Disease progression and the overall health of young people with cystic fibrosis (CF) can be evaluated by putting them through the modified shuttle test (MST) once, as its repeated use showed no significant differences in exercise capacity, a study reports.
This test involves repeated movement along a 10-meter course with external prompts of varying intensity, and is a validated measure of a CF patient’s ability to exercise. As such, it’s important in assessing their respiratory health and likely disease outcomes (prognosis).
It is also inexpensive and easily adapted to clinic use, the researchers wrote.
The study, “Clinical use of the modified shuttle test in children with cystic fibrosis: Is one test sufficient?,” was published in the journal Pediatric Pulmonology.
Because exercise capacity is useful in evaluating people with CF and their likely prognosis, a number of tests exist. Some, like the cardiopulmonary exercise test (CPET) that measures heart rate and blood oxygenation while pedaling a specialty bike, are considered gold standard for this purpose. CPET, for instance, allows a doctor to evaluate both submaximal and peak exercise response in a patient. But it is expensive, restricting its general use.
MST, a portable field test that also requires increasing effort and can capture the same measures as CPET, is considered a valid option.
However, some studies suggest that the modified shuttle test might need to be given at least twice on a first visit to establish a reliable baseline measure for a patient.
Researchers in Brazil evaluated whether MST needed to given more than once to children and adolescents with CF to adequately judge their exercise capacity.
Their nine-month study initially enrolled 48 stable patients (60.4% boys, mean age of about 10); 35 patients finished the study and their data was analyzed.
At each clinic visit, once every three months, patients went through the modified shuttle test twice.
To perform the MST, they were instructed via external prompts to walk or run at increasing speeds along that 10-meter course, until either their oxygen saturation — oxygen levels in the blood — dropped below 85% or they were no longer able to complete the course.
Exercise capacity was measured by comparing the results of two shuttle tests done on the same day with those from other visits. Before and after each test, cardiorespiratory health measures that included oxygen saturation, heart rate, respiratory rate, and blood pressure were taken.
Lung function was analyzed by spirometry, with the team determining patients’ forced vital capacity — FVC, a measure of the amount of air that is forcibly exhaled after taking the deepest breath possible — and the volume of air that can be blown out forcibly in one second (FEV1).
Most patients, 54%, had the most common disease-causing mutation, that of the F508del mutation in one of the two CFTR gene copies, and 16.5% had chronic colonization by P. aeruginosa. On average, the group’s percentage predicted FEV1 was 73.5%.
Comparisons of measures taken on each of the two MSTs done on a single visit found no significant differences in initial heart rate, peak heart rate, or distance achieved.
Likewise, no significant differences were seen in distances patients achieved in the two tests on any of the three visits.
As such, MST was found to be “reproducible and reliable” as a test of exercise capacity, and that changes in heart rate best associated with the distance achieved on this test over time.
“The main findings of the present study confirm the hypothesis that it is not necessary to perform the MST more than once in the evaluation of the exercise capacity of children and adolescents with CF,” the researchers wrote.
“MST is considered a reproducible and reliable test for this population. The cardiovascular variables and DA [distance achieved] are the most appropriate test variables for monitoring the performance of this population over time,” they added.
A limited to this study, its authors noted, included the absence of gas analysis, which could precisely detect exercise intolerance in CF patients.
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