**Figure 1:** Some indices of airway responsiveness, such as the doseresponse
slope, are continuous variables. Anyone can then be classified
as hypo-, normo- or hyperresponsive, provided that arbitrary cutoffs are
allocated. The graph demonstrates the theoretical frequency curves of the
level of airway responsiveness in the total population (red) and the asthmatic
population (blue). The difference between the average level of airway
responsiveness between non-asthmatic and asthmatic populations is the
airway hyperresponsiveness (AHR) that characterizes asthma. Notice that
there is a lot of overlap; so that non-asthmatics can be hyperresponsive and
asthmatics can be normoresponsive. The risk of suffering for asthma is lowered
by a lot for someone hyporesponsive. AHR is thus perceived by many as a
prerequisite to suffer asthma. The level of airway responsiveness is also not
stable in time. The circles and arrows indicate how anyone in the population
can be shifted along this frame. The dashed curves indicate how the average
of the entire population can be shifted by different interventions. Whereas
increasing inflammation can increase airway responsiveness (moves the
population curve to the right), decreasing inflammation, by treating asthmatics
with glucocorticoids for example, can decrease airway responsiveness (move
the population curve to the left). The magnitude of those shifts is variable in
between individual. |