 
  A. spring-loaded bellows
  B. proportional solenoid valve
  C. piston attached to a rotating crank
  D. electric motor/rack and pinion

Question 2

What tidal volume would the therapist need to set on the ventilator to achieve the desired tidal volume of 750 ml?
 
  A. 760 ml
  B. 775 ml
  C. 840 ml
  D. 1000 ml

[ndhahbi]

Answer to Question 1

ANS: CA. Incorrect response: Spring-loaded bellows, such as a linear-driven piston, produces a square (rectangular) flow waveform, a linear ascending ramp volume waveform, and an ascending ramp pressure waveform.
B. Incorrect response: A proportional solenoid valve is not a drive mechanism. It is a flow control valve. Flow control valves ensure the precise flow of gas to patients as the gas flows from high-pressure sources.
C. Correct response: A piston attached to a rotating crank is a drive mechanism that provides output waveforms that are sinusoidal for pressure, volume, and flow.
D. Incorrect response: A linear drive piston, as with an electric motor/rack and pinion drive mechanism, produces an output of a rectangular flow, ascending ramp volume, and a linear ascending ramp pressure waveform. These ventilators are only of historical interest.

Answer to Question 2

ANS: CA. Incorrect response: See the explanation associated with choice C.
B. Incorrect response: See the explanation associated with choice C.
C. Correct response: Because 90 ml of volume are compressed in the patient's breathing circuit at the end of inspiration, the therapist must add 90 ml to the original tidal volume, which was set at 750 ml. Therefore the therapist needs to reset the tidal volume to 840 ml to compensate for the 90 ml lost in the tubing. That is,
set VT  Vcompressed = patient tidal volume
840 ml  90 ml = 750 ml
D. Incorrect response: See the explanation associated with choice C