Chapter 13: Respiratory Physiology

The mechanics of ventilation operate according to pressure-volume relationships, whereby changes in thoracic cavity dimensions alter intrapulmonary pressure gradients and drive airflow during inspiration and expiration. The diaphragm and external intercostal muscles generate the pressure differentials necessary for inhalation, while exhalation may occur passively or require active muscular effort during exercise. Pulmonary surfactant plays a critical role in reducing alveolar surface tension, thereby preventing alveolar collapse and maintaining lung compliance across varying lung volumes. Gas transfer across the alveolar-capillary interface follows diffusion principles, with oxygen and carbon dioxide moving along their respective partial pressure gradients. The efficiency of gas exchange depends on appropriate ventilation-perfusion matching, where misalignment between regional ventilation and blood perfusion results in inadequate oxygenation. Oxygen transport is mediated by hemoglobin, whose binding affinity varies with pH, temperature, and 2,3-bisphosphoglycerate concentrations, collectively described as the Bohr effect. Carbon dioxide exists in multiple forms during transport, including dissolved gas, carbaminohemoglobin complexes, and bicarbonate ions, with carbonic anhydrase catalyzing rapid interconversion between these species. Breathing regulation integrates input from central and peripheral chemoreceptors that sense arterial carbon dioxide, oxygen, and hydrogen ion concentrations, along with neural signaling from medullary and pontine respiratory centers. The chapter concludes by examining pathophysiological conditions including obstructive diseases such as asthma and chronic obstructive pulmonary disease, restrictive disorders like pulmonary fibrosis, and ventilatory disturbances, with clinical implications demonstrated through case analysis.