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Changes of time constants during infancy and early childhood
F A Ratjen1, A A Colin, A R Stark
1Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02115.
Insights
Infant respiratory mechanics show significant changes in expiratory time constants (tau) during the first 10 months of life. After this period, tau stabilizes, reflecting lung development and balanced respiratory system properties.
Area of Science:
- Pediatric Pulmonology
- Respiratory Physiology
- Infant Development
Background:
- Understanding respiratory mechanics in infants and children is crucial for diagnosing and managing respiratory conditions.
- Tidal breathing patterns and expiratory dynamics change significantly during early childhood development.
Purpose of the Study:
- To investigate changes in expiratory time constants (tau) during sleep in healthy infants and children.
- To correlate these changes with lung growth and development from 1 month to 8 years of age.
Main Methods:
- Respiratory inductance plethysmography was used to measure rib cage and abdominal movements during sleep in 27 healthy children.
- Flow-volume curves were derived to calculate expiratory time constants (tau) by analyzing the linear portion of the expiratory flow-volume relationship.
Main Results:
- Expiratory time constants (tau) significantly increased during the first 10 months of life.
- After 10 months, the rate of increase in tau slowed considerably, becoming non-significant.
- Prolongation of tau was accompanied by an increase in expiratory time (Te), with no significant change in the Te/tau ratio in the first two years.
Conclusions:
- The observed changes in expiratory time constants (tau) in infancy likely result from increased lung compliance due to alveolar growth.
- Beyond the first year, expiratory time constants appear to stabilize, suggesting a balance between lung compliance and airway resistance.
- These findings provide insights into the developmental trajectory of respiratory mechanics in children.
Abstract:
We used respiratory inductance plethysmography to record tidal respiration in 27 healthy unsedated infants and children 1 mo to 8 yr of age during sleep. Rib cage and abdominal outputs were present at approximately equal gains and summed to obtain an estimate of volume. Flow-volume curves were generated from the uncalibrated volume signal and its flow derivative. Expiratory time constants (tau) were obtained by visually drawing a line through the linear portion of the expiratory flow-volume relationship. tau increased significantly during the first 10 mo of life. After 10 mo, the estimated rate of increase of tau for older children was less than 5% of the estimated initial rate and not significantly different from zero. Prolongation of tau was paralleled by an increase in expiratory time (Te), and no changes in Te/tau were observed in the first 2 yr of life. These changes in tau likely reflect the increase in lung compliance induced by rapid alveolar growth during infancy. After the first year, expiratory time constants appear to remain relatively constant and may be consistent with balanced changes in compliance and resistance beyond infancy.