[Bronchiolitis in infants. Respiratory functional exploration in the acute phase].

Respiratory function tests were performed in infants hospitalized for bronchiolitis immediately after the acute stage, in order to appreciate the function of the respiratory muscles. A study of the ventilatory mechanics, of the transdiaphragmatic pressure, of the ventilatory rate and of the blood gases was performed. Results were compared with those obtained in 10 "healthy" infants. They showed: a decrease in the dynamic compliance (DYN.C) (p less than 0.001) and an increase in the total pulmonary resistances (TPR) (p less than 0.05) providing evidence for the intensity of bronchial and bronchiolar obstruction; an increase in the abdominal and intrathoracic pressures difference (Pdi) (p less than 0.01) which may reach 3 times the normal value and which is proportional to the decrease in DYN.C. (r = 0.74; p less than 0.001), providing evidence for the intensification of the inspiratory diaphragmatic effort and of its adjustment to the degree of obstruction; a reverse of the abdominal pressure curve with respect to that in normal subjects, with an increased pressure level, providing evidence for abdominal distension and increased pressure during all the expiration, suggesting the active participation of the abdominal muscle to expiration; a change in the ventilatory rate, characterized by a high respiratory frequency, a decreased tidal volume, a shortened inspiratory time and a normal inspiratory time/total time ratio. this rate is opposed to that observed in older children with bronchial obstruction. It might optimize the respiratory muscles output, as at this age, they have not yet reached all their contractile capacity.