Respiration II

Question 1

What is a spirometer and what is its purpose?

Answer 1

A spirometer is a cannister connected to a tube and a pen. Its purpose is to measure volumes of inhaled or exhaled gas, so it can be used to measure tidal volume, vital capacity, inspiratory capacity, expiratory reserve volume, and inspiratory reserve volume.

Question 2

How do you read a spirometry result?

Answer 2

An upward inflection signifies inhalation and a downward inflection signifies exhalation.

Question 3

What metrics can spirometry be used to measure? What metrics can’t it be used to measure?

Answer 3

It can measure: tidal volume, vital capacity, inspiratory capacity, expiratory reserve volume, inspiratory reserve volume
It can’t measure: functional residual capacity, total lung capacity, residual volume

Question 4

Define and describe tidal volume.

Answer 4

Tidal volume is the amount of air inhaled or exhaled during relaxed, quiet breathing.

Question 5

Define and describe residual volume.

Answer 5

Residual volume is the amount of air remaining in the lungs after maximum expiration.

Question 6

When you expire, are your lungs empty? Explain.

Answer 6

No. Even after maximum effort to expire, there will still be air remaining in the lungs that keeps the alveoli inflated and that will mix with fresh air on the next inspiration. This is called residual volume.

Question 7

Define and describe vital capacity.

Answer 7

Vital capacity is the amount of air that can be exhaled with maximum effort after maximum inspiration.

Question 8

Define and describe inspiratory reserve volume.

Answer 8

Inspiratory reserve volume is the amount of air in excess of tidal inspiration that can be inhaled with maximum effort.

Question 9

Define and describe expiratory reserve volume

Answer 9

Expiratory reserve volume is the amount of air in excess of tidal expiration that can be exhaled with maximum effort.

Question 10

Define and describe inspiratory capacity

Answer 10

Inspiratory capacity is the maximum amount of air that can be inhaled after a normal tidal expiration (tidal volume + inspiratory reserve volume).

Question 11

Define and describe total lung capacity.

Answer 11

The total lung capacity is the maximum amount of air the lungs can contain (residual volume + vital capacity).

Question 12

What method can be used to measure functional residual capacity? Explain the setup.

Answer 12

Helium dilution. A spirometer is filled with helium, and the subject is made to mouth-breathe into the spirometer after breathing all the way out to functional residual capacity, diluting the volume of helium. After equilibration between the lungs and the spirometer, you can calculate the functional residual capacity.

Question 13

What is the formula used in helium dilution? Explain the variables.

Answer 13

FRC = (C1 x V1 / C2) - V1
Where FRC = functional residual capacity
C1 = initial concentration of helium in spirometer
V1 = volume of spirometer
C2 = final concentration of helium at equilibrium

Question 14

What is minute ventilation?

Answer 14

It is the amount of air inspired or expired into the lungs over the course of one minute.

Question 15

What is the formula for minute ventilation?

Answer 15

VE = VT x f
Where VT is the tidal volume and f is the number of breaths per minute.

Question 16

What is alveolar ventilation? How is it different from minute ventilation?

Answer 16

Not all the air calculated for minute ventilation actually makes it into the alveoli due to anatomical dead space, meaning that it remains in the conducting airways. Alveolar ventilation is the amount of air that reaches the respiratory zone per minute and is available for gas exchange.

Question 17

What is the typical volume of anatomical dead space in an individual?

Answer 17

The volume of the anatomical dead space in the adult subject is about 150 mL. It is hard to measure, but it can be approximated with the individual’s weight in pounds.

Question 18

In an 150 lb male with tidal volume = 500 ml and frequency = 12 breaths/minute, calculate the minute ventilation and the alveolar ventilation.

Answer 18

In a normal individual, minute ventilation = 6000 mL (500 x 12).

The volume of anatomical dead space is about 150 mL. Alveolar ventilation = (500-150) x 12 = 4200 ml/min

Question 19

Explain what alveolar dead space is. Is this a physiologial or pathological condition?

Answer 19

Alveolar dead space is a pathological condition where a certain amount of inspired air, although reaching the respiratory zone, does not take part in gas exchange. This can be due to decreased or lack of blood supply (due to clotting, for example). These alveoli therefore represent alveolar dead space.

Question 20

What is physiological dead space? How do you calculate dead space ventilation?

Answer 20

The sum of alveolar and anatomical dead space is the physiological dead space.
Dead space ventilation is calculated is the difference between minute and alveolar ventilation. VD = VE - VA

Question 21

What are the partial pressures of oxygen and carbon dioxide in the atmosphere at sea level? How are they calculated?

Answer 21

pO2 = 150 mm Hg
pCO2 = 0.2 mm Hg
These are calculated based on a water vapor pressure of 47 mm Hg.

Question 22

How do the concentrations of O2 and CO2 compare between air outside the body and air in the alveoli?

Answer 22

Outside the body: PO2 = 160 mm Hg, PCO2 = 0.3 mm Hg
Alveoli: PO2 = 105 mm Hg, PCO2 = 40 mm Hg

Question 23

Describe the concentration of oxygen and carbon dioxide in the blood at the before arriving at the alveoli, after passing by the alveoli, before arriving at cells, and after arriving at cells.

Answer 23

After cells and before alveoli (in systemic veins and pulmonary arteries): 46 mm Hg CO2, 40 mm Hg O2
After alveoli and before cells (pulmonary veins and systemic arteries): 100 mm Hg O2, 40 mm Hg CO2

Question 24

What is the goal of normal alveolar ventilation?

Answer 24

The alveolar ventilation keeps arterial CO2 at a constant level of around 40 mm Hg. This is what drives us to breathe.

Question 25

Compare CO2 and O2 in terms of concentration gradient between air and blood and solubility.

Answer 25

The concentration gradient from alveoli to blood is much more dramatic for O2 than CO2. The solubility of CO2 in the fluids is greater than that of oxygen, so it diffuses faster and doesn’t need such a large concentration gradient to diffuse within the same amount of time.

Question 26

What is alveolar hyperventilation? How does it affect CO2 and O2 concentrations?

Answer 26

This occurs when more O2 is supplied and more CO2 is removed than the metabolic rate requires (minute ventilation is higher than needed). Both PAO2 and PaO2 rise and PACO2 and PaCO2 decrease.

Question 27

What is alveolar hypoventilation? How does it affect O2 and CO2 concentrations?

Answer 27

The rate at which O2 is added to alveolar gas and the rate at which CO2 is eliminated is lowered. As a result, Both PAO2 and PaO2 decrease and PACO2 and PaCO2 rise.

Question 28

Name 4 instances where alveolar hypoventilation could occur.

Answer 28

1. During severe lung disease
2. When there is damage to the respiratory muscles
3. When the chest cage is injured and the lungs collapse
4. When the central nervous system is depressed.

Question 29

When breathing air with low PO2 how will the following change:
a) Alveolar PO2
b) Alveolar PCO2

Answer 29

a) Decreases
b) No change

Question 30

When increasing alveolar ventilation without changing the metabolism, how will the following change:
a) Alveolar PO2
b) Alveolar PCO2

Answer 30

a) Increases
b) Decreases

Question 31

When decreasing alveolar ventilation with unchanged metabolism how will the following change:
a) Alveolar PO2
b) Alveolar PCO2

Answer 31

a) Decreases
b) Increases

Question 32

When increasing metabolism without changing alveolar ventilation, how will the following change:
a) Alveolar PO2
b) Alveolar PCO2

Answer 32

a) Decreases
b) Increases

Question 33

When decreasing metabolism without changing alveolar ventilation, how will the following change:
a) Alveolar PO2
b) Alveolar PCO2

Answer 33

a) Increases
b) Decreases

Question 34

For proportional increases in metabolism and alveolar ventilation, how will the following change:
a) Alveolar PO2
b) Alveolar PCO2

Answer 34

a) No change
b) No change

Question 35

The transfer of oxygen across the alveolar-capillary membrane via […], which is governed by […]

Answer 35

passive diffusion, which is governed by Fick’s Law

Question 36

Diffusion rate of oxygen is proportional to what 3 factors?

Answer 36

• Surface area
• Partial pressure gradient
• 1/thickness

Question 37

How does the diffusion rate of O2 compare to CO2? Explain why.

Answer 37

In order for a gas to diffuse through a liquid, the gas must be soluble in the liquid. Since CO2 is considerably more soluble than O2, it diffuses approximately 20 times per rapidly than O2.

Question 38

The time required for equilibrium between alveolar air and capillary blood is […] between oxygen and carbon dioxide.

Answer 38

approximately the same

Question 39

The transit time of a red blood cell is […], and the diffusion time of CO2 and O2 is […]

Answer 39

0.75 seconds, 0.25 seconds

Question 40

How does the transit time of a red blood cell change during exercise?

Answer 40

The RBC will travel faster through capillary during exercise. So, the transit time will shorten to around 0.3 seconds. Under normal conditions, this is still enough time to saturate the RBCs with O2 and desaturate them with CO2.

Question 41

If a patient has cardiac failure or edema, how might this affect gas exchange? Explain.

Answer 41

The alveolar capillary membrane increases, so the diffusion of the two gases is slowed down. This is the dashed line - it takes longer to saturate in O2 and desaturate in CO2. In this example, this subject still had enough time to complete the exchange. But if that subject exercises and increases their cardiac output, the transit time shortens to 0.3 and they run out of time if diffusion is slower. They are unable to saturate in O2 and desaturate in CO2 in time.