Review of Pulmonary Physiology

David A. Kaminsky, MD

Kathryn A. Hibbert, MD

Andrew M. Luks, MD

It is our great honor and pleasure to present this special issue of Seminars in Respiratory and Critical Care Medicine devoted to pulmonary physiology. In this modern day of cell and molecular biology, the basics of pulmonary physiology are often overlooked and misunderstood by students and practitioners alike. These physiologic principles remain central to understanding human disease and treating patients, and while there are many excellent textbooks and other sources that cover the basics of pulmonary physiology, our goal was to provide a definitive source of information on not just the basics but also the wonderful complexities of the respiratory system.

We have had the great privilege to invite authors from around the world who are leading experts in each of the topic areas included. Dr. Ramon Farre starts the special edition with a discussion of the static mechanical properties of the respiratory system. Static lung volumes are determined by the pressure-volume characteristics of the mechanically linked lungs and chest wall, together with the surface tension forces modified by surfactant. The equation of motion relates pressure to drive airflow to static elastic forces as well as resistive forces, linking this first topic to the next article on the dynamic properties of the respiratory system by Drs. David Kaminsky, Don Cockcroft, and Beth Davis. This section examines how airway geometry determines airflow resistance during breathing, and why flow limitation develops due to the compressible nature of the bronchial tree. Consequences of flow limitation including airway obstruction, dynamic hyperinflation, and airway hyperresponsiveness are also discussed.

A number of highly specialized articles on the gas exchange functions of the lung follow. First, Drs. Susan Hopkins and Michael Stickland describe the intricate anatomy of the pulmonary vasculature, emphasizing its unique properties of recruitment and distension, the determinants of pulmonary vascular resistance, and its response to hypoxia. Next, Drs. Robb Glenny and Johan Petersson examine how gas exchange is influenced by the matching of ventilation and perfusion, and the role of gas diffusion. An extensive, two-part article written by Dr. Peter Wagner follows, which delineates the detailed steps involved in transport of oxygen and carbon dioxide and how these properties are uniquely determined by their respective binding curves with hemoglobin. Once oxygen reaches the tissue level, cellular respiration occurs, as described by Dr. Connie Hsai, who emphasizes the unique interactions of oxygen with hemoglobin and myoglobin and other molecules that optimize gas transport by convection and gas transfer by diffusion. Assessment of blood oxygenation and acid–base status is commonly accomplished by interpretation of arterial blood gases, which are discussed by Drs. Sarah Sanghavi and Erik Swenson. Such an analysis gives insight into how various blood gas disturbances are related to the bicarbonate/carbon dioxide buffer system and the effects of ventilation. Finally, Drs. Jerome Dempsey and Joseph Welch discuss the mechanisms involved in the control of breathing, with an emphasis on the relationship between alveolar ventilation and CO₂ production, and how these mechanisms relate to common disorders of breathing control.

In the next section, Drs. Michael Pinsky and Natsumi Hamahata describe the global interaction of the heart and lungs, including an examination of the hemodynamic effects of intrathoracic pressure and ventilation under conditions of mechanical ventilation. The heart and lungs, of course, interact intricately during exercise, and the details of exercise physiology and measurement through cardiopulmonary exercise testing are described in the next article by Drs. Sietsma and Harry Rossiter.

We end this special edition with a survey of how the respiratory system performs in extreme environments. Drs. Marc Berger and Andrew Luks describe how hypobaric hypoxia and other environmental effects of high altitude affect the cardiorespiratory system. At the other extreme of pressure, Dr. Kay Tetzlaff discusses how the cardiorespiratory system copes with the high pressure and oxygen debt associated with diving. Finally, and particularly pertinent to the early 21st century, Drs. Jan Stepanek, Rebecca Blue, and Desmond Connolly take us on a journey to space and explain how microgravity, low ambient pressure, and other environmental stressors associated with space travel affect the functioning of the cardiorespiratory system.

The guest editors sincerely thank all of the contributing authors for providing such thorough and engaging discussion of each of the topics at the highest level of understanding. We hope this special edition not only provides a rich source of information on the physiology of the respiratory system but also challenges the reader to deepen their understanding of the inner workings of how we breathe and support cellular respiration both at rest and under various forms of stress.

Publication History

Article published online:
10 October 2023