Respiratory System Flashcards
(70 cards)
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.
