Respiratory sinus arrhythmia in children with severe cyanotic breath-holding spells.

In this study we sought to investigate parasympathetic activity among children with severe cyanotic breath-holding spells by examining respiratory sinus arrhythmia. The study sample was composed of two groups of patients, 16 subjects with cyanotic breath-holding spells (5 male, 11 female; mean age, 37.5 mo) and 17 controls (8 male, 9 female; mean age, 37.7 mo). Each subject's electrocardiogram was recorded in a quiet room and digitized by an 80386 personal computer during five 1-minute periods. R-R intervals within each 1-minute period were converted to heart rate in 120 successive 0.5 second intervals. The resultant heart rate time series was converted to its underlying frequency composition by a fast Fourier transform and averaged across minutes. Respiratory sinus arrhythmia was defined as the variability in the time series over a frequency range (0.096-0.48 Hz) corresponding to a range of respiratory rates from 6 to 30 breaths per minute. Analysis revealed after ANCOVA adjustment for age and gender with subject group and frequency bin as dependent measures, that subjects with cyanotic breath-holding spells had similar variability in their heart rates as did controls (group x frequency bin: F = 0.74, P = 0.71). This study supports the hypothesis that autonomic dysregulation in cyanotic breath-holding spells is not due to a primary disturbance in central parasympathetic control over cardiac rate and rhythm.