Pleural physiology: What do we understand and what should we measure in clinical practice?

The pleura has been preserved throughout mammalian evolution, despite its relatively modest contribution to cardiopulmonary physiology, and is the site of numerous pathological conditions with associated morbidity, mortality and healthcare costs. It contains a small amount of pleural fluid, allowing the pleural membranes to slide over one another with minimal friction, optimising respiratory mechanics. The pleural space is also thought to serve as an extrapulmonary reservoir for pulmonary oedema arising from the interstitium, minimising interference with gas exchange. Despite a large body of research that has informed clinical practical in the past decade, the physiological underpinnings of pleural pathology have been relatively less studied and are notoriously underappreciated by clinicians. Here, we review the basic physiology of pleural fluid formation and reabsorption, and our current knowledge on pleural pathology and breathlessness, and explain the rationale and methods for measuring pleural pressure as well as the clinical utility of manometry. We also describe how physiology-based interventions may improve clinical decision making in specific clinical scenarios.