Lecture #22: Pulmonary Ventilation

Question 1

Which muscles are used in passive and forced expiration?

Answer 1

• expiration is passive at rest
• forceful expiration:
  > abdominal muscles
  > internal intercostals

Question 2

What is the difference between volume and capacity?

Answer 2

• Capacity is a combination of 2 or more volumes.

Total lung capacity = maximum volume of gas the lungs can hold

Total lung capacity is made up of distinct, non-overlapping sub-compartments referred to as lung volumes.

Combinations of lung volumes form lung capacities.

Question 3

What is the volume and definition of tidal volume?

Answer 3

> 500 ml

> Volume of air that is inspired or expired with each breath at rest.

Question 4

What is the volume and definition of inspiratory reserve volume?

Answer 4

> 3000 ml

> volume of air that can be inspired in addition to tidal volume with forceful inspiration.

Question 5

What is the volume and definition of expiratory reserve volume?

Answer 5

> 1100 ml

> Additional volume of air that can be expired at end of tidal volume by forceful expiration.

Question 6

What is the volume and definition of residual volume?

Answer 6

> 1200 ml

> volume of air remaining in lungs after forceful expiration.

Question 7

What is the average capacity and definition of vital capacity?

Answer 7

> 4600 ml
sum of all the volumes that can be inspired or exhaled.
Inspiration to the maximum extent + expiration to the maximum extent.

Question 8

What is the average capacity and definition of total lung capacity?

Answer 8

> 5800 ml

> Sum of all the volumes = vital capacity + residual volume

Question 9

What is the average capacity and definition of inspiratory capacity?

Answer 9

> 3500 ml

> Sum of volumes above resting capacity = tidal volume + inspiratory reserve volume

Question 10

What is the average capacity and definition of function residual capacity?

Answer 10

> 2300 ml

> Sum of volumes below resting capacity = expiratory reserve volume + residual volume

Question 11

What is the definition of minute ventilation and how do you calculate it? Also, what is the average minute ventilation?

Answer 11

Total volume of gases moved into or out of the lungs per minute = minute ventilation (VE)

Minute Ventilation = (breaths per minute) x (tidal volume)

8000 ml/min or 8 L/min

Question 12

What is the definition of alveolar ventilation and how is it calculated? Also, what is the average alveolar ventilation?

Answer 12

Total volume of gases that enter spaces participating in gas exchange per minute = alveolar ventilation (VA)

Alveolar Ventilation = (breaths/min) x (tidal volume - dead space)

5600 ml/min or 5.6 L/min

Question 13

What organs make up the anatomic dead space?

Answer 13

> trachea
bronchi
bronchioles

Question 14

What makes up physiological dead space?

Answer 14

anatomic dead space + ventilated alveoli with poor or absent perfusion

Question 15

What is the total dead space in a normal individual?

Answer 15

0.15 liters

Question 16

What are the two formulas for minute and alveolar ventilation?

Answer 16

Minute Ventilation = 0.5 x breathing rate

Alveolar Ventilation = 0.35 x breathing rate

Question 17

What are the two observations that have to be taken into account when calculating dead space?

Answer 17

> dead space does not participate in ventilation and contains negligible CO2

> amount of CO2 in regions of lungs involved in gas exchange = that of arterial blood (PaCO2)

Question 18

What is the definition of trans-pulmonary pressure and how do you calculate it?

Answer 18

Transpulmonary pressure -> difference between the alveolar pressure and the pleural pressure during any point in the inspiration of expiration cycles.

• measured in centimeters of water

Question 19

What is the pleural pressure?

Answer 19

Pressure of fluid in the space between the visceral and parietal pleura.

• measured in centimeters of water
• during inspiration = -5 to -7.5 cm H20
• during expiration = -7.5 to -5 cm H20

Question 20

What is alveolar pressure?

Answer 20

Pressure of air inside the alveoli.

• measured in centimeters of water
• during inspiration = 0 to -1 cm H20
• during expiration = 0 to +1 cm H20

Question 21

Know the definition of compliance as it applies to the lungs and compare it with elastance?

Answer 21

Compliance is a measure of the ease with which a hollow viscus may be distended; i.e., the volume change resulting from the application of a unit pressure differential between the inside and outside of the viscus; the reciprocal of elastance.

Elastance is a measure of the tendency of a hollow viscus to recoil toward its original dimensions upon removal of a distending or collapsing force.

Compliance -> the extent (volume) to which lungs will expand for each unit increase in the transpulmonary pressure.

Compliance is expressed in liters (volume of air) per centimeter of water (pressure)
- normal = 200 ml air/ cm H20

Compliance is a measure of the expansibility of the lungs and trachea.

Compliance (capacitance) = increase in volume/increase in pressure

Question 22

What is surface tension?

Answer 22

When water forms a surface with air, the water molecules on the surface of the water have an especially strong attraction for one another. As a result, the water surface is always attempting to contract. In lungs, this would cause the alveoli to try to collapse.

Question 23

What are the most important components of surfactant?

Answer 23

> dipalmitylphophatidylcholine (a phospholipid)
surfactant apoproteins
calcium ions

Question 24

What type of cells produce surfactant?

Answer 24

Type II alveolar cells

Question 25

True or False:

If there is not surfactant, the pressure would calculate to about 18 cm of water pressure; about 4.5 times as great.

Answer 25

True

Question 26

True or False:

If air passages leading from the alveoli are blocked, the surface tension in the alveoli collapses the alveoli. This creates negative pressure in the alveoli.

Answer 26

False - this creates positive pressure in the alveoli.

Question 27

Which muscles are used in inspiration?

Answer 27

• respiratory diaphragm
• external intercostal muscles (limited)
• sternomastoids
• serratus anterior muscles
• scalene muscles