Mean magnitude and phase of transfer function (bold line) and standard deviation (gray shading) from arterial input to cervical spinal cerebrospinal fluid (CSF) flow, A and B, at the level of C3–C4, and to aqueductal CSF flow, C and D, of elderly (gray line) and young (black line) groups as a function of frequencies.

<p>Significant differences of the magnitude and phase as detected by the Mann-Whitney test are depicted at the respective frequency. At 2 Hz the phases of the arterial-to-aqueductal flows hardly overlap <b>D</b>, resulting in an asymptotic 2-tailed p-value of .</p

Juxtaposed frequency components (Hz) of flow in the elderly (gray, left) and young groups (black, right) illustrated using Boxplots.

<p>The upper and lower edges of each box represent the 25th and 75th percentiles, respectively. The center line represents the median and the whiskers extend to the most extreme data points not considered outliers, which are plotted individually (+). In each subfigure, frequency components are separated by dotted lines. In <b>A</b>, the first to the 10th frequency components of the combined flow rates in the carotid and the vertebral arteries are plotted, in <b>B</b>, the first to the seventh frequency components of the cerebrospinal fluid (CSF) flow rate in the cervical spinal canal at the level of C3–C4 and in <b>C</b>, the first to the 5th frequency components of CSF flow rate in the aqueduct. Curly brackets indicate significant differences of the respective frequency component's magnitudes detected with the Mann-Whitney test. Note that the fourth frequency components of the arterial flows <b>A</b> hardly overlap, thus the corresponding asymptotic 2-tailed p-value is 0.0001.</p

Legend of waveform feature points (Fig. 1) in the corresponding compartments.

<p>Legend of waveform feature points (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037502#pone-0037502-g001" target="_blank">Fig. 1</a>) in the corresponding compartments.</p

Feature points with corresponding standard deviation (SD) error bars and piecewise cubic Hermite interpolated polynomial fits [<b>22</b>] of arterial and cerebrospinal fluid (CSF) flow in the elderly (gray line) and young groups (dashed black line) as a function of time.

<p>The left column <b>A</b>–<b>C</b> shows results for females, right for males <b>D</b>–<b>F</b>. Top row: Sum of mean (over subjects) normalized flow velocity curves in the left and right common carotid arteries and the left and right vertebral arteries. Middle row: Mean CSF flow in the cervical spinal canal at the level of C3–C4 (between the third and fourth vertebrae). Positive values correspond to flow in cranial direction. Bottom row: Mean CSF flow in the aqueduct (positive values: cranial flow). In panels <b>A</b> and <b>D</b>, the feature points are labeled ar1–ar6, in <b>B</b> and <b>E</b> sp1–sp6 and in <b>C</b> and <b>F</b> aq1–aq5 (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037502#pone-0037502-t002" target="_blank">Table 2</a>).</p

Cross-correlation of arterial input to cervical spinal A (at the level of C3–C4) and to aqueductal B cerebrospinal fluid flow, mean (bold line) and standard deviation (gray shading) of elderly (gray line) and young (black line) groups' results.

<p>The vertical lines depict the mean delays from the maximum systolic peak flows to the maximum caudal flows in either CSF compartment.</p

Mean and standard deviation (SD) of subjects' age, body mass index (BMI) and height, as well as aqueductal stroke volume [101] and average flow rate [11], (1).

<p>The average (avg) spinal CSF and systolic (syst) arterial flows used to normalize the data are listed. Significant differences and correlations are summarized below.</p><p>Difference between female and male volunteers:</p>*<p>P = 0.033;</p>**<p>P = 0.028.</p><p>Correlation in entire population of height with age  = 0.44, P = 0.04; and sex  = 0.75, P0.0001.</p><p>Correlation of height with sex in young group  = 0.87, P = 0.0006; and in elderly group  = 0.70, P = 0.017.</p

Additional file 1: of Unconscious physiological response of healthy volunteers to dynamic respiration-synchronized couch motion

The questionnaires and their results. (PDF 1275ย�kb