Pulmonary Physiology II

Question 1

What is the role of the pulmonary system in carbon dioxide removal?

Answer 1

The system transports CO₂, generated by cellular respiration, back to the lungs to be expelled during exhalation.

Question 2

What is meant by the matching of ventilation and perfusion?

Answer 2

It refers to the coordination between airflow (ventilation) and blood flow (perfusion) in the lungs for optimal gas exchange.

Question 3

What is gas exchange, and where does it occur in the body?

Answer 3

Gas exchange is the process of oxygen entering the blood and carbon dioxide leaving the blood, occurring in the lungs and tissues.

Question 4

How does gas transport work in the circulatory system?

Answer 4

Oxygen and carbon dioxide are carried in the blood through the circulatory system to reach tissues or return to the lungs for removal.

Question 5

What is the main process through which gas exchange occurs in the lungs?

Answer 5

Gas exchange in the lungs occurs by diffusion.

Question 6

What drives the diffusion of gases during gas exchange?

Answer 6

Diffusion is driven by partial pressure gradients.

Question 7

What is the partial pressure of oxygen (PO₂) in dry inspired air at sea level?

Answer 7

160 millimeters of mercury.

Question 8

Why does the partial pressure of oxygen decrease to 150 mm Hg in the conducting airways?

Answer 8

The air is humidified in the conducting airways, which decreases the partial pressure of oxygen.

Question 9

What are the partial pressures of oxygen and carbon dioxide in the alveolus?

Answer 9

Oxygen: 100 mm Hg, Carbon dioxide: 40 mm Hg.

Question 10

How does mixed venous blood become oxygenated in the lungs?

Answer 10

Oxygen from the alveolus diffuses into the blood, increasing the blood’s PO₂ from 40 mm Hg to 100 mm Hg.

Question 11

What three factors determine the rate of diffusion during gas exchange?

Answer 11

The pressure gradient, surface area, and membrane thickness.

Question 12

How does an increased membrane thickness, like in fibrosis, affect gas exchange?

Answer 12

It slows the rate of diffusion, potentially leading to incomplete oxygenation of blood.

Question 13

Why is it harder to breathe at high altitudes?

Answer 13

The barometric pressure is lower, which decreases the pressure gradient for oxygen diffusion.

Question 14

What happens to the alveolar PO₂ at high elevations?

Answer 14

It decreases, leading to a smaller pressure gradient for oxygen diffusion (e.g., 50 mm Hg instead of 100 mm Hg).

Question 15

How quickly does blood equilibrate with alveolar oxygen under normal conditions?

Answer 15

It equilibrates within the first third of the pulmonary capillary length.

Question 16

What is the effect of a smaller pressure gradient on gas exchange, as seen at high altitudes?

Answer 16

It slows the exchange of oxygen between the alveolus and the capillary.

Question 17

What is ventilation, and how does it differ from gas exchange?

Answer 17

Ventilation is the bulk flow of air into and out of the lungs, while gas exchange involves the diffusion of gases between the alveoli and blood.

Question 18

What condition is likely to limit gas exchange in a healthy person under normal conditions?

Answer 18

High altitude or diseases that increase membrane thickness or decrease surface area can limit gas exchange.

Question 19

What are the two forms in which oxygen is carried in the blood?

Answer 19

Oxygen is carried in the blood bound to hemoglobin and dissolved in plasma.

Question 20

What is the equation for blood oxygen content?

Answer 20

Blood oxygen content = (constant × hemoglobin concentration × percent saturation) + (partial pressure of oxygen × solubility).

Question 21

What percentage of oxygen in the blood is bound to hemoglobin?

Answer 21

98% of oxygen is bound to hemoglobin, while only 2% is dissolved in plasma.

Question 22

How do we determine the oxygen saturation of hemoglobin?

Answer 22

Oxygen saturation is determined through laboratory tests or estimated using a pulse oximeter.

Question 23

What is the oxyhemoglobin dissociation curve?

Answer 23

It describes the relationship between partial pressure of oxygen (PO2) and the saturation of hemoglobin with oxygen, typically in an S-shaped curve.

Question 24

What happens to hemoglobin saturation as the PO2 decreases in the lungs?

Answer 24

Hemoglobin saturation changes only slightly with large changes in PO2 in the lungs due to the flat portion of the curve.

Question 25

Why is the shape of the oxyhemoglobin dissociation curve advantageous?

Answer 25

It allows for efficient oxygen loading in the lungs and unloading in the tissues, with small changes in PO2 leading to significant changes in saturation at the tissue level.

Question 26

What is the P50 value?

Answer 26

The P50 value is the partial pressure of oxygen at which hemoglobin is 50% saturated with oxygen.

Question 27

How does exercise affect the oxyhemoglobin dissociation curve?

Answer 27

Exercise increases temperature, CO2, and decreases pH, shifting the curve to the right, which decreases hemoglobin’s affinity for oxygen and facilitates unloading.

Question 28

What are the three modes of carbon dioxide transport in the blood?

Answer 28

Carbon dioxide is transported dissolved in plasma, bound to hemoglobin, and as bicarbonate.

Question 29

What percentage of carbon dioxide is transported as bicarbonate?

Answer 29

Approximately 92% of carbon dioxide is transported in the form of bicarbonate.

Question 30

What role does carbonic anhydrase play in carbon dioxide transport?

Answer 30

Carbonic anhydrase catalyzes the reaction of carbon dioxide with water to form carbonic acid, which dissociates into bicarbonate and protons.

Question 31

How does the relationship between carbon dioxide and protons relate to acidosis?

Answer 31

Increased carbon dioxide levels lead to more protons being produced, contributing to acidosis.

Question 32

What is the relationship between PaO2 and SaO2?

Answer 32

The partial pressure of oxygen (PaO2) and the oxygen saturation (SaO2) are related by the oxyhemoglobin dissociation curve.

Question 33

What are the three primary blood gases that regulate ventilation?

Answer 33

Oxygen, carbon dioxide, and pH.

Question 34

What is hypoxemia and what is its threshold value?

Answer 34

Hypoxemia is low blood oxygen levels, defined as a PaO2 of 80 mmHg or less.

Question 35

What is hypercapnia?

Answer 35

Hypercapnia refers to high levels of carbon dioxide in the blood, generally above 45 mmHg.

Question 36

What blood pH value indicates acidosis?

Answer 36

A pH of less than 7.35 is considered acidosis.

Question 37

How are low oxygen levels and high carbon dioxide levels sensed in the body?

Answer 37

They are sensed by chemoreceptors: central chemoreceptors in the brainstem and peripheral chemoreceptors in the blood vessels around the aorta.

Question 38

What is the role of chemoreceptors in regulating ventilation?

Answer 38

Chemoreceptors send signals to the medulla and pons to increase ventilation in response to disturbances in blood gas values, such as hypoxemia or hypercapnia.

Question 39

What happens to ventilation when there is acidosis and hypercapnia?

Answer 39

Ventilation increases, which helps exhale more carbon dioxide and return levels to normal, also increasing oxygen levels.

Question 40

What is one cause of hypoxemia related to external factors?

Answer 40

Breathing a hypoxic gas, such as at high altitudes.

Question 41

How does hypoventilation lead to hypoxemia?

Answer 41

In hypoventilation, insufficient breathing causes both PaO2 and arterial PaO2 to fall while carbon dioxide levels rise.

Question 42

What conditions can cause hypoventilation?

Answer 42

Causes include decreased ventilatory drive from brain damage or drug overdose, paralysis or weakness of ventilatory muscles, or chest wall damage.

Question 43

What is diffusion limitation in relation to hypoxemia?

Answer 43

Diffusion limitation occurs when conditions like fibrosis slow the diffusion of gases across the alveolar-capillary membrane, leading to hypoxemia.

Question 44

Why is the ventilation-perfusion (V/Q) mismatch important?

Answer 44

A mismatch between ventilation and perfusion can lead to hypoxemia and is a significant factor in various disease conditions.

Question 45

What do “v” and “Q” stand for in the context of ventilation and perfusion?

Answer 45

“v” stands for ventilation (airflow in liters per minute), and “Q” stands for perfusion (blood flow).

Question 46

What is the normal ventilation-perfusion (V/Q) ratio?

Answer 46

The normal V/Q ratio is approximately 0.8.

Question 47

How does gravity affect ventilation and perfusion in the lungs?

Answer 47

Gravity impacts both ventilation and perfusion; the bases of the lungs are better ventilated and perfused than the apices.

Question 48

What happens to the V/Q ratio when ventilation is obstructed, such as by a mucus plug?

Answer 48

The V/Q ratio becomes 0, resulting in arterial blood gas composition similar to venous blood (e.g., PaO2 ~ 40 mmHg, PaCO2 ~ 46 mmHg).

Question 49

What occurs when there is normal ventilation but obstructed blood flow, such as in a pulmonary embolism?

Answer 49

The V/Q ratio becomes infinity, and the alveolar gas composition resembles fresh air rather than equilibrated alveolar air.

Question 50

What is the relationship between V/Q ratio and arterial blood composition?

Answer 50

A low V/Q ratio leads to arterial blood resembling venous blood; a high V/Q ratio results in arterial blood resembling atmospheric air.

Question 51

How do ventilation and perfusion differ in the apex versus the base of the lungs?

Answer 51

The apex is underperfused and overventilated (high V/Q), while the base is overperfused and underventilated (low V/Q).

Question 52

What is the impact of underperfusion and overventilation on blood gases in the apex of the lung?

Answer 52

Arterial blood in the apex has higher PaO2 and lower PaCO2, resembling fresh air.

Question 53

What happens to blood gases in the base of the lung?

Answer 53

Arterial blood in the base has lower PaO2 and higher PaCO2, resembling mixed venous blood.

Question 54

How does the V/Q relationship affect blood gas composition in normal lung regions?

Answer 54

In the middle of the lung, the V/Q ratio is average (0.8), leading to typical arterial blood gases (PaO2 ~ 100 mmHg, PaCO2 ~ 40 mmHg).

Question 55

What can result from defects in the ventilation-perfusion ratio?

Answer 55

Defects in the V/Q ratio are a major cause of hypoxemia in pathological conditions.

Question 56

How much can the pulmonary system adapt to increased metabolic demand during exercise?

Answer 56

The pulmonary system can adapt to a 20-fold increase in metabolic demand by increasing minute ventilation, also by about 20-fold.

Question 57

What are the phases of the ventilatory response during moderate intensity exercise?

Answer 57

The ventilatory response has two phases: an initial rapid increase (neural origin) followed by an exponential increase that eventually plateaus.

Question 58

How does venous carbon dioxide (CO2) change during exercise?

Answer 58

Venous CO2 increases with exercise due to higher metabolic activity, but arterial CO2 remains stable as ventilation matches CO2 production.

Question 59

What happens to ventilation during heavy exercise compared to moderate exercise?

Answer 59

In heavy exercise, ventilation continues to increase beyond a plateau, with ventilation rising more than CO2 production and oxygen consumption, indicating a ventilatory threshold.

Question 60

What are the two components of minute ventilation?

Answer 60

Minute ventilation is the product of respiratory rate and tidal volume.

Question 61

How does the reliance on tidal volume and respiratory rate change with exercise intensity?

Answer 61

At low intensities, there is a greater reliance on increasing tidal volume; at higher intensities, reliance shifts to increasing respiratory rate.

Question 62

What effect does lung compliance have on ventilation at different volumes?

Answer 62

At low lung volumes, compliance is high (easy to expand), but at high volumes, compliance is low (more effort required to expand).

Question 63

What occurs to the ventilation-perfusion (V/Q) ratio during exercise?

Answer 63

The V/Q ratio approaches 1, indicating better matching of ventilation and perfusion.

Question 64

What can happen to oxygen levels in highly trained athletes during high-intensity exercise?

Answer 64

Blood can flow so fast through pulmonary capillaries that diffusion limitations may occur, leading to hypoxemia (decreased blood oxygen levels).

Question 65

What physiological change occurs to the oxyhemoglobin dissociation curve during exercise?

Answer 65

There is a rightward shift in the curve, decreasing hemoglobin’s affinity for oxygen, facilitating oxygen delivery to tissues.

Question 66

What is the primary limitation to exercise capacity in healthy individuals?

Answer 66

In healthy subjects, the pulmonary system is generally not the limiting factor for exercise capacity; the cardiovascular system is the major limiting factor.

Question 67

What triggers the inflection point known as the ventilatory threshold during heavy exercise?

Answer 67

The ventilatory threshold is driven by acidosis resulting from anaerobic glycolysis, leading to increased ventilation beyond CO2 production.