The effects of respiratory training with inspiratory flow resistive loads in premature infants

Respiratory training of premature infants was performed to determine whether improved respiratory muscle strength and/or endurance would result. Twenty-two premature infants were randomized into control and training groups for 2 wk, using inspiratory flow-resistive loads for training (75 cm H₂O·L^-1·s in wk 1 and 90 cm H₂O·L^-1·s in wk 2). Respiratory endurance was assessed by the time interval required for the development of a 5-torr rise in transcutaneous CO₂ tension during the hypoventilation induced by loaded breathing, using a moderately severe resistive load (250 cm H₂O·L^-1·s at 1 L·min^-1). Respiratory strength was assessed by the maximum negative airway pressure generated during occluded breaths, a pressure-time integral, and an effort index. Results revealed that respiratory muscle endurance, which was not initially different between control and trained groups, increased significantly after 2 wk in the trained group by 137% (median value, p < 0.05), whereas it remained unchanged in the control group (-24%). The trained group of infants also showed a significant decrease in baseline breathing frequency between the initial and final measurements taken 2 wk apart when compared with controls (p < 0.05) and a lesser increase in inspiratory time with loading in the final measurement as compared with the initial value (p < 0.05). There was no significant difference between the control and trained groups in initial or subsequent measures of respiratory muscle strength. Inspiratory flow-resistive load training appears to improve the respiratory endurance of premature infants in whom respiratory muscle fatigue has been described to play a role in the development of respiratory failure.