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Respiratory muscle responses to changes in chemoreceptor drive in infants
1Department of Pediatrics, Rainbow Babies and Childrens Hospital, Case Western Reserve University, Cleveland, Ohio 44106.
Insights
Upper airway muscles have higher carbon dioxide (CO2) thresholds than the diaphragm. This difference in CO2 threshold may lead to upper airway instability and obstructive apnea in infants.
Area of Science:
- Neonatal Physiology
- Respiratory Control
- Sleep Medicine
Background:
- The diaphragm and upper airway muscles play critical roles in maintaining airway patency and ventilation.
- Differential responses of respiratory muscles to chemical stimuli may impact airway stability, particularly in vulnerable populations like preterm infants.
Purpose of the Study:
- To compare the quantitative responses of upper airway muscles (genioglossus, alae nasi, posterior cricoarytenoid) and the diaphragm to changes in carbon dioxide (CO2) levels in preterm infants.
- To investigate the relationship between CO2 thresholds and muscle activation patterns in respiratory control.
Main Methods:
- Electromyograms (EMGs) were recorded from surface electrodes of the genioglossus, alae nasi, posterior cricoarytenoid, and diaphragm in 10 ventilator-dependent preterm infants.
- Infants underwent passive hyperventilation to apnea followed by hypoventilation to assess respiratory muscle responses to varying CO2 levels.
Main Results:
- Apneic CO2 thresholds for all tested upper airway muscles were significantly higher than that of the diaphragm (P < 0.05).
- Above their respective CO2 threshold levels, the responses of upper airway muscles were proportional to the diaphragm's response.
- Differences in CO2 thresholds suggest non-proportional activation patterns among respiratory muscles under hypercapnic conditions.
Conclusions:
- Differential CO2 thresholds between upper airway muscles and the diaphragm may explain non-proportional respiratory muscle responses to hypercapnia.
- These disparities in CO2 thresholds could lead to an imbalance in respiratory muscle activation, potentially causing upper airway instability and obstructive apnea in preterm infants.
Abstract:
Upper airway muscles and the diaphragm may have different quantitative responses to chemoreceptor stimulation. To compare the respiratory muscle responses to changes in CO2, 10 ventilator-dependent preterm infants (gestational age 28 +/- 1 wk, postnatal age 40 +/- 6 days, weight 1.4 +/- 0.1 kg) were passively hyperventilated to apnea and subsequently hypoventilated. Electromyograms from the genioglossus, alae nasi, posterior cricoarytenoid, and diaphragm were recorded from surface electrodes. Apneic CO2 thresholds of all upper airway muscles (genioglossus 46.8 +/- 4.3 Torr, alae nasi 42.4 +/- 3.6 Torr, posterior cricoarytenoid 41.6 +/- 3.2 Torr) were higher than those of the diaphragm (38.8 +/- 2.6 Torr, all P less than 0.05). Above their CO2 threshold levels, responses of all upper airway muscles appeared proportional to those of the diaphragm. We conclude that nonproportional responses of the respiratory muscles to hypercapnia may be the result of differences in their CO2 threshold. These differences in CO2 threshold may cause imbalance in respiratory muscle activation with changes in chemical drive, leading to upper airway instability and obstructive apnea.