Changes in Airway Resistance
Airway resistance is not constant. As shown above airway resistance is markedly affected by changes in the diameter of the airways, therefore diseases affecting the respiratory tract can increase airway resistance. Airway resistance can change over time, for example, in asthma during an attack the airways constrict causing an increase in airway resistance. Airway resistance can also vary between inspiration and expiration, for example, in emphysema there is destruction of the elastic tissue of the lungs which help hold the small airways open, therefore during expiration, particularly forced expiration, these airways may collapse causing increased airway resistance.
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