Respiratory control of body temperature: a theoretical model

Area of Science:

• Physiology
• Biophysics
• Thermoregulation

Background:

• The Grodins et al. (1954) ventilatory CO2 chemostat model is a foundational concept in respiratory control.
• Panting is a critical physiological response for heat dissipation in many animals, particularly dogs.

Purpose of the Study:

• To modify the existing chemostat model to accurately describe the physiological requirements of panting.
• To investigate the influence of environmental factors and physiological parameters on panting behavior and body temperature regulation.

Main Methods:

• A modified two-compartment model was developed, incorporating heat production during panting.
• Differential equations were formulated and solved, considering the ventilation/perfusion ratio.
• Steady-state and unsteady-state solutions were calculated using experimentally determined constants for dogs.

Main Results:

• Panting is significantly induced above 30°C ambient temperature and is exacerbated by increased relative humidity.
• The ventilation/perfusion ratio showed no influence on the panting response.
• The oxygen cost of panting imposes limits on effective body temperature regulation, dependent on respiratory muscle energy demands, set-point temperature, and controller gain.
• The ventilatory response to heat stress is relatively slow, with a half-time of approximately 15 minutes for a 20 kg dog.

Conclusions:

• The developed model provides insights into the physiological mechanisms and limitations of panting as a thermoregulatory strategy.
• The high specific heat of tissues compared to expired air is a key factor determining the model's properties.
• Effective thermoregulation via panting is constrained by energy expenditure and physiological control parameters.