B2 W1 - Ventilation and Perfusion

Question 1

What is the primary function of the respiratory system?

Answer 1

The primary function of the respiratory system is gas exchangeTaking oxygen in from the environment and releasing carbon dioxide from the body.

Question 2

Besides gas exchange, what other function does the respiratory system serve regarding blood?

Answer 2

Acts as a reservoir for bloodHolds approximately 7-10% of the body’s total circulating blood volume within the pulmonary capillaries.

Question 3

Aside from gas exchange, what are some other functions of the respiratory system?

Answer 3

The respiratory system also:Serves as a reservoir for blood and gasesServes as a site for metabolism of circulating substancesServes as a filter for the bloodPlays a role in immune defence.

Question 4

How does the respiratory system contribute to gas storage, and what is an example of this?

Answer 4

Acts as a gas store, particularly for oxygen.Even after exhaling, the lungs retain around 2.5 litres of oxygen-containing gas, allowing for continued gas exchange between breaths.

Question 5

Why is the respiratory system considered a site for metabolism, and what is an example?

Answer 5

Due to the entire blood volume passing through the lungs, it becomes a site for metabolising circulating substances. E.g. Conversion of angiotensin I to angiotensin II by angiotensin-converting enzyme present on pulmonary endothelial cells.

Question 6

What role does the respiratory system play in immune defence? (3)

Answer 6

The respiratory system contributes to immune defence by:Producing and secreting immunoglobulins into the bronchial mucus liningSynthesising specific immune compoundsFacilitating phagocytosis of pathogens by immune cells residing in the lungs.

Question 7

How does the respiratory system contribute to the renin-angiotensin-aldosterone system (RAAS)?

Answer 7

Pulmonary endothelial cells contain angiotensin-converting enzyme (ACE), which converts angiotensin I to angiotensin II, a key step in the RAAS pathway.

Question 8

What is ventilation, in the context of the respiratory system?

Answer 8

Ventilation is the movement of air in and out of the lungs.

Question 9

What is perfusion?

Answer 9

Perfusion is the flow of blood through a tissueSpecifically the alveolar tissue in the context of respiration.

Question 10

How do ventilation and perfusion relate to the primary function of the respiratory system?

Answer 10

Both ventilation and perfusion are essential for establishing a gradient that allows for efficient gas exchange (oxygen and carbon dioxide) between the alveoli and the blood.

Question 11

What happens to the partial pressure of oxygen and carbon dioxide in the alveoli if ventilation stops, assuming perfusion continues?

Answer 11

If there was no ventilation, the partial pressure of oxygen in the alveolus would fall, and the partial pressure of carbon dioxide in the alveolus would rise.

Question 12

How does ventilation affect the partial pressure gradient of oxygen and carbon dioxide across the alveolar-capillary membrane?

Answer 12

Fresh oxygen brought in during inspiration - increasing alveolar oxygen partial pressureRemoval of carbon dioxide during expiration, decreasing alveolar carbon dioxide partial pressure.

Question 13

What would happen to gas exchange if ventilation stopped, and why?

Answer 13

If ventilation stopped, the partial pressures of oxygen and carbon dioxide across the alveolar-capillary membrane would eventually equalise, and gas exchange would cease.

Question 14

What is alveolar ventilation?

Answer 14

Alveolar ventilation is the volume of air that reaches the respiratory airways (alveoli) per minute and is therefore available for gas exchange.

Question 15

What is dead space in the respiratory system?

Answer 15

Dead space refers to the volume of airways and lungs that does not participate in gas exchange.

Question 16

What is tidal volume?

Answer 16

Tidal volume is the volume of air moved in and out of the lungs during a normal quiet breath, typically around 500 mls.

Question 17

What is minute ventilation?

Answer 17

Minute ventilation, or total ventilation, is the volume of air moved in and out of the lungs per minute, calculated by multiplying tidal volume by respiratory rate.

Question 18

What are the two main types of dead space?

Answer 18

Anatomical dead spacePhysiological dead space.

Question 19

What is anatomical dead space?

Answer 19

Anatomical dead space, also known as serial dead space, is the volume of air in the conducting airways where no gas exchange occursAbout 150 ml or 2 ml/kg of body weight.

Question 20

What is physiological dead space?

Answer 20

Physiological dead space encompasses the total volume of air that does not participate in gas exchangeIncluding BOTH anatomical dead space and alveolar dead space.

Question 21

What is alveolar dead space, and what is the most important reason for it?

Answer 21

Alveolar dead space, also called functional dead space, refers to the volume of alveoli that are ventilated but not perfused. The most common reason for this is a ventilation-perfusion mismatch, where ventilated alveoli do not receive adequate blood flow.

Question 22

In a healthy individual, how does physiological dead space compare to anatomical dead space?

Answer 22

In a healthy individual, physiological dead space is almost equal to anatomical dead space because alveolar dead space is minimal.

Question 23

How can pathology affect physiological dead space?

Answer 23

Conditions that lead to ventilation-perfusion mismatch can increase physiological dead space.

Question 24

What is the equation for calculating alveolar ventilation? (using tidal volume, dead space and respiratroy rate)

Answer 24

Alveolar Ventilation (VA) = (Tidal Volume - Dead Space) x Respiratory Rate

Question 25

For a given minute ventilation, how does breathing pattern affect alveolar ventilation?

Answer 25

Rapid, shallow breathing reduces alveolar ventilation as the effect of dead space is amplifiedSlower, deeper breathing increases alveolar ventilation, making it more efficient.

Question 26

Why is slow, deep breathing a more efficient way of ventilating the alveoli?

Answer 26

Slow, deep breathing maximises the volume of fresh air reaching the alveoli for gas exchange because the difference between tidal volume and dead space volume is larger.

Question 27

Medically, what does hyperventilation mean, and what are its effects on ventilation?

Answer 27

Hyperventilation refers to an increase in both the rate and depth of breathing. This results in significant increases in both minute ventilation and alveolar ventilation.

Question 28

How does alveolar ventilation relate to the diffusion rate of gases across the alveolar-capillary membrane, according to Fick’s Law?

Answer 28

Alveolar ventilation influences the partial pressure gradient, which is the driving force for diffusion. Increasing alveolar ventilation increases the partial pressure difference across the membrane, thereby increasing the diffusion rate.

Question 29

How does increasing alveolar ventilation affect carbon dioxide removal from the body?

Answer 29

Increasing alveolar ventilation lowers the alveolar partial pressure of carbon dioxide, increasing the partial pressure difference across the alveolar-capillary membraneThus enhancing carbon dioxide diffusion from the blood into the alveolar air for removal.

Question 30

What is the alveolar ventilation equation? (The more complicated one)

Answer 30

VA = (VCO2 x K) / PACO2where VA is alveolar ventilationVCO2 is carbon dioxide production ratePACO2 is alveolar partial pressure of carbon dioxideK is a constant.

Question 31

What relationship does the alveolar ventilation equation illustrate?

Answer 31

It demonstrates that, assuming a constant carbon dioxide production, alveolar partial pressure of carbon dioxide is inversely proportional to alveolar ventilation - increasing ventilation decreases PCO2 and vice versa.

Question 32

How does the alveolar ventilation equation apply to situations with changes in carbon dioxide production?

Answer 32

If carbon dioxide production changes, ventilation must adjust proportionally to maintain a normal partial pressure of carbon dioxide. For example, if carbon dioxide production doubles during exercise, alveolar ventilation must also double.

Question 33

Why is the relationship between alveolar ventilation and carbon dioxide partial pressure important for acid-base regulation?

Answer 33

The partial pressure of carbon dioxide in the blood is linked to pH. Increasing alveolar ventilation helps remove carbon dioxide, impacting blood pH.

Question 34

Why can the partial pressure of carbon dioxide in arterial blood (PaCO2) be used interchangeably with the partial pressure of carbon dioxide in the alveoli (PACO2) in the alveolar ventilation equation?

Answer 34

As blood flows through pulmonary capillaries, CO2 partial pressures in the alveoli and blood reach equilibrium due to diffusion, making PaCO2 and PACO2 nearly identical.

Question 35

What is the primary function of the upper respiratory tract, and what structures does it include?

Answer 35

The upper respiratory tract conducts air from the atmosphere to the lower respiratory tract, warming, humidifying, and protecting it. It includes the nasal cavity, pharynx, and larynx.

Question 36

Describe the structure of the lower respiratory tract.

Answer 36

The lower respiratory tract is a series of branching tubes, starting with the trachea, which divides into two main bronchi. The bronchi further divide into smaller bronchi and bronchioles, eventually leading to the alveolar sacs. This branching pattern creates 23 generations of divisions.

Question 37

What is the difference between conducting airways and respiratory airways?

Answer 37

Conducting airways (trachea to terminal bronchioles) transport air but do not participate in gas exchange. Respiratory airways, starting from the respiratory bronchioles, have alveoli and allow for gas exchange.

Question 38

How is air movement in the conducting airways driven, and what are the additional roles of these airways?

Answer 38

Pressure differences drive bulk flow in the conducting airways. They also warm and humidify air and protect the lower airways by removing debris.

Question 39

What structures mark the beginning of the respiratory airways, and what is their primary function?

Answer 39

Respiratory bronchioles (with occasional alveoli) and alveolar ducts (entirely lined by alveoli) mark the start of the respiratory airways. These structures are designed for gas exchange between the alveoli and the pulmonary circulation.

Question 40

Describe the structure and function of alveoli.

Answer 40

Alveoli are tiny, pouch-like structures (200-300 micrometres in diameter). Their thin walls, primarily composed of type I pneumocytes, minimise the distance between air and blood for efficient gas exchange. The lungs have approximately 300 million alveoli, creating a massive surface area for this process.

Question 41

What structural features contribute to the large surface area for gas exchange in the lungs?

Answer 41

The vast number of alveoli (roughly 300 million) creates a large surface area.Additionally, a dense capillary network, as seen in electron micrographs, surrounds each alveolus, maximising the area for gas exchange between air and blood.

Question 42

Explain the concept of the bellows system in the respiratory system.

Answer 42

The bellows system encompasses the chest wall, pleura, respiratory muscles, conducting airways, nerves, and higher control centres. This system is responsible for ventilation, the movement of air between the atmosphere and the alveoli.

Question 43

What constitutes the gas exchange system, and what is its function?

Answer 43

The gas exchange system includes the alveoli, associated capillaries, and the pulmonary circulation. Its primary function is oxygenation, enabling the exchange of oxygen and carbon dioxide between the air and blood.

Question 44

How does gas exchange occur in the alveoli?

Answer 44

Gas exchange occurs by diffusion across the thin alveolar-capillary membrane, driven by the partial pressure differences of oxygen and carbon dioxide.

Question 45

Define pulmonary ventilation.

Answer 45

Pulmonary ventilation is the movement of air into and out of the lungs.

Question 46

What is tidal volume?

Answer 46

Tidal volume is the volume of air moved in and out of the lungs during a normal, quiet breath, typically around 500 ml.

Question 47

How is minute ventilation (total ventilation) calculated?

Answer 47

Minute ventilation is calculated by multiplying tidal volume by respiratory rate (breaths per minute).

Question 48

What is the typical range for minute ventilation?

Answer 48

A typical minute ventilation is 6 to 8 litres per minute.

Question 49

How does exercise affect minute ventilation?

Answer 49

Exercise increases minute ventilation by increasing both the depth (tidal volume) and rate (respiratory rate) of breathing.

Question 50

Distinguish between pulmonary ventilation and alveolar ventilation.

Answer 50

Pulmonary ventilation refers to the total air moved in and out of the lungsAlveolar ventilation refers to the volume of air that reaches the respiratory airways (alveoli) per minute and participates in gas exchange.

Question 51

How does anatomical dead space relate to alveolar ventilation?

Answer 51

During inspiration, the first 150 ml of air (anatomical dead space volume) entering the alveoli is air that was already present in the conducting airways from the previous breath. This air has already undergone gas exchange and does not contribute to alveolar ventilation.

Question 52

What is the relationship between physiological and anatomical dead space in healthy individuals?

Answer 52

In healthy lungs, physiological dead space is almost equal to anatomical dead space because alveolar dead space is minimal.

Question 53

Under what conditions can physiological dead space increase?

Answer 53

Physiological dead space increases with pathology, particularly in the presence of a ventilation-perfusion mismatch, where ventilated alveoli are not adequately perfused with blood.

Question 54

How does alveolar ventilation affect the partial pressure of carbon dioxide (PCO2) in the alveoli?

Answer 54

Increasing alveolar ventilation lowers alveolar PCO2, while decreasing alveolar ventilation increases alveolar PCO2. This inverse relationship is described by the alveolar ventilation equation.

Question 55

Describe the alveolar ventilation equation and its components.

Answer 55

The alveolar ventilation equation: VA = (VCO2 x K) / PACO2VA = alveolar ventilation (L/min or ml/min)VCO2 = rate of carbon dioxide production from metabolismPACO2 = partial pressure of carbon dioxide in the alveoliK = a constant

Question 56

Explain how changes in carbon dioxide production affect the required alveolar ventilation to maintain PCO2.

Answer 56

If carbon dioxide production increases (e.g., during exercise), alveolar ventilation must also increase to maintain a stable PCO2. Conversely, if carbon dioxide production decreases, alveolar ventilation must decrease.

Question 57

Why is it important to understand the relationship between alveolar ventilation and carbon dioxide levels in the context of acid-base regulation?

Answer 57

The partial pressure of carbon dioxide in the blood is directly related to pH. By regulating alveolar ventilation, the body can control the removal of carbon dioxide and therefore help maintain acid-base balance.

Question 58

Why can the partial pressure of carbon dioxide in arterial blood (PaCO2) be used as a surrogate for the alveolar partial pressure (PACO2)?

Answer 58

PaCO2 can be used interchangeably with PACO2 because carbon dioxide rapidly equilibrates between the alveoli and the blood as it passes through pulmonary capillaries. Therefore, PaCO2 is a close reflection of PACO2.

Question 59

What is the medical definition of hyperventilation?

Answer 59

Hyperventilation is an increase in both the rate and depth of breathing.

Question 60

Provide an example of how tidal volume and respiratory rate might change during hyperventilation.

Answer 60

Tidal volume might increase to 1 litre, and respiratory rate might increase to 24 breaths per minute.

Question 61

What is the effect of hyperventilation on minute ventilation and alveolar ventilation?

Answer 61

Hyperventilation significantly increases both minute ventilation and alveolar ventilation.

Question 62

Why is it important to understand the consequences of hyperventilation in relation to gas exchange?

Answer 62

The significant increases in minute ventilation and alveolar ventilation associated with hyperventilation will have notable effects on gas exchange.

Question 63

What is the relationship between alveolar ventilation and the diffusion rate of gases?

Answer 63

Alveolar ventilation influences the partial pressure gradients of gases, which, according to Fick’s Law, is a key factor driving diffusion across the alveolar-capillary membrane.

Question 64

According to Fick’s Law, what factors determine the rate of gas diffusion across a membrane?

Answer 64

The rate of diffusion is proportional to the partial pressure difference of the gas and the surface area available for diffusion and inversely proportional to the thickness of the membrane.

Question 65

How does increasing alveolar ventilation affect the diffusion rate of carbon dioxide (CO2)?

Answer 65

Increasing alveolar ventilation removes CO2 from the alveoli, creating a larger partial pressure difference between the blood and alveoli, thus enhancing CO2 diffusion from the blood into the alveolar air.

Question 66

What does the alveolar ventilation equation demonstrate about the relationship between alveolar ventilation and the alveolar partial pressure of CO2?

Answer 66

It shows an inverse relationship: increasing alveolar ventilation decreases PACO2, and decreasing alveolar ventilation increases PACO2, assuming a constant rate of CO2 production.

Question 67

If CO2 production increases, how must alveolar ventilation change to maintain a normal alveolar PCO2?

Answer 67

Alveolar ventilation must increase proportionally to the increase in CO2 production to keep PACO2 within a normal range.

Question 68

Why is the relationship between alveolar ventilation and CO2 levels important for acid-base regulation?

Answer 68

Because the partial pressure of CO2 in the blood is directly related to pH, regulating alveolar ventilation helps control CO2 removal and maintain acid-base balance.

Question 69

Can the partial pressure of carbon dioxide in arterial blood (PaCO2) be used to represent the alveolar partial pressure (PACO2)? Why or why not?

Answer 69

Yes, PaCO2 can be used interchangeably with PACO2. This is because CO2 rapidly reaches equilibrium between the alveoli and the blood as it passes through the pulmonary capillaries, making PaCO2 a reliable indicator of PACO2.

Question 70

Why is understanding the relationship between alveolar ventilation and diffusion rate important?

Answer 70

This relationship is crucial for understanding the physiological control of respiration and the consequences of respiratory pathologies.

Question 71

Briefly describe how breathing is controlled.

Answer 71

Breathing is an involuntary process controlled by the brainstem (medulla and pons). These centres receive sensory information about lung volume (from mechanoreceptors) and blood gas composition (from chemoreceptors) to adjust the rate and depth of breathing. The cortex can temporarily override this automatic control, allowing for conscious breathing adjustments.

Question 72

Is breathing a voluntary or involuntary process?

Answer 72

Breathing is primarily an involuntary process, regulated by the brainstem.

Question 73

Which parts of the brain are involved in the control of breathing?

Answer 73

The medulla, which houses the respiratory control centre, and the pons play key roles in breathing regulation.

Question 74

What types of sensory information do brainstem respiratory centres receive?

Answer 74

They receive information about lung volume from mechanoreceptors that sense stretch and about blood gas composition (oxygen and carbon dioxide levels) from chemoreceptors.

Question 75

How does the brainstem control breathing?

Answer 75

It sends efferent signals to the diaphragm and other respiratory muscles, adjusting the rate and depth of breathing.

Question 76

Can conscious control influence breathing?

Answer 76

Yes, the cortex can temporarily override the automatic brainstem control, allowing for conscious adjustments to breathing patterns.

Question 77

What is the primary role of central chemoreceptors in breathing control?

Answer 77

Central chemoreceptors are crucial for the minute-to-minute regulation of breathing, primarily responding to changes in the pH of the cerebrospinal fluid, which reflects arterial carbon dioxide levels.

Question 78

Where are central chemoreceptors located?

Answer 78

They are situated on the ventral surface of the medulla.

Question 79

What is the primary stimulus for central chemoreceptors?

Answer 79

Central chemoreceptors primarily respond to changes in the pH of the cerebrospinal fluid (CSF), which reflects changes in arterial carbon dioxide levels.

Question 80

How do central chemoreceptors respond to changes in arterial carbon dioxide (PaCO2)?

Answer 80

An increase in PaCO2 leads to an increase in CO2 in the cerebrospinal fluid, lowering its pH. This decrease in pH signals the respiratory centre to increase ventilation, reducing PaCO2. Conversely, a decrease in PaCO2 leads to reduced ventilation.

Question 81

What is the main function of peripheral chemoreceptors in breathing control?

Answer 81

Peripheral chemoreceptors are primarily responsible for detecting changes in arterial oxygen levels (PaO2), especially when PaO2 falls below 8 kilopascals.

Question 82

Where are peripheral chemoreceptors located?

Answer 82

They are found in the carotid bodies at the bifurcation of the common carotid artery and in the aortic bodies in the aortic arch.

Question 83

How do peripheral chemoreceptors respond to changes in PaO2?

Answer 83

When PaO2 drops below a certain threshold, peripheral chemoreceptors trigger a steep, linear increase in ventilation rate. Above this threshold, they have minimal effect on ventilation.

Question 84

Do peripheral chemoreceptors respond to changes in PaCO2 and pH?

Answer 84

Yes, but their role in responding to PaCO2 changes is less significant than that of central chemoreceptors. They also respond to changes in arterial pH independently of PaCO2.

Question 85

Explain the mechanism by which central chemoreceptors respond to changes in arterial PCO2.

Answer 85

When arterial PCO2 increases, more CO2 crosses the blood-brain barrier into the CSF. In the CSF, CO2 reacts with water to form hydrogen ions (H+) and bicarbonate ions. The increased H+ concentration lowers CSF pH, which is sensed by the central chemoreceptors. They then signal to the respiratory centre to increase ventilation and remove excess CO2.

Question 86

How do peripheral chemoreceptors contribute to the respiratory compensation for metabolic acidosis?

Answer 86

In metabolic acidosis, the decrease in arterial pH, independent of PaCO2 changes, stimulates peripheral chemoreceptors to increase ventilation, aiding in the removal of excess acid.

Question 87

What is meant by the pulmonary circulation being a ‘low pressure, low resistance’ system?

Answer 87

This means that the gradient across the pulmonary circulation and the resistance are both much lower than in the systemic circulation.

Question 88

How does the pulmonary circulation achieve low pressure and resistance?

Answer 88

This is achieved through the large area for blood flow, provided by many small arteries and arterioles that are dilated and contain less smooth muscle.

Question 89

How does the pulmonary circulation respond to an increase in cardiac output?

Answer 89

Open capillaries distend and closed capillaries are recruited, accommodating the increased flow without massively increasing pressure.

Question 90

How can lung volume impact the radius of blood vessels?

Answer 90

Overinflation compresses alveolar vessels, increasing resistance, while underinflation causes vessels to become coiled and kinked, also increasing resistance.

Question 91

What is hypoxic pulmonary vasoconstriction?

Answer 91

It is a mechanism where reduced alveolar partial pressure of oxygen causes vascular smooth muscle cells to contract, constricting blood vessels and reducing blood flow to that area.

Question 92

What is the purpose of hypoxic pulmonary vasoconstriction?

Answer 92

It helps redirect blood flow away from poorly ventilated areas of the lung to well-ventilated areas where gas exchange is more efficient.

Question 93

What are two limitations of hypoxic pulmonary vasoconstriction?

Answer 93

It may be insufficient in cases of widespread lung issues, and chronic hypoxia can lead to pulmonary hypertension and right heart failure.

Question 94

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

Answer 94

It describes how well ventilation and perfusion are matched in an alveolus, indicating the efficiency of gas exchange.

Question 95

What is the ideal V/Q ratio?

Answer 95

A V/Q of 1 represents perfectly matched ventilation and perfusion.

Question 96

What is the average V/Q for the entire lung?

Answer 96

The normal range for V/Q is 0.8.

Question 97

What happens in an area of the lung where there is ventilation but no perfusion?

Answer 97

This creates dead space, where the alveolus is ventilated but there is no blood flow for gas exchange.

Question 98

What happens in an area of the lung where there is perfusion but no ventilation?

Answer 98

This creates a shunt, where blood bypasses the alveolus without undergoing gas exchange, resulting in low oxygen and high carbon dioxide levels.

Question 99

How does gravity affect pulmonary blood flow in an upright person?

Answer 99

Blood flow is lowest at the apex (top) and highest at the base (bottom) due to hydrostatic pressure differences.

Question 100

How does gravity affect ventilation in an upright person?

Answer 100

Ventilation is better at the base of the lung, which is more compressed and has greater potential for expansion, than at the apex, which is relatively expanded.

Question 101

How do the rates of change for ventilation and perfusion compare throughout the lung?

Answer 101

Perfusion changes more dramatically than ventilation due to the greater density of blood compared to air.

Question 102

What are the consequences of the differing rates of change for ventilation and perfusion?

Answer 102

This creates regional differences in V/Q ratios, with the bases being relatively overperfused and the apices being relatively overventilated.

Question 103

What is the effect of a low V/Q ratio on gas exchange?

Answer 103

A low V/Q ratio leads to reduced oxygen uptake and increased carbon dioxide levels in the blood leaving that region.

Question 104

Why can’t high and low V/Q areas in the lung cancel each other out?

Answer 104

Because haemoglobin is already nearly fully saturated at normal V/Q, high V/Q areas can only add a small amount of dissolved oxygen and cannot compensate for the low oxygen levels from low V/Q areas.

Question 105

What would the chest X-ray of a patient with right lower lobe pneumonia likely show?

Answer 105

The chest X-ray would likely show a consolidated area in the right lower lobe, indicating the presence of fluid and pus in the alveoli.

Question 106

How does the accumulation of fluid and pus in the alveoli, as seen in pneumonia, affect gas exchange?

Answer 106

The fluid and pus physically block the alveoli, preventing air from reaching them and thus hindering ventilation and disrupting the exchange of oxygen and carbon dioxide.

Question 107

In the case study, what are the hypothetical oxygen saturation levels (SaO2) in the blood leaving the affected and unaffected areas of the lung?

Answer 107

The blood leaving the unaffected area is estimated to have a high oxygen saturation of 98%, while the blood leaving the pneumonia-affected area is estimated to have a much lower saturation of 58%.

Question 108

What is the equation for calculating oxygen content, taking into account both bound and dissolved oxygen?

Answer 108

Oxygen content = (Hb x 1.34 x SaO2) + (PaO2 x 0.0225), where Hb is haemoglobin concentration, 1.34 is a constant, SaO2 is oxygen saturation, PaO2 is the partial pressure of oxygen in arterial blood, and 0.0225 is the solubility coefficient of oxygen in water.

Question 109

How does hypoxic pulmonary vasoconstriction help to mitigate the effects of pneumonia in this case?

Answer 109

By constricting the blood vessels supplying the poorly ventilated, pneumonia-affected area, hypoxic pulmonary vasoconstriction reduces blood flow to that region. This lessens the V/Q mismatch, reduces the amount of blood bypassing the alveoli without gas exchange (shunt), and improves overall arterial oxygen saturation.

Question 110

What is the relationship between alveolar ventilation and the partial pressure of carbon dioxide in the alveoli?

Answer 110

As alveolar ventilation increases, the partial pressure of carbon dioxide in the alveoli decreases. This is because increased ventilation removes more carbon dioxide from the alveoli.