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

1. We have measured the relationship between tidal volume ( V T ) and the duration of inspiration ( T i ) and expiration ( T e ) for individual breaths (30 in each steady state). 2. Ten pre‐term and ten term infants were studied during steady state while breathing 21% O 2 , then 21% O 2 plus 2 and 4% CO 2 . 3. In all infants, the average T i at the various chemical drives was remarkably constant, and did not decrease as the tidal volume increased. However, at any given level of respiratory drive, there was a slightly positive correlation of V T with T i and T e in 95% of the cases. 4. In four pre‐term and two term infants, T e increased with increasing respiratory drive. In these infants, therefore, instantaneous respiratory frequency (1/( T i + T e )) actually decreased as lung volume increased. 5. We suggest that T i is independent of V T within the range of volumes studied (up to 2 times the resting V T ) and that changes in instantaneous respiratory frequency (1/( T i + T e )) result from changes in T e .