Does Severity of Airflow Obstruction Correlate to Static Lung Volumes

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.

Inclusion Criteria:A minimum of 10 patients from each group will be included; normal lung function/ no airflow obstruction (FEV1/FVC >70%), mild airflow obstruction (FEV1/FVC <70% and FEV1 >80% predicted), moderate airflow obstruction (FEV1/FVC <70% and FEV1 50-80% predicted), severe airflow obstruction (FEV1/FVC <70% and FEV1 30-50% predicted) and very severe (FEV1/FVC <70% and FEV1 >30% predicted).Al patients will be over the age of 18 with no upper age limit. No children will be included in this study.Patients must have withheld their inhalers.Exclusion Criteria:[15:10] Jessica ArmstrongContraindications to performing the test include (if occurred within last 8 weeks):Heart attackStrokeHaemoptysisPneumothoraxSurgery to the abdomen/thoraxEye surgeryAn individuals spirometry cannot be included if:There is a cough during the first second of the manoeuvreA leak at the mouthpieceEarly termination of manoeuvreSub optimal effortThey are unable to comprehend the instructionsObstruction of the mouthpiece (tongue/teeth)Lung volume measurements cannot be included if:There is a leak around the mouthpieceThe patient has a ruptured eardrumThey are unable to comprehend the instructionsObstruction of the mouthpiece (tongue/teeth)The patient is on supplementary oxygen and cannot come off it (this must be discontinued for a suitable period prior to nitrogen washout)Patients who are CO2 retainers may not be able to undergo nitrogen washoutThe patients test results must meet the acceptability criteria of the ARTP pulmonary function testing statement (updated 2020). For spirometry this states that there must be 3 technically acceptable attempts within 150ml, however, if the the individual has an FVC <1.00L this can be 100ml. Nitrogen washout requires two technically acceptable attempts within 10% (as per trust policy), whereas, for body plethysmography three technically acceptable attempts should be obtained within 5%.