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Maturation of ventilation and ventilatory pattern in normal sleeping infants
Insights
Infant breathing patterns change with age, with tidal volume (VT) and inspiratory flow increasing. Sleep state also influences ventilation, affecting respiratory cycle times and tidal volume in infants.
Area of Science:
- Pediatric Pulmonology
- Neonatal Physiology
- Respiratory Control
Background:
- Infant respiratory control undergoes significant development in the first few months of life.
- Sleep state profoundly impacts cardiorespiratory function in neonates and infants.
Purpose of the Study:
- To investigate serial changes in noninvasive ventilation and ventilatory patterns in normal infants.
- To compare respiratory parameters during REM and quiet sleep in early infancy.
Main Methods:
- Noninvasive barometric method used for serial measurements in 15 healthy infants up to 4 months of age.
- Key parameters measured: tidal volume (VT), total respiratory cycle time (Ttot), inspiratory time (Ti), expiratory time (TE), mean inspiratory flow (VT/Ti), and duty cycle (Ti/Ttot).
Main Results:
- VT, Ttot, Ti, TE, VT/Ti, and VT/Ttot increased with age.
- Ttot, Ti, and TE were longer in quiet sleep compared to REM sleep across all age groups.
- VT was greater in quiet sleep for younger infants (0-2 months), while VT/Ttot was smaller in quiet sleep for older infants (>2 months).
- Mean inspiratory flow (VT/Ti) significantly increased with age, contributing to the rise in VT/Ttot.
Conclusions:
- The increase in overall ventilation (VT/Ttot) with age is primarily driven by enhanced mean inspiratory flow, not changes in the respiratory duty cycle.
- Both the initiation ('on-switching') and cessation ('off-switching') of inspiratory activity are dependent on the infant's sleep state.
Abstract:
Noninvasive studies of ventilation and ventilatory pattern were performed serially in 15 normal infants in the first 4 mo of life during REM and quiet sleep with the barometric method. We measured tidal volume (VT), total respiratory cycle time (Ttot), inspiratory time (Ti), expiratory time (TE), mean inspiratory flow (VT/TI), and respiratory "duty cycle" (TI/Ttot). Vt, Ttot, TI, TE, VT/TI, and VT/Ttot but not TI/Ttot increased with age. In all age groups, Ttot, TI, and TE but not VT/TI were greater in quiet than in REM sleep. In the first 2 mo of life, VT was greater in quiet than in REM sleep; in the older infants, VT/Ttot was smaller in quiet than in REM sleep. TI/Ttot was not dependent on sleep state. Thus, because VT/Ttot = VT/TI X TI/Ttot, the increase in VT/Ttot with age results from an increase in mean inspiratory flow rather than from changes in respiratory "duty cycle". Further, the "on-switching" as well as the "off-switching" of inspiratory activity depends on sleep state.