Flashcards in Respiratory Function Tests Deck (29)
What are the limitations of lung function tests?
Patients may be unable to perform the test, or unable to understand the instructions
What is involved in spirometry?
Spirometry involves maximal effort by the individual and volume is plotted against time
What is measured in a spirometry trace?
Volume is plotted against time
How will an obstructive lung disorder affect FEV1/VC?
FEV1 is reduced more than the vital capacity as there are issues associated with expiration as the blockage will become more lodged on expiration than on inspiration, but there are no issues that affect the actual available lung volume. Therefore, FEV1 is smaller but VC remains the same and therefore the FEV1/VC is reduced.
How will a restrictive lung disorder affect the FEV1/VC?
In restrictive lung disease, the vital capacity is reduced due to reduced chest expansion or lung fibrosis which reduces the amount of available lung volume. FEV1 isn't really affected, and therefore FEV1 is divided by a smaller number, and therefore the ratio is elevated in this form of disorder.
How can you calculate FEV1 from a spirometry trace?
As volume is plotted against time, you ask the patient to breath out as quickly and as powerfully as they can, and then you will see the maximum volume that they managed to exhale in the timeframe of 1 second from exhalation onset
What conditions reduce peak flow?
Reduced in large airway obstruction, upper airway obstruction and asthma (OBSTRUCTIVE LUNG DISORDERS)
How would small airways disease present on a flow-volume loop?
There will be 'scooping out' of the expiratory portion of the flow-volume loop as expiration is mainly implicated by this obstructive disorder
What type of disorder is small airways disease?
Physiologically, which should be larger: maximal inspiratory flow or maximal expiratory flow?
Maximal expiratory flow as this is accompanied by compression of the alveoli and therefore this increases the flow rate.
What are examples of small airway disease?
These are obstructive respiratory diseases and include emphysema and asthma
How would restrictive lung disease present on a flow-volume loop?
The flow-volume loop is the same shape but is narrower as a result of decreased lung volumes
What is variable extra thoracic obstruction?
An obstruction that occurs outside of the thorax
What causes variable extra thoracic obstruction?
Unilateral vocal cord paralysis or dysfunction as this causes the vocal cord to move passively with the pressure gradient across the glottis. Therefore, during forced inspiration it's drawn in and causes a plateau in inspiratory flow whereas in forced expiration it is passively forced aside and therefore expiratory flow is unimpaired
How does variable extra thoracic obstruction appear on a flow-volume loop? (unilateral vocal cord paralysis or dysfunction)
The inspiratory flow-loop will be plateaud due to impeded forced inspiration but expiratory flow isn't impaired and therefore appears normal.
What is variable intrathroacic obstruction?
In forced inspiration the negative pleural pressure keeps the trachea opening, but in the absence of this pressure in forced expiration this causes tracheal narrowing when there is a lack of structural support, and therefore this impedes expiratory flow
What causes variable intrathoracic obstruction?
Tracheomalacia (floppy trachea)
How does variable intra thoracic obstruction (tracheomalacia) appear on a flow-volume loop?
Inspiration is normal as the negative pleural pressure keeps the trachea open, but expiration peak as and then plateaus due to tracheal narrowing as pressure decreases.(due to lack of structural support to hold the trachea open)
What is fixed intrathoracic obstruction?
This is where there is permanent non-variable obstruction in the thorax that impedes airflow
What causes fixed intrathoracic obstruction?
Goitre and tracheal stenosis
How does fixed intrathoracic obstruction appear on a flow-volume loop?
There is decreased and plated inspiratory and expiratory flow, and therefore the flow-volume loop looks rectangular
How can you measure gas transfer in the lungs?
A single, large breath of air with carbon monoxide and helium in it, that is held for 10 seconds, allows the alveolar volume and gas transfer to be calculation.
What is the transfer factor of the lung for carbon monoxide (TLCO)?
This is indicative of the total diffusing capacity of the lung
What is the Fick principle?
The volume of gas per unit time (flow) which diffuses across a tissue sheet is proportional to the area of the sheet, inversely proportional to sheet thickness, and is proportional to the difference in pressure on the two sides and dependent on the permeability coefficient for that gas.
How may disease reduced gas transfer by the Fick principle?
> Reduced 'sheet' surface area - this occurs if there is surgical removal of lung tissue or reduced effective area due to emphysema, or if there are increased amounts of 'dead space'
> Increased 'sheet' thickness - this can occur with pulmonary fibrosis and alveolar proteinosis in acute lung injury
> Reduced pressure difference - this is seen in high altitude
What is meant by the airway resistance?
The pressure different between the alveoli and the mouth
How does emphysema effect lung compliance and elastic recoil?
Increases lung compliance but reduces elastic recoil
How does lung fibrosis effect lung compliance and elastic recoil?
Decreases compliance but increases elastic recoil