We examined heart rate variability (HRV) during exercise testing in 20 children with sickle cell anaemia (SCA) and 12 controls. Subjects achieved lower median HRV at peak exercise [standard deviation of R-wave to R-wave intervals (SDNN), 2·3 vs 2·9 ms, P = 0·027; logarithmic transformation of high frequency power (lnHF), 0·9 vs 1·3 ln(ms2), P = 0·047] and had lower post-exercise HRV across minute-by-minute analysis of recovery. After adjustment for haemoglobin, fitness and SCA status, subjects had lower HRV at the end of recovery with differences increasing as baseline HRV increased. Further investigation of HRV and exercise safety in SCA is warranted.
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