Figure 6.
Example lung impedance spectra from a Type A asthmatic (left) and a Type B asthmatic (right)6. Both types of asthmatics have elevated lung resistance (RL) at all frequencies (open circles) that is reduced by the bronchodilator albuterol (closed circles). Bronchodilation has little effect on, lung elastance (EL) in Type A asthmatics, but in Type B asthmatics there is a substantial change indicative of a reduction in the amount of central airway shunting. That is, prior to albuterol the distal airways are significantly constricted so that the oscillations in flow that are applied to the lung to measure impedance become progressively more confined to the central airways as oscillation frequency increases. The albuterol relieves the distal airway constriction so that the flow can move past them and into the alveolar regions of the lung. The result is a major reduction in the apparent stiffness of the system as a whole. (Reprinted with permission of the American Thoracic Society. Copyright © 2016 American Thoracic Society. The American Journal of Respiratory and Critical Care Medicine is an official journal of the American Thoracic Society.)