Exercise capacity is the most common measure of cardiovascular and metabolic efficiency. The six minute walk test (6MWT) is a standard procedure used to evaluate exercise capacity in pulmonary and cardiac patients[
1]. Although the cardiopulmonary exercise test with gas exchange is the “gold standard” method for measuring exercise in respiratory medicine, its use in routine clinical practice is limited because it requires expensive and complex technology. The 6MWT is the most widely used because it is both simple and reliable as a measure of exercise capacity.
The 6MWT is internationally used to measure functional status and prognosis in patients with a wide variety of diseases, such as pulmonary hypertension, congestive heart failure or chronic obstructive pulmonary disease (COPD). It can also be utilized to investigate the effects of several interventions (rehabilitation, pharmacological therapy, oxygen supplementation) on the patients’ walking capacity[
2,
3]. This test, referred to as a sub-maximal high-intensity constant-load exercise, is conducted for a period of 6 minutes while the patient is walking as far as possible. A supervised measurement of the distance walked (in meters), with associated pulse oximetry evaluations, and rating of dyspnea detected with the Borg scale or with visual analogic scale are then recorded as outcome measures[
3]. In COPD patients the distance walked correlates moderately with either an individual’s health-related quality of life, symptoms, peak work capacity as assessed by CPET or pulmonary function[
2,
3]. Most important, the distance walked is a surrogate marker of long-term survival in COPD patients, even when they are in the most advanced status of their disease[
3].
Many patients with chronic respiratory diseases, particularly those with COPD present a dysfunction related to a disorder of the skeletal muscles that reflects a limitation in exercise capacity[
3]. COPD is a pulmonary disorder that is characterized by progressive irreversible airflow limitation resulting from alveolar wall destruction, bronchiolar narrowing, and airways inflammation[
4]. Individuals with COPD usually show a limited capacity to perform exercise. When compared to healthy individuals they demonstrate lower maximum exercise capacities with the lowest levels observed in subjects with more severe COPD[
5]. Patients with COPD typically experience dyspnea during exercise and stop exercising because of dyspnea or leg fatigue or a combination of both. Patients with mild COPD usually perceive dyspnea more intensely than leg fatigue[
6,
7]. In this group the breathing pattern is more rapid and shallow and is the cause of dynamic hyperinflation which generates an inspiratory threshold due to positive end-expiratory pressure which results in a reduction of inspiratory capacity strictly related to dyspnea and in respiratory effort[
7]. Dynamic hyperinflation is the result of expiratory flow limitation: most people with COPD are able to maintain a stable end expiratory lung volume (EELV) and inspiratory capacity (IC) at rest. However, with the increased ventilatory demand imposed by exercise, the expiratory flow limitation arise. This leads to increased EELV and reduced IC.These two parameters have been identified as major contributory factors to dispnea in COPD patients[
8].Treatments to reduce airflow obstruction and/or dynamic hyperinflation include pursed lip breathing (PLB)[
9], several non-pharmacological therapies that include supplemental oxygen, heliox, breathing helium-oxygen mixtures, and non-invasive ventilation[
7,
9]. There is evidence that non-invasive ventilation reduces the work of breathing during exercise which in turn decreases dyspnea and increases endurance time in patients with moderate to severe COPD. Several studies have demonstrated a relationship between decreased dyspnea and reduced work of breathing[
7,
10‐
12]. Only few evidences exist concerning the use of positive expiratory devices: these devices should permit a reduction in lung hyperinflation and an increasing in exercise duration (endurance)[
13]. On this regard we decided to investigate if the use of a positive expiratory pressure device could improve the distance walked by patients with moderate to severe COPD.