Pulmonary physiology and response to exercise

Abstract

The pulmonary system is a key element within the integrated network responsible for maintaining blood gas homeostasis. In all physiologic states, including rest, sleep, and dynamic exercise, its primary function is to ensure that mixed venous blood is transformed into arterial blood with appropriate partial pressures of O2 and CO2. This system faces several significant challenges to its ability to maintain blood gas homeostasis during dynamic exercise. With a simultaneous increase in mixed venous carbon dioxide content and decrease in mixed venous oxygen content, ventilatory demands are significantly greater during exercise than during rest. A reduction in transit time of red blood cells through the pulmonary capillaries, resulting from an increased cardiac output, also decreases the time available for gas exchange. To maintain blood gas homeostasis despite these challenges, medullary neural networks and sensory reflex mechanisms tightly regulate alveolar ventilation. The structural capacity for producing ventilation and increasing diffusion surface area to meet the demands of dynamic exercise in the healthy respiratory system is truly remarkable.