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THE CONTROL OF RESPIRATORY FREQUENCY IN PREMATURE INFANTS

There are two components to respiratory frequency in the premature infant: a phasic component related to the Hering Breuer reflex and a tonic component set by the bulbo-pontine centres. We have previously shown that the phasic component is related to gestational age.* We have now attempted to quantitate the bulbo-pontine output by measuring the inspiratory duration and pressure developed during airway occlusion at FRC. We have studied 10 infants under 1400g., all with periodic breathing, and correlated the results with the blood gases. There is a significant (p>0.01) correlation between inspiratory duration (1/Tiocc) and the rate of change of pressure (dP/dt) with pCO2 (1/Tiocc = 0.09 pCO2 - 1.66). There is no correlation with the pO2. These results suggest that the bulbo-pontine output is primarily determined by pCO2. However, because inspiratory duration becomes so short, the maximum pressure developed falls with rising pCO2. This makes the respiratory system very vulnerable to respiratory loads. This vulnerability is lost in older premature infants as they develop large pressures when breathing against an obstruction.* Pediat. Res. 7, 291, 1973.