Spirometry & Peak Flow Meters

What is Spirometry

Non-invasive test of lung function

What does spirometry measure?

• amount of air in/out of the lungs 

  • speed of air in/out 

Results of spirometry indicate

Lung size

Airway size

Respiratory muscle strength

What is spirometry used for ?

Diagnose and differentiate diseases causing ventilatory abnormalities

• Obstructive lung disease

• Restrictive lung disease

Monitor disease progression

Monitor response to therapy

Assess pre-operative risk

Assess smoking related damage

Vital Capacity (VC)

Total amount of air that can be exhaled when blowing out at a steady rate

Forced Vital Capacity (FVC)

Total amount of air expelled after a full inspiration and a full expiration with a forceful effort

• reduced in pulmonary fibrosis, ILD, COPD due to airway closure

Forced Expiratory Volume in 1 seconds (FEV1) 

The volume that can be exhaled in the first second of expiration 

• reduced in people with narrow airways (ie. asthma, smoking, COPD) 

FEV1/FVC ratio

How much of the total air blown ou tin 1 second

Normally 70-90%

Peak Expiratory Flow Rate (PEF)

Liters/sec.

Maximal flow that can be exhaled blowing out as fast as possible

Peak Cough Flow (PCF) 

Can measure cough strength, not routinely measure

Tidal Volume- Vt

Volume of air air inspired during quiet respiration

Average ~500ml adult

Minute Ventilation

Vt x RR = ~500ml x 12 = 6.0L/min

Spirometry Contraindications and Precautions

Pneumothorax

Unstable cardiovascular status

Increased intracranial pressure

Abdominal, thoracic or eye surgery in the previous 8 weeks

Haemptysis

Nausea, diarrhea or vomiting

Key Step to Performing Spirometry 

Prepare device- calibration 

Establish rapport with patient 

Gather patient data- height, weight, age, gender, ethnicity 

Provide clear instructions 

Coach patient or client through procedure 

Performing Spirometry

Instruct the patient

• “this test is to see how much air you can blow in and out”

Demonstrate the manoeuvre

• Demonstrate to patient with required effort

Patient test performance

• Patient performs test at least 3 times

Correct patient errors

• Identify errors affecting accuracy and correct technique

Interpertation of Results

Print out of values

Actual and predicted

Graphs

Is the test acceptable?

They are free from artefacts

• Cough or glottis closure during the first second of exhalation 

• Early termination or cut-off 

• Variable effort

• Leak

• Obstructed mouthpiece

Have good starts 

• Extrapolated volume less than 5% of FVC or 0.5L, whichever is greater 

• OR time-to-PEF of less than 120ms 

Have satisfactory exhalation 

• 6sec of exhalation and/or or a plateau in volume-time curve; OR reasonable duration if the subject cannot or should not continue to exhale 

Check reproducibility criteria

After 3 acceptable results have been obtained, apply the following tests:

• Are the 2 largest FVS within 0.2L of each other?

• Are the 2 largest FEV1 within 0.2L of each other

If both of these criteria are not met, continue testing until:

• Both of the criteria are met with analysis of additional acceptable spirograms; OR

• A total of 8 tests have been performed OR

• The patient/subject cannot or should not continue

Record as a minimum the 3 best test values

Ventilatory Patterns- Normal

FEV1 and FVC above 80% predicted

FEV1/FVC ratio above 0.7

Ventilatory Patterns- Obstructive 

FEV1 below 80% predicted 

FVC can be normal or reduced - usually to a lesser degree than FEV1 

FEV1/FVC ratio below 0.7

Ventilatory Patterns- Restrictive

FEV1 below 80% predicted or normal

FVC below 80% predicted

FEV1/FVC ratio normal - above 0.7

Ventilatory Patterns- Mixed

FEV1 below 80% predicted

FVC below 80% predicted

FEV1/FVC ratio below 0.7

Peak Flow Meters (PFM) 

Measurement of flow - not volume 

Can be used as a monitoring tool for patients

• Most commonly asthmatics 

• Also some neurological conditions (ie. GBS) 

• Not useful for all - in collaboration with respiratory physician 

Instructing a Patient to Use a PFM

Move the marker to the bottom of the numbered scale.

Stand up straight.

Take a deep breath. Fill your lungs all the way.

Hold your breath while you place the mouthpiece in your mouth, between your teeth. Close your lips around it.

(Do not put your tongue against or inside the hole)

Blow out as hard and fast as you can in a single blow. Your first burst of air is the most important.

(So blowing for a longer time will not affect your result)

Write down the number you get. But, if you coughed or did not do the steps right, do not write down the number. Instead, do the steps over again.

Move the marker back to the bottom and repeat all these steps 2 more times. The highest of the 3 numbers is your peak flow number. Write it down in your log chart

Monitoring Using a PFM - Short Term

To help identify asthma triggers

To monitor response to a new treatment or a change in dose (up or down)

To calculate the “trigger point” for a written asthma action plan

Monitoring Using a PFM - Long Term

For people with asthma who have frequent flare-ups

For people with moderate to severe asthma who have little warning of flare-ups 

For people with asthma who are anxious or tend to over treat minor events 

For people with asthma who are “poor perceivers” of airway narrowing 

Obstructive Disease Pattern

FEV1- Low - Less than 80%

FEV- Normal

FEV1/FVC Ratio- Low - Less than 0.7

Restrictive Disease Pattern 

FEV1- Normal or low - under 80%

FVC- Normal or low - under 80%

Ratio- High (ie. 0.9)

Typically one is low and one is normal

Mixed Pattern

FEV1- Low

FVC- Low

FEV1/FVC- Low

Below 80%

and below  0.7