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Expiratory pattern of newborn mammals.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|February 1, 1985
Summary
Respiratory system time constants differ between passive and dynamic breathing in newborns. Dynamic expiratory time constants (tau exp) vary with breathing rate (f) and species, impacting functional residual capacity (FRC).
Area of Science:
- Comparative Physiology
- Respiratory Mechanics
- Neonatal Biology
Background:
- The passive mechanical time constant (tau pass) of the respiratory system is similar across newborn mammals (~0.15-0.2 s).
- Breathing rate (f) increases in smaller species to meet higher metabolic demands, while tidal volume per kilogram remains constant.
- High breathing rates in small species may lead to dynamic increases in functional residual capacity (FRC) due to short expiratory times.
Purpose of the Study:
- To investigate differences between passive and dynamic expiratory time constants in newborn mammals.
- To analyze expiratory flow patterns during resting breathing in nine unanesthetized newborn species.
- To determine how dynamic expiratory time constants (tau exp) relate to breathing rate and inspiratory time.
Main Methods:
- Analysis of expiratory flow-volume curves from nine newborn mammalian species during resting breathing.
- Determination of the dynamic expiratory time constant (tau exp) from the slope of the linear portion of the expiratory flow-volume curve.
- Comparison of tau exp with the passive time constant (tau pass) across species with varying breathing rates.
Main Results:
- The dynamic expiratory time constant (tau exp) varied significantly (0.1–0.7 s) among species, correlating positively with inspiratory time and inversely with breathing rate (f).
- In slow-breathing newborns (e.g., infants, piglets), tau exp exceeded tau pass, likely due to increased laryngeal resistance, resulting in elevated FRC.
- In fast-breathing newborns (e.g., rats, mice), tau exp was similar to or less than tau pass, with lower dynamic lung compliance and minimal FRC elevation.
Conclusions:
- The dynamic expiratory time constant (tau exp) is a key factor influencing respiratory mechanics in newborn mammals.
- Species-specific adaptations in tau exp and breathing patterns maintain the product of tau exp and f within narrow limits under dynamic conditions.
- Differences in tau exp contribute to variations in functional residual capacity (FRC) and respiratory efficiency across newborn species.