Background

Chronic obstructive pulmonary disease (COPD) is usually assessed by forced expiratory volume in 1 second (FEV₁) and forced vital capacity (FVC). These parameters use distinct data points for flow and volume during the manoeuvre (e.g. 1 second). FEV₁ is considered less sensitive to small airway disease. Several parameters have been published that utilise other sections of the flow-volume curve, or the whole curve, that may be more sensitive to small airways disease. These parameters have not been evaluated at the same time in a COPD cohort.

Aim

To assess novel spirometric parameters in COPD patients versus healthy volunteers (HV).

Methods

Data from 78 COPD patients (GOLD 2-4) and 36 age-matched HV was assessed. Novel parameters included area under the flow volume curve (AUC%), rectangular area ratio (RAR), area of obstruction (Ao%PEF), shape factors (SF₅₀ & SF₇₅), shape ratio (SR₅₀), respiratory time constant (RC_exp), angle ?, flow ratio (FR), central concavity (CC), peripheral concavity (PC), and obstruction index (OI). COPD patients had >10 pack year smoking history, FEV₁ <80%, and FEV₁/FVC <0.7. HV had <1 pack year smoking history, FEV₁ >80%, and FEV₁/FVC ?0.7. Data was analysed using T-tests, and p<0.05 was considered significant.

Results

The mean values for all parameters were significantly different in COPD compared to HV (p<0.05), except SF₇₅ (p=0.67). FEV₁%, FEF_25%-75%%, AUC% (all 0%), Ao%PEF (3%), angle ? (4%), CC and RC_exp (both 6%) had low overlap of COPD values with the HV group, while for other measurements there was more overlap.

Conclusion

Some novel parameters assessed showed little overlap between COPD patients and HV. These parameters may have utility in assessing COPD physiological impairment.