Conduit arterial wave reflection promotes pressure transmission but impedes hydraulic energy transmission to the microvasculature

Abstract

With aging, a reduction in the stiffness gradient between elastic and muscular arteries is thought to reduce wave reflection in conduit arteries, leading to increased pulsatile pressure transmission into the microvasculature. This assumes that wave reflection limits pressure transmission in arteries. However, using a computational model, we showed that wave reflection promotes pulsatile pressure transmission, although it does limit hydraulic energy transmission. Increased microvascular pulse pressure with aging is instead related to decreasing arterial compliance.

Age, sex, and the vascular contributors to cerebral pulsatility and pulsatile damping

“…Our data indicate that carotid wave reflection (RIx), but not aortic:carotid stiffness ratio, carotid diameter or the forward traveling “suction” wave (W 2 ), is a prominent vascular contributor to cerebral pulsatile damping in the MCA. Wave reflections, although often portrayed in a negative light ( 10 ), reduce blood flow pulsatility without altering mean flow, thereby helping attenuate blood flow pulsatility en route to sensitive end-organs ( 17 , 21 , 31 ). Our findings are consistent with the notion that wave reflections at the carotid-cerebral interface protect the brain from pulsatile energy ( 27 ).…”

“…The area under the dP/dt × dU/dt curve represents the energy transfer of the wave ( 13 , 45 ) and is used to calculate the energy of each wave component (W 1 , W 2 , NA). W 1 represents a forward traveling energy wave generated by the left ventricle during early systole that increases pulsatility via accelerating blood flow and increasing pressure ( 2 ); NA immediately following W 1 is a backward traveling compression wave stemming from reflected waves from the periphery that can increase pressure pulsatility (by increasing pressure) but decrease blood velocity pulsatility (by decelerating flow) ( 2 , 21 ). NA measured in the carotid has been suggested to reflect cerebrovascular tone ( 2 ).…”

“…Based on the current literature there are several potential factors that may influence cerebral pulsatility and pulsatile damping (see Supplemental Table S1; all supplemental material is available at: https://doi.org/10.6084/m9.figshare.12943217 ), including vascular structure (wall thickness, diameter [ 28 , 40 )], vessel wall properties [stiffness ( 26 )], and regional hemodynamics [pulse pressure, energy wave dynamics ( 21 , 26 )]. Therefore, the purpose of this study was to examine vascular contributors to 1) cerebral pulsatility and 2) cerebral pulsatile damping from the common carotid to middle cerebral artery (MCA) in males and females across the aging spectrum.…”

Impact of acute changes in blood pressure and arterial stiffness on cerebral pulsatile haemodynamics in young and middle‐aged adults

“…Reductions in carotid wave reflection would be expected to reduce pulsatile damping (Kondiboyina et al, 2020;Lefferts et al, 2020). (Yonai et al, 2010) and cognitive activity (Heffernan et al, 2015).…”

“…Forward‐travelling energy waves can be partly reflected (Bleasdale et al., 2003) by cerebral vessels through a combination of arterial tapering, bifurcations, tortuosity and functional vasomotion. Partial wave reflection in this setting prevents forward‐travelling waves from penetrating smaller cerebral vessels and increasing blood flow pulsatility (Hughes et al., 2014; Kondiboyina et al., 2020; Mitchell et al., 2011). As such, greater transmission of pulsatile energy from arterial stiffening increases the reliance on the cerebrovasculature to damp cerebral blood flow pulsatility.…”