Respiratory sinus arrhythmia of brainstem lesions

In this pilot study we investigated the hypothesis that intrinsic and extri nsic brainstem lesions situated within the pontomedullary region would effe ct the integrity of respiratory sinus arrhythmia. The study sample consiste d of three patients with anatomic brainstem abnormalities associated with i solated Chiari I malformation, Chiari II malformation with syringobulbia, a nd achondroplasia with cervicomedullary compression. They were compared to an age- and sex-matched control group of nine patients. Each subject's elec trocardiogram was recorded in a quiet room and digitized by a personal comp uter during five 1-minute periods. RR intervals within each I-minute period were converted to heart rate in 120 successive 0.5 second intervals. The r esultant heartrate time series was converted to its underlying frequency co mposition by a fast Fourier transform and averaged across minutes. Respirat ory 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 respirato ry rates from 6 to 30 breaths per minute. Analysis revealed a significant r eduction in respiratory sinus arrhythmia (P <.05), defined as the summated area under the curve, with a mean for controls of 35.42 +/- 28.13 SD and fo r subjects of 17.20 +/- 11.50 SD. There was a gradient of abnormality noted , with the mildest deviation in respiratory sinus arrhythmia for the patien t with isolated Chiari I malformation and maximum deviation seen in the pat ient with extrinsic cervicomedullary compression.