Lecture 13: Pulmonary Shunts, Physiological Dead Space, LaPlace's Law (Exam III)

Question 1

What are the values of all four Starling pulmonary capillary forces?

Answer 1

P_CAP: 7 mmHg

π_CAP: 28 mmHg

P_ISF: -8 mmHg

π_ISF: 14 mmHg

Question 2

What contributes to the negative interstitial capillary hydrostatic pressure?

Answer 2

The -8 mmHg comes from the intrathoracic pressure of -4 mmHg along with the actions of the lymphatic system acting as a small vacuum pump.

Question 3

In Alveolus B there is adequate perfusion, but no ventilation. This mimics a ____________ shunt.

Answer 3

Right-to-left shunt

A circulatory shunt is going from the right side of the heart to the left side of the heart. And in the process, the blood is not becoming oxygenated. So that would basically mimic a right-to-left shunt.

Question 4

In Alveolus C, we have fresh air coming in, but it’s not participating in gas exchange. This will be known as ___________.

Answer 4

Alveolar Dead Space / Physiological Dead Space

Question 5

What is the formula for Total Dead Space?

Answer 5

V_TotalDS = V_AnatomicDS + V_AlveolarDS

Question 6

What would be the alveolar dead space volume (V_ADS) for a healthy 20-year-old?

Answer 6

0 mmHg

Alveolar Deadspace Volume will increase after 20.

Question 7

Alveolar and anatomical dead space share some similarities in that expired air coming from either of these places should have a similar composition as to __________.

What would expired P_AO2 and P_CO2 from alveolar dead space be equal to?

Answer 7

inspired air

Expired P_AO2 = 150 mmHg
Expired P_A CO2 = 0 mmHg

Question 8

During the expiration portion of a normal tidal volume what components of the V_T is expired first?

Answer 8

150 mL anatomical DS air

Question 9

During the inspiration portion of a normal tidal volume the first amount of air inspired will go to the _______.

Answer 9

Alveoli

Question 10

As expiration moves forward after the first 150 mL, the next 350 mL of air will contain ________(more/less) CO2 and (more/less) O2.

Answer 10

More CO2
Less O2

Last 350 mL will come from area in the lungs involved with gas exchange.

Question 11

What happens if there is simultaneous emptying of both good alveoli and alveoli with dead space?

Answer 11

The gas coming from the alveolar dead space is going to typically dilute out the CO2 that’s going to be in the healthy parts of the lung as well as increased the O2 that’s coming out of the lung.

Question 12

Good Expired Alveolar Air:
P_AO2 =
P_ACO2 =

Answer 12

Good Expired Alveolar Air:
P_AO2 = 100 mmHg
P_ACO2= 40 mmHg

Last 350 mL of expired breath.

Question 13

What does it mean if our EtCO₂ is less than 40 mmHg?

Answer 13

The patient is either getting too much fresh air or there may be some alveolar dead space.

Question 14

What is a good rule of thumb for just estimating somebody’s anatomical dead space?

When will this rule not work so well?

Answer 14

• 1mL of anatomical dead space for 1 pound bodyweight.
• If someone is incredibly overweight, it will be a gross overestimation of anatomical dead space.

Question 15

Are pulmonary shunts or dead space easier to fix?

Answer 15

Alveolar dead space is easier to fix. Just put more fresh air into the lungs.

Question 16

How will the body naturally compensate for a pulmonary shunt (Alveolus B)?

Answer 16

Hypoxic Pulmonary Vasoconstriction

Question 17

How will CRNAs inhibit HPV?

Answer 17

Volatile anesthetics will inhibit HPV.

Question 18

Surfactant helps decrease __________ and make it easier for air to get into the lungs.

Answer 18

Surface tension

Question 19

If P1 and P2 had the same amount of surfactant, which alveolus will be more compliant and have the lower surface tension? (Ignore the blue arrow)

Answer 19

P1 will be more compliant and have less surface tension due to a higher concentration of surfactant which breaks more surface tension in the smaller alveolus.

Surfactant guards against uneven ventilation.

Question 20

Demonstrating Laplace’s Law:
Which sphere will have a higher internal pressure?

Answer 20

P1

Question 21

What is the relationship between wall tension and radius?

Answer 21

It is an inversely proportional relationship. Wall tension will decrease as the radius increases.

Question 22

Laplace’s law states that the pressure inside an inflated elastic container with a curved surface (alveoli) is _________ proportional to the radius as long as the surface tension is constant and containers are filled to a reasonable size.

Answer 22

inversely

Question 23

_________ prevents the unequal distribution of ventilation that Laplace predicts.

Answer 23

Surfactant

Question 24

With COPD, there will be surfactant deficiency which will lead to _________ ventilation.

Answer 24

uneven