AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 3 638-R646, Copyright © 1993 by American Physiological Society
Heart rate control in normal and aborted-SIDS infants
S. M. Pincus, T. R. Cummins and G. G. Haddad
Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut 06510.
Approximate entropy (ApEn), a mathematical formula quantifying regularity
in data, was applied to heart rate data from normal and aborted-sudden
infant death syndrome (SIDS) infants. We distinguished quiet from
rapid-eye-movement (REM) sleep via the following three criteria, refining
the notion of REM as more "variable": 1) REM sleep has greater overall
variability (0.0374 +/- 0.0138 vs. 0.0205 +/- 0.0090 s, P < 0.005); 2)
REM sleep is less stationary (StatAv = 0.742 +/- 0.110) than quiet sleep
(StatAv = 0.599 +/- 0.159, P < 0.03); 3) after normalization to overall
variability, REM sleep is more regular (ApEnsub = 1.224 +/- 0.092) than
quiet sleep (ApEnsub = 1.448 +/- 0.071, P < 0.0001). Fifty percent of
aborted-SIDS infants showed greater ApEn instability across quiet sleep
than any normal infant exhibited, suggesting that autonomic regulation of
heart rate occasionally becomes abnormal in a high-risk subject. There was
an association between low ApEn values and aborted-SIDS events; 5 of 14
aborted-SIDS infants had at least one quiet sleep epoch with an ApEn value
below the minimum of 45 normal-infant ApEn values.
