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Control of inspiratory duration in premature infants
R E Fox1, P C Kosch, H A Feldman
1Department of Pediatrics, Harvard Medical School, Boston, Massachusetts.
Insights
Premature infants
Area of Science:
- Neonatal physiology
- Respiratory control
- Infant development
Background:
- Maturation influences respiratory control in infants.
- Understanding reflex control of inspiratory duration is crucial for preterm infants.
Purpose of the Study:
- To investigate if infant maturation affects the reflex control of inspiratory duration.
- To analyze the impact of mechanical loads and airway occlusions on respiratory timing in preterm infants.
Main Methods:
- Measurements of flow, volume, airway pressure, and diaphragmatic electromyogram (EMG) in 10 preterm infants.
- Application of resistive and elastic loads, and occlusions during single breaths.
- Analysis of neural and mechanical inspiratory duration (TI) in response to loads.
Main Results:
- All loads significantly decreased inspired volumes.
- Both neural and mechanical TI were prolonged by loads and occlusions.
- Resistive loading prolonged mechanical TI more than elastic loading for comparable volume decrements.
- Neural TI response to volume decrements was comparable to full-term infants.
Conclusions:
- Reflex control of neural TI in preterm infants depends on inspired volume magnitude.
- The volume trajectory does not influence neural TI control.
- Respiratory control mechanisms in preterm infants show maturational similarities to full-term infants.
Abstract:
We used single-breath mechanical loads and airway occlusions in premature infants to determine whether maturation influences the reflex control of inspiratory duration. We measured flow, volume, airway pressure, and surface diaphragmatic electromyogram (EMG) in 10 healthy preterm infants [33 +/- 1 (SD) wk gestation], 2-7 days of age. Three resistive and two elastic loads and occlusions were applied to the inspiratory outlet of a two-way respiratory valve. Application of all loads resulted in inspired volumes significantly decreased from control (P less than 0.001), and these decreases were progressive with increasing loads. Inspiratory duration (TI) was prolonged from control by all loads and occlusions when measured from the diaphragmatic EMG (neural TI) and by all but the smaller elastic load when measured from the flow tracing (mechanical TI). Similar decreases in inspired volume at the end of neural TI produced by application of both elastic and resistive loads resulted in comparable prolongation of neural TI. In contrast, for comparable volume decrements, resistive loading prolonged mechanical TI more than elastic loading (P less than 0.001). Mechanical and neural TI values of the breath after the loaded breath were unchanged from control values. Comparison of the neural volume-timing relationship in premature infants with our data in full-term infants suggests that the strength of the timing response to similar relative decrements in inspired volume is comparable. We conclude that reflex control of neural TI in premature infants depends on the magnitude of inspired volume and is independent of the volume trajectory.(ABSTRACT TRUNCATED AT 250 WORDS)