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Reflex control of inspiratory duration in newborn infants
Insights
Neural inspiratory timing in healthy infants is influenced by the volume of air inhaled. Increased inspiratory load prolongs neural inspiratory duration, suggesting a volume-dependent "off-switch" mechanism.
Area of Science:
- Neonatal physiology
- Respiratory control
- Infant breathing mechanics
Background:
- Understanding infant respiratory control is crucial for identifying potential breathing disorders.
- Neural and mechanical aspects of breathing in newborns are not fully elucidated.
Purpose of the Study:
- To investigate the impact of inspiratory loading on neural and mechanical inspiratory duration in healthy, full-term infants.
- To explore the relationship between inspired volume and the termination of inspiration.
Main Methods:
- Six healthy, full-term infants (2-3 days old) were studied using a face mask and pneumotachograph.
- Graded resistive and elastic loads, and total airway occlusions were applied during single inspirations.
- Diaphragm electromyogram (EMG), airflow, volume, and airway pressure were recorded.
Main Results:
- All loads decreased inspired volumes progressively.
- Neural inspiratory duration (TIEMG) prolonged with all loads, showing a volume-independent curvilinear relationship.
- Mechanical inspiratory duration (airflow-based TI) varied with load type due to respiratory system time constants.
Conclusions:
- Neural inspiratory timing in infants is dependent on the magnitude of phasic volume change.
- Findings support an "off-switch" mechanism for inspiration termination, triggered by vagally mediated inhibition proportional to inspired volume.
Abstract:
We applied graded resistive and elastic loads and total airway occlusions to single inspirations in six full-term healthy infants on days 2-3 of life to investigate the effect on neural and mechanical inspiratory duration (TI). The infants breathed through a face mask and pneumotachograph, and flow, volume, airway pressure, and diaphragm electromyogram (EMG) were recorded. Loads were applied to the inspiratory outlet of a two-way respiratory valve using a manifold system. Application of all loads resulted in inspired volumes decreased from control (P less than 0.001), and changes were progressive with increasing loads. TI measured from the pattern of the diaphragm EMG (TIEMG) was prolonged from control by application of all elastic and resistive loads and by total airway occlusions, resulting in a single curvilinear relationship between inspired volume and TIEMG that was independent of inspired volume trajectory. In contrast, when TI was measured from the pattern of airflow, the effect of loading on the mechanical time constant of the respiratory system resulted in different inspired volume-TI relationships for elastic and resistive loads. Mechanical and neural inspired volume and duration of the following unloaded inspiration were unchanged from control values. These findings indicate that neural inspiratory timing in infants depends on magnitude of phasic volume change during inspiration. They are consistent with the hypothesis that termination of inspiration is accomplished by an "off-switch" mechanism and that inspired volume determines the level of vagally mediated inspiratory inhibition to trigger this mechanism.