Ventilation and Compliance Flashcards
What is the average tidal volume?
500ml
What is tidal volume?
Volume of air breathed in and out of the lungs at each breath, while not reaching the limits of inhalation and exhalation
Define anatomical dead space and its volume
Volume of gas occupied in the conducting airways, not available for gas exchange
150ml
Define the expiratory reserve volume
Maximum volume of air that can be expelled from the lungs at the end of a normal expiration
Define the inspiratory reserve volume
Maximum volume of air that can be drawn into the lungs at the end of a normal inspiration
Define the residual volume
Volume of gas in the lungs at the end of a maximal expiration, necessary to prevent he collapse of alveoli and smaller airways.
Can be affected by anaesthetics
Define vital capacity
Sum of:
- tidal volume
- inspiratory reserve volume
- expiratory reserve volume
Expresses maximum volume a person can exhale after a maximal inhalation
Define total lung capacity
Vital capacity + residual volume
Represents all the air in the airways, despite some not partaking in gas exchange
Define Inspiratory capacity
Tidal volume + inspiratory reserve volume
Define functional residual capacity
expiratory reserve volume + residual volume
What does FEV1:FVC represent?
Fraction of forced vital capacity is expired in 1 second
What is the difference between pulmonary ventilation and alveolar ventilation?
Pulmonary - Total air movement in/out of lungs, not significant in functional terms
Alveolar - fresh air getting into the alveoli and therefore available for gas exchange
How much of the tidal volume is made up of stale air?
150ml of 500ml is stale (held in dead space)
Upon inhalation, how much of the tidal volume is made up of fresh air?
350ml ( +150ml stale air from dead space)
What usually occurs in those who are anxious - hypoventilation or hyperventilation?
Hypoventilation
What usually occurs in those who are relaxed - hypoventilation or hyperventilation?
Hyperventilation
Define partial pressure
Pressure of a single gas in a mixture is equivalent to the % of that particular gas in the mixture
What % of inspired air is O2?
21%
What % of inspired air is N2?
79%
If there is an increase in CO2 in the blood, is it due to an error in inhalation or exhalation?
Exhalation
What is the value of normal ventilation in a minute?
4.2L/min
What is normal Po2 and Pco2 in inspired air?
Po2 = 100mmHg Pco2 = 40mmHg
What happens to Po2 and Pco2 in hyperventilation?
Po2 = 120mmHg Pco2 = 20mmHg
What happens to Po2 and Pco2 in hypoventilation?
Po2 = 30mmHg Pco2 = 100mmHg
How does surfactant reduce surface tension?
Hydrophobic surfactant goes between water molecules in the alveoli. Normally, these molecules are attracted together, and in the alveoli their attraction towards each other and creation of H bonds causes an increase in pressure in the alveoli, leading to their collapse. By getting in the way, surfactant prevents this, therefore reducing surface tension
Why is surfactant more effective in smaller airways?
Surfactant is more concentrated
What is LaPlace’s law?
The larger the vessel radius, the larger the wall tension required to withstand a given internal fluid pressure
When does surfactant production start?
~25 weeks gestation
When is surfactant production complete?
~36 weeks gestation
What stimulates surfactant production?
Thyroid hormones
Cortisol
Both increased towards the end of pregnancy
What is infant respiratory distress syndrome?
Caused by developmental deficiency in the production of surfactant, as well as the structural immaturity of the lungs, leading to the increased difficulty of the baby to breath following birth
Define compliance
Change in volume of the lungs relative to a change in pressure (stretchability of the lungs)
Define high compliance
Large increase in lung volume following a small decrease in intrapleural pressure
Define low compliance
Small increase in lung volume following a large decrease in intrapleural pressure
What effect does emphysema have on the work of respiration?
Loss of elastic tissue means expiration requires effort
What effect does fibrosis have on the work of respiration?
Inert fibrous tissue means effort of inspiration increases
Why is alveolar ventilation greater in the base of the lung than the apex?
At the base the alveoli are more compressed by gravity and the weight of the lungs, and are therefore more complaint on inspiration
Describe the effect of obstructive lung disease on air flow
Obstruction of airway affects mainly expiration
Describe the effect of restrictive lung disease on air flow?
Restriction of air flow during lung expansion due to loss of lung compliance, affects inspiration
Name some obstructive lung diseases
Asthma
Emphysema
Bronchitis
COPD = emphysema + bronchitis
Name some restrictive lung diseases
Fibrosis
Infant respiratory distress syndrome
Oedema
Pneumothorax
What test is usually used to measure lung function?
Spirometry
Whats the difference between static and dynamic spirometry?
Static - only considers volumes
Dynamic - considers volumes and time taken
What is the FEV1 of a normal healthy male?
4L
What is the FVC of a normal healthy male?
5L
What is the normal FEV1/FVC of a normal healthy male?
80% (4L/5L)
What happens to FEV1/FVC as you age?
Absolute values for each volume increase, but the ratio stays the same (80%)
What happens to FEV1/FVC in those with obstructive lung disease?
Both are reduced, but more so for FEV1, making FEV1/FVC ratio reduced
What happens to FEV1/FVC in those with restrictive lung disease?
Both FEV1 and FVC drop, so the ratio can seem the same despite extensive disease
What is FEF25-75?
Average expired flow for air over the middle of an FVC, from around time of 25%-75% air movement
What are the benefits of examining FEF over FEV1?
Correlates but changes in FEF are more striking in disease
What are the drawbacks of examining FEF over FEV1?
Normal range is broader
