Lectures 3 & 4

Question 1

According to Dalton’s Law, what is the Partial Pressure of Oxygen and Nitrogen in ROOM AIR at Sea Level (760 mmHg)

Answer 1

Oxygen 21%- (0.21 x 760)= 160 mmHg

Nitrogen 78%- (0.78 x 760)= 600 mmHg

Question 2

What is the Alveolar Gas Equation at sea level?

Answer 2

pAO2= FiO2 × (760-47) -(pACO2)/R

Question 3

What is a “good” partial pressure of CO2 and where is this present?

Answer 3

1. 40 mmHg

2. Alveolus and the Artery

Question 4

What is the Partial Pressure of O2 (ppO2 or pO2) in Room Air, Trachea, Alveolus (pAO2), and the Artery (paO2)?

Answer 4

Room Air 160 mmHg
Trachea 150 mmHg
Alveolus 100 mmHg
Artery 95 mmHg

Question 5

Where is the Partial Pressure of Water Vapor present at what value is it?

Answer 5

1. In Trachea and the Alveolus

2. 47 mmHg

Question 6

What is the Partial Pressure of Nitrogen (ppN or pN) in Room Air, Trachea, Alveolus (pAN), and the Artery (paN)?

Answer 6

Room Air 600 mmHg
Trachea 563 mmHg
Alveolus 523 mmHg
Artery 578 mmHg

Question 7

What is the Alveolar-Arterial Gradient and what is a typical value for it?

Answer 7

1. Difference between pAO2 (Alveolar) and (paO2) arterial

2. Typically between 5-10 mmHg

Question 8

What could lead to an increase in the Alveolar-Arterial Gradient?

Answer 8

A Diffusion problem where not all of the blood from the right side of the heart is oxygenated

Question 9

What is Anatomic Dead Space?

Answer 9

1. Tissue that is not involved in gas exchange like the first 16 generations of the lung
2. 150 mL
3. Measured via Fowler’s Method (N2 concentration by O2 washout)

Question 10

Under normal circumstances, what are the Ventilation Volumes, Flows, and Rates?

Answer 10

Ventilation= 7500 mL/min
Frequency- 15 breathes/min
Tidal Volume- 500 mL each breath
Anatomic Dead Space- 150 mL each breath (2250 mL/min)
Alveolar Ventilation- 5250 mL/min
Pulmonary Blood Flow- 5L/min

Question 11

What are the 4 Capacities measured via Spirometry?

Answer 11

1. Functional Residual Capacity- All of the air beneath Tidal Volume (FRC= ERV+RV)
2. Inspiratory Capacity (IC=TV+IRV)
3. Vital Capacity- all you can move (VC= IRV+TV+ERV)
4. Total Lung Capacity- everything (TLC= IRV+TV+ERV+TV)

Question 12

What are the 4 Volumes measured via Spirometry?

Answer 12

1. Tidal Volume- 500 mL moved each breath
2. IRV (Inspiratory Reserve Volume)- 3000 mL moved with max inspiration not including Tidal Volume
3. ERV (Expiratory Reserve Volume)- 1100 mL moved with max expiration not including Tidal Volume
4. Residual Volume- 1200 mL always in the Lung to keep alveolar open

Question 13

What is Vital Capacity and what is the equation for it?

Answer 13

1. Maximum amount of air you can move going from with Max inspiration and expiration
2. VC=IRV+TV+ERV

Question 14

What is Forced Vital Capacity?

Answer 14

Same as Vital Capacity (maximum amount of air you can move going from with Max inspiration and expiration) BUT it is less than VC because you get less air out when it is forced

Question 15

What volume of the lung CANNOT be measured by Simple Spirometry? What capacities CANNOT be calculated because of this?

Answer 15

1. Residual Volume CANNOT be measured

2. Therefore Functional Residual Capacity and Total Lung Capacity CANNOT be calculated

Question 16

What is Functional Residual Capacity?

Answer 16

1. FRC= ERV+RV

2. Represents Volume of lung where tendency of the lung to spring out and the chest wall to recoil are balanced

Question 17

What is Physiological Dead Space?

Answer 17

1. Volume of gas that does NOT participate in gas exchange and does NOT eliminate CO2
2. Measured via Bohr’s Method

Question 18

How can you measure Anatomical Dead Space?

Answer 18

Fowler’s Method- Individual breathes in 100% O2 and N2 in exhaled air is measured. This basically measures the amount of N2 displaced by the inhaled O2.

Question 19

How can you measure Physiological Dead Space?

Answer 19

Since Physiological Dead Space does not contribute CO2, use the Bohr Equation:
Physiological Dead Space Volume= TV x {(paCO2-peCO2)/paCO2}
peCO2 is expired CO2
SIDENOTE: pACO2=paCO2

Question 20

How can you measure Communicating Gas (all of the parts of the lung that can be reached by the outside)?

Answer 20

Helium Dilution Method- have person breathe Helium from Spirometer for several breaths then measure how much Helium is left

Question 21

What is Alveolar Ventilation?

Answer 21

VA= TV- (Dead Space x Rate)

Question 22

What is the equation for the Volume of CO2 exhaled per unit time?

Answer 22

VCO2= Alveolar Ventilation x (%CO2/100) x K

Question 23

What happens to CO2 if Ventilation is cut in half?

Answer 23

CO2 is DOUBLED if Ventilation is HALVED

Question 24

What is Hypoxemia?

Answer 24

Abnormally low concentration of O2 in blood (low paO2)

Question 25

What is Hypercarbia?

Answer 25

Abnormally high concentration of CO2 in blood (high paCO2)

Question 26

At high altitude what comes first, Hypoxemia or Hypercarbia?

Answer 26

Hypoxemia (Abnormally low concentration of O2 in blood)

Question 27

With Interstitial Lung Disease what comes first, Hypoxemia or Hypercarbia?

Answer 27

Hypoxemia (Abnormally low concentration of O2 in blood) because this would mean the interstitium is fibrotic

Question 28

During Hypoventilation what comes first, Hypoxemia or Hypercarbia?

Answer 28

Hypercarbia (Abnormally high concentration of CO2 in blood)

Question 29

What can be measured by Carbon Monoxide?

Answer 29

Diffusion since CO immediately binds to Hemoglobin and doesn’t change concentration in the blood

Question 30

What is the difference between Hypoxia and Hypoxemia?

Answer 30

1. Hypoxemia is low oxygen in the blood (low paO2)

2. Hypoxia is low oxygen in the tissue

Question 31

What are some causes of Hypoxemia?

Answer 31

1. Hypoventilation (low inspired O2)
2. Interstitial Disease
3. Ventilation-Perfusion Inequality
4. Shunt

Question 32

How can you calculate Alveolar O2?

Answer 32

Alveolar O2= Ambient O2- Inspired O2
(0.21 x Air Pressure) - [0.21 x (Air Pressure - 47)]
Answer should be around 90-100

Question 33

How can you increase low inspired O2 (low paO2)?

Answer 33

By increasing the proportion of O2 in the gas mixture from 21% to a larger fraction

Question 34

What does Hypoventilation do to pACO2 and paCO2 concentrations?

Answer 34

Hypoventilation ALWAYS INCREASES pACO2 and paCO2

Question 35

How can we overcome Diffusion Limitation?

Answer 35

By increasing the change in Pressure so O2 will diffuse more rapidly into the blood. This can be done by adding oxygen

Question 36

What is a V/Q mismatch and what does it cause?

Answer 36

V= Ventilation or Airflow
Q= Perfusion or Blood flow
Normally V/Q=1, but:
1. While choking V=0 so V/Q is decreasing to 0
2. Bloodclot means Q=0 so V/Q is increasing to infinity

Question 37

What is Total Deadspace?

Answer 37

Sum of Anatomic Deadspace (parts where gas exchange does NOT occur) + Physiological Deadspace (Alveolar space that is well ventilated but perfusion is blocked by pulmonary embolus)

Question 38

What is an Anatomic Shunt?

Answer 38

It is a type of Physiological Shunt where blood enters the arterial system without ever going through ventilated areas of the lungs

Question 39

What is Anatomic Deadspace?

Answer 39

Space that may have ventilation but has NO perfusion so gas exchange does NOT occur

Question 40

What is the only case of Hypoxemia that CANNOT be resolved by administering Oxygen?

Answer 40

Anatomic Shunt

Question 41

Where is Perfusion (Blood Flow) greatest in the lung and why?

Answer 41

At the BOTTOM because Alveoli are small so blood vessels are all fat allowing blood to flow easily

Question 42

Where is Ventilation (Air Flow) greatest in the lung and why?

Answer 42

At the BOTTOM because they change size more easily at the bottom

Question 43

What happens to the slope of a V/Q graph as you move from the bottom of the lung to the top?

Answer 43

It goes up (sort of like a J) and is greatest at the top because Perfusion (Q) decreases much faster than Ventilation (V)