Heart Rate Variability And CHIME

Professor Ron Harper is a prominent basic neuroscientist at the Brain Research Institute at UCLA. He will be the co-recipient of the 1997 Apnea of Infancy Award, to be presented at the Annenberg Conference on Apnea of Infancy in Palm Springs, California, in January, 1997. He is very a bright and talented researcher, and we are fortunate to have him interested in SIDS.

Heart rate variability relates to the issue that your heart does not beat at the same rate all of the time. When you sleep, it falls. When you must run up stairs, it increases. This ability to change heart rate is a measure of your ability to adapt to changes in the environment. Thus, as a simplification, decreased heart rate variability is bad (implies decreased ability to respond to changes in the envornment) and increased heart rate variability is good. However, I caution that there is no clear clinical correlation with health and changes in heart rate variability.

Ron Harper and his coworkers applied an analytic technique which assesses beat-to-beat heart rate variability to the overnight recordings of ECG on babies who subsequently died from SIDS compared to controls (tapes recorded by David Southall in England). They found that the GROUP of SIDS victims had decreased heart rate variability (recorded some weeks prior to death) compared to the GROUP of control infants. However, there was quite a bit of overlap between the groups. Therefore, not even Professor Harper would suggest that this is a diagnostic test which can be used to identify a baby who is likely to die from SIDS. Other conditions can also decrease beat-to-beat heart rate variability, so this is certainly not specific to SIDS. More recently, Professor Harper and his colleagues published a paper showing qualitatively similar results with respiratory rate variability.

The importance of this work is that it provides further evidence that SIDS may have its origins in brainstem dysfunction. Heart rate variability is a measure of autonomic nervous system function. This is the same area of the brain which controls breathing, sleep/wakefulness, etc. However, this is not offered as a test which can be applied to infants to predict whether or not they will die from SIDS.

These data are available in the CHIME Monitor, which is used on infants enrolled in the CHIME Study. We specifically designed the CHIME Monitor to acquire heart rates and respiratory rates during the entire time a baby is on the monitor. Therefore, these types of analyses will be able to be performed on babies in the CHIME study.

I hope this helps. Thank you.

Thomas G. Keens, M.D.
Childrens Hospital Los Angeles

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