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Table 1: Application of respiratory function tests in COPD and their relationship with parametric mapping computed tomography. |
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Test |
Clinical outcomes of PFTs |
Correlation with CT |
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Body plethysmography |
CI, increased RV/CPT indicate increased dyspnea, risk of death and may be indicative of volume reduction surgery when severe hyperinflation is present |
The ITGV and percentage predicted CPT have a positive correlation (R2 0.33) with the percentage of emphysema, with an AUC of 0.79, indicating hyperinflation |
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Carbon monoxide diffusion |
A DLco with values < 60% is associated with decreased exercise capacity and risk of death. Decreased in precapillary pulmonary hypertension. In non-obstructed values < 80% predict a risk of developing COPD |
A percentage of predicted decreased KCO and DLco have a positive correlation with the percentage of emphysema especially when greater than 10% with AUC of 0.78 |
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Oscillometry |
IOS is more sensitive than spirometry in identifying peripheral airway pathology. In addition, in COPD patients with FEV1 < 50%, Xrs is a very sensitive indicator of exacerbations and mortality |
IOS analysis especially an R5-R20 index > 0.07 kPa has a positive correlation (r2 = 0.599) with small airway disease related to air trapping (OR 2.01) identifying early disease |
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6 min walk |
Reduced distance at 6MW indicates functional disability and increased risk of mortality |
The 6-minute walk has a positive correlation with the severity and percentage of emphysema (r = 0.55) |
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Other spirometry values or indexes |
FEV1/FEV6 is simple, has good sensitivity, specificity and is a good predictor of exacerbations. FEV3/FEV6 values below LLN are associated with poor quality of life, exacerbations and obstruction. Useful for early diagnosis |
FEV1/FEV6 increased gas trapping and airway wall thickness FEV3/FEV6 has a good correlation with small airway disease and emphysema |
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PFT = pulmonary function tests. AUC = area under the curve. IQ = inspiratory capacity. TLC = total lung capacity. 6MW = 6-minute walk. DLco = diffusing capacity of the lungs for carbon monoxide. COPD = chronic obstructive pulmonary disease. FEV1 = forced expiratory volume in the first second. FEV3 = forced expiratory volume at second 3. FEV6 = forced expiratory volume at second 6. KCO = Korgh’s constant. kPa = kilopascals. LLN = lower limit of normal. OR = odds ratio. R5 = total resistances. R20 = central resistances. Xrs = reactance area. ITGV = intrathoracic gas volume. RV = dual volume. |
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