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Effect of lung volume on expiratory time in the newborn infant
Insights
Increased positive airway pressure in newborns significantly lengthens expiratory time and decreases respiratory rate. This finding suggests altered lung volumes impact respiratory control in term infants.
Area of Science:
- Neonatal Physiology
- Respiratory Control Mechanisms
Background:
- Newborn respiratory system undergoes rapid development and adaptation.
- Understanding respiratory mechanics is crucial for managing neonatal respiratory distress.
Purpose of the Study:
- To investigate the impact of elevated end-expiratory lung volume on inspiratory and expiratory timing in term infants.
- To explore the relationship between continuous positive airway pressure (CPAP) and respiratory cycle parameters.
Main Methods:
- Studied 13 term infants at 4, 30, and 70 hours of age.
- Administered CPAP (0, 3, 6 cmH2O) via face mask connected to a pneumotachometer.
- Measured respiratory cycle timing over 1-minute intervals.
Main Results:
- Increasing functional residual capacity (FRC) led to longer expiratory time (TE) and reduced respiratory rate.
- Inspiratory time (TI) showed variable effects.
- The TI/TE ratio decreased significantly with increasing CPAP across all time points.
Conclusions:
- Elevated end-expiratory lung volume significantly alters expiratory duration in term newborns.
- Findings may reflect vagally mediated control of expiratory time, similar to observations in animals.
- CPAP influences respiratory timing in neonates, with implications for respiratory support.
Abstract:
The effect of an increased end-expiratory lung volume on inspiratory and expiratory duration was examined in 13 term infants at 4, 30, and 70 h of age. This was accomplished by the administration of a continuous positive airway pressure (CPAP) of 0, 3, and 6 cmH2O by use of a face mask connected to a pneumotachometer, and by measurement of the timing of the respiratory cycle over 1-min intervals. At increasing functional residual capacity (FRC) there was a progressive increase in expiratory time (TE) and fall in respiratory rate, with a variable effect on inspiratory time (TI). As CPAP increased from 0 to 6 cmH2O, the TI/TE ratio fell from 0.75 to 0.62 (P less than 0.01), 0.90 to 0.66 (P less than 0.001), and 0.87 to 0.64 (P less than 0.001) at 4, 30, and 70 h, respectively. We conclude that alterations in end-expiratory lung volume significantly alter expiratory duration in the newborn infant at term. This may be analogous to the vagally mediated tonic control of expiratory time with changing FRC recently described in anesthetized animals.