B2 W1 - Ventilation and Perfusion Flashcards
(110 cards)
1
Q
What is the primary function of the respiratory system?
A
The primary function of the respiratory system is gas exchangeTaking oxygen in from the environment and releasing carbon dioxide from the body.
2
Q
Besides gas exchange, what other function does the respiratory system serve regarding blood?
A
Acts as a reservoir for bloodHolds approximately 7-10% of the body’s total circulating blood volume within the pulmonary capillaries.
3
Q
Aside from gas exchange, what are some other functions of the respiratory system?
A
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.
4
Q
How does the respiratory system contribute to gas storage, and what is an example of this?
A
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.
5
Q
Why is the respiratory system considered a site for metabolism, and what is an example?
A
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.
6
Q
What role does the respiratory system play in immune defence? (3)
A
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.
7
Q
How does the respiratory system contribute to the renin-angiotensin-aldosterone system (RAAS)?
A
Pulmonary endothelial cells contain angiotensin-converting enzyme (ACE), which converts angiotensin I to angiotensin II, a key step in the RAAS pathway.
8
Q
What is ventilation, in the context of the respiratory system?
A
Ventilation is the movement of air in and out of the lungs.
9
Q
What is perfusion?
A
Perfusion is the flow of blood through a tissueSpecifically the alveolar tissue in the context of respiration.
10
Q
How do ventilation and perfusion relate to the primary function of the respiratory system?
A
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.
11
Q
What happens to the partial pressure of oxygen and carbon dioxide in the alveoli if ventilation stops, assuming perfusion continues?
A
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.
12
Q
How does ventilation affect the partial pressure gradient of oxygen and carbon dioxide across the alveolar-capillary membrane?
A
Fresh oxygen brought in during inspiration - increasing alveolar oxygen partial pressureRemoval of carbon dioxide during expiration, decreasing alveolar carbon dioxide partial pressure.
13
Q
What would happen to gas exchange if ventilation stopped, and why?
A
If ventilation stopped, the partial pressures of oxygen and carbon dioxide across the alveolar-capillary membrane would eventually equalise, and gas exchange would cease.
14
Q
What is alveolar ventilation?
A
Alveolar ventilation is the volume of air that reaches the respiratory airways (alveoli) per minute and is therefore available for gas exchange.
15
Q
What is dead space in the respiratory system?
A
Dead space refers to the volume of airways and lungs that does not participate in gas exchange.
16
Q
What is tidal volume?
A
Tidal volume is the volume of air moved in and out of the lungs during a normal quiet breath, typically around 500 mls.
17
Q
What is minute ventilation?
A
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.
18
Q
What are the two main types of dead space?
A
Anatomical dead spacePhysiological dead space.
19
Q
What is anatomical dead space?
A
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.
20
Q
What is physiological dead space?
A
Physiological dead space encompasses the total volume of air that does not participate in gas exchangeIncluding BOTH anatomical dead space and alveolar dead space.
21
Q
What is alveolar dead space, and what is the most important reason for it?
A
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.
22
Q
In a healthy individual, how does physiological dead space compare to anatomical dead space?
A
In a healthy individual, physiological dead space is almost equal to anatomical dead space because alveolar dead space is minimal.
23
Q
How can pathology affect physiological dead space?
A
Conditions that lead to ventilation-perfusion mismatch can increase physiological dead space.
24
Q
What is the equation for calculating alveolar ventilation? (using tidal volume, dead space and respiratroy rate)
A
Alveolar Ventilation (VA) = (Tidal Volume - Dead Space) x Respiratory Rate
25
For a given minute ventilation, how does breathing pattern affect alveolar ventilation?
Rapid, shallow breathing reduces alveolar ventilation as the effect of dead space is amplifiedSlower, deeper breathing increases alveolar ventilation, making it more efficient.
26
Why is slow, deep breathing a more efficient way of ventilating the alveoli?
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.
27
Medically, what does hyperventilation mean, and what are its effects on ventilation?
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.
28
How does alveolar ventilation relate to the diffusion rate of gases across the alveolar-capillary membrane, according to Fick's Law?
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.
29
How does increasing alveolar ventilation affect carbon dioxide removal from the body?
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.
30
What is the alveolar ventilation equation? (The more complicated one)
VA = (VCO2 x K) / PACO2where VA is alveolar ventilationVCO2 is carbon dioxide production ratePACO2 is alveolar partial pressure of carbon dioxideK is a constant.
31
What relationship does the alveolar ventilation equation illustrate?
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.
32
How does the alveolar ventilation equation apply to situations with changes in carbon dioxide production?
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.
33
Why is the relationship between alveolar ventilation and carbon dioxide partial pressure important for acid-base regulation?
The partial pressure of carbon dioxide in the blood is linked to pH. Increasing alveolar ventilation helps remove carbon dioxide, impacting blood pH.
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?
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.
35
What is the primary function of the upper respiratory tract, and what structures does it include?
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.
36
Describe the structure of the lower respiratory tract.
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.
37
What is the difference between conducting airways and respiratory airways?
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.
38
How is air movement in the conducting airways driven, and what are the additional roles of these airways?
Pressure differences drive bulk flow in the conducting airways. They also warm and humidify air and protect the lower airways by removing debris.
39
What structures mark the beginning of the respiratory airways, and what is their primary function?
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.
40
Describe the structure and function of alveoli.
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.
41
What structural features contribute to the large surface area for gas exchange in the lungs?
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.
42
Explain the concept of the bellows system in the respiratory system.
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.
43
What constitutes the gas exchange system, and what is its function?
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.
44
How does gas exchange occur in the alveoli?
Gas exchange occurs by diffusion across the thin alveolar-capillary membrane, driven by the partial pressure differences of oxygen and carbon dioxide.
45
Define pulmonary ventilation.
Pulmonary ventilation is the movement of air into and out of the lungs.
46
What is tidal volume?
Tidal volume is the volume of air moved in and out of the lungs during a normal, quiet breath, typically around 500 ml.
47
How is minute ventilation (total ventilation) calculated?
Minute ventilation is calculated by multiplying tidal volume by respiratory rate (breaths per minute).
48
What is the typical range for minute ventilation?
A typical minute ventilation is 6 to 8 litres per minute.
49
How does exercise affect minute ventilation?
Exercise increases minute ventilation by increasing both the depth (tidal volume) and rate (respiratory rate) of breathing.
50
Distinguish between pulmonary ventilation and alveolar ventilation.
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.
51
How does anatomical dead space relate to alveolar ventilation?
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.
52
What is the relationship between physiological and anatomical dead space in healthy individuals?
In healthy lungs, physiological dead space is almost equal to anatomical dead space because alveolar dead space is minimal.
53
Under what conditions can physiological dead space increase?
Physiological dead space increases with pathology, particularly in the presence of a ventilation-perfusion mismatch, where ventilated alveoli are not adequately perfused with blood.
54
How does alveolar ventilation affect the partial pressure of carbon dioxide (PCO2) in the alveoli?
Increasing alveolar ventilation lowers alveolar PCO2, while decreasing alveolar ventilation increases alveolar PCO2. This inverse relationship is described by the alveolar ventilation equation.
55
Describe the alveolar ventilation equation and its components.
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
56
Explain how changes in carbon dioxide production affect the required alveolar ventilation to maintain PCO2.
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.
57
Why is it important to understand the relationship between alveolar ventilation and carbon dioxide levels in the context of acid-base regulation?
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.
58
Why can the partial pressure of carbon dioxide in arterial blood (PaCO2) be used as a surrogate for the alveolar partial pressure (PACO2)?
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.
59
What is the medical definition of hyperventilation?
Hyperventilation is an increase in both the rate and depth of breathing.
60
Provide an example of how tidal volume and respiratory rate might change during hyperventilation.
Tidal volume might increase to 1 litre, and respiratory rate might increase to 24 breaths per minute.
61
What is the effect of hyperventilation on minute ventilation and alveolar ventilation?
Hyperventilation significantly increases both minute ventilation and alveolar ventilation.
62
Why is it important to understand the consequences of hyperventilation in relation to gas exchange?
The significant increases in minute ventilation and alveolar ventilation associated with hyperventilation will have notable effects on gas exchange.
63
What is the relationship between alveolar ventilation and the diffusion rate of gases?
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.
64
According to Fick's Law, what factors determine the rate of gas diffusion across a membrane?
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.
65
How does increasing alveolar ventilation affect the diffusion rate of carbon dioxide (CO2)?
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.
66
What does the alveolar ventilation equation demonstrate about the relationship between alveolar ventilation and the alveolar partial pressure of CO2?
It shows an inverse relationship: increasing alveolar ventilation decreases PACO2, and decreasing alveolar ventilation increases PACO2, assuming a constant rate of CO2 production.
67
If CO2 production increases, how must alveolar ventilation change to maintain a normal alveolar PCO2?
Alveolar ventilation must increase proportionally to the increase in CO2 production to keep PACO2 within a normal range.
68
Why is the relationship between alveolar ventilation and CO2 levels important for acid-base regulation?
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.
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?
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.
70
Why is understanding the relationship between alveolar ventilation and diffusion rate important?
This relationship is crucial for understanding the physiological control of respiration and the consequences of respiratory pathologies.
71
Briefly describe how breathing is controlled.
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.
72
Is breathing a voluntary or involuntary process?
Breathing is primarily an involuntary process, regulated by the brainstem.
73
Which parts of the brain are involved in the control of breathing?
The medulla, which houses the respiratory control centre, and the pons play key roles in breathing regulation.
74
What types of sensory information do brainstem respiratory centres receive?
They receive information about lung volume from mechanoreceptors that sense stretch and about blood gas composition (oxygen and carbon dioxide levels) from chemoreceptors.
75
How does the brainstem control breathing?
It sends efferent signals to the diaphragm and other respiratory muscles, adjusting the rate and depth of breathing.
76
Can conscious control influence breathing?
Yes, the cortex can temporarily override the automatic brainstem control, allowing for conscious adjustments to breathing patterns.
77
What is the primary role of central chemoreceptors in breathing control?
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.
78
Where are central chemoreceptors located?
They are situated on the ventral surface of the medulla.
79
What is the primary stimulus for central chemoreceptors?
Central chemoreceptors primarily respond to changes in the pH of the cerebrospinal fluid (CSF), which reflects changes in arterial carbon dioxide levels.
80
How do central chemoreceptors respond to changes in arterial carbon dioxide (PaCO2)?
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.
81
What is the main function of peripheral chemoreceptors in breathing control?
Peripheral chemoreceptors are primarily responsible for detecting changes in arterial oxygen levels (PaO2), especially when PaO2 falls below 8 kilopascals.
82
Where are peripheral chemoreceptors located?
They are found in the carotid bodies at the bifurcation of the common carotid artery and in the aortic bodies in the aortic arch.
83
How do peripheral chemoreceptors respond to changes in PaO2?
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.
84
Do peripheral chemoreceptors respond to changes in PaCO2 and pH?
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.
85
Explain the mechanism by which central chemoreceptors respond to changes in arterial PCO2.
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.
86
How do peripheral chemoreceptors contribute to the respiratory compensation for metabolic acidosis?
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.
87
What is meant by the pulmonary circulation being a 'low pressure, low resistance' system?
This means that the gradient across the pulmonary circulation and the resistance are both much lower than in the systemic circulation.
88
How does the pulmonary circulation achieve low pressure and resistance?
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.
89
How does the pulmonary circulation respond to an increase in cardiac output?
Open capillaries distend and closed capillaries are recruited, accommodating the increased flow without massively increasing pressure.
90
How can lung volume impact the radius of blood vessels?
Overinflation compresses alveolar vessels, increasing resistance, while underinflation causes vessels to become coiled and kinked, also increasing resistance.
91
What is hypoxic pulmonary vasoconstriction?
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.
92
What is the purpose of hypoxic pulmonary vasoconstriction?
It helps redirect blood flow away from poorly ventilated areas of the lung to well-ventilated areas where gas exchange is more efficient.
93
What are two limitations of hypoxic pulmonary vasoconstriction?
It may be insufficient in cases of widespread lung issues, and chronic hypoxia can lead to pulmonary hypertension and right heart failure.
94
What is the ventilation perfusion ratio (V/Q)?
It describes how well ventilation and perfusion are matched in an alveolus, indicating the efficiency of gas exchange.
95
What is the ideal V/Q ratio?
A V/Q of 1 represents perfectly matched ventilation and perfusion.
96
What is the average V/Q for the entire lung?
The normal range for V/Q is 0.8.
97
What happens in an area of the lung where there is ventilation but no perfusion?
This creates dead space, where the alveolus is ventilated but there is no blood flow for gas exchange.
98
What happens in an area of the lung where there is perfusion but no ventilation?
This creates a shunt, where blood bypasses the alveolus without undergoing gas exchange, resulting in low oxygen and high carbon dioxide levels.
99
How does gravity affect pulmonary blood flow in an upright person?
Blood flow is lowest at the apex (top) and highest at the base (bottom) due to hydrostatic pressure differences.
100
How does gravity affect ventilation in an upright person?
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.
101
How do the rates of change for ventilation and perfusion compare throughout the lung?
Perfusion changes more dramatically than ventilation due to the greater density of blood compared to air.
102
What are the consequences of the differing rates of change for ventilation and perfusion?
This creates regional differences in V/Q ratios, with the bases being relatively overperfused and the apices being relatively overventilated.
103
What is the effect of a low V/Q ratio on gas exchange?
A low V/Q ratio leads to reduced oxygen uptake and increased carbon dioxide levels in the blood leaving that region.
104
Why can't high and low V/Q areas in the lung cancel each other out?
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.
105
What would the chest X-ray of a patient with right lower lobe pneumonia likely show?
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.
106
How does the accumulation of fluid and pus in the alveoli, as seen in pneumonia, affect gas exchange?
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.
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?
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%.
108
What is the equation for calculating oxygen content, taking into account both bound and dissolved oxygen?
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.
109
How does hypoxic pulmonary vasoconstriction help to mitigate the effects of pneumonia in this case?
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.
110
What is the relationship between alveolar ventilation and the partial pressure of carbon dioxide in the alveoli?
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.
