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Dynamics of breathing in infants
Insights
Infant respiratory mechanics show increased stiffness and work of breathing shortly after birth. This active stiffening enhances respiratory system stability and responsiveness, despite higher energy demands.
Area of Science:
- Neonatal Physiology
- Respiratory Mechanics
Background:
- Infant respiratory system undergoes rapid changes post-birth.
- Understanding respiratory mechanics is crucial for neonatal care.
Purpose of the Study:
- To measure and compare passive and active respiratory mechanics in newborns at different early postnatal ages.
- To assess changes in compliance, resistance, and time constants.
Main Methods:
- Mouth pressure measurements during airway occlusions at end-inspiration and end-expiration.
- Calculation of passive and active compliance (C, C'), resistance (R, R'), and time constants (tau, tau').
Main Results:
- End-expiratory volume is maintained above functional residual capacity, increasing with age.
- Passive time constant is shorter in younger infants due to lower compliance.
- Active stiffening increases respiratory system stability but elevates work of breathing.
Conclusions:
- Newborns exhibit active stiffening of the respiratory system shortly after birth.
- This adaptation enhances stability and responsiveness at the cost of increased work of breathing.
- Inspiratory flow patterns are optimized to minimize energy loss.
Abstract:
Passive compliance (C) has been measured in 10 infants at 10--90 min after birth and in 10 infants at a few days of life by recording mouth pressure after airways occlusions at end inspiration. From the slope of the expiratory flow-volume curve, the passive time constant (tau) and resistance (R = tau/C) have been also computed. Examination of the changes of C with time and of the expiratory flow-volume curves indicates that the end-expiratory volume is maintained above functional residual capacity at both ages, but significantly more so at a few days (7.6 ml) than at 10--90 min (3.5 ml). The passive time constant (tau = C . R) is shorter at the early age due to the smaller C. The active compliance (C') and resistance (R') values have been estimated from the pressure generated by the infant when the airways are occluded at end expiration. The active time constant of the respiratory system (tau' = C' . R') is less than tau, due to a smaller active compliance, particularly at a few days. The active resistance is on the contrary similar to R. The active stiffening of the respiratory system provides more stability of the infant's respiratory system and a more ready volume response for any given change in pressure; its price, however, is a higher work of breathing. At optimal breathing rates, in fact, the active work is 127% (10--90 min) to 183% (a few days) higher than that computed from the passive values. The inspiratory flow wave tends to be squared at both ages minimizing the energy losses due to friction.