Effects of geomagnetic disturbance on heart rate variability (HRV), the 1/f fractal scaling in particular, are being assessed in adults living at high latitude, where magnetic storms are more frequent and more intense than at lower latitudes. The latter may constitute a signal or a proxy, and possibly a mechanism underlying both undesirable and desirable effects, depending upon circumstances yet to be elucidated. Any circadecadal stage-dependence of morbidity and/or mortality from certain conditions such as myocardial infarctions remains to be studied in both adult and pediatric populations. Further work could thus examine whether any associations of geomagnetic disturbances may account, at least in part, through effects upon the circulation, for long-term infra-annual changes, possibly anchored in the population's gene pool, observed in a number of anthropologic measurements at birth as well as in other population statistics. In order to assess the development of several chronome components of the electrocardiogram (ECG), around-the-clock ambulatory ECG were recorded from 19 infants (25 days-3 months of age), 22 children (3-9 years of age), 18 boys and girls (10-14 years of age), pubertal boys (15-20 years of age), and 10 young men (21-29 years of age). Time- and frequency-domain measures of HRV were obtained by spectral analysis, using the maximal entropy method (MEM). The frequency of detection of the circadian, circasemidian and circaoctohoran components, with periods of about 24, 12 and 8 h, respectively, was compared among the five groups for several HRV endpoints, notably 1/f fractal scaling, total spectral power within a 5-min span, and its distribution into several frequency regions. A circadian component is already detectable in a sizeable proportion of infants and children for most of the HRV indices considered. The incidence of detection of the circadian component increases with age for the spectral power in different frequency regions, notably around 10.5 s ("LF") and around 3.6 s ("HF"); it peaks around puberty for I If in our data; and it did not detectably change with age for the total spectral power. Similar changes with age are not observed for the circasemidian or circaoctohoran components. The latter characterizes primarily 1/f and less so the about 3.6 s power ("HF"). Several aspects of the HRV chronome may thus develop differently as a function of age. In 2000, we began a community-based study named "Longitudinal Investigation of Longevity and Aging in Hokkaido County (LILAC study)". The ambulatory blood pressure (BP)of middle-aged subjects, aged 40-74 years, was monitored 7-day/24-h, and the cardiovascular and neurobehavioral functions of elderly people above 75 years were evaluated. Our goal was the prevention of stroke and myocardial infarction and the decline in cognitive function of the elderly in a community. Of 115 elderly people recruited in a longitudinal community-based study in 2000, 72 completed yearly follow-ups in 2002. A cardiovascular score based on BP, pulse wave velocity, and 1-h ECG-based HRV endpoints served to distinguish between normal, mildly disordered, or disordered participants. A comparison of cognitive function in 2002 vs. 2000, assessed with the MMSE, HDSR, the Up & Go and Functional Reach tests, gauged any effect of social intervention. Cognitive function was maintained or improved, especially for people suffering from hypertension, tachycardia, or a decreased HRV, suggesting that cardiovascular function is a major factor affecting cognitive function. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
