Respiratory

Question 1

How does the pulmonary artery compare to systemic arteries and the aorta in terms of length, thickness, and compliance?
A:

Answer 1

• It is shorter than systemic arteries.
• It is thinner than the aorta, with about 1/3 the aortic diameter.
• It has high compliance, around 7 ml/mmHg, meaning it can stretch easily.

Question 2

What happens when alveolar PO₂ falls below 70% of normal?

Answer 2

A: Alveolar cells start secreting vasoconstrictors.

Question 3

Why do pulmonary vessels constrict when alveolar PO₂ is low?

Answer 3

A: To redirect blood flow to better-aerated alveoli.

Question 4

How does pulmonary blood pressure vary at different lung levels (apex, hilum, base)?
A:

Answer 4

• Apex: Systolic = 10 mmHg, Diastolic = -7 mmHg
• Hilum: Systolic = 25 mmHg, Diastolic = 8 mmHg
• Base: Systolic = 33 mmHg, Diastolic = 16 mmHg

Question 5

What are the location, intra-alveolar pressure, and pulmonary artery pressure characteristics of Zone 2 in the lung?
A:

Answer 5

• Located at the apex (top) of the lung.
• Intra-alveolar pressure (IAP) is zero mmHg.
• Pulmonary artery pressure is approximately 10 mmHg systolic / -7 mmHg diastolic

Question 7

What happens to blood flow in Zone 2 when systolic pressure is greater than intra-alveolar pressure and when diastolic pressure is less than intra-alveolar pressure?
A:

Answer 7

• When systolic pressure > intra-alveolar pressure, blood flow occurs.
• When diastolic pressure < intra-alveolar pressure, no blood flow occurs.

Question 8

What is the pattern of blood flow in Zone 2?

Answer 8

A: Intermittent blood flow – only during systole.

Question 9

Where is Zone 3 located in the lung and what is the intra-alveolar pressure (IAP)?
A:

Answer 9

• Located at the hilum and base levels of the lung.
• Intra-alveolar pressure (IAP) is zero mmHg.

Question 10

What are the pulmonary artery pressures at the hilum and base in Zone 3?
A:

Answer 10

• At the hilum: approximately 25/8 mmHg (systolic/diastolic).
• At the base: approximately 33/16 mmHg (systolic/diastolic).

Question 11

What is the pattern of blood flow in Zone 3 of the lung?

Answer 11

A: Continuous blood flow during both systole and diastole.

Question 12

Under what conditions is only Zone 3 visible in the lung?

Answer 12

A: When lying down or exercising.

Question 13

Is Zone 1 normally found in healthy lungs, and what is the blood flow like during the cardiac cycle?
A:

Answer 13

• Zone 1 is pathological and not found in normal lungs.
• There is no blood flow at any time during the cardiac cycle in Zone 1.

Question 14

Under what condition does Zone 1 occur?

Answer 14

A: When pulmonary systolic pressure is too low.

Question 15

In what clinical situations is Zone 1 seen?

Answer 15

A: Seen in severe blood loss and pulmonary embolism.

Question 16

What is the main inward force and its value?

Answer 16

A: Plasma colloid osmotic pressure = 28 mmHg (constant).

➔ Pull fluid into the capillary

Question 17

What are the main outward forces that push fluid into the interstitium in the lungs, and what are their values?
A:

Answer 17

• Capillary hydrostatic pressure: 7 mmHg
• Negative interstitial fluid pressure: 8 mmHg (constant)
• Interstitial fluid (ISF) colloid osmotic pressure: 14 mmHg (constant)

Question 18

What is the total net outward force in pulmonary capillaries?

Answer 18

A: 29 mmHg (7 + 8 + 14)

Question 19

Why is interstitial pressure called “negative” in the lungs?

Answer 19

A: Because it draws excess fluid from the alveoli into the interstitium.

Question 20

How is excess interstitial fluid removed from the lungs?

Answer 20

A: It is pumped back to the circulation through the pulmonary lymphatic system.

Question 21

What happens when interstitial fluid pressure becomes positive?

Answer 21

A: Water fills the alveoli, leading to pulmonary edema.

Question 22

By how much must pulmonary capillary hydrostatic pressure increase to cause pulmonary edema, and what is the acute safety factor?
A:

Answer 22

• It must rise from 7 mmHg to more than 28 mmHg.
• This provides an acute safety factor of 21 mmHg against pulmonary edema.

Question 23

What happens with chronic elevation of pulmonary capillary pressure?

Answer 23

• Pulmonary lymph vessels expand greatly

Question 24

What is the chronic safety factor against pulmonary edema?

Answer 24

A: 35 mmHg

Question 25

Causes of pulmonary edema?

Answer 25

➔ Left-sided heart failure or mitral valve disease ➔ Damage to the pulmonary capillary membranes

Question 26

What are the mechanisms that increase pulmonary blood flow during exercise? A:

Answer 26

• Opening more capillaries • Distending existing capillaries • Increasing pulmonary arterial pressure (minor contribution)

Question 27

What are the partial pressures of O₂ and CO₂ in the pulmonary artery? A:

Answer 27

• PO₂ = 40 mmHg • PCO₂ = 45–46 mmHg

Question 28

What are the partial pressures of O₂ and CO₂ in the alveoli and pulmonary vein? A:

Answer 28

• PO₂ = 100–104 mmHg • PCO₂ = 40 mmHg

Question 29

What are the normal values for alveolar ventilation, pulmonary perfusion, and the V/Q ratio? A:

Answer 29

• Alveolar ventilation: 4200 ml/min (4.2 L/min) • Pulmonary perfusion: 5000 ml/min (5 L/min) • V/Q ratio: Approximately 0.8

Question 30

What does a V/Q ratio greater than normal indicate? A:

Answer 30

• Caused by poor perfusion • Considered a physiological dead space

Question 31

What does a V/Q ratio less than normal indicate? A:

Answer 31

• Caused by low ventilation • Considered a physiologic shunt (poor oxygenation)

Question 32

How does gravity affect the V/Q ratio at the apex of the lung? A:

Answer 32

• Both ventilation and perfusion are lower • Perfusion decreases more than ventilation • V/Q ratio is high (> 0.8) • Represents physiological dead space (wasted ventilation)

Question 33

What happens to the V/Q ratio at the lowest point of the lung base? A:

Answer 33

• Inadequate ventilation • Over-perfused relative to ventilation • Low V/Q ratio (< 0.8) • Leads to a physiological shunt → poor blood oxygenation

Question 34

What happens when V/Q = 0 (zero)? A:

Answer 34

• Indicates no ventilation → physiological shunt • Alveolar PO₂ = 40 mmHg • Alveolar PCO₂ = 45 mmHg

Question 35

What happens when V/Q = ∞ (infinity)? A:

Answer 35

• Indicates no perfusion → physiological dead space • Alveolar PO₂ = 149 mmHg • Alveolar PCO₂ = 0 mmHg

Question 36

What happens when V/Q is normal (≈ 0.8)? A:

Answer 36

• Normal ventilation and perfusion • Alveolar PO₂ = 104 mmHg • Alveolar PCO₂ = 40 mmHg

Question 37

What is the effect of chronic obstructive lung disease (COPD) on V/Q ratio? A:

Answer 37

• Bronchial obstruction + alveolar wall damage • Some areas → physiological shunt • Other areas → physiological dead space • Overall: inefficient gas exchange

Question 38

What are the partial pressures of gases in the alveoli after addition of CO₂? A:

Answer 38

• PO₂ = 104 mmHg • PCO₂ = 40 mmHg

Question 39

How does the composition of expired air differ from that of alveolar air? A:

Answer 39

• Expired air has higher PO₂ than alveolar air • Expired air has lower PCO₂ than alveolar air

Question 40

What are the six layers of the respiratory membrane? A:

Answer 40

1. Fluid layer with surfactant 2. Alveolar epithelium (pneumocytes) 3. Basement membrane of the epithelium 4. Interstitial space between alveolus and capillary 5. Capillary basement membrane 6. Capillary endothelial cells

Question 41

Which gas diffuses more easily across the respiratory membrane: CO₂ or O₂?

Answer 41

A: CO₂ diffuses more easily than O₂ because it is more soluble in plasma, despite having a lower pressure gradient.

Question 42

What law governs the rate of gas diffusion across the respiratory membrane?

Answer 42

A: Fick’s law of diffusion.

Question 43

What are the diffusion coefficients for common gases? A:

Answer 43

• O₂ = 1 • CO₂ = 20 • CO = 0.8 • N₂ = 0.5

Question 44

Which factors increase the rate of gas diffusion? A:

Answer 44

• Higher pressure gradient (ΔP) • Larger surface area (A) • Higher solubility (S) • Smaller molecular weight (MW) • Higher diffusion coefficient (S/√MW)

Question 45

Rate of diffusion is inversely proportional to:

Answer 45

▪ Distance ‘thickness’ of the respiratory membrane ▪ Molecular weight of the diffusing gas

Question 46

Under non-exercising conditions, how quickly does blood become saturated with O₂ in the pulmonary capillaries?

Answer 46

A: Blood becomes almost fully saturated with O₂ after passing through only one-third of the pulmonary capillary length.

Question 47

How much of the alveolar air is replaced by new atmospheric air with each breath?

Answer 47

A: Only about one-sixth to one-seventh of the total alveolar air is replaced with each breath.

Question 48

How many breaths are needed to exchange most of the alveolar air?

Answer 48

A: Many breaths are required to fully exchange most of the alveolar air.

Question 49

How long does it take to remove half of the excess gas at different alveolar ventilation rates? A:

Answer 49

• Normal alveolar ventilation: 17 seconds • Half-normal ventilation: 34 seconds • Twice-normal ventilation: 8 seconds

Question 50

Slow replacement of alveolar air is important in preventing?

Answer 50

➔ Sudden changes in gas concentrations in the blood ➔ Excessive increase & decrease in tissue oxygenation ➔ Excessive increase & decrease in tissue CO2 concentration ➔ Excessive increase & decrease in tissue pH

Question 51

How much must alveolar ventilation increase to maintain alveolar PO₂ at 104 mmHg and PCO₂ at 40 mmHg?

Answer 51

A: Alveolar ventilation must increase fourfold (4x) to maintain both PO₂ at 104 mmHg and PCO₂ at 40 mmHg.

Question 52

Can alveolar PO₂ exceed 149 mmHg with increased alveolar ventilation when breathing normal atmospheric air?

Answer 52

A: No, even with extreme increases in ventilation, alveolar PO₂ cannot exceed 149 mmHg when breathing normal atmospheric air.