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Brief guide for the use and interpretation of spirometry.
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Spirometry in Practice
• A technique used to measure air flow in and out of the lungs.
• A recording of lung volumes and capacities defined by the respiratory process. These recordings may be static (untimed) or dynamic (timed).
• Assesses the integrated mechanical functions of lungs, chest wall and respiratory muscles.
•The gold standard for diagnosis, assessment and monitoring of COPD.
• Better than PEFR (which is effort dependent) for demonstrating airway obstruction in BA.
• The most commonly used PFT.
Indications
• Measure airflow obstruction to help make a definitive diagnosis of COPD
• Detect airflow obstruction in smokers who may have few or no symptoms
• Assess one aspect of response to therapy
• Perform pre-operative assessment
• Distinguish between obstruction and restriction as causes of breathlessness
• Perform pre-employment screening in certain professions
1) Volume Displacement
Spirometer
• Conventional old spirometers
• Derived indices are generally manually calcualated.
• High resistance to airflow
•Time consuming, inconvenient.
• Difficult disinfection
2) Flow Sensitive
Spirometer
• Utilize a sensor that measures air flow as the primary signal and calculate volume by integration.
• Automatically calculate a wide range of ventilatory indices and draw curves, which provide an immediate feedback on quality.
•Easier for the patient and operator.
•Easy disinfection, some have disposable flow sensors eliminating the need for disinfection.
3) Portable Spirometer,
Peak Flowmeter
• Readings have limited accuracy and are flow dependent.
• Limited role in intitial ssessment of respiratory disease.
•Reasonably reliable for patients to monitor their own disease progression or response to therapy.
4) Incentive Spirometer
Rather than a diagnostic tool, it is used to improve the patient incentives to comply with treatment and to do respiratory exercises.
How to DO?
Before the Test
1) Exclude contraindications: • Haemoptysis of unknown origin.• Current chest infection or within in last 6 weeks.• Pneumothorax.• Recent MI or PE (< 3 m).• Unstable angina in last 24 hours.• Recent surgery (eye, chest, abdomen) (< 3m).• Recent CVA (< 3m).• Aneurysm (cerebral, thoracic, abdominal).
How to DO?
Before the Test
2) Stop Asthma Medications: • SABA 6h• LABA 12h• Ipratropium 6h• Tiotropium 24hMedications may be continued if the test aims to assess the patient condition on treatment.
How to DO?
Before the Test
3) Other Precautions: • Physical and mental rest.• No coffee or smoking for 30 mins.• Empty the bladder in females or those with history of urinary incontinence.
How to DO?
• Patient is sitting comfortably, not leaning forwards, legs not crossed, feet firm on floor.
• No tight clothes or collars.
• Explain the procedure to the patient.
• Nasal clip is optional.
During the Test
How to DO?
• Ask the patient to do a
Forced Expiratory Maneuver (FEM):
- Take a maximal inspiration.
- Hold the breath and seal your lips tightly around the mouth piece.
- Blow as fast as possible (blast expiration) until the lungs feel completely empty (at least 6 sec., up to 12 sec in obstructive disease)
- Examine the graph and record:
o FEV1.
o FVC.
o FEV1/FVC (FER)
During the Test
How to DO?
• Get 3 readings that meet acceptability criteria –two of them with repeatability criteria.
• Record the highest reading.
• Continue watching, explanation and encouragement throughout the procedure.
• If inspiratory flow is to be tested as well, inspiration is likewise tested.
During the Test
Acceptability Criteria• The patient followed instructions
• A continuous maximal expiratory manoeuvre throughout the test (i.e. no stops and
starts) was achieved and was initiated from full inspiration.
• There was no evidence of hesitation during the test
• The PEF has a sharp rise (flow-volume)• No premature termination, i.e. expiration
continued until there was no change in volume and the patient had blown for ≥ 6
seconds• There were no leaks
• No cough (FEV1 may be valid if cough occurs after the first second)
• No glottic closure.• No obstruction of the mouthpiece (e.g. by the
tongue or teeth)• No evidence that the patient took an
additional breath during the expiratory manoeuvre
Repeatability Criteria• Obtain 3 acceptable tests
• The two largest values for FVC should agree to within 5% or 150 mL.
• The two largest values for FEV1 should agree to
within 5% or 150mL.
• Submaximal efforto Submaximal effort
o Air leak around the mouthpiece (lips not tight enough)o Air leak through nose
o Incomplete inspiration before the forced expiratory maneuver (not at TLC)
o Incomplete or weak expiration (lack of blast effort)o Slow start of expiration
o Cough (particularly within the first second of expiration)o Glottic closure
o Obstruction of the mouthpiece by the tongueo Vocalisation during the forced manoeuvre
o Poor posture (leaning forwards).o Extra- breath during the blow
Causes of Poor Record
Vol
um
e, li
ters
Time, seconds
Unacceptable Trace – Premature Termination or
Glottic Closure
Normal
Vol
um
e, li
ters
Time, seconds
Unacceptable Trace – Slow Start
Normal
Vol
um
e, li
ters
Time, seconds
Unacceptable Trace - Coughing
Normal
Vol
um
e, li
ters
Time, seconds
Unacceptable Trace – Extra Breath
Normal
Spirometry includes:
• Lung volumes (most simple).
• Lung capacities (composite of > 2 volumes)
• Volume per time: as FEV1,2,3,4,5,6
• Volume / time: flow rate (values + curve)
• Flow rate / Volume: (values + loop)
Adverse Effects
• Light headedness• Headache
• Fainting: reduced venous return or vasovagal attack (reflex)
• Transient urinary incontinence
TotalLung
Capacity
Tidal Volume
Inspiratory ReserveVolume
Expiratory ReserveVolume
Residual Volume
Inspiratory Capacity
Vital Capacity
End Normal Exp
End Normal Insp
End Maximal Insp
End Maximal Exp
Functional ResidualCapacity
Predicted Normal Values
Age
Height
Sex
Ethnic Origin
Affected by biodemographic variables:
No
rmal
Ob
stru
ctiv
e
Res
tric
tive
Flow Volume Loop
Expiratory flow rateL/sec
Volume (L)
FVC
Peak expiratory flow (PEF)
Inspiratory flow rate
L/sec
RVTLC
Peak Inspiratory flow (PIF)
As noted by the red line, a curve which is scalloped out and leaning away from the Y axis suggests obstruction.
A curve that is straighter (green line) and leaning to the Y axis supports the diagnosis of restriction.
(> 0.7)
(< 80%)
(< 0.7)
(< 80%)(< 80%) (< 80%)
(< 80%)
Bronchodilator Reversibility Testing
•FEV1 should be measured (minimum twice,
within 5% or 150mls) before a bronchodilator is given
Bronchodilator*
DoseFEV1 before and after
Salbutamol400 µg via large volume spacer
15 minutes
Terbutaline500 µg via Turbohaler 15 minutes
Ipratropium160 µg via spacer 45 minutes
Bronchodilator Reversibility Testing• An increase in FEV1 that is both greater than 200
ml and 12% above the pre-bronchodilator FEV1 (baseline value) is considered significant (Up to 8% increase may occur in normal persons).
• It is usually helpful to report the absolute change (in mL) as well as the % change from baseline to set the improvement in a clinical context .
• The absence of reversibility does not exclude asthma because an asthmatic person’s response can vary from time to time and at times airway calibre is clearly normal and incapable of dramatic improvement.
Bronchoprovocation
Useful for diagnosis of asthma in the setting of normal pulmonary function tests
Common agents:
- Methacholine, Histamine, others
Diagnostic if: ≥20% decrease in FEV1
Look ONLY at FEV1/FVC, FVC
FEV1/FVC > 0.7FVC > 80%P
FEV1/FVC< 0.7FVC > 80%P
FEV1/FVC > 0.7FVC < 80%P
FEV1/FVC < 0.7FVC < 80%P
NORMAL OBSTRUCTIVE RESTRICTIVE MIXED orOBSTRUCTIVE + AT
Provocation Test
BD ReversibilityTest
See LaterBD Reversibility
TestIf asthma suspected
Reversible Not Reversible Reversible Not Reversible
BA COPD OBSTRUCTIVE + AT RV, TLC
Mixed
High Low