The concept of detection of dynamic lung hyperinflation using cardiopulmonary exercise testing

Dynamic lung hyperinflation (DLH) caused by air trapping, which increases residual air volume, is a common cause of shortness of breath on exertion in chronic obstructive pulmonary disease (COPD). DLH is commonly evaluated by measuring the decrease in maximal inspiratory volume during exercise, or using the hyperventilation method. However, only few facilities perform these methods, and testing opportunities are limited. Therefore, we investigated the possibility of visually and qualitatively detecting DLH using data from a cardiopulmonary exercise test (CPET). Four men who underwent symptom-limiting CPET were included in this study, including a male patient in his 60s with confirmed COPD, a 50s male long-term smoker, and 2 healthy men in their 20s and 70s, respectively. We calculated the difference between the inspiratory tidal volume (TV I) and expiratory tidal volume (TV E) per breath (TV E-I) from the breath-by-breath data of each CPET and plotted it against the time axis. No decrease in TV E-I was observed in either of the healthy men. However, in the patient with COPD and long-term smoker, TV E-I began to decrease immediately after the initiation of exercise. These results indicate that DLH can be visually detected using CPET data. However, this study was a validation of a limited number of cases, and a comparison with existing evaluation methods and verification of disease specificity are required.