Ventilation

Question 1

What is Boyle’s Law (P-V)?

Answer 1

Volume is inversely proportional to pressure

Question 2

What is Charles’ Law (T-V)?

Answer 2

Volume is directly proportional to temperature

Question 3

What is Gay-Lussac’s Law (P-T)?

Answer 3

Pressure is directly proportional to temperature

Question 4

What is the normal PaO2 in blood?

Answer 4

~100 mmHg

Question 5

How is the PaO2 calculated?

Answer 5

PaO2 = PiO2 (inspired) - PaCO2/R

R - respiratory quotient = excreted CO2/O2 taken up

Question 6

What is alveolar CO2 related to?

Answer 6

It is inversely related to ventilation and is directly related to CO2 production

Question 7

What is the partial pressure of O2 in air?

Answer 7

160 mmHg

Question 8

If the partial pressure of O2 in air is 160, why is it only 100 in blood?

Answer 8

The humidification of the air by the upper airway causes the dilution of the gases due to the water vapor that was added.

Question 9

If ventilation is cut in half what will happen to the PaCO2?

Answer 9

It will double

Question 10

Where does the most ventilation occur in the lung?

Answer 10

In the lower regions. As you go up the lung, there is less and less ventilation

Question 11

Why is inspired air preferentially shunted to the base of the lung?

Answer 11

• The lung has a triangular structure with the base being the widest part of it so there are more alveoli at the base than at the apex
• At FRC the base of the lung is more compliant than the apex so airflow causes a greater volume change in the base

Question 12

What does the rate of alveolar filling depend on?

Answer 12

Resistance

Compliance

Question 13

What happens to the rate of alveolar filling when resistance is increased?

Answer 13

The rate will decrease

Question 14

What happens to the rate of alveolar filling when the compliance is decreased.

Answer 14

The rate will increase, but the alveoli is stiffer and fills up less than normal

Question 15

What is a nitrogen washout test?

Answer 15

Patients inhale 100% O2 from RV and then exhale slowly where N2 % is measured.

Question 16

What is the 1st part on the single-breath nitrogen washout test?

Answer 16

N2% is at 0% initially as the dead spaces filled with 100% O2 empty first.

Question 17

What is the 2nd part on the single-breath nitrogen washout test?

Answer 17

N2% rapidly increases as the alveolar regions are being emptied

Question 18

What is the 3rd part on the single-breath nitrogen washout test?

Answer 18

There is a plateau as there is an equal emptying of the alveolar regions in the lungs

Question 19

What is the 4th part on the single-breath nitrogen washout test?

Answer 19

There is a second increase in the N2% because of the slowly emptying alveoli

Question 20

What is the first air to reach the deep alveoli?

Answer 20

It is the “dirty” air from the previous exhalation

Question 21

What can be used to determine the anatomical dead space?

Answer 21

Fowler’s Method

Question 22

Describe Fowler’s Method.

Answer 22

The nitrogen washout test is used and by plotting the expired volume VS N2% and a curve is drawn that will show the volume of the dead space.

Question 23

What is anatomical dead space?

Answer 23

It is the dead space where gas exchange is not possible, like in the conducting pathways of the mouth and trachea.

Question 24

What is physiological dead space?

Answer 24

It is the total volume that does not participate in gas exchange and is equal to:

Anatomical Dead Space + Alveoli Ventilated but not Perfused

Question 25

What is the equation for the dead space?

Answer 25

Vd = Vt * (PaCO2-PeCO2)/PaCO2

Question 26

What is the normal ratio for Vd/Vt?

Answer 26

0.2-0.35

Question 27

What is Vd normally?

Answer 27

150 mL

Question 28

As tidal volume increases, what happens to the dead space ventilation?

Answer 28

It decreases

Question 29

In order to increase alveolar ventilation, what is the most effective method?

Answer 29

Increasing the tidal volume is more effective that increasing the respiratory rate