Perform and interpret Respiratory
 Function Tests
Devangna Bhatia

Lung Function Tests
Lung function tests measure:
•How much air you can take into your lungs. This amount is compared to that of other people your
age, height, and sex. This allows the doctor to see whether you're in the normal range.
•
•How much air you can blow out of your lungs and how fast you can do it.
•
•How well your lungs deliver oxygen to your blood.
•The strength of your breathing muscles.

Peak flow meter Test
This measures the fastest speed you can blow out.
To do the test you take the biggest breath in that you can and then blow out as fast as you can.
The results are useful in diagnosing asthma and deciding on its treatment.

Spirometry Test
Most common lung function test
Tests the amount (volume) and/or speed of air that can be inhaled and exhaled
Results are displayed in pneumotachographs
Helpful in assessing conditions, such as - asthma, COPD, pulmonary fibrosis and cystic fibrosis.

FEV1/FVC (FEV1%) = In healthy adults  = 75–80%.
Obstructive diseases (asthma, COPD, chronic bronchitis, emphysema) FEV1 is diminished because of
increased airway resistance to expiratory flow and the FVC may be decreased (for instance by
premature closure of airway in expiration). This generates a reduced value (<80%, often ~45%).
In restrictive diseases (pulmonary fibrosis) the FEV1 and FVC are both reduced proportionally and
the value may be normal or even increased as a result of decreased lung compliance.
FEV1 = Forced Expiratory Volume in 1 second. Expiration after max. inspiration.
FVC = Forced Vital Capacity, volume of air that can forcibly be blown out after full inspiration,
measured in liters.

Other values:
FEF = Forced Expiratory Flow - flow/speed of air coming out of the lungs during the middle portion
of a forced expiration. The usual intervals at which it is measured are 25%, 50% and 75% (FEF25,
FEF50 and FEF75), or 25% and 50% of FVC
FIF = Forced Inspiratory Flow - similar to FEF but measured during inspiration!
PEF = Peak Expiratory Flow - the maximal flow/speed achieved during the maximally forced expiration
initiated at full inspiration, measured in litres per minute.
TV = Tidal volume - specific volume of air drawn into, and then expired out of, the lungs during
normal tidal breathing.
TLC = Total Lung Capacity - maximum volume of air present in the lungs

Blood Gas Test
A.k.a - Arterial blood gas (ABG)
It involves using a needle to draw blood from the radial artery OR the brachial artery OR the
femoral artery.
In rare cases, blood from veins can be used.
Function of the test:
Used to measure the CO2 and O2 levels blood
Can also determine the acidity (pH) of the blood
Aims: To make sure patients are receiving the right amount of O2, to check if the current treatment
is effective and to measure the acid-base level in patients with heart or kidney failure,
uncontrolled diabetes, severe infections or sleeping disorders.

Indications
1) If patients show signs of an oxygen/carbon dioxide or pH imbalance
2) Respiratory, kidney or metabolic disease and are suffering from respiratory distress
3) Have head or neck trauma
4) Have just undergone prolonged anaesthesia for procedures such as cardiac bypass or brain
surgery.
Generally, there are no special steps that patients must take in preparation for a blood gas test.
The only exception applies to patients receiving oxygen therapy, whose oxygen concentration must
not change during the 20 minutes before the test.
Preparation

Pulse Oximeters
Device to measure indirect oxygen saturation of patient’s blood. Very useful, since it is
non-invasive.
When used in hospitals, it is linked up to a medical monitor to allow continuous oxygenation.
Portable devices are also available - use at home.
Acceptable normal range: 95-100%
Situations/locations where it’s highly useful:
Intensive Care (ICU)
Operating room and Recovery
Emergency and hospital ward settings

*



*