Airway hyperresponsiveness (AHR) is a very complex relationship between smooth muscle and localized inflammation with little known about the exact physiology behind a response. It is typically measured by using stimuli to act directly on the airway smooth muscle to induce bronchonstriction, such as methacholine. It is also measured indirectly using exercise, hypertonic saline, various allergens which cause bronchoconstriction by releasing of upstream mediators1.
Imaging studies in humans and animals have previously shown that bronchoconstriction causes patchy ventilation defects within the lungs2. In a recent publication, Dr. Waters utilized a specialized dynamic in-vivo imaging technique, microfocus X-ray computer tomography, which provides high resolution imaging in small subjects. The imaging allowed for investigation into the airway narrowing in response to methacholine challenges to compliment the lung mechanics measurements3.
Figure 1: Subject paced on rotating stage between X-ray source and detector– much like clinical CT systems, alternatively can have the stage fixed and imaging device rotate around subject (Pinar & Jones 2018).
In-vivo imaging with the flexiVent allowed Dr. Waters and his group to visualize the physiological heterogeneity observed within the lungs in response to a methacholine challenge.
In addition, they show that employing multiple (3-7) deep inflations affects resistance outcomes by significantly increasing the diameter of the airways.
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