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. 2019 Oct 29;9:15510. doi: 10.1038/s41598-019-52029-4

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Comparison of flow velocity parameters between the waking and sleep stages. Subjects were divided into two subgroups according to age (≤50 and >50 years). In each subgroup, the mean flow velocity (MFV) increased (panel A), the pulsatility index (PI) decreased (panel B), the variance of MFV increased (panel C), and the absolute power of the peak in the very-low–frequency (VLF) band (panel D) and the relative power of the VLF band in the spectral density analysis (panels E and F) significantly increased during the sleep status, compared to the waking status. The sleep/waking ratios of these parameters were not significantly different between the age subgroups. Horizontal lines above the bars denote standard errors. Abbreviations: ULF, ultra-low frequency; LF, low frequency; HF, high frequency.