The Differences Between Helium Dilution And Body Plethysmography And Its Relationship With Airway Resistance

COPD is characterized by progressive airflow obstruction and eventually lung hyperinflation. Whole body plethysmography (Pleth) and Helium Dilution (He) are the most common techniques used for the evaluation of lung volume, although there is no agreement on the method of choice. In our study we aim to compare Pleth and He derived lung volume in COPD patients, how much difference there is between the two methods in terms of TLC, RV, RV/TLC and the influence of airflow obstruction. We also assess the relationship between hyperinflation and airway resistance. Methods: 50 COPD patients were enrolled. TLC, RV and RV/TLC were obtained both with He and Pleth. Results: We reported a statistically significant difference between these two techniques in terms of Mean percentage value of TLC (p= 0.02) and RV (p=0.04),while RV/TLC measured with the two methods was similar. We described a much significant difference among patients with severe airflow obstruction (FEV1<50%) compared with patients with FEV1> 50%. Moreover, we reported that the values of effective specific airways resistance (SReff) and RV/TLC have a strong positive correlation (r:0.78; p<0.001). Conclusion: RV/TLC can represent the most reliable parameter in the assessment of hyperinflation, considering its close relationship with airways resistance and the absence of significant difference in its measurement between the two techniques.