Respiratory Physiology 3.4- lung function tests and common lung conditions Flashcards
Obstructive vs. restrictive lung disease?
obstructive- obstruction of air flow, especially on expiration
restrictive- restrictive of lung expansion
Why are obstructive lung disorders felt particularly on expiration?
Because during inspiration the physical forces on the lung are such that the lung is being expanded, airways being expanded.
And so diameter of those airways increases and we get a reduction in resistance to airflow.
Whereas on expiration, the chest wall is being compressed. And therefore we also have compression of the airways and therefore any pathologies are aggravated on expiration because the airways are being further compressed by the physical forces that we experience on expiration.
Give examples of obstructive lung disorders?
asthma
(Chronic Obstructive Pulmonary disease)
-chronic bronchitis
-emphysema
Describe asthma?
inappropriate constriction of the bronchial smooth muscle
- expiration harder
Describe bronchitis?
inflammation of the bronchi
-expiration harder
Describe emphysema?
destruction of the alveoli
loss of elasticity
-expiration harder
What are restrictive lung disorders accompanied by?
loss of lung compliance
What is needed when there is a restriction of lung expansion?
invest more effort in inspiration in order to get the same change in volume
Do restrictive lung diseases impact on expiration or inspiration?
impact on inspiration because they restrict lung expansion
Give examples of restrictive lung disorders?
fibrosis
infant respiratory distress syndrome
oedema
pneumothorax
Describe fibrosis?
fibrous tissue gets laid down around the elastic tissue in the lungs.
Fibrous tissue resists stretch
idiopathic- origin of the disease is unknown or unspecified
Describe asbestosis?
individuals who have been exposed to asbestos dust over a long period of time .
Leads to a stiffening of the lung
Describe infant respiratory distress syndrome?
babies born prior to 36 weeks suffer from infant respiratory distress syndrome because they have an increase in surface tension.
Lung less willing to expand on inspiration because of that increase in surface tension
Describe oedema?
fluid building up around the alveoli.
Fluid creates a pressure that resists inflation of the alveoli.
Resists lung expansion.
Describe pneumothorax?
Occurs where you get air introduced to pleural cavity.
Pushes apart the parietal pleural membrane from the visceral pleural membrane.
Lung that is no longer related to the chest wall and diaphragm.
Complete loss of lung expansion.
Describe spirometry?
technique commonly used to measure lung function
What are the two classes of spirometry?
static - the only consideration made is the volume exhaled or inhaled
dynamic- where the time taken to exhale a certain volume is what is being measured
What can’t be measured by spirometry?
residual volume
total lung capacity
functional residual capacity
as involves residual volume
Describe FEV1 / FVC?
FEV1- forced expiratory volume in one second
(in fit, healthy, young adult males: 4.0L)
FVC- forced vital capacity - total amount of air that you can expire over whatever time
(in fit, healthy, young adult males: 5.0L)
What is FEV1 to FVC ration in a healthy adult male?
80%
What is normal ratio of FEV1/FVC? regardless of sex
80%
Describe FEV1/ FVC in obstructive lung diseases?
takes much longer to get all air out because there is obstruction to air flow.
Reduced volume of air being expired in the first second and we also tend to have a total reduction in the total expired air aswell.
Ratio less than normal.
FRC may be increased.
Describe FEV1/FVC in restrictive lung diseases?
Not much air in the lungs to start with because of the restriction of expansion.
FEV1 decreases but only because there’s less air in the lungs in the first place- air that is flowing is flowing at a normal rate as there is no obstruction to air flow.
FEV reduced and your FVC reduced.
Ratio normal or slightly increased.
What are the limitations of the FEV1/FVC ratio?
Obstructive: both FEV and FVC fall but FEV more so, so ratio is reduced
Restrictive: both FEV and FVC fall so ratio remains normal, or may even increase, despite severe compromise of function
Describe pressure-volume relationship and compliance in inspiration?
compliances increases as we move through the inspiratory phase.
Compliance is pretty low at the start of inspiration.
Increases greatly at end of inspiration
Why do we require a greater change in pressure (from FRC) to reach a particular lung volume during inspiration, than to maintain that volume during expiration?
Overcome lung inertia during inspiration (overcome the reluctance of our tissues to change their shape)
Overcome surface tension during inspiration
During expiration compression of the airways means more pressure is required for air to be pushed out.
Describe pressure-volume relationship and compliance in expiration?
compliance is low at start of expiration but then increases significantly once intrapleural pressure reaches about -0.4kPa.
Compliance increases towards end of expiration
