The effect of lung inflation on the control of respiratory frequency in the neonate

Abstract

The relationship between tidal volume (VT) and the duration of inspiration (Ti) and expiration (Te) for individual breaths (30 in each steady state) was measured. Pre-term (10) and (10) term infants [human] were studied during steady state while breathing 21% O2, then 21% O2 plus 2 and 4% CO2. In all infants, the average Ti at the various chemical drives was remarkably constant, and did not decrease as tidal volume increased. At any given level of respiratory drive, there was a slightly positive correlation of VT with Ti and Te in 95% of the cases. In 4 pre-term and 2 term infants, Te increased with increasing respiratory drive. In these infants, instantaneous respiratory frequency (1/(Ti + Te)) decreased as lung volume increased. Probably, Ti is independent of VT within the range of volumes studied (up to 2 times the resting VT), and changes in instantaneous respiratory frequency (1/(Ti + Te)) result from changes in Te.