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.
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