Measuring lung function Flashcards
Tidal volume
The amount of air inspired and expired during quiet breathing
500 ml
Dead space
The volume of air inspired that does not undergo gaseous change.
150/500ml
Total minute ventilation
The volume of air inhaled and exhaled in a minute.
This is 6L/min.
Generations of conducting zones in the airway
1-16
Do not contain alveoli
Composed of trachea, bronchi, bronchioles.
1-4 are cartilaginous
Respiratory zones
Zones 17-22
23rd generation
The end of the respiratory tract- the alveoli
Pneumotachograph
A piece of equipment that measures flow and converts it to volume.
Inspiratory reserve volume
The maximal amount of air forcefully inhaled above normal inspiration.
Expiratory reserve volume
The maximum amount of air exhaled above normal expiration.
Residual volume
The amount of air left in the lungs after maximum expiration
Tidal volume
The amount of air inspired and expired during quiet breathing.
Functional residual capacity
The amount of air left in the lung after normal expiration.
Total lung capacity
The maximum amount of air that can be inspired in the lung.
TLC= VC +RV
Vital capacity
The amount of air that can be expired after the deepest inspiration.
VC= IRV+TV+ERV
FEV1
FEV1
The volume of air expired forcefully at the end of the first second.
FEV1/ FVC ratio
The ratio between the volume of air expired forcefully at the end of the first second compared to the total volume of air expired forcefully.
Normal value> 70%. If it is less than this, then obstruction in the airway is present.
FVC
Forced vital capacity
The amount of air expired forcefully after the deepest breath.
Normal value is >80% of predicted FVC, according to general data.
Normal data is made from averaging gender, age, race, height.
Albuterol
Bronchodilator that is used in asthmatic patients.
Using spirometry to measure responsiveness to albuterol
- The FEV1 is taken using the spirometer and recorded.
- Albuterol is then administered to patient and FEV1 is measured 15 minutes later.
- An increase in FEV1 by 12%/ 200 mL indicates reversible obstruction.
Spirogram
Gram plotted from a spirometer to show the change in volume over time.
The first second will show the FEV1 value.
The graph should plateau after a few seconds due FVC being reached.
Flow-volume loop
A graph plotted from a spirometer that shows flow (L/sec) in expiration and inspiration, against time.
The graph is read from the left on the x axis, in an anticlockwise direction.
TLC is when volume and rate is 0 at the end of expiration.
Volume at the end of inspiration is the residual volume.
Effort and flow rates during expiration
It is important to ensure that the patient takes a full deep breath before blowing into spirometer.
Effort-dependant phase
During flow rate measurements, this is when increasing effort, increases flow rates.
Decreasing effort and increased resistance decreases flow rate.
Effort-independant phase
This is when despite increasing effort whilst measuring the peak expiratory flow rate, there is no change in flow rate.
This is due to airway resistance
Peak expiratory flow rate
A measurement that shows volume of air forcefully expired in L/min.
PEFR is the lowest in the morning for everyone.
There is a wide variation in PEFR shown in asthmatics compared to healthier people.
This is combated through- anti-inflammatory treatments and long acting beta agoinsts
Salmeterol
Long acting beta-2 agonist used by asthmatics which is used to prevent asthmatic symptoms and control COPD symptoms
Effort independent flow
Occurs when an increase in effort doesn’t increase the flow rate.
Due to airway resistance dropping the pressure of air from alveoli to the mouth.
When pleural pressure exceeds alveolar pressure during expiration, this narrows the airway and creates greater resistance.
Therefore since there is no cartilage to resist collapsing, the airway can collapse.
Alveolar pressure
Alveolar pressure= pleural pressure + elastic recoil
Equal pressure point
In cartilage free-bronchioles, this is when the intrapleural pressure is equal to the alveolar pressure.
Cartilage-free bronchioles act as starling resistors therefore when intrapleural pressure exceeds alveolar pressure, resistance is increase in the bronchioles.
Increased effort will increase alveolar pressure and pressure at the EPP but pressure difference and flow in unchanged.
Variable intrathoracic large airway obstruction
An airway lesion in the thoracic trachea.
Inspiration peaks but expiration does not.
During inspiration the trachea is pushed outwards as the tracheal pressure exceeds pleura pressure.
BUT during expiration, the trachea is pulled inwards due to the pleural pressure exceeding the tracheal pressure. This increases resistance and is why there is no peak during expiration.
Variable large extrathoracic airway obstruction
Occurs when there is a lesion in the trachea, in the extrathoracic region.
During inspiration, atmospheric pressure exceeds tracheal pressure, which pulls trachea inwards. This increases resistance in trachea and narrows airway.
Whereas during expiration, tracheal pressure exceeds atmospheric pressure which pushes trachea outwards- hence why obstruction is variable
Methacholine test
Tests for a hyperactive airway response.
Spirometry test is taken to record FEV1.
Methacholine is administered with the dose increased every 5 minutes.
If there is a positive test result- a DECREASE in FEV1 by 20 % is seen, indicating a hyperactive airway- easily triggered bronchospasm
What lung volumes are reduced in restrictive airway conditions?
Residual volume
Functional residual capacity
Total lung capacity
This reduction can be determined by measuring TV, ERV and IRV to indirectly calculate FRC, TLC and RV.
Methods of measuring lung volumes
Plethysmography- body box
P1V1= P2V2
P1- alveolar pressure at the mouth at FRC
V1= FRC
P2= Alveolar pressure during inspiratory effort against closed shutter V2= FRC + change in the volume of the box
Conditions that show decreased lung volumes?
Pleural disease
Chest wall disease
Lung parenchymal process/ airspace filling process- expansion of the interstitial space due to water, scarring/inflammation.
Weakness of the lung-
Nerve/ muscle based
Focal/ global
Pathologies that show elevated lung volumes
Emphysema- increased lung compliance and FRC
Hyperinflation- COPD
Air trapping
Hyperinflation
Increased TLC volume
Air trapping
Increased residual volume.
Seen in when airway, especially bronchioles collapse and is unable to expel air.
Therefore there is more air left in the lungs after ex
Diffusing capacity
Measurement of how well gases diffuse across alveoli.
Measurement= CO transfer factor.
Patients perform a breath hold with an inhaled gas that is diffusion-limitted.
Amount of diffusion= inspired CO- expired CO.
Gives DLCO
Factors that affect gas exchange
The alveolar surface area- increase SA increases GE
Thickness of respiratory membrane- increased thickness decreases GE
DLCO
Diffusion capacity- the extent to which O2 passes from the alveoli into the blood.
Pulmonary conditions that show reduced DLCO
Emphysema
Lung infiltration
Lobectomy
CV and haematological conditions that reduces DLCO
Pulmonary hypertension
Low CO
Pulmonary oedema
Anaemia
Effect of polycythemia on DLCO
Increases- more O2 in blood
Effect of pulmonary haemorrhage on DLCO
Increases- more O2 in lungs due to blood in lunds.
