CO2 responsivity in the mouse measured by rebreathing

Area of Science:

• Physiology
• Respiratory Control
• Animal Models

Background:

• Assessing carbon dioxide (CO2) responsivity is crucial for understanding respiratory control.
• Existing methods are often challenging to apply to very small mammals, including neonates.
• A refined technique is needed for accurate CO2 response studies in these populations.

Purpose of the Study:

• To modify the rebreathing method for precise CO2 responsivity measurements in small mammals.
• To evaluate the effectiveness of the modified method in anesthetized mice.
• To analyze the impact of CO2 on respiratory parameters and underlying mechanisms.

Main Methods:

• Developed a modified rebreathing circuit for pentobarbital-anesthetized mice.
• Measured tidal volume (VT) and breathing frequency (f) during rebreathing from a CO2-enriched, oxygen-primed circuit.
• Utilized a plethysmograph, CO2 analyzer, and pump for continuous circuit PCO2 (PctCO2) monitoring.
• Constructed CO2 response curves based on extrapolated minute ventilation (V), VT, f, and breath timing parameters.

Main Results:

• Circuit PCO2 rapidly equilibrated with end-tidal PCO2, validating the method.
• CO2 was found to stimulate minute ventilation (V) by increasing both breathing frequency (f) and tidal volume (VT).
• CO2 facilitated central inspiratory-expiratory phase switching and inspiratory drive, though the phase switching effect was transient.

Conclusions:

• The modified rebreathing method is suitable and advantageous for studying CO2 responsivity in small mammals, including neonates.
• The method provides insights into the mechanisms of CO2-induced respiratory stimulation, involving phase switching and inspiratory drive.
• This technique offers a valuable tool for respiratory physiology research in small animal models.