Exam 2 - Pulmonary Lecture 3

Question 1

Why is a P_AO2 of 104 mmHg more accurate than 100 mmHg?

Answer 1

104 mmHg is the more accurate number, but that number is reduced when pulmonary venous circulation empties into the left atrium diluting systemic PO2 down to 100 mmHg

Question 2

How does PaO2 change as we age?

Answer 2

Decreases as we age, lungs start slowly declining in function after age 20

Question 3

What is normal anatomical dead space volume?

Answer 3

150 mL

Question 4

What happens to the concentrations of gases as they’re inhaled?

Answer 4

• The portion that makes it to the respiratory zones becomes diluted by the 3.0L already in the lungs (FRC)
• The dead space gas remains the same concentration as it’s not mixing with FRC

Question 5

What is alveolar dead space? Example?

Answer 5

Ventilated alveoli that are not perfused
Pulmonary embolism and positive pressure ventilation

Question 6

Equation for tidal volume based on physiologic dead space?

Answer 6

V_T = V_D + V_A
500 = 150 + 350

Question 7

What is normal alveolar minute ventilation?

Answer 7

12 bmp x 350 mL = 4.2 L/min

Question 8

What is normal minute dead space ventilation?

Answer 8

12 bpm x 150 mL = 1.8 L/min

Question 9

What does this symbol mean?
What is it equal to?

Answer 9

Expired gas minute ventilation
Equivalent to Total minute ventilation

Question 10

How can you calculate total alveolar minute ventilation?

Answer 10

Question 11

What happens to gas concentrations as they are expired?

Answer 11

The dead space gas that remained concentrated now becomes diluted by gas that was involved in gas exchange

Question 12

What do expect to happen to P_AO2 if we increase or decrease from normal alveolar ventilation?

Answer 12

Normal alveolar ventilation is 4.2 L/min, if we increase our ventilation P_AO2 increases. If we decrease ventilation P_AO2 decreases

Question 13

What do expect to happen to P_ACO2 if we increase or decrease from normal alveolar ventilation?

Answer 13

As ventilation increases P_ACO2 decreases, as ventilation decreases P_ACO2 increases

Question 14

What is normal pulmonary capillary pressure (P_cap)?

Answer 14

7 mmHg

Question 15

What is normal pulmonary capillary oncotic pressure (∏_cap)?

Answer 15

28 mmHg

Question 16

What is pulmonary interstitial hydrostatic pressure (P_IS)?
Why is different than the periphery?

Answer 16

-8 mmHg
The extra negative pleural pressure (-4 mmHg/-5cmH2O) adds to the negative pressure of the lymphatics

Question 17

What is normal pulmonary interstitial oncotic pressure (∏_IS)?

Answer 17

14 mmHg

Question 18

What is the net filtration pressure in pulmonary capillaries?

Answer 18

NFP = P_cap + ∏_IS + P_IS - ∏_cap
= 7 + 14 + 8 - 28 = + 1 mmHg

Question 19

How can anesthesia affect pulmonary lymphatics?

Answer 19

PPV can compress the lymphatics and lead to edema

Question 20

At what LAP does edema begin to form?
What else can encourage pulmonary edema formation?

Answer 20

23 mmHg
Hemorrhage - loss of oncotic pressure

Question 21

What is the capillary filtration coefficient (K_f)?

Answer 21

The permeability characteristics of the membrane to fluids AND the surface area of the alveolar-capillary barrier

Question 22

What is Q_f?
How is it calculated?

Answer 22

Net flow of fluid or perfusion
K_f × NFP

Question 23

What clinical problems can lead to pulmonary edema by increasing capillary permeability (K_f)?

Answer 23

• ARDS
• O2 toxicity
• Inhaled or circulating toxins

Question 24

What clinical issues can increase capillary hydrostatic pressure (P_c) and cause pulmonary edema?

Answer 24

Increased LAP from mitral stenosis or LV MI

Question 25

What could decrease P_IS and lead to pulmonary edema?

Answer 25

- Rapid evacuation of a pneumothorax or stripping the chest tube - Strong person attempting to breath against a closed airway (will generate flash pulmonary edema)

Question 26

What can decrease colloid osmotic pressure (∏_pl)?

Answer 26

- Protein starvation - IV fluid dilution - Renal protein loss

Question 27

What clinical issues will cause insufficent pulm lymphatic drainage?

Answer 27

- Tumors - Fibrosis - High altitude pulmonary edema - Head injury

Question 28

What areas of the lung recieve the most ventilation (upright)?

Answer 28

The base; this is also where most perfusion is which creates V/Q matching

Question 29

What are the P_IP at the top and bottom of the lung at FRC?

Answer 29

There is a pressure gradient where P_IP is lower at the apex (-8.5 cmH2O) and higher at the base ( -1.5 cm H2O) due the weight from the diaphragm

Question 30

Why does air go to the base of the lung first during inspiration? What term describes these alveoli?

Answer 30

Because the top of the lung has more negative pleural pressure it makes those alveoli larger and they smaller towards the base of the lung. The larger alveoli have more air in them, so air will choose to go to the less full alveoli at the base first. These alveoli are more *compliant*

Question 31

How full are the alveoli at the apex and base of the lung at FRC?

Answer 31

Apex = 60 % full Base = 25 % full

Question 32

What does the steepness of the curve tell you at the indicated points?

Answer 32

- At the top the curve is almost flat, this means the alveoli are **not compliant** - evidenced by a large increase in Ptp is not increasing volume. - At the bottom the curve is very steep, meaning the alveoli are **very compliant** - a small increase in Ptp greatly increases alveolar volume Air will always go to the more compliant alveoli

Question 33

What is histeresis?

Answer 33

The lungs are more compliant on expiration than inspiration, hence the two curves below

Question 34

What are the pleural pressures in the lung at RV? Why?

Answer 34

- At the apex it's - 2.2 cm H2O - At the base it's +4.8 cm H2O This is because we have to force air out to get down to RV

Question 35

How full are the alveoli at the apex and base of the lung at RV?

Answer 35

- At the apex - 30 % full - At the base - 20 % full (as empty as they can be)

Question 36

Where does air travel first during inspiration from RV?

Answer 36

To the apex, because the very positive Pip at the base causes the lower airways to pinch off preventing airflow to enter. After the upper airways being to fill, they will stretch out the lower airways and then the air will being to to fill them.

Question 37

What is the compliance at the arrow?

Answer 37

No compliance, there is no increase in volume with an increase in Ptp

Question 38

What happens to lung volumes during anesthesia?

Answer 38

Lung volumes drop, closer to RV This is because of supine positioning and muscle relaxation

Question 39

Explain hypoxic pulmonary vasoconstriction? How is this different than systemic vessels?

Answer 39

- When the pulmonary capillary detects low PAO2, it constricts to redirect blood flow to better ventilated areas. - In all other tissues, capillaries dilate in response to low O2 levels

Question 40

How do volatile anesthetics inhibit HPV?

Answer 40

Volatiles increase K+ conductance, relaxing smooth muscle. This prevents them from contracting when they need to redirect blood flow

Question 41

How does the alveoli react to decrease perfusion?

Answer 41

Decreased perfusion causes the alveolar gas concentrations to look more like the inspired concentrations d/t decreased exchange. This causes the airway smooth muscle to constrict to redirect air flow to better perfused alveoli to prevent dead space ventilation

Question 42

What do you need to keep in mind when oxygenating a patient?

Answer 42

* If you cause hyperoxyia, the smaller airways can become reactive and close off * This happens because the P_AO2 will be much higher than normal (say 300 mmHg instead of 100). The airways may think that perfusion is decreased to this alveoli because of the high O2 and close them off

Question 43

How much does FRC decrease when moving to the supine position? What volumes change?

Answer 43

About 1 L - ERV gets smaller and IRV increases, allowing vital capacity to remain the same

Question 44

Label each of the waveforms below on the spirometry tracing

Answer 44

1. Vital capacity 2. Inspiratory Reserve volume 3. Expiratory Reserve Volume 4. Tidal Volume 5. Inspiratory Capacity