Respiratory System Flashcards
How does salbutamol work in asthma?
It is a sympathomimetic drug that activates beta-2 receptors, causing airway dilation.
How does inspiration affect blood flow resistance (perfusion)?
Inspiration increases blood vessel radius, reducing resistance to blood flow.
What happens to resistance when blood vessel length increases?
Longer vessels lead to less resistance.
How does increased blood pressure affect lung capillaries?
It leads to capillary distension and recruitment, reducing resistance and preventing oedema.
What is pulmonary hypoxic vasoconstriction?
A process where blocked airways cause constriction of blood vessels supplying that lung region.
What is the normal alveolar-arterial oxygen difference?
Normally around 5 mmHg.
How is the alveolar-arterial oxygen difference estimated clinically?
It can be estimated using the P/F ratio: partial pressure of arterial oxygen (PaO₂) divided by the fraction of inspired oxygen in the air (FiO₂). A low ratio may indicate acute respiratory distress syndrome (ARDS).
What is a physiological shunt?
There is adequate perfusion to the alveolus but no gas exchange due to a lack of ventilation. Results in a decreased V/Q ratio.
3 main categories, 5 quoted conditions total.
What are common causes of physiological shunt?
Airway obstruction (asthma, chronic bronchitis), problems alveolar filling (pneumonia, pulmonary edema), atelectasis (collapsed alveoli).
What are common causes of alveolar dead space? In healthy individuals, this is 0.
Pulmonary embolism, emphysema.
Why does the V/Q ratio decrease progressively down the lung?
Blood is heavier than air, so its flow is more greatly impacted by gravity. Whilst rates of ventilation and perfusion both increase progressively down the lung, perfusion increases at a higher rate down the lung.
What is the V/Q ratio and how does it vary in the lung?
The ventilation-perfusion (V/Q) ratio describes the balance between alveolar ventilation and pulmonary blood flow. It is higher at the lung apex (more ventilation than perfusion) and lower at the base (more perfusion than ventilation).
What is a right-to-left anatomical shunt?
Some deoxygenated bronchial blood drains into the left atrium instead of returning to the lungs (via the right atrium), slightly reducing arterial oxygen levels. In a healthy individual, this accounts for ~2% of cardiac output. It results in the Alevolar-Arterial Difference in Oxygen.
What is perfusion limitation in gas exchange?
Gas exchange is limited by the rate of pulmonary capillary blood flow, not by the ability of gas to diffuse across the alveolar membrane. The partial pressure gradient between capillaries and alveoli is lost quickly, due to rapid equilibration.
What is diffusion limitation in gas exchange?
Gas exchange is restricted by the ability of the gas to diffuse across the alveolar-capillary membrane (e.g., due to a thickened membrane). Partial pressure gradient between the pulmonary capillaries and alveoli persists due to incomplete equilibration.
Exchange of which gas is diffusion limited
Carbon monoxide (CO) is an example of a diffusion-limited gas. It has a very high affinity for haemoglobin, keeping plasma partial pressure low, maintaining the partial pressure gradient between pulmonary capillaries and alveoli. It does not fully equilibrate.
Give explanations
Which gases are examples of perfusion limited gases?
Oxygen: Normally perfusion limited, unless diffusion is impaired in some way (e.g. thickening of alveolar wall).
N2O does not bind to haemoglobin, so is completed dissolved in plasma. This results in extremely quick equilibration and loss of partial pressure gradient between pulmonary capillaries and alveoli.
What is the oxygen-carrying capacity of hemoglobin?
1 gram of hemoglobin binds approximately 1.39 ml of oxygen.
How does anaemia affect oxygen transport? How does in impact saturation of haemoglobin with oxygen?
Anaemia reduces hemoglobin concentration, lowering oxygen content in the blood, but saturation levels may remain normal.
What is the difference between hypoxia and hypoxemia?
Hypoxia refers to low oxygen levels in the tissues. Hypoxemia refers to low oxygen levels in the arterial blood.
What is the Hypocapnic brake?
Decrease in PO2 (hypoxia) stimulates peripheral chemoreceptors, increasing ventilation rate. This hyperventilation causes a decrease in PaCO2, reducing stimulation of central chemoreceptors and preventing ventilation rate from rising too much.
What is the Haldane effect in respiratory physiology?
The phenomenon of deoxygenated haemoglobin being able to carry more carbon dioxide than oxygenated haemoglobin.
This facilitates CO₂ uptake in tissues and CO₂ release in the lungs.
What is the chloride shift an what is its purpose in respiratory physiology?
As bicarbonate ions diffuse out of erythrocytes, chloride ions diffuse in, to maintain electrical neutrality. This ensures that there can be continued production of bicarbonate - increasing carbon dioxide carrying capacity of the blood. Bicarbonate also acts as a buffer in the blood.
What does the term ‘hypercapnia’ refer to?
High partial pressure of arterial carbon dioxide (PaCO2). It occurs when CO2 production exceeds alveolar ventilation.
What is the Bohr shift and what are its implicaitons?
Oxygen-Haemoglobin dissociation curve shifts leftwards in increased PaCO2. Implications - Lungs: Decreased PaCO2, increased affinity of oxygen-haemoglobin, faciliating uptake of oxygen in the blood. Tissues: increased Pa CO2 (produced in respiration), oxygen has lower affinity for haemoglobin, facilitates delivery of oxygen to respiring tissues.
How is carbon dioxide transported in the blood?
Around 65% carbon dioxide is transported in the form of bicarbonate ions. Carbon dioxide reversibly combines with water to form carbonic acid (catalysed by carbonic anhydrase) which dissociates into hydrogen ions and bicarbonate ions. Around 30% carbon dioxide combines with haemoglobin to form carbaminohaemoglobin. Around 5% of carbon dioxide is dissolved in solution.
Give the four different types of causes of tissue hypoxia.
Hypoxic hypoxia: insufficient oxygen is available to the lungs and therefore saturation of haemoglobin is reduced e.g. pneumonia or high altitude. Ischaemic hypoxia: cardiac output (Q) is reduced e.g. heart failure. Anaemic hypoxia: the concentration of functioning haemoglobin is decreased e.g. iron deficiency anaemia, sickle-cell anaemia, carbon monoxide poisoning. Histotoxic hypoxia: inability to utilise available oxygen e.g. cyanide poisoning.
When using a spirometer to measure lung volumes, why will there be a decrease in the volume of air in the drum over time, despite the subject breathing in and out? Why does this reduction represent?
The subject consumes oxygen from the air in the drum and exhales air with a higher PaCO2. CO2 is absorbed by the soda lime in the drum, so decrease in volume of air is the volume of oxygen consumed.
What is the respiratory minute volume and why is it not useful when determining rate of gas exchange?
Volume of air we breathe in an out of our lungs each minute. It is tidal volume multiplied by respiratory rate. It is not useful because a significant portion of the air inhaled does not reach the alveoli: it is accommodated in the anatomical deadspace.
Which static lung volumes cannot be measured using a spirometer filled with 100% oxygen and what alternative technique could be used to measure these?
- Residual Volume
- Functional Residual Capacity
- Total Lung Capacity
To measure these volumes a helium dilution technique would be used.
Which factors from the list may cause variation in the various static lung volumes? Intelligence, gender, mass, height, handedness and age.
Gender, mass, height and age.
How can vital capacity be calculated from other static lung volumes?
Expiartory Reserve Volume + Tidal Volume + Inspiratory Reserve Volume.
How can functional residual capacity be calculated from other static lung volumes?
Residual Volume + Expiratory Reserve Volume
How can residual volume be estimated?
(Vital Capacity / 0.8) - Vital Capacity
How does a change in barometric pressure change gas composition?
It does not affect the proportion of oxygen in the air, just PO2 as overall pressure is altered.
What is atelectasis?
Alveolar Collapse
What are the 3 factors that affect ventilation?
- Resistance to flow in the airways.
- Elastic properties of the lung.
- Surface tension of the alveoli.
What is meant by the term ‘lung compliance’ and what 2 main factors is it dependent on?
How easy it is to open and stretch the lung. Main factors: Elasticity of the the lung tissue and thoracic cage tissue and Alveolar Surface Tension.
What is the total barometric pressure of the atmosphere at sea level in mmHg?
760 mmHg
How does the solubility of carbon dioxide compare to the solubility of oxygen?
Carbon dioxide is approximately 20 x more soluble.
What are the two factors that govern the rate of gas diffusion into a fluid from air?
- Partial pressure of the gas
- Solubility of the gas
Do bound gases exert a partial pressure?
No, only free gases in solution exert a partial pressure.
Air taken in through upper airways is saturated with water vapour and we must account for the partial pressure of this gas when calculating other partial pressures or gases in air. What is the partial pressure of water vapour in inspired air?
47 mmHg
What happens during inspiration?
The diaphragm contracts, external intercostal muscles contract, and in forceful inspiration, accessory muscles (scalene) elevate the first two ribs.
What muscles are involved in forceful expiration?
Abdominal muscles contract, pressurising the abdomen.
What are the two pleural membranes and their function?
Parietal pleura (lines chest wall) and Visceral pleura (covers lungs). They secrete intrapleural fluid for lubrication.
What drives airflow during inspiration?
The pressure difference between atmospheric pressure and alveolar pressure.
Describe what Functional Residual Capacity (FRC) is.
The volume of air remaining in the lungs after passive exhalation, where lung elastic recoil and chest wall expansion are balanced.
What is intrapleural pressure?
A negative (relative to atmospheric) pressure between the lungs and the chest wall.
What is transpulmonary (transmural) pressure?
The difference between intra-alveolar pressure and intrapleural pressure. It is always positive to prevent lung collapse.
What happens if alveolar pressure is lower than intrapleural pressure?
The lung would collapse.
Why does intrapleural pressure decrease during inspiration?
The chest expands, increasing volume and reducing pressure relative to atmospheric pressure.
What are the two airway zones?
Conducting Zone: Moves air in and out, no gas exchange (anatomical dead space).
Respiratory Zone: Includes respiratory bronchioles and alveoli, site of gas exchange.
What are the two distinct cell types in alveoli?
- Simple squamous epithelial cells: Allow gas diffusion.
- Type 2 epithelial cells: Secrete surfactant.
What is deadspace in the lungs?
Volume of air that does not participate in gas exchange. Assumed to be 2.2 ml per kg of body mass OR 30% of tidal volume.
What are the three types of deadspace?
- Anatomical deadspace (conducting airways).
- Alveolar deadspace (non-functioning alveoli).
- Physiological deadspace (Anatomical + Alveolar deadspace).
What is physiological deadspace in a healthy person?
Equal to anatomical deadspace, as there is no alveolar deadspace in health.
How does fibrosis affect lung compliance?
In fibrosis elastin is replaced with collagen, making the lung stiff and inflexible, reducing compliance.
How does emphysema affect lung compliance?
Emphysema destroys elastic fibres, increasing compliance. The lung expands easily but cannot deflate efficiently.
What stimulates the release of surfactant?
Lung expansion.
What is Young-Laplace’s Law?
The relationship between alveolar pressure, tension and alveolar radius. It assumes that alveoli are perfectly spherical (not always the case).
How does surfactant prevent alveolar collapse (atelectasis)?
Surfactant disrupts hydrogen bonds between water molecules, reducing surface tension and equalising pressure between alveoli.
How does pulmonary oedema affect lung compliance?
It decreases compliance by increasing interstitial fluid, making lung expansion more difficult.
In a healthy individual, is airway resistance high or low?
Low.
How does COPD affect airway resistance?
COPD increases airway resistance, making it harder to breathe.
How does inspiration affect airway resistance?
Inspiration increases lung tension, pulling airways open, increasing radius, and reducing resistance.
Where is airway resistance highest in the respiratory system?
In the upper airways due to a lower surface area to volume ratio.
How does the parasympathetic nervous system affect airway resistance?
It causes bronchoconstriction via acetylcholine acting on muscarinic receptors, increasing resistance.
How does the sympathetic nervous system affect airway resistance?
It causes bronchodilation via adrenaline acting on beta-2 receptors, decreasing resistance.
Equations Knowledge:
How do you calculate Alveolar Ventilation (VA) in L/min from Tidal Volume (VT), Deadspace and Respiratory Rate?
VA=(VT-deadspace)xRR
VT is tidal volume, RR is respiratory rate.
