Does severity of airflow obstruction correlate to static lung volumes.
Research type
Research Study
Full title
Does severity of airflow obstruction correlate to static lung volumes obtained by nitrogen washout and body plethysmography?
IRAS ID
311553
Contact name
Virginia Hawkins
Contact email
Sponsor organisation
Manchester Metropolitan University
Clinicaltrials.gov Identifier
Duration of Study in the UK
0 years, 6 months, 0 days
Research summary
Research summary
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.
Lay summary of study results: Spearman’s rank analysis was computed to investigate the relationship between TLC (total lung capacity) (N2) and TLC (pleth) in patients with obstructive lung disease. This uncovered a significant positive correlation between the variables, r(8)=0.94, p=0.017, and a significant difference in TLC (N2) and TLC (pleth) in patients with obstructive lung function. Due to the small sample size this study was not able to look at group intra-variability and determine if the severity of airflow obstruction correlates to an increasing difference between lung volumes measured using nitrogen washout and body plethysmography.
Summary of results
Introduction: Obstructive lung diseases, such as COPD (chronic obstructive pulmonary disease) and asthma, can lead to hyperinflation of the lungs over time. Hyperinflation is diagnosed, and monitored, using lung volume measurement techniques. Nitrogen washout and body plethysmography are two such techniques, however, there is debate over the accuracy of these tests in patients with airflow obstruction. This project aims to uncover if there is a difference between total lung capacity (TLC) values obtained using these methodologies in patients with airflow obstruction.Methods: Patients attending routine lung function testing as requested by their physician were asked to participate in the study, where the additional test was then carried out as part of their routine appointment. Patients gave informed consent, and spirometry, nitrogen washout and body plethysmography were performed to determine the severity of any airway obstruction, along with the TLC, and RV(Residual volume) /TLC ratio. Correlation tests were performed to determine whether the two tests were in agreement.
Results: In total, ten patients were recruited, including four control patients with no airflow obstruction and six patients with mild-severe airflow obstruction. We found that in patients with obstructive lung disease there was a significant positive correlation between TLC values measured by the two techniques, but this was not apparent in healthy controls. Furthermore, the average difference between both TLC and RV/TLC values was larger in those with airway obstruction rather than those without, and differences between the values measured correlated with the severity of the airway obstruction.
Conclusions: The findings of this study highlight that discrepancies between the methods in patients with obstructive lung disease may be apparent, particularly with more severe disease. With the low number of patients tested so far these findings should be regarded as preliminary, but they support the need for a larger scale study to determine which test is most appropriate for patients with obstructive airway diseases and how important it is to always asses patients with the same approach during their routine appointments.
REC name
London - City & East Research Ethics Committee
REC reference
23/LO/0027
Date of REC Opinion
26 Jan 2023
REC opinion
Further Information Favourable Opinion