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CO2-induced changes in ventilation and ventilatory pattern in normal sleeping infants
Insights
Infant breathing patterns respond to carbon dioxide (CO2) by increasing tidal volume (VT), not by changing breathing rate. This response remains consistent across different sleep states in the first four months of life.
Area of Science:
- Pediatric Respiratory Physiology
- Neonatal Sleep Studies
- Cardiorespiratory Control
Background:
- Understanding infant respiratory control is crucial for identifying potential issues.
- The ventilatory response to carbon dioxide (CO2) is a key indicator of respiratory system maturity.
- Infant sleep states (REM and quiet sleep) can influence respiratory patterns.
Purpose of the Study:
- To investigate the effects of inhaled 2% CO2 on the ventilatory pattern of normal infants.
- To assess these effects across different sleep states (REM and quiet sleep) during the first four months of life.
- To determine the primary mechanism driving changes in minute ventilation (VT/Ttot) in response to CO2.
Main Methods:
- Studied 18 normal infants at monthly intervals up to 4 months of age.
- Utilized the barometric method to measure tidal volume (VT), total respiratory cycle time (Ttot), inspiratory time (TI), and expiratory time (TE).
- Administered 2% CO2 inhalation during both quiet sleep and REM sleep.
Main Results:
- Inhalation of 2% CO2 led to a significant increase in tidal volume (VT) and mean inspiratory flow (VT/TI).
- No significant changes were observed in inspiratory time (TI), expiratory time (TE), or total respiratory cycle time (Ttot).
- The percentage increase in minute ventilation (VT/Ttot) during CO2 inhalation was similar in both REM and quiet sleep states.
Conclusions:
- In infants during the first four months of life, the increase in minute ventilation (VT/Ttot) in response to 2% CO2 is solely due to an increase in tidal volume (VT).
- This ventilatory response to CO2 is consistent across both quiet and REM sleep states.
- The findings suggest that the reflex termination of inspiration by lung inflation plays a minimal role in eupnea during sleep in early infancy.
Abstract:
The effect of CO2 on the ventilatory pattern of 18 normal infants was studied during sleep at monthly intervals through the age of 4 mo. Using the barometric method, we measured tidal volume (VT), respiratory cycle time (Ttot), inspiratory time (TI), and expiratory time (TE). Two percent CO2 produced no change in TI and a significant increase in VT and mean inspiratory flow (VT/TI). There was no consistent change in TE or Ttot in either sleep state at any age. The percent increase from base line in instantaneous minute ventilation (VT/Ttot) during REM sleep was similar to that during quiet sleep. We conclude that with inhalation of 2% CO2 in the first 4 mo of life 1) the increase in VT/Ttot results solely from an increase in VT and the percent increase in VT/Ttot is the same in both sleep states and 2) the reflex termination of inspiration by inflation does not play an important role in eupnea during sleep because the increase in VT is not associated with a decrease in TI.