Minimal Important Difference of Walking Test in Subjects With Bronchial Asthma

The Six Minute Walking Test (6MWT) efficiently represents the exercise capacity in subjects with chronic respiratory disease, as asthma. The variation of the walking distance is a parameter used to evaluate the effectiveness of pharmacologic and non-pharmacologic interventions, asPulmonary Rehabilitation (PR). However, statistically significant changes in the walking distance do not always represent clinically significant variations. For this reason, it is important to understand in terms of clinical impact, how to interpret the 6MWT when the walking distance changes over time in the same subject (for example, at the beginning and after PR) or when it differs between subjects (some subjects may improve more and some subjects less). It is not enough to state that the intervention works, it is necessary to say how much it works. The demonstration of a clinically relevant effect must be the primary goal of every treatment. A clinically relevant effect is defined as the minimum achievable benefit, which may lead the medical doctor to change his strategy towards the patient, for example by recommending a particular therapy or treatment. The international scientific community calls the minimum achievable benefit with different names; one of the most common is the Minimal Important Difference (MID). The identification of MID is relevant for the clinician, for the agency that is paying the treatment, for the Regulatory Agency and is equally important for the patient for whose health these groups are responsible. MID for 6MWT has been estimated in subjects with different respiratory diseases and not. In Chronic Obstructive Pulmonary Diseases, a variation of 25 meters is considered significant. Recent studies have shown that asthmatic subjects cover a distance of about 500 meters during 6MWT, and that this distance improves after PR on average of 30-60 meters. Up to-day, however, the 6MWT MID in asthmatic patients has not been investigated. The aim of this prospective study is to determine the MID for the 6MWT in subjects affected by asthma, regardless of the severity of the disease.