Respiratory sinus arrhythmia in patients with Prader-Willi syndrome

In this investigation, we sought to further test the hypothesis that parasympathetic deficiency exists among persons with Prader-Willi syndrome, by examining respiratory sinus arrhythmia. The study sample comprised two groups of patients: 14 subjects with Prader-Willi syndrome and 14 age- and sex-matched controls. Each subject's electrocardiogram was recorded in a quiet room and digitized by a personal computer during five 1-minute periods. RR 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 to 0.48 Hz) corresponding to a range of respiratory rates from six to 30 breaths/minute. Analysis revealed significantly less variability in the heart rates of subjects with Prader-Willi syndrome relative to age- and sex-matched controls (group x frequency bin: F = 2.26, P < .05). An analysis of covariance adjusting for body mass index differences between the groups produced identical results. These findings support the existence of a parasympathetic deficiency among subjects with Prader-Willi syndrome independent of their body mass. This is likely due to dysregulation of the central autonomic network.