How does heart rate recovery after sub-maximal exercise correlate with maximal exercise testing in children with CF?

BackgroundDisease progression in cystic fibrosis (CF) is marked by worsening exercise tolerance. Further, maximal exercise capacity (VO2 peak) correlates with survival in CF, but maximal tests are uncomfortable and resource-intensive. A three-minute step test (STEP) has been validated in CF. Heart rate (HR) recovery after exercise correlates with all-cause mortality in adult non-CF populations. We compared HR recovery after the three-minute step test with VO2 peak in children with CF.Methods: Twenty-four children with CF performed STEP and a maximal exercise test. Correlation between the tests was assessed.Results: Maximum HR on STEP was lower than on the maximal test (140 vs. 190, p < 0.01). Peak HR during STEP correlated inversely with VO2 peak. In subjects with mild lung disease, faster HR recovery after STEP correlated with higher VO2 peak.Conclusions: The three-minute step test is a feasible submaximal test in this patient population. HR during and after a three-minute step test may reflect VO2 peak in children with CF.