Ventilation and compliance (physiology) Flashcards
What is the tidal volume
The volume of air inspired and the volume of air expired (they are equal)
What are the volumes of the lung during a tidal volume sequence
1.5L-3L-2.5L
What is the vital capacity
The maxiumum amount of air which can be breathed out or in
What is the residual volume
The air left in the lungs which remains even when the maximum amount if air is exhaled
Vital capacity + residual volume =
Total lung capacity
What are the two types of ventilation?
Minute ventilation and alveolar ventilation
How do you work out minute ventilation
Tidal volume (ml/breath) x respiratory rate (breaths/min)
At rest this should be roughly 5L/min
How do you work out alveolar ventilation?
(Tidal volume - dead space*) x respiratory rate
This takes into account the areas of the lungs where no gas exchange occurs.
Will be lower than the minute ventilation
*dead space = volume of the conducting airways ~150ml)
Give 2 examples of lung function tests
Spirometer
Peak flow meter
What are the main parameters used to measure lung function
Forced vital capacity - max volume exhaled
Forced Expiratory Volume in 1sec FEV¹- will be 80% of FVC
List the 3 obstructive lung diseases and explain their impact on lung function tests
COPD (emphysema, chronic bronchitis), asthma, CF
- FEV¹ reduced due to increased resistance in obstructed airways. It will be <80% of FVC
- FVC normal
Give an example of a restrictive lung disease and explain its impact on lung function tests
Fibrosis
FVC is reduced when compared to healthy lungs (there is restricted movement due to stiffening or the lungs)
FEV¹ is >80% FVC
What is lung compliance
A measure of how well the lungs change volume
What two characteristics does healthy lung tissue possess
Elasticity (elastin) and strength (collagen)
In a healthy individual, what does an increase in transpulmonary pressure lead to
An increase in lung volume in
In an individual with emphysema, what does the same increase in transpulmonary pressure lead to
A larger increase in volume due to the loss of alveolar tissue, loss of elasticity and loss of elastic recoil. This is know as high compliance
In an individual with oedema, pneumonia or fibrosis what does the same increase in transpulmonary pressure lead to
A much smaller increase in volume. This is known as low lung compliance
Explain the impact fibrosis has on lung compliance
Reduced lung compliance due to an increased expression of collagen and inflammation
Explain the concept of lung surfactants
Type II cells in the lung produce surfactants
They are a complex mixture of lipids and proteins
They decrease surfactants tension at air/liquid interface in the alveoli - aiding breathing
What is the link between premature babies and lung surfactants
Premature babies have under developed type II cells meaning they have reduced surfactqnt production. This increases surface tension and is known as newborn respiratory distress syndrome
What is the link between lung compliance and arthritis
Painful disorders affecting movement of the ribs and spine make breathing difficult so reduce compliance
Lung compliance =
Equation
Change in lung volume/change in transpulmonary pressure
Why is it important to have optimal ventilation and blood flow within the lungs
To maximise uptake of O2 and release toxic CO2. If this isn’t optimised it can cause shortness of breath, headache, dizziness and liss of consciousness
Describe the impact emphysema has on lung tissue
Degradation of alveolar and bronchiole walls and capillaries
The release of protease enzymes by leukocytes also damages tissue
What percentage of cases of emphysema are caused by smoking
80-90%
Describe the impact emphysema has on gaseous exchange
The breakdown of alveolar tissue reduces surface area available for gaseous exchange. In diseased alveoli less O2 is able to diffuse effectively into capillaries reducing uptake of O2 into the body
What is the treatment for emphysema
Oxygen (only in severe cases when FEV¹<30%FVC)
