Figure 2
From: Effects of thermal environment on sleep and circadian rhythm
Changes of heart rate and high frequency, percentage of low frequency and ratio of low frequency to high frequency components in three conditions. The vertical line represents the standard error. *indicates the significant level after Friedman test; P <0.05. †indicates the significant level after Scheffe’s post-hoc test; P <0.05. Reprinted from Okamoto-Mizuno K, Tsuzuki K, Mizuno K, Ohshiro Y: Effects of low ambient temperature on heart rate variability during sleep in humans. Eur J Appl Physiol 2009, 105:191–197 with kind permission from Springer Science and Business Media.