Module B: Physical Aspects of Mechanical Ventilation

Question 1

Describe the equation of motion in the respiratory system

Answer 1

○ Describes the relationships between pressure, volume, flow during a spontaneous or mechanical breath

Muscle pressure + ventilator pressure = elastic recoil pressure + flow resistance

Pmusc+ Ptr = Palv + Pta

Question 2

Describe the factors that are controlled and measured during inspiration.

Answer 2

According to the equation of motion, the four variables controlled by the ventilator during inspiration are flow, volume, pressure, and time

Question 3

Explain how the patient may not receive the set VT due to tubing compressibility

Answer 3

In most adult circuits about 1-3ml of gas is lost to tubing compressibility for every 1cm H20 that is measured by the airway pressure sensor

As a result, a relatively large volume of gas may be compressed in the circuit when the patient is being ventilated with high pressures

Question 4

control variable

Answer 4

The primary variable the ventilator adjusts to achieve inspiration

Question 5

trigger variable

Answer 5

begins inspiration

Question 6

cycle variable

Answer 6

ends inspiration and begins exhalation

Question 7

baseline variable

Answer 7

establishes the baseline during expiration before inspiration is triggered.

Question 8

limit variable

Answer 8

the maximum value that the variables of pressure, volume, flow, or time can attain before being stopped from exceeding