4.5 Respiratory Investigations - spirometry etc

why order a pulmonary function test (PFT)

1. investigation for respiratory disease

2. ongoing management of lung disease

3. assess response to treatment

4. pre-operative assessment

5. physical injury

how is spirometry performed

1. maximal breath in (to total lung capacity)

2. sharp “blast out” with maximum force ad without hesitation

3. full expiration until no air left in lungs

peak expiratory flow

is the highest speed of expiration measured during a forced spirometry test,

contraindications for spirometry

1. Hemoptysis (coughing blood) of unknown origin

2. Unstable cardiovascular status (recent heart attack)

3. Pneumothorax (collapsed lung)

4. Recent eye, thoracic, abdominal surgery

5. Nausea/Vomiting

6. Inability to comply with required maneuver

quality criteria

acceptability: how well eaxh individual attempt of the test went

• max 8 attempts allowed

• poor attempt can look like a lung disease

repeatability

• how well each trial relates to one another

spirometry needs to take into account

• age

• height

• sex

FVC - force vital capacity

total amount of air that can be forcefully blown out after full inspiration

FEV1 - forced expiratory volume in 1 seconds

amount of air that can be forcefully blown out in one second

FEV1/FVC ratio

important marker for airflow obstruction

restrictive lung disease

a condition characterized by reduced lung volumes and difficulty in fully expanding the lungs, often leading to decreased total lung capacity.

obstructive lung disease

a condition where airflow is obstructed, leading to difficulty in exhaling air from the lungs.

• can exhale the same amount of air but struggle to get it out at the same speed

• reduced FEV1/FVC ratio

obstructive lung diseases such as

• asthma

• cystic fibrosis

restrictive lung disease such as

neuromuscular weakness

• inability to fully inflate lungs due to diaphragmatic weakness

what is a mixed condition for obstructive and restrictive

scoiliosis

• unable to fully inflate lungs

• atelectasis (partial collapse of airway/alveoli)

how lung disease affects spirometry - obstructive

• reduced FEV1

• normal FVC

• reduced FEV1/FVC ratio

how lung disease affects spirometry - restrictive

• reduced FEV1

• reduced FVC

• normal OR elevated FEV1/FVC ratio

how lung disease affects spirometry - mixed

• reduced FEV1

• reduced FVC

• reduced FEV1/FVC ratio

bronchodilator response

• do spirometry test

• take bronchodilator

• wait 15 min

• do test again

disease like asthma will show improvements but those with chronic disease like emphysema is fixed

other complex PFTs

• diffusing capacity of the lung for carbon monoxide (DLco)

• lung volumes (whole-body plethsmography)

• cardiopulmonary exercise test (CPET)