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Rib cage and abdominal contributions to ventilatory response to CO2 in infants
Insights
Newborn infants
Area of Science:
- Neonatal Physiology
- Respiratory Control
Background:
- Infant sleep states significantly influence cardiorespiratory control.
- Understanding ventilatory responses to carbon dioxide (CO2) is crucial for assessing respiratory stability in newborns.
Purpose of the Study:
- To investigate the ventilatory response to inhaled CO2 in newborn infants during different sleep states (REM and NREM).
- To differentiate the contributions of rib cage and abdominal compartments to the ventilatory response.
Main Methods:
- Utilized the Read rebreathing technique to measure ventilatory response to CO2.
- Employed respiratory inductance plethysmography to partition volume contributions from the rib cage and abdomen.
- Defined sleep states using electroencephalogram, electrooculogram, and behavioral criteria.
Main Results:
- A significant linear correlation between tidal volume (VT), minute ventilation (VI), and CO2 was observed in NREM sleep.
- Differences in VT response slopes among infants were primarily attributed to variations in rib cage contribution.
- In REM sleep, ventilatory responses were less steep and more variable, with reduced rib cage contribution compared to NREM sleep.
Conclusions:
- The rib cage's recruitment significantly determines the slope of the CO2 response curve in newborn infants.
- Sleep state modulates the ventilatory control, particularly affecting the rib cage's role in CO2 response.
Abstract:
We have measured the ventilatory response to inhaled CO2 of six newborn infants in rapid-eye-movement (REM) and non-REM (NREM) sleep. Ventilatory responses were measured using the Read rebreathing technique. The response was further partitioned into the volume contributions of the rib cage and abdominal compartment using the respiratory inductance plethysmograph. Sleep state was defined by electroencephalogram, electrooculogram, and behavioral criteria. In NREM sleep, there was a highly significant linear correlation between both tidal volume (VT) and instantaneous minute ventilation (VI) with CO2. Among infants, the slope of VT varied from 1.0 to 0.34 ml X Torr-1 X kg-1. However, these differences were largely due to differences in rib cage contribution, which varied from 0.56 to -0.08 ml X Torr-1 X kg-1. The abdominal contribution was similar among infants (0.41-0.56 ml X Torr-1 X kg-1). In REM, the slopes of VI were less steep than in NREM, with greater breath-to-breath variability. Slopes of VT also tended to be lower. The abdominal responses were similar to those in NREM, whereas the rib cage response was low and negative in three studies. We conclude that the slope of the CO2 response curve is primarily determined by the extent of rib cage recruitment.