Volume history response of airway resistance.

Abstract

Airways exhibit pressure volume hysteresis. The degree of airway hysteresis is directly proportional to smooth muscle tone. The lung parenchyma also exhibits similar pressure volume hysteresis. The effect on airway size depends on the relative difference between parenchymal and airway hysteresis as demonstrated by Froeb and Mead [1]. Hysteretic behaviour of airways and lung can be demonstrated by an act of deep inhalation, which is called a volume history (VH) manoeuvre. The model of Mead and Froeb has been analysed by Burns and Taylor [2]. These authors have shown that if airway volume represented by dead space (VD) is plotted against lung volume and the subject is asked to breath in from FRC to TLC and back, three different pattern of responses emerge. First, an anticlockwise loop represents bronchodilation in response to VH; second, a clockwise loop will indicate bronchoconstriction; third, no loop will show absence of VH response. When airway hysteresis exceed parenchymal hysteresis, airway size is greater on the deflation limb than it is at any given lung volume along the inflation limb. Airway hysteresis less than parenchymal hysteresis leads to the opposite volume history response Finally, if airway and parenchymal hysteresis are equal, volume history has no effect on airway size. It has been shown that this volume history response is maximal almost immediately after a deep inhalation, decays rapidly during the first minute and usually is completely reversed within 2–3 minutes following inspiration in normal subjects.KeywordsLung VolumeAirway ResistanceFunctional Residual CapacityTotal Lung CapacityConstrictor ResponseThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.