A step in the right direction: Assessing exercise tolerance in cystic fibrosis

Abstract

Summary. Exercise tolerance may be reduced in patients with cystic fibrosis, but it is not always possible to predict this from standard lung function measurements. Formal exercise testing may, therefore, be necessary, and the test should be simple and readily available. We have developed a ''3-minute step test'' and compared it with the standard 6-minute walking test. Subjects stepped up and down a 15-cm-high single step at a rate of 30 steps per minute for 3 minutes. The effect of the step test on spirometry was tested first in 31 children with CF (mean age, 12.0 years), who had a mean (range) baseline forced expired volume in 1 second (FEV 1 ) of 64% (18-94%) of predicted values. The step test was then compared with the standard 6-minute walk in a further 54 patients with cystic fibrosis (mean age, 12.5 years), with mean (range) baseline FEV 1 of 61% (14-103%) of predicted values. Outcome measures were minimum arterial oxygen saturation (SaO 2 ), maximum pulse rate, and the modified Borg dyspnea score.Post-step test spirometry showed mean (95% CI) changes of −1.1% (−6.0+3.9%) for forced vital capacity, of −1.6% (−4.2+1.1%) for FEV 1 , and +0.25% (−2.8+3.3%) for peak expiratory flow, although 5/31 children showed >15% drop in one or more parameters. The step and walk tests both produced significant changes (P < 0.0001) in all outcomes, with a mean (range) minimum SaO 2 of 92% (75-98%) versus 92% (75-97%), a maximum pulse rate of 145 b.p.m. (116-189) versus 132 (100-161), and a Borg score of 2.5 (0-9) versus 1.0 (0-5), respectively. Comparison of the two tests showed that the step test increased breathlessness (mean change Borg score, 2.3 vs. 0.8; P < 0.0001) and pulse rate (mean change, 38% vs. 24%, P < 0.0001) significantly more than the walk, whereas the decrease in SaO 2 was similar (mean change, −2.9% vs. −2.6%; P = 0.12). Some patients with a significant drop in SaO 2 (>4%) would not have the decrease predicted from their baseline lung function. Reproducibility for the two tests was similar. The step test is quick, simple and portable, and is not dependent on patient motivation. Although the step test is more tiring, its effect on SaO 2 is similar to the 6-minute walking test. It is a safe test that may prove to be a valuable measure of exercise tolerance in children with pulmonary disease, although longitudinal studies are now needed. Pediatr Pulmonol. 1998; 25:278-284.

3‐Min step test and treadmill exercise for evaluating exercise-induced asthma

“…In the current study sample the 3-min step test also produced reproducible results, as others have reported [8]. Moreover, even if it decreases test sensitivity, performing exercise testing in a climate-controlled room, as in the current study, reduces variability related to temperature and humidity since cold air and dry ambient air (with low relative humidity, f50%) increase airways hyperresponsiveness.…”

Exercise testing for children with cystic fibrosis: A systematic review

“…In line with the findings of Lima et al 89 , our review determined that the 6MWT challenges cardiorespiratory function less in comparison to other field tests such as the MST and 3MST 32,33,37,90 . This suggests a ceiling effect may exist secondary to the upper limit on exercise intensity inherent to a walking test.…”

Desaturation During the 3-Minute Step Test Predicts Impaired 12-Month Outcomes in Adult Patients With Cystic Fibrosis

“…The current study shows that the test was acceptable to adults and could be performed by almost all participants, regardless of disease severity. Physiological responses to the 3-minute step test were similar to those reported in 54 children with CF and similar disease severity, 7 with comparable changes in oxyhemoglobin saturation, heart rate, and dyspnea scores. This suggests that it may be feasible to use the 3-minute step test across the lifespan in CF.…”