Photo Credit: Jacob Wackerhausen
The incremental step test (IST) reliably, conveniently, and cost-effectively assesses exercise capacity in moderate-to-severe asthma.
A small study from Brazil suggests the incremental step test (IST) is a reliable, convenient, and less costly alternative to the cardiopulmonary exercise test (CPET) for assessing exercise capacity in certain patients with asthma.
“The IST showed excellent reproducibility and strong validity in subjects with moderate to severe asthma,” Celso R F Carvalho, PhD, MS, and colleagues wrote in Pulmonology. “These results suggest that the IST provides a reliable measure of exercise capacity and can be used in clinical practice and research.”
People with asthma tend to limit their activity to avoid respiratory symptoms. Testing their exercise capacity is important, but the “gold standard” CPET is expensive and requires specialized equipment and personnel. Field walk tests are simple, less costly, and less time consuming, but they require corridors longer than may be available. By contrast, the IST offers a low-cost, portable alternative that occupies little space.
IST Results Similar to CPET
While the IST is considered reproducible and reliable in other pulmonary diseases, this study is, to the researchers’ knowledge, the first to describe its reliability, measurement error, construct validity, and interpretability for patients “with moderate or severe asthma following the recommendations of COSMIN measurement properties.”
Dr. Carvalho and his colleagues recruited adult patients with moderate to severe persistent asthma who were treated at an academic asthma specialty hospital. Of the 50 adult participants who completed the study, 38 were female, the mean age was 43.9 years, the mean BMI was 28.7 kg/m2, and the mean forced expiratory volume in the first second (FEV1) was 70.1% of predicted.
Participants performed tests on two days at least 48 hours apart. On day 1, they provided anthropometric measures, completed the Asthma Control Questionnaire, and took spirometry tests, including FEV1, forced vital capacity (FVC), and FEV1/FVC ratio absolute values. They were later randomized to take either the CPET or the IST. On day 2, they performed the test they had not performed on day 1.
The researchers recorded peak oxygen uptake (peak VO2), minute ventilation, respiratory exchange ratio, heart rate, modified Borg dyspnea score, and Borg leg discomfort score during the tests.
For the CPET, each participant set a preferred treadmill speed, and the slope gradually increased over time until the test was interrupted before or at the start of limiting symptoms.
The STI involved patients stepping up and down on a 20-cm high, 40-cm wide, 60-cm deep wooden bench to the rhythm of an increasingly fast audio signal until they could not keep the pace for 15 seconds. After a break to allow their vital signs to return to baseline, they repeated the test.
Dr. Carvalho and his colleagues used the results from the first and second ISTs to perform reliability analyses and used the ISTs with better peak VO2 values for validity and interpretability analyses.
They determined reliability by intraclass correlation coefficient (ICC), measurement error by standard error of measurement and minimum detectable difference, construct validity by Pearson correlation coefficient (r), and interpretability by ceiling and floor effects. They found that:
- Peak VO2 for CPET, first IST, and second IST were 27.6, 22.3, and 23.3 ml/kg/min, respectively.
- According to COSMIN classification, for peak VO2, IST showed excellent reliability (ICC=0.93; 95% CI, 0.88-0.96), very good measurement error (2.5%), and strong construct validity compared to CPET (r=0.85; P<0.001) to assess exercise capacity in patients with moderate to severe asthma, with appropriate ceiling (10%) and floor (0%) effects.
The authors acknowledged that the small sample size and the preponderance of female participants were limitations to the study but noted that randomizing participants to CPT and IST reduced bias.
Additional Testing Options
“The data are surprising because they show that a simple-to-perform and low-cost test yielded results that were similar to the more expensive and elaborate CPET. The IST can allow clinicians to assess their patients in clinical practice,” Dr. Carvalho said.
“In clinical practice, having options is important,” he added, and his research team plans to explore the applicability of further tests in this population. “It is important to understand whether other field tests—the six-minute walk test, the incremental shuttle walk test, the endurance shuttle walk test—could also assess physical capacity in this population.”
