Thoracic gas compression profile during forced expiration in healthy and asthmatic schoolchildren

Gas compression profile may aid in the diagnosis of airway obstruction. However, the behavior of this parameter in repeated tests and the deviations in patients with bronchial asthma have not been thoroughly described. Thirty-six health subjects aged 6-16 years were studied in two test sessions with a pressure/flow plethysmograph, and 57 asthmatic patients of similar age were studied once. Three volumes of compressed thoracic gas (Vcomp) were obtained: with 25%, 50% and 75% of vital capacity (VC) expired. Relative Vcomp was calculated using the actual amount of gas remaining in the lungs. Regarding the best and second best manoeuvre, coefficient of variation (CoV) in Vcomp ranged from 47 to 79% (controls) and from 48 to 112% (patients). Regarding the best manoeuvre in the first and second test session (controls), CoV in Vcomp ranged from 73 to 159%. Bronchodilator response had an extreme individual variation, and the changes were insignificant in both groups. In the paediatric population, the poor repeatability of Vcomp invalidates its use in clinical assessment of pulmonary function.