Pulmonary Function Tests

Question 1

Pulmonary function tests - define

a.k.a spirometry

Answer 1

> Measurement of Breathing

• static lung volumes (volumes + capacities)
• Dynamic lung volumes (flow of volume of air - ie over time period)

Question 2

Measures

Answer 2

> Static + Dynamic Volumes

> shows abnormalities vs. normative values (not disease specific)

Question 3

Indications

Answer 3

> To Diagnose/Monitor/Assess disability

• Evaluate symptoms/signs
• Measure effect of treatment
• Screen at risk groups
• Assess pre-operative risk
• Assess impairment/risk (disease/exposure)

Question 4

Contra-indications

Answer 4

> Pneumothorax - pressure changes will make worse
Haemoptysis with unknown origin (coughing up blood)
Aneurysm (possible to rupture)
Recent MI or unstable angina (pressure changes will affect cardiac output + stress on heart)
CVS instability
Cerebral instability (intra-cranial pressure will change also)
Recent surgery - especially chest/abdomen/eyes
Recent Chest infection (2/52) - not normative results
*Spirometry is best for chronic conditions

Question 5

What is measured

Answer 5

> Forced Vital Capacity (FVC) - Following max inspiration; volume expired until residual volume is reached
- Within 80% is normal
Forced Expiratory Volume in One Second (FEV-1) - maximal exhalation; volume exhaled in first second
- Within 80% of value is normal
FEV-1:FVC - volume exhaled in first second vs. total volume exhaled (FEV-1 should be 80% of FVC)
- within 75% is normal

• Peak expiratory flow rate (PEFR)- max rate of expiration (static volume only)
  - influenced by airway diameter (used to assess bronchospasm in asthma)
  - may indicate if spirometry is needed

Question 6

Procedure

Answer 6

> Sat upright + loose clothing
- compromise between abdomen compression + possible dizziness from test
maximal breath in
Form tight seal around the mouthpiece (teeth + tongue aren’t in the way of the end)
Breath out as fast as possible for as long as possible (until no more air)
- minimum of 6 seconds (may not be possible if healthy)
- no coughing (smooth line on graph)
- 3x round + want two best to be within 5 seconds of each other
- best is then compared to normative data

CONSENT FIRST

Question 7

Results

Answer 7

Graph

• Volume vs time
• Slope = flow
• FVC = top of curve
• FEV-1 = curve @ 1 seconds
• Peak flow = steepest part of curve

*May not always be an indication for breathlessness as this is a perceived feeling - ie spirometry is not a measure of QoL

Question 8

Obstructive Conditions

Answer 8

> COPD/Asthma/emphysema - air can’t flow out as quickly
Reduced FEV-1
- 50-80% = moderate
- 30-50% = severe
- <30% = v. severe
FVC may be unchanged if given enough time to completely breath out but will be slower
(will be decreased if airways collapse - emphysema = floppy airways)
FEV-1:FVC ratio will be decreased - less steep curve

Question 9

Restrictive lung conditions

Answer 9

> Interstitial lung disease/ idiopathic pulmonary fibrosis/chest wall neuromuscular problems
Both FEV-1 + FVC reduced as total lung capacity is reduced (ie can’t take full in breath)
Ratio may remain the same as both values are decreased (ie shorter curve but same gradient)

Question 10

Combined (obstructive + restrictive)

Answer 10

> Both FVC + FEV-1 will be reduced (FEV-1 maybe more so)

Question 11

What is flow

Answer 11

> Ability to overcome airway + tissue resistance
affected by:
- types of airflow (laminar/turbulent)
- lung volume (gender/height/age/race specific)
- elastic recoil
- smooth muscle tone
- airway obstructions

Question 12

Causes of reduced FVC

Answer 12

> Reduced expansion
> Reduced Inspiratory muscle strength 
> Obesity 
> Reduced expiratory muscle strength 
> Increased airway resistance

Question 13

Chronic vs. acute conditions

Answer 13

> Unlikely to look at for acute patient - main purpose is to monitor + diagnose chronic lung conditions