title: Impact of mild orthostatic stress on aortic-cerebral hemodynamic transmission: insight from the frequency domain.
abstract: High cerebral pressure and flow fluctuations could be a risk for future cerebrovascular disease. This study aims to determine whether acute systemic vasoconstriction affects the dynamic pulsatile hemodynamic transmission from the aorta to the brain. We applied a stepwise lower body negative pressure (LBNP) (-10, -20, and -30 mmHg) in 15 young men to induce systemic vasoconstriction. To elucidate the dynamic relationship between the changes in aortic pressure (AoP; estimated from the radial arterial pressure waveforms) and the cerebral blood flow velocity (CBFV) at the middle cerebral artery (via a transcranial Doppler), frequency-domain analysis characterized the beat-to-beat slow oscillation (0.02-0.30 Hz) and the intra-beat rapid change (0.78-9.69 Hz). The systemic vascular resistance gradually and significantly increased throughout the LBNP protocol. In the low-frequency range (LF: 0.07-0.20 Hz) of a slow oscillation, the normalized transfer function gain of the steady-state component (between mean AoP and mean CBFV) remained unchanged, whereas that of the pulsatile component (between pulsatile AoP and pulsatile CBFV) was significantly augmented during -20 and -30 mmHg of LBNP (+28.8% and +32.4% vs. baseline). Furthermore, the relative change in the normalized transfer function gain of the pulsatile component at the LF range correlated with the corresponding change in systemic vascular resistance (r= 0.41,P= 0.005). Regarding the intra-beat analysis, the normalized transfer function gain from AoP to CBFV was not significantly affected by the LBNP stimulation (P= 0.77). Our findings suggest that systemic vasoconstriction deteriorates the dampening effect on the pulsatile hemodynamics toward the brain, particularly in slow oscillations (e.g., 0.07-0.20 Hz).NEW & NOTEWORTHYWe characterized the pulsatile hemodynamic transmission from the heart to the brain by frequency-domain analysis. The low-frequency transmission was augmented with a mild LBNP stimulation partly due to the elevated systemic vascular resistance. A systemic vasoconstriction deteriorates the dampening effect on slow oscillations of pulsatile hemodynamics toward the brain.
authors.affiliation: Human Informatics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan; jun.sugawara@aist.go.jp.
authors.forename: Jun
authors.initials: J
authors.lastname: Sugawara
authors.affiliation: Human Informatics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan.|Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Japan.
authors.forename: Tsubasa
authors.initials: T
authors.lastname: Tomoto
authors.affiliation: Center for General Education, Aichi Institute of Technology, Toyota, Japan; and.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Imai
authors.affiliation: Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan.
authors.forename: Seiji
authors.identifier: http://orcid.org/0000-0003-1642-4644
authors.initials: S
authors.lastname: Maeda
authors.affiliation: Department of Biomedical Engineering, Toyo University, Kawagoe, Japan.
authors.forename: Shigehiko
authors.initials: S
authors.lastname: Ogoh
mesh_terms: D000328:Adult; D001011:Aorta / Q000502:physiology*; D062186:Arterial Pressure / Q000502:physiology*; D001683:Biological Clocks / Q000502:physiology; D001783:Blood Flow Velocity / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006801:Humans; D008150:Lower Body Negative Pressure / Q000379:methods*; D008297:Male; D009991:Oscillometry / Q000379:methods; D011673:Pulsatile Flow / Q000502:physiology*; D014655:Vascular Resistance / Q000502:physiology
keywords: Windkessel function; lower body negative pressure; power spectral analysis; transcranial Doppler method