Three sets of pressure, flow, and volume waveforms are depicted ...

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Three sets of pressure, flow, and volume waveforms are depicted below from a patient who is receiving continuous mandatory ventilation. Identify the control variable, and which set of waveforms reflects a decreased lung compliance.
 
  A. control variable: pressure; decreased lung compliance: set C
  B. control variable: pressure; decreased lung compliance: set A
  C. control variable: volume; decreased lung compliance: set B
  D. control variable: volume; decreased lung compliance: set C

Question 2

Which of the following devices are output control valves used to regulate the flow of gas to the patient? I. rack and pinion poppet valves II. proportional valves III. electromagnetic poppet valves IV. pneumatic poppet valves
 
  A. I, II only
  B. III, IV only
  C. I, II, III only
  D. II, III, IV only

[nixon_s]

Answer to Question 1

ANS: D
A. Incorrect response: Pressure is not the control variable because its value is different in each set of waveforms. Set C is the correct set of waveforms reflecting decreased lung compliance (stiffer lungs).
B. Incorrect response: Pressure is not the control variable because its value is different in each set of waveforms; therefore it is not constant.
C. Incorrect response: Volume is the control variable because it remains constant in each of the three sets of waveforms. The pressure tracing in set B represents the lowest pressure value among the three presented. Therefore the pressure waveform in set B does not reflect decreased pulmonary compliance.
D. Correct response: Volume is the control variable because it remains constant in each of the three sets of waveforms. The expression volume control means that volume is the control variable, and does not change. Set C signifies the response to decreased lung compliance. Especially, note that the pressure tracing in set C indicates the highest pressure among the three tracings. This finding is consistent with decreased pulmonary compliance.

Answer to Question 2

ANS: DI. Incorrect response: The electric motor/rack and pinion is a ventilator drive mechanism. The drive mechanism of a ventilator produces the force needed to deposit gas into the lungs of the patient.
II. Correct response: A proportional valve resembles a solenoid valve. It is operated via an electric motor whose rotation can be controlled in discrete arcs, or steps. Proportional valves change the size of their openings, thus influencing the shape of the flow-time waveform during inspiration. In fact, because the size of the opening can vary significantly, a variety of waveforms can be produced.
III. Correct response: The electromagnetic poppet valve is the same as a solenoid valve. It uses magnetism created by an electric current to control pneumatic pressure.
IV. Correct response: The pneumatic poppet valve uses small pneumatic pressure to control large pneumatic pressure.

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Thanks for the timely response, appreciate it

[Joy Chen]

Gracias!