An overview of the anatomy and physiology of slowly adapting pulmonary stretch receptors

Since the original work of by Hering and Breuer in 1868 numerous studies ha ve demonstrated that slowly adapting pulmonary stretch receptors (SARs) are the lung vagal afferents responsible for eliciting the reflexes evoked by moderate lung inflation. SARs play a role in controlling breathing pattern, airway smooth muscle tone, systemic vascular resistance and heart rate. Bo th anatomical and physiological studies support the contention that SARs, b y their close association with airway smooth muscle, continuously sense the tension within the myoelastic components of the airways caused by lung inf lation, smooth muscle contraction and/or tethering of small intrapulmonary airways to the lung parenchyma. In addition, intrapulmonary SAR discharge a ctivity is sensitive to changes in P-CO2 within the physiological range. De spite this extensive characterization of SARs, their role in determining br eathing pattern and airway tone in individuals with respiratory diseases is only recently being appreciated. (C) 2001 Elsevier Science B.V. All rights reserved.