A STEP IN THE RIGHT DIRECTION - ASSESSING EXERCISE TOLERANCE IN CYSTIC-FIBROSIS

Exercise tolerance may be reduced in patients with cystic fibrosis, bu t it is not always possible to predict this from standard lung functio n 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 w alking 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 te st 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 (FEV1) of 64% (18-94%) of predicted values. The step test was t hen compared with the standard 6-minute walk in a further 54 patients with cystic fibrosis (mean age, 12.5 years), with mean (range) baselin e FEV1 of 61% (14-103%) of predicted values. Outcome measures were min imum 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 FEV1, and +0.25% (-2.8+3.3%) for peak expiratory flow , although 5/31 children showed >15% drop in one or more parameters. T he 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%) ve rsus 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), respec tively. Comparison of the two tests showed that the step test increase d 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 baselin e lung function. Reproducibility for the two tests was similar. The st ep 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. (C) 1998 Wiley-Liss, Inc.