We wish to show that cardiologic variability can be examined with benefit by the concepts and computer methods of chronobiology, the science (logos) of life's (bios) time (chronos) structure. From heart rate data in a recent article,1 dynamic end points are obtained to quantify health.2 On a group basis, when conventional end points applied to 2 sets of electrocardiographic records fail to separate for sudden adult death, chronobiologic end points already do so.2 Novel information not obtained by conventional location or dispersion indexes3 can be provided by the computation of the circadian and other amplitudes.4 Beyond sudden death after myocardial infarction, the importance of these amplitudes has been demonstrated in several additional cases of cardiologie interest2: (1) the amplitudes of several rhythmic components of systolic or diastolic blood pressure separate groups of human newborns with a positive versus negative family history of high blood pressure or cardiovascular diseases, or both, when the mean based on the same data does not do so; (2) in children ≥9 years old, the circadian amplitude and acrophase of blood pressure, but not the mean, separate groups at low or high risk of developing high blood pressure later in life; (3) at 15 years of age, the circadian amplitude of diastolic blood pressure, but not the mean, correlates with the thickness of the interventricular septum of the heart.
Bibliographical noteFunding Information:
From the Chronobiology Laboratories, University of Minnesota, 420 Washington Avenue, SE, Minneapolis, Minnesota 55455, Medtronic Inc., 7000 Central Avenue, NE, Minneapolis, Minnesota 55432, Karo-linska Institute, Stockholm, Sweden, and the University of Milan, Milan, Italy. This study was supported in part by Grant GM-13981 from the U.S. Public Health Service and Grant HL-40650 from the National Heart, Lung, and Blood Institute, Bethesda, Maryland, and by the Dr.h.c. Dr.h.c. Earl Bakken Fund and the Dr. Betty Sullivan Fund, Minneapolis, Minnesota. Manuscript received March 8, 1990; revised manuscript received May 25, 1990, and accepted May 28.