Exercise limitation in individuals with asthma may be attributed to a wide range of factors including exercise-induced bronchoconstriction (EIB), which has been shown to affect up to 90% of patients with asthma.1 While cardiopulmonary exercise testing (CPET) is commonly used to identify EIB in this population and patients with other chronic respiratory diseases, this approach may also prove useful in assessing additional measures of functioning as well as treatment response in asthma.
In a review published in Respiratory Medicine, Boutou et al examined the limited available evidence regarding the potential clinical applications of CPET in the management of asthma, as highlighted below.1
Identifying Nonpulmonary Determinants of Exercise Capacity
In a retrospective study of 39 patients with difficult to treat asthma, researchers investigated the use of maximum CPET to identify contributing factors to persistent exertional breathlessness.2 Most patients demonstrated a single explanatory feature such as EIB, hyperventilation, ventilatory limitation, or deconditioning. However, the researchers noted that patients showing no pulmonary limitation on CPET had been prescribed similar doses of steroid therapy as the patients with pulmonary limitation.
The findings prompted dosage reductions in the latter group (median, 1300 μg [IQR, 800-2000 μg] to 800 μg [IQR, 400-1000 μg]; P <.001), while adjunctive therapies were added to the regimen for patients with pulmonary limitation. This study illustrated that patients with “nonpulmonary limitation are prescribed inappropriately high doses of steroid therapy, and [CPET] can identify the primary mechanism of breathlessness, facilitating steroid reduction,” the study authors concluded.2
Other CPET studies have observed reduced quadriceps force in children with severe persistent asthma and adults with difficult-to treat asthma, as well as signs of mitochondrial dysfunction and oxidative damage in the skeletal muscles of patients with peripheral muscle weakness related to corticosteroid use.1
In 2013, a study of 88 adult patients with moderate to severe persistent asthma demonstrated that peak oxygen consumption (VO2) on maximum CPET discriminated between patients with lower and higher levels of depression (higher and lower peak VO2, respectively), and lower health-related quality of life was noted in the group with higher depression levels.1,3 “Our results suggest an association between reduced exercise capacity, low [health-related quality of life] and increases in depressive symptoms in clinically stable asthmatic [patients],” indicating the “need to assess physical fitness and psychosocial distress during asthma treatment and the importance of a multidisciplinary approach,” the researchers stated.3
Additional research suggests that a low VO2 change to work rate change ratio and a high value of VE/VCO2 slope to peak VO2 ratio on CPET may help to discriminate between deconditioning and circulatory problems as the cause of exercise limitation in patients with asthma.1
Further investigation is warranted to explore the role of CPET in establishing nonpulmonary contributors to exercise limitation in asthma.
Detecting Dynamic Hyperinflation
In an earlier study, dynamic hyperinflation was noted on CPET in 13 of 20 patients with stable asthma who had normal spirometric results and absence of exercise-induced asthma.4 Other researchers found dynamic hyperinflation during CPET in 72.2% of obese women with asthma (vs 38.9% of non-obese patients with asthma, P <.05), and this finding was also linked to reduced exercise capacity in this group.5 These results point to dynamic hyperinflation as a significant factor in the exercise limitation often observed in patients with asthma.
Evaluating Treatment Response
In addition to its utility in assessing gains in exercise capacity over time, data from multiple studies indicate that CPET could have a role in evaluating improvements in disease-related outcomes associated with prescribed exercise in patients with asthma. Following exercise training, CPET assessments have shown improvements in measures of aerobic fitness, quality of life, and disease control in children with moderate to severe persistent asthma; exercise capacity and quality of life in adults with asthma; and peak VO2 and ventilatory capacity in patients with mild asthma.1