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 respi ratory sinus arrhythmia. The study sample was composed of two groups o f patients, 16 subjects with cyanotic breath-holding spells (5 male, 1 1 female; mean age, 37.5 mo) and 17 controls (8 male, 9 female; mean a ge, 37.7 mo), Each subject's electrocardiogram was recorded in a quiet room and digitized by an 80356 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 trans form and averaged across minutes. Respiratory sinus arrhythmia was defined as the variability in the time series ov er a frequency range (0.096-0.48 Hz) corresponding to a range of respi ratory 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 (g roup x frequency bin: F = 0.74, P = 0.71), This study supports the hyp othesis that autonomic dysregulation in cyanotic breath-holding spells is not due to a primary disturbance in central parasympathetic contro l over cardiac rate and rhythm.