Table 1 Pulmonary function tests for the evaluation of COPD patients.
From: Pulmonary function testing in COPD: looking beyond the curtain of FEV1
Pulmonary function test | Indicator of airflow limitation | Advantages |
|---|---|---|
FEV1/FVC | Decreased FEV1/FVC Decreased FEV1 | Gold-standard Reflects severity of airflow limitation. |
Flow-volume curve | Scooping | First indication of small airway obstruction in patients with normal FEV1. Effective in differentiating between healthy adults and patients with mild COPD. |
PEFR | A PEFR of < 80% predicted detects airflow limitation (90% sensitivity, 50% specificity) | PEFR measurements alone cannot reliably be used as the only diagnostic test for COPD due to the weak specificity. A potential monitoring tool |
PIFR | No clear correlation between airflow limitation or FEV1 and PIFR | PIFR is related to optimal drug delivery with dry powder inhalers used to treat COPD. It can be reduced at the time of COPD exacerbation. |
Resting lung volumes and capacities | Decreased IC | May indicate flow limitation even in patients with milder disease, in whom FEV1 is preserved. Resting IC may predict patients’ tolerance to exercise. IC/TLC is a predictor of mortality and respiratory failure. |
Specific airway resistance (Sraw) Breathing loops | Increased specific airway resistance Flattening and open appearance | Opening in breathing loops indicate airway obstruction, trapped air, and it has been significantly associated with RV/TLC ratio. |
DLCO | Low DLCO | Indicative of emphysema. Predictor of exertional hypoxemia. |
KCO | Low KCO | KCO better reflects emphysema compared to DLCO. Predictor of COPD exacerbations and outcome |
DLNO | Low DLNO | DLNO could be more sensitive in detecting alveolar destruction and emphysema than the DLCO or KCO. |
Oscillometry | Increased expiratory Zrs | Can detect lung dysfunction in smokers, before any symptoms arise and small airway disease Zrs correlates to the severity of airway narrowing. More sensitive than FEV1 in detecting expiratory flow limitation. |
Field exercise tests (6 MW test) | Decreased distance achieved | Representative of the day-to-day physical activity of the patients. Correlates with mortality. |
CPET | Combines various parameters measured during a symptom-limited exercise test (e.g., decreased VO2, decreased SpO2, decreased TV) | Adequately detects patients with mild airway obstruction but disproportionately severe dyspnea. Can reveal dynamic physiological abnormalities in smokers with normal spirometry. |
Anthropometry | Malnutrition Sarcopenia (low muscle mass) | Correlate with the severity of airway obstruction. Indicative of higher mortality. |
MIP | Low MIP | Indicative of inspiratory muscle weakness |
SMIF | Low SMIF | Associated with functional exercise capacity, dyspnea, airflow obstruction, greater hyperinflation, worse health and mental status and impaired quality of life |
SNIP | Low SNIP | Impaired diaphragm activity and inspiratory accessory muscle dysgunction Related to severity Predictor of Mortality |
MEP | Low MEP | Expiratory muscle weakness |
