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SUPPLEMENTARY GUIDE www.ace-hta.gov.sg Published: 7 Nov 2018 Flow-volume curve (Figure 2) With a normal lung, the curve steeply ascends to the maximum expiratory flow rate before it descends evenly to the end of expiration. 1 In obstructive disorders, the peak of the curve is lower followed by a concave dip. 1 In restrictive disorders, the FVC is reduced (moved to the left). 1 Examine curve shape to confirm pattern Volume-time curve (Figure 1) With a normal lung, the curve steeply ascends and plateaus in three to four seconds. 1 In obstructive disorders, expiration takes longer and the slope is less steep. 1 In restrictive disorders, the shape is normal but the curve is lower. 1 The spirometry curve shapes indicate the type of ventilatory pattern. Refer to a specialist when spirometry is abnormal but not diagnostic. 1 Figure 2. Flow-volume curves Expiratory flow rate (L/sec) Volume (L) FVC Maximum expiratory flow A.Normal Expiratary flow rate L/sec Volume (L) B. Obstruc�ve Expiratary flow rate L/sec Volume (L) C. Restric�ve Normal Abnormal Figure 1. Volume-time curves B. Restric�ve C. Mixed Volume (L) Time A.Obstructive Volume (L) Time Volume (L) Time Normal Abnormal Increased Decreased Spirometry indices Normal pattern Abnormal ventilatory patterns Obstructive Restrictive Mixed FEV 1 /FVC >0.70 Normal or FEV 1 >80% predicted Normal or FVC >80% predicted Normal or Interpreting spirometry reports When suspecting COPD Spirometry is a reliable test to measure airflow limitation. It identifies three abnormal ventilatory patterns: obstructive (such as in COPD and asthma) , restrictive (such as in pulmonary fibrosis and pleural disease) , and mixed (when both obstructive and restrictive lung diseases are present). Compare the patient’s spirometry indices against reference or predicted values Table 1. Features of ventilatory patterns FEV 1 , Forced expiratory volume in one second is the air volume forcibly expelled in the first second following a maximum inspiration. FVC, Forced vital capacity is the total air volume forcibly expelled following a maximum inspiration. FEV 1 /FVC, the ratio of both measurements. If FEV 1 /FVC <0.70, there is airflow limitation. 2 Post-bronchodilator FEV 1 /FVC <0.70, in patients with pertinent risk factors and symptoms, confirms COPD. 2,3 1. Global Initiative for Chronic Obstructive Lung Disease (GOLD). Spirometry for Healthcare Providers. 2010. 2. Global Initiative for Chronic Obstructive Lung Disease (GOLD). Global Strategy for the Diagnosis, Management, and Prevention of COPD. 2018. 3. Singapore Ministry of Health. Clinical Practice Guidelines: Chronic Obstructive Pulmonary Disease. 2017. References This Supplementary Guide has been adapted with permission from the Global Initiative for Chronic Obstructive Lung Disease (GOLD), Global Strategy for the Diagnosis, Management, and Prevention of COPD (2018) and GOLD, Spirometry for Healthcare Providers (2010).
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Interpreting spirometry reports

Dec 01, 2022

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Sophie Gallet
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• Flow-volume curve (Figure 2)
With a normal lung, the curve steeply ascends to the maximum expiratory flow rate before it descends evenly to the end of expiration.1 In obstructive disorders, the peak of the curve is lower followed by a concave dip.1 In restrictive disorders, the FVC is reduced (moved to the left).1
Examine curve shape to confirm pattern
• Volume-time curve (Figure 1)
With a normal lung, the curve steeply ascends and plateaus in three to four seconds.1 In obstructive disorders, expiration takes longer and the slope is less steep.1 In restrictive disorders, the shape is normal but the curve is lower.1
The spirometry curve shapes indicate the type of ventilatory pattern. Refer to a specialist when spirometry is abnormal but not diagnostic.1
Figure 2. Flow-volume curves
Vo lu
m e
Obstructive Restrictive Mixed
Interpreting spirometry reports When suspecting COPD
Spirometry is a reliable test to measure airflow limitation. It identifies three abnormal ventilatory patterns: obstructive (such as in COPD and asthma), restrictive (such as in pulmonary fibrosis and pleural disease), and mixed (when both obstructive and restrictive lung diseases are present).
Compare the patient’s spirometry indices against reference or predicted values
Table 1. Features of ventilatory patterns
FEV1, Forced expiratory volume in one second is the air volume forcibly expelled in the first second following a maximum inspiration. FVC, Forced vital capacity is the total air volume forcibly expelled following a maximum inspiration. FEV1/FVC, the ratio of both measurements.
If FEV1/FVC <0.70, there is airflow limitation.2 Post-bronchodilator FEV1/FVC <0.70, in patients with pertinent risk factors and symptoms, confirms COPD.2,3
1. Global Initiative for Chronic Obstructive Lung Disease (GOLD). Spirometry for Healthcare Providers. 2010.
2. Global Initiative for Chronic Obstructive Lung Disease (GOLD). Global Strategy for the Diagnosis, Management, and Prevention of COPD. 2018.
3. Singapore Ministry of Health. Clinical Practice Guidelines: Chronic Obstructive Pulmonary Disease. 2017.
References