Cybernetic aspects of heat tachypnea

Abstract

The panting mechanism is considered as resulting from the joint effort of the two systems regulating the body temperature and the blood gas tensions respectively. Equations are derived which describe the equilibrium conditions for each system. A nomogram for the evaluation of the amount of heat taken up by one liter of respiratory air is given. Combination of the equilibrium equations leads to a infinite series due to the fact that heat dissipation by the respiratory tract involves increased heat production by the respiratory muscles. The conditions of convergence for the infinite series are derived assuming a quadratic relation between heat production of the respiratory muscles and respiratory minute volume. It is shown that the system will become unstable if the series diverges. Equations for the partial washout of the dead space are given which are essential for the independent control of alveolar ventilation and dead space ventilation by proper adjustment of tidal volume and respiratory rate. Two examples demonstrate the limited value of the panting mechanism as compared with the heat dissipation by sweat production, when the animals are subjected to high environmental temperatures. Panting seems superior however for eliminating an increased heat production due to muscular exercise at very low temperatures as for instance in sled dogs.