No abstract

Core body temperature (CBT) shows a diurnal rhythm, and the nocturnal decrease in CBT is blunted in older people. The physiological mechanisms responsible for the blunted nocturnal decrease in CBT in older people remain to be revealed. The aim of this study was to compare heat production and heat dissipation in young and old subjects during sleep, as assessed by indirect calorimetry and the distal–proximal temperature gradient (DPG) of skin temperature. A complete dataset of 9 young (23.3 ± 1.1 years) and 8 old (72.1 ± 2.5 years) females was analyzed. CBT and energy metabolism were monitored during sleep using an ingestible temperature sensor in a metabolic chamber maintained at 25 °C. Skin temperature was measured at proximal and distal parts of the body. CBT, distal skin temperature, and DPG in older subjects were higher than in young subjects. Protein oxidation was similar between the two groups, but fat oxidation was lower and carbohydrate oxidation was higher in old subjects compared to young subjects. On the other hand, energy expenditure was similar between the two age groups. Thus, the elevated CBT in older subjects was not attributed to deteriorated heat dissipation or enhanced heat production, suggesting an alternative explanation such as deteriorated evaporative heat loss in old subjects.

Study objectiveTraditionally, age-related deterioration of sleep architecture in older individuals has been evaluated by visual scoring of polysomnographic (PSG) recordings with regard to total sleep time and latencies. In the present study, we additionally compared the non-REM sleep (NREM) stage and delta, theta, alpha, and sigma wave stability between young and older subjects to extract features that may explain age-related changes in sleep.MethodsPolysomnographic recordings were performed in 11 healthy older (72.6 ± 2.4 years) and 9 healthy young (23.3 ± 1.1 years) females. In addition to total sleep time, the sleep stage, delta power amplitude, and delta, theta, alpha, and sigma wave stability were evaluated by sleep stage transition analysis and a novel computational method based on a coefficient of variation of the envelope (CVE) analysis, respectively.ResultsIn older subjects, total sleep time and slow-wave sleep (SWS) time were shorter whereas wake after sleep onset was longer. The number of SWS episodes was similar between age groups, however, sleep stage transition analysis revealed that SWS was less stable in older individuals. NREM sleep stages in descending order of delta power were: SWS, N2, and N1, and delta power during NREM sleep in older subjects was lower than in young subjects. The CVE of the delta-band is an index of delta wave stability and showed significant differences between age groups. When separately analyzed for each NREM stage, different CVE clusters in NREM were clearly observed between young and older subjects. A lower delta CVE and amplitude were also observed in older subjects compared with young subjects in N2 and SWS. Additionally, lower CVE values in the theta, alpha and sigma bands were also characteristic of older participants.ConclusionThe present study shows a decrease of SWS stability in older subjects together with a decrease in delta wave amplitude. Interestingly, the decrease in SWS stability coincided with an increase in short-term delta, theta, sigma, and alpha power stability revealed by lower CVE. Loss of electroencephalograms (EEG) variability might be a useful marker of brain age.