Supplementary
Structural MRI
Anatomical images were acquired using a MP-RAGE three-dimensional turbo field-echo sequence (137 sagittal slices of 1.1 mm thickness; in-plane resolution 1x1 mm2; TR: 6.9 s; TE: 2.8 ms; TI: 900ms; and flip angle 9o).
Phase Contrast Mapping (PCM)
Measurements were obtained with a matrix size of 320x320 (TR: 12 ms, TE: 7.44 ms, flip angle: 10o, voxel size: 0.75x0.75x8 mm3). The sequence was ECG-gated (retrospective gating, 20 frames/cycle). The measurements were performed with a velocity-encoding gradient (VENC) of 150cm/s, and images were always checked for phase aliasing and repeated if necessary.
MR Angiography (time-of-flight)
The 3D time-of-flight acquisition was performed with TR: 25 ms, TE: 3.5 ms, field of view: 200 mm, matrix: 1024x1024, SENSE factor: 2.5, 74 slices, voxel size: 0.75x0.75x1 mm3, VENC (Velocity Encoding): 100cm/s. Imaging was performed in the axial plane and was centred on the Circle of Willis.
Electrical stimulation
Functional image acquisition of the electrical stimulation paradigm used a gradient-echo, echo planar imaging (EPI) sequence (24 slices of 4.0 mm thickness; slice gap 0.1 mm; field of view: 230x230 mm2; in-plane acquired resolution: 1.8x1.8 mm2; TR: 2000 ms; TE: 35 ms; flip angle: 76o; with SENSE (SENSitivity Encoding) turned off). The slices were oriented along a line from the glabella to the posterior part of the foramen magnum. A total of 547 volumes were acquired and the first two volumes of each run were discarded to avoid saturation effects. Recording of somatosensory evoked potentials (SEP) during the same electrical stimulation task was performed outside the scanner on the same table as used in the magnet with all possible parameters kept constant (stimulus strength and electrode position). Acquisition was done using 2 active channels, reference and ground electrodes (Brain products GmbH, Munich, Germany). Electrodes were placed according to the 10-20 system and placed at C3 and C4. The SEPs were sampled with 5000Hz and post-processing including averaging of the SEPs was done using an in-house Matlab script (The MathWorks, Natick, MA, USA).
Visual and motor stimulation
The functional data for the visual and motor task where obtained similarly to that during the electrical stimulation with only the following modifications (33 axial slices, repetition time of 3000 ms, flip angle of 90o and a SENSE factor of 2). A total of 90 volumes were recorded in a boxcar setup with 9 blocks of 10 dynamics (4 active and 5 rest blocks) of 30 seconds each.
Pseudo Continuous Arterial Spin Labelling
Perfusion imaging was performed using a single time point pseudo Continuous Arterial spin Labelling (pCASL) sequence with a 2D readout, and 16 axial slices placed on the top of cerebellum and upwards were obtained with a resolution of 2.4x2.4x6 mm3, a repetition time of 4000 ms and an echo time of 14.47 ms. Interleaved label and control scans (30 pairs) were acquired with a labelling duration of 1650 ms and a post-labelling delay of 1600 ms.
For the dual echo version of the pCASL used in the hypercapnia challenge the imaging parameters were identical to the ones above with only changes to the resolution (2.8x2.8x6mm2) and the echo times (TE1: 10.11 ms, TE2: 28.65 ms) that lead to an increase in repetition time (TR: 4100 ms). The hypercapnia challenge was performed as a boxcar setup with 5 blocks of 15 dynamics (2 active and 3 rest blocks).
Supplementary tables and figures
Table S1. Measurements of the middle cerebral artery (MCA) in the patients analysed in this study (n=12).
Measurement / Side / Baseline / Placebo / Sildenafil / p-valueCircumference, mm / Right / 8.7 ± 1.5 / 8.6 ± 1.4 / 8.4 ± 1.1 / 0.46
Left / 8.7 ± 1.1 / 8.6 ± 1.1 / 8.5 ± 0.9 / 0.94
Cross sectional area, mm2 / Right / 5.4 ± 1.7 / 5.4 ± 1.9 / 5.0 ± 1.5 / 0.29
Left / 5.4 ± 1.2 / 5.4 ± 1.6 / 5.2 ± 1.3 / 0.82
Mean diameter, mm / Right / 2.6 ± 0.4 / 2.6 ± 0.4 / 2.5 ± 0.4 / 0.40
Left / 2.6 ± 0.3 / 2.6 ± 0.4 / 2.6 ± 0.3 / 0.84
Data are reported as mean ± SD. The p-value was determined using repeated measures ANOVA.
Supplementary figure 1. The mean group somatosensory evoked potentials for placebo (red) and sildenafil (blue).