A comparison between carbon dioxide inhalation and increased dead space ventilation in chickens

Area of Science:

• Comparative Physiology
• Respiratory Regulation
• Avian Biology

Background:

• The chemical control of breathing is crucial for maintaining homeostasis.
• Intrapulmonary chemoreceptors are known to play a role in avian respiratory control.
• Understanding how different stimuli affect ventilation is key to deciphering respiratory regulation mechanisms.

Purpose of the Study:

• To compare the ventilatory response to elevated partial pressure of carbon dioxide (PICO2) with the response to increased dead space volume (delta VD) in chickens.
• To investigate the role of avian intrapulmonary chemoreceptors in the chemical control of ventilation and arterial carbon dioxide (PaCO2) regulation.

Main Methods:

• Experiments were conducted on anesthetized, hyperoxic chickens.
• Two series of experiments were performed: Series I varied PICO2, and Series II increased delta VD using tubing.
• Ventilatory and arterial blood gas parameters (PaCO2) were measured and analyzed as a function of CO2 load (delta L).

Main Results:

• Elevated PICO2 led to increased ventilation with constant PaCO2 at lower levels.
• Increased delta VD resulted in rising PaCO2 at low levels.
• When normalized to CO2 load, ventilation changes were greater and PaCO2 changes were less in response to PICO2 compared to delta VD.

Conclusions:

• The distinct ventilatory responses suggest a significant role for avian intrapulmonary chemoreceptors in sensing CO2.
• Differences in lung CO2 concentration patterns and receptor discharge timing may explain the observed responses.
• These findings provide further evidence for the substantial contribution of intrapulmonary chemoreceptors to avian respiratory control and PaCO2 homeostasis.