Effect of intravenous antibiotics on exercise tolerance (3-min step test) in cystic fibrosis

Most children with cystic fibrosis (CF) feel better and display more energy after a course of intravenous antibiotics (IVABs), but this is not always reflected by a satisfactory improvement in lung function. We assessed the c hange in exercise tolerance after treat ment with IVABs using the 3-min ste p test, and compared it with changes in spirometric lung function and arter ial oxygen saturation (SaO(2)). Thirty-six children (mean age,13.8 years) w ere enrolled from two tertiary CF centers during an inpatient stay for IVAB s. After 10-14 days of treatment, there was a significant improvement in media n FEV1 from 43% to 57% of predicted Values (P < 0.0001), and median FVC fro m 66% to 73% of predicted values (P < 0.0001), while median SaO(2) signific antly increased from 95% to 96.5% (P < 0.05). This was accompanied by a red uction in resting heart rate (median 118 bpm to 109 bpm, P < 0.005) and sub jective breathlessness at rest (median Visual analogue score 2.2 to 0.8, P < 0.005). All outcomes of exercise tolerance were improved after IVABs. The re was a reduction in maximum heart Fate (median 156 bpm to 150 bpm, P < 0. 05) and an increase in minimum SaO(2) (median 93.5% to 94.5%, P = 0.08) mea sured during the step test. There was also a reduction in subjective breath lessness (median Visual analogue score of 5.5 to 4.2, P < 0.005) and object ive breathlessness (median 15-count score of 3 to 2, P < 0.0001) measured i mmediately after the step test. Exercise testing was a useful outcome measure for monitoring effectiveness of inpatient therapy, and complemented spirometry and SaO(2) monitoring. Th e simple ward-based 3-min step test was found to be a particularly suitable method for measuring changes in exercise tolerance in children with CF. (C ) 2001 Wiley-Liss, Inc.