Abstract
The ageing process is associated with sleep and circadian rhythm (SCR) frailty, as well as greater sensitivity to chronodisruption. This is essentially due to reduced day/night contrast, decreased sensitivity to light, napping and a more sedentary lifestyle. Thus, the aim of this study is to develop an algorithm to identify a SCR phenotype as belonging to young or aged subjects. To do this, 44 young and 44 aged subjects were recruited, and their distal skin temperature (DST), activity, body position, light, environmental temperature and the integrated variable TAP rhythms were recorded under free-living conditions for five consecutive workdays. Each variable yielded an individual decision tree to differentiate between young and elderly subjects (DST, activity, position, light, environmental temperature and TAP), with agreement rates of between 76.1% (light) and 92% (TAP). These decision trees were combined into a unique decision tree that reached an agreement rate of 95.3% (4 errors out of 88, all of them around the cut-off point). Age-related SCR changes were very significant, thus allowing to discriminate accurately between young and aged people when implemented in decision trees. This is useful to identify chronodisrupted populations that could benefit from chronoenhancement strategies.
Highlights
The circadian system is composed of a hierarchically organized set of structures which are responsible for generating circadian rhythms and synchronizing them to the environmental conditions
Thermoregulation is impaired due to a reduction in the efficacy of heat retention, and to heat loss caused by impaired cutaneous vasoconstriction and vasodilatation mechanisms, together with a reduction in thermal sensitivity, which is more pronounced with warm temperatures[19]. The results of these thermoregulatory changes are a reduction in mean core body temperature, a phase advance and a decrease in amplitude of the core body temperature rhythm[19,20], whereas distal skin temperature (DST) presents higher mean values, especially during the daytime, and a phase advance[22]
In young participants, daytime is characterized by a decrease that bottoms out in the late evening, corresponding to the “wake maintenance zone”, while in aged participants, the lowest daytime values appeared in the morning, increasing until they reached a plateau (33.6 °C) from 16:00 to 22:00 h
Summary
The circadian system is composed of a hierarchically organized set of structures which are responsible for generating circadian rhythms and synchronizing them to the environmental conditions. With regard to sleep, aged people tend to wake up earlier and experience more fragmented sleep and daytime sleepiness than other adults They show higher interdaily stability[15,16] and higher activity values during night-time hours, which is associated with lower sleep efficiency[17]. Thermoregulation is impaired due to a reduction in the efficacy of heat retention, and to heat loss caused by impaired cutaneous vasoconstriction and vasodilatation mechanisms, together with a reduction in thermal sensitivity, which is more pronounced with warm temperatures[19] The results of these thermoregulatory changes are a reduction in mean core body temperature, a phase advance and a decrease in amplitude of the core body temperature rhythm[19,20], whereas distal skin temperature (DST) presents higher mean values, especially during the daytime (related to daytime sleepiness21), and a phase advance[22]. Taking into account that at least part of these negative effects on circadian health could be reduced by prompting changes in the habits of the elderly, the aim of this study is to develop an algorithm to identify SCR frailty
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