Chapter 03: How a Breath Is Delivered Cairo: Pilbeam’s Mechanical Ventilation: Physiological and Clinical Applications, 6th Edition

Chapter 03: How a Breath Is Delivered
Cairo: Pilbeam’s Mechanical Ventilation: Physiological and Clinical Applications, 6th
Edition


MULTIPLE CHOICE

1. The equation of motion describes the relationships between which of the following?
a. Pressure and flow during a mechanical breath
b. Pressure and volume during a spontaneous breath
c. Flow and volume during a mechanical or spontaneous breath
d. Flow, volume, and pressure during a spontaneous or mechanical breath
ANS: D
The mathematical model that relates pressure, volume, and flow during ventilation is known
as the equation of motion for the respiratory system. This means that: Muscle pressure +
Ventilator pressure = (Elastance  Volume) + (Resistance  Flow).

REF: pg. 27 | pg. 28

2. The equation of motion is represented by which of the following?
a. PTA = PA  Raw
b. PTR = Paw + PA
c. Pvent + Pmus = Raw + PTA
d. Pvent + Pmus = Raw  PA

ANS: B
The transrespiratory pressure (PTR) is the pressure generated by either the patient contracting
the respiratory muscles or by the ventilator pushing the volume into the patient. This pressure
is opposed by the elastic recoil pressure (PE) and the flow resistance pressure (PR). The
transairway pressure (PTA) is the pressure gradient between the airway opening and the
alveolus. This produces airway movement in the conductive airways. It represents only part of
the equation of motion, the pressure needed to overcome the airway resistance. The equation
of motion may be represented, on one side, by Pvent + muscle pressure (Pmus). However, this is

equal to the elastic recoil pressure (V/C) plus the flow resistance pressure (Raw  ) or Pvent +

Pmus = V/C + (Raw  ).

REF: pg. 27

3. How many variables can a ventilator control at one time?
a. One
b. Two
c. Three
d. Four
ANS: A
As the equation of motion shows, the ventilator can control four variables: pressure, volume,
flow, and time. It is important to recognize that the ventilator can control only one variable at
a time.

, REF: pg. 28

4. Calculate the transrespiratory pressure given the following information: volume 0.6 L;
compliance 1 L/cm H2O; airway resistance 3 cm H2O/L/sec; flow 1 L/sec.
a.0.9 cm H2O
b.1.8 cm H2O
c.3.6 cm H2O
d.4.6 cm H2O
ANS: C

Transrespiratory pressure (PTR) = Pvent + Pmus = V/C + ( Raw  ).

REF: pg. 29

5. An increase in airway resistance during volume-controlled ventilation will have which of the
following effects?
a. Volume increase
b. Flow decrease
c. Pressure increase
d. Rate decrease
ANS: C
When a ventilator is volume-controlled the ventilator will maintain the volume, which will
remain unchanged, along with the flow, but the pressure will vary with changes in lung
characteristics. An increase in airway pressure will require more pressure to deliver the set
volume. The set rate is independent of the changes in pressure.

REF: pg. 28 | pg. 29

6. An increase in airway resistance during pressure-targeted ventilation will have which of the
following effects?
a. Volume decrease
b. Flow increase
c. Pressure increase
d. Rate decrease
ANS: A
During pressure-targeted (pressure-controlled) ventilation, pressure is unaffected by changes
in lung characteristics. However, an increase in airway resistance will cause less volume to be
delivered and will change the flow waveform. The set pressure will not be able to overcome
the increased resistance, resulting in less volume delivery and a decrease in flow (V/TI).

REF: pg. 28

7. A patient who has a decrease in lung compliance due to acute respiratory distress syndrome
during volume-limited ventilation will cause which of the following?
a. Increased volume delivery
b. Increased peak pressure
c. Decreased flow delivery
d. Decreased peak pressure