Chapter 21: Neural & Chemical Control of Ventilation

Neural & Chemical Control of Ventilation begins by examining the neural genesis of the respiratory rhythm within the brainstem, specifically identifying the dorsal respiratory group (DRG) and ventral respiratory group (VRG) in the medulla oblongata, which function alongside the central pattern generator and the central inspiratory activity (CIA) integrator to produce cyclic breathing. The text explores how this automatic rhythm is modulated by higher cortical centers for voluntary control and by various peripheral reflexes, including the Hering-Breuer inflation reflex mediated by pulmonary stretch receptors, as well as input from irritant receptors, J receptors, and proprioceptors. A significant portion of the chapter is dedicated to chemical regulation, differentiating between central chemoreceptors in the medulla, which are exquisitely sensitive to the pH of cerebrospinal fluid (influenced by carbon dioxide crossing the blood-brain barrier), and peripheral chemoreceptors in the carotid and aortic bodies that respond to arterial hypoxia, hypercapnia, and acidemia. The discussion extends to physiological responses under specific conditions, such as the three phases of exercise-induced hyperpnea involving neurogenic feedforward mechanisms and metabolic tracking, and the altered respiratory control seen during sleep, including the blunting of chemosensitivity and the pathophysiology of central and obstructive sleep apnea. Furthermore, the chapter investigates acclimatization to high-altitude environments, explaining how hypoxia-induced hyperventilation leads to respiratory alkalosis that is eventually compensated by renal bicarbonate excretion, alongside hematological changes like polycythemia. Finally, it addresses the diving reflex, characterized by bradycardia and peripheral vasoconstriction, and warns against the dangers of shallow water blackout caused by pre-dive hyperventilation reducing the carbon dioxide drive to breathe.