MAINTENANCE OF TIDAL VOLUME IN INFANTS ON CONTINUOUS DISTENDING AIRWAY PRESSURE (CDAP) BY INCREASED INSPIRATORY MUSCLE ACTIVITY

Abstract

We have previously shown that tidal volume is unaffected and that respiratory system compliance decreases when CDAP is applied to healthy infants. To determine if changes in respiratory muscle activity cause tidal volume to remain constant, we measured electromyograms (EMG) in healthy infants. Seven full term infants were studied during the first four days of life while sleeping and enclosed below the neck in a negative pressure box. EMG were recorded using surface electrodes in the right sixth intercostal space and on the right lateral abdominal wall before and after application of five and ten cm H2O continuous negative pressure to the box. Changes in thoraco-abdominal configuration were monitored with anterior-posterior magnetometers and showed that most of the lung volume increase was accounted for by rib cage expansion. Inspiratory EMG amplitude from the intercostal space increased in all infants on CDAP. The increase was greater with greater amounts of distending pressure. Small increases in abdominal muscle activity were observed in four of the infants on CDAP. The increase in EMG with CDAP may compensate for a small decrease in mechanical advantage of the inspiratory muscles to hold tidal volume constant, and may offset the decrease in compliance. This is consistent with a reflex mechanism that allows rapid compensation for changes in lung volume.