Spirometry Flashcards
What does a spirometer do?
It records the volume of air that is breathed in and out and generates tracings of airflow (i.e. pneumotachographs).
These tracings are then used to calculate:
- Vital capacity
- Tidal volume
- Flow rate of air movement
Why do you do pumonary function tests?
Diagnosis
Although these tests are rarely diagnostic on there own. They are usually taken in conjunction with a history and examination.
Patient assessment
Most common reason for test
- Serial changes
- Response to therapy
- Assessment for compensation
- Pre-surgical assessment
Research purposes
- Epidemiology
- Study of growth and development
- Investigation of disease processes
What is a vitalograph?
A make of spirometer which records the volume expired during a vital capacity breath.
How do you express inspiration and expiration on a spirometry tracing?
Inspiration - upwards deflection
Expiration - downwards deflection.
This is because of the old fashioned spirometers and the traces they used to produce.
How did an old fashioned spirometer work?
- Floating bell jar
- Expired gas passes into water seal
- Increased pressure causes jar to rise
- Movement tansmitted to pen
- Pen movement proportional to volume breathed in and out.
What is tidal volume (VT)?
Volume of air moved in normal (quiet) breathing
What are our inspiratory (IRV) / expiratory (ERV) reserve volume?
Max we can breath in / out on top of the tidal volume.
What is the residual volume?
Air in our lungs what we can’t breath in and out.
Why can’t we easily measure our total lung capacity?
We cant easily measure the residual volume of our lungs.
What do we measure instead of total lung capacity?
Vital capacity (VC)
What different values can we quote as lung capacity?
Inspiratory capacity: VT + IRV (tidal volume + inspiratory reserve volume)
FRC (functional reserve volume)
VT (tital volume)
VC (vital capacity)
What can we quote as inspirational capacity?
VT + IRV
What can we quote as functional residual capacity?
ERV + RV
What do forced flow-volume measurements show us?
- How much air can be blown out - reduced in restrictive disorders or if airway narrowing precipitating early airway closure (asthma)
- How fast is the air expelled? - reduced with narrowing
- Pattern of changein flow-volume curve can indicate the site of obstruction
- Can see the response to treatment
- Change with age or growth
- Progression fo disease
What is FVC?
Forced vital capacity - maximal amount of air that the patient can forcibly exhale after taking a maximal inhalation
What is FEV1?
Volume exhaled in the first second
-most useful and reproducible especialu in diagnosing and monitoring patient with obstructive pulmonary disorders (COPD and asthma)
What does a time-volume graph look at?
It is a graph of volume expired against time.
How do volume-time graphs change is obstructive disease?
FVC = relatively normal if given sufficient time to breath out (narrowed airways redice the speed as which air can be breathed out)
FEV1 = reduced
FEV1/FVC ratio - less than 70%
What is a flow volume loop?
How does a flow volume loop change in an obstructive lung condition (e.g. asthma / COPD)?
Scolloping
How does a flow-volume loop change in an restrictive lung condition (e.g. fibrosis)?
Narrower
