CW, UCW and Sit: 20min during the state period). The analysis of
the difference between the cold and warm conditions was carried
out by paired t-test. One-sample t-tests were used to analyze the differences
between the delta value and baseline. The effects of the two
factors (ambient temperature and sleep stage) on changes of autonomic
activities were assessed by two-way mixed design ANOVA
(two ambient temperatures two sleep stages) [33]. When pinpointed
by a significant F-statistic, the differences between states
were isolated using post hoc comparisons and Fisher’s least-significant
difference test. As LF% in cycle 2 in warm conditions was not
normally distributed, the comparisons of LF% between cycle 2 and
cycle 3were assessed by Friedman two-way analysis.When a statistically
significant interaction was identified, simple main-effect
analysis of factor was applied. The correlation between changes in
autonomic activities and NBT was examined by a simple linear
regression model. P < 0.05 was considered significant