Complexity Changes in Human Wrist Temperature Circadian Rhythms through Ageing - Foundations on Natural and Artificial Computation - page 400

Complexity Changes in Human Wrist
Temperature Circadian Rhythms through
Ageing

R. Marin 1 , ,M.Campos 1 ,A.Gomariz 1 ,A.Lopez 1 ,M.A.Rol 2 ,
and J.A. Madrid 2

1 Computer Science Faculty, University of Murcia, Spain
2 Chronobiology Laboratory, Department of Physiology, University of Murcia, Spain

Abstract. Circadian rhythms are cycles in physiological processes that
have a near-daily frequency. The wrist skin temperature has proven to
be a good marker of circadian rhythmicity. In this paper we attempt
to establish whether complexity changes in human circadian rhythms
in ageing can be assessed through phase variability in individual wrist
temperature records. To this end, we propose some phase complexity
measures that are based on Lempel-Ziv complexity, Approximate En-
tropy, instantaneous phase, Hilbert transform and a complex continuous
wavelet transform. A sample consisting of 53 healthy subjects has been
studied. Our experimental results consistently show that a significant
decrease in phase complexity happens when ageing.

Keywords: circadian rhythms, wrist temperature, complexity measures,
age-dependent changes.

1 Introduction

Chronobiology is a scientific discipline that deals with the study of the biologi-
cal rhythms and their underlying mechanisms. Biological processes that repeat
themselves approximately every 24 hours are called daily or circadian rhythms.
Most physiological, behavioural and biochemical variables, such as body tempe-
rature, blood pressure, sleep, feeding and neuroendocrine factors exhibit circa-
dian rhythmicity. Circadian rhythms under artificially constant environmental
conditions run with a period slightly different from 24 hour; however, under
natural conditions their phase and period entrain to light dark cycle [13,20].
The circadian system of mammals is composed by a network of structures
responsible for the generation and synchronization of circadian rhythms to en-
vironment. It is composed of a central pacemaker, located in the suprachias-
matic nucleus of hypothalamus (SCN) and several peripheral clocks. At mole-
cular level, circadian clocks are composed of a set of genes and proteins that
The authors wish to thank the Seneca Foundation, the Ministry of Science and
Innovation and the Instituto de Salud Carlos III for their financial support of this
study through the projects 08853/PI/08, TIN2009-14372-C03-01, TRA2009-0141,
RETICEF (RD06/0013/0019) and BFU 2010-21945-CO1.