Does Severity of Airflow Obstruction Correlate to Static Lung Volumes

Measurement of lung volumes by two routine techniques in patients referred for pulmonary function testing.

Obstructive lung disease is defined by limitations in expiratory airflow, caused by excess
 mucus, loss of muscle tone, and structural changes. Over time airflow reduction can lead to
 gas trapping in the lungs (hyperinflation). Hyperinflation is linked to diminished exercise
 tolerance, shortness of breath, and a poor quality of life. Early treatment options include
 inhalers and pulmonary rehabilitation; however, surgical intervention and oxygen therapy may
 be required in the later stages. More prompt, accurate diagnosis will help to improve patient
 outcomes and optimise their treatment pathways.
 
 Two methodologies used to determine lung volumes and hyperinflation, are nitrogen washout and
 body plethysmography. The accuracy of each in defining lung volumes in patients with
 obstructive lung disease is debated in literature. Plethysmography requires the patient to
 sit in an enclosed box and perform a panting manoeuvre and uses measured changes in volume
 and pressure to derive lung volumes. Plethysmography has been suggested to overestimate lung
 volumes in patients with obstructive lung disease. On the other hand, nitrogen washout relies
 on 'washing out' all the nitrogen from the lungs to calculate lung volumes. Gas trapping and
 poor airflow circulation that occurs in patients with airflow obstruction may lead to
 underestimated lung volumes.
 
 This study will aim to investigate if there is a significant difference between lung volumes
 obtained by both nitrogen washout and body plethysmography in patients with obstructive lung
 disease. Subjects with mild, moderate, severe, and very severe obstruction, including those
 with no obstruction for comparison will be included, with approximately 10 from each group.
 They will be asked if they consent to undergo an extra test during their routine hospital
 appointment, which will add ~15 minutes to their visit.