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Developmental changes in the ventilatory response of the newborn to added airway resistance
W A LaFramboise1, T A Standaert, R D Guthrie
1Division of Neonatal and Respiratory Diseases, University of Washington, Seattle, USA..
Insights
Newborn monkeys struggle to maintain minute ventilation (Vl) against inspiratory resistive loads, unlike older monkeys. However, both groups show compensatory mechanisms to defend blood gases during respiratory challenges.
Area of Science:
- Respiratory Physiology
- Developmental Biology
Background:
- Understanding the postnatal development of respiratory control is crucial for assessing infant respiratory health.
- Inspiratory resistive loading is a common method to study respiratory system's compensatory mechanisms.
Purpose of the Study:
- To investigate the developmental changes in the steady-state respiratory response to inspiratory resistive loading in infant and juvenile non-human primates.
- To compare the ventilatory and blood gas responses to added respiratory resistance between two distinct postnatal age groups.
Main Methods:
- Tracheostomized infant (48-hour-old) and juvenile (24-day-old) monkeys were subjected to incremental inspiratory resistive loads.
- Minute ventilation (Vl), tidal volume (VT), respiratory frequency, inspiratory time (Tl), total breath time (Ttot), airway occlusion pressure, and respiratory work output were measured.
- Arterial carbon dioxide (PaCO2) and oxygen (PaO2) levels were monitored.
Main Results:
- Newborn monkeys failed to maintain Vl with increasing loads, while older monkeys maintained constant Vl.
- Both groups exhibited prolonged Tl and Tl/Ttot, reduced respiratory frequency, and increased occlusion pressure and respiratory work output.
- Despite differences in Vl maintenance, both age groups effectively defended arterial CO2 and O2 levels, indicating robust blood gas regulation.
Conclusions:
- Newborn monkeys possess load compensatory mechanisms, evidenced by increased inspiratory effort and stable blood gases, despite an inability to maintain minute ventilation under resistive loads.
- Significant developmental differences exist in the ventilatory control strategy for managing inspiratory resistance between early postnatal life and juvenile stages.
Abstract:
Postnatal development of the steady-state response to inspiratory resistive loading was studied in eight 48-hour-old and seven 24-day-old tracheostomized monkeys. The newborn subjects did not maintain minute ventilation (Vl) with increasing loads of from 2 to 6 times baseline respiratory resistance, whereas the older subjects kept Vl constant when challenged by the same added resistances. The response patterns in both groups were characterized by a prolongation of Tl and Tl/Ttot, a reduction of respiratory frequency, and increases in airway occlusion pressure and respiratory work output. Apart from Vl, tidal volume (VT) was the only other ventilatory variable that differed significantly between age groups during loading. Arterial CO2 and O2 did not change from baseline in either group during loading, indicating that both age groups defended blood gas values equally well. The increases in occlusion pressures, inspiratory work output, and the maintenance of PaCO2 in the newborns indicated the presence of load compensatory mechanisms despite the fact that Vl was not strictly defended.