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NEUROHUMORAL CONTROL OF CARDIOVASCULAR FUNCTION

Temporal asymmetries of short-term heart period variability are linked to autonomic regulation

¹Department of Technologies for Health, Galeazzi Orthopaedic Institute, University of Milan, Milan, Italy; ²Department of Clinical Sciences, Internal Medicine II, L. Sacco Hospital, University of Milan, Milan, Italy; ³Departamento de Fisiologia, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil; ⁴Department of Cardiology, S. L. Mandic Hospital, Merate, Italy; ⁵Department of Biomagnetism, Gronemeyer Institute for Microtherapy, Bochum, Germany; and ⁶Department of Medical Theory and Complementary Medicine, University of Witten/Herdecke, Herdecke, Germany

Submitted 22 February 2008 ; accepted in final form 16 May 2008

We exploit time reversibility analysis, checking the invariance of statistical features of a series after time reversal, to detect temporal asymmetries of short-term heart period variability series. Reversibility indexes were extracted from 22 healthy fetuses between 16th to 40th wk of gestation and from 17 healthy humans (aged 21 to 54, median = 28) during graded head-up tilt with table inclination angles randomly selected inside the set {15, 30, 45, 60, 75, 90}. Irreversibility analysis showed that nonlinear dynamics observed in short-term heart period variability are mostly due to asymmetric patterns characterized by bradycardic runs shorter than tachycardic ones. These temporal asymmetries were 1) more likely over short temporal scales than over longer, dominant ones; 2) more frequent during the late period of pregnancy (from 25th to 40th week of gestation); 3) significantly present in healthy humans at rest in supine position; 4) more numerous during 75 and 90° head-up tilt. Results suggest that asymmetric patterns observable in short-term heart period variability might be the result of a fully developed autonomic regulation and that an important shift of the sympathovagal balance toward sympathetic predominance (and vagal withdrawal) can increase their presence.

heart rate variability; autonomic nervous system; head-up tilt; fetal maturation; nonlinear dynamics

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