Analysis of both pulsatile and streamline blood flow patterns during aerobic and resistance exercise

Blood flow-induced endothelial shear stress (ESS) during aerobic (AX) and resistance (RX) exercise can regulate endothelial function. However, non-invasive in vivo ESS estimation is normally obtained only according to Poiseuille's laws for streamline flow, rather than using Womersley's approximation for pulsatile flows. Here, we sought to determine brachial and femoral artery blood flow patterns, based on ESS, flow direction, and flow turbulence, using both pulsatile and streamline flow approximations during low- and moderate-intensity AX and RX. We performed high-resolution ultrasound imaging and Doppler peak blood flow velocity (V) measurements of the brachial and femoral arteries in eight young, healthy men during rest and two intensities of AX and RX at 40 and 70% of VO2max and 1-RM, respectively. Microhematocrit measurement was used to determine blood density (ρ) and viscosity (μ). ESS was calculated using Poiseuille's law, ESS = 2μ × SR (V/artery diameter), and Womersley's approximation, ESS = 2 Kμ × SR, where K is a function of Womersley's parameter α. Turbulence was determined using Reynolds number (Re). Re was calculated using Re = V × artery diameter × ρ/μ and normalized to resting steady-state values (nRe). ESS increases in a dose-dependent manner in the femoral and brachial arteries during both AX and RX when using either streamline or pulsatile approximations. However, our findings indicate that ESS is underestimated when using Poiseuille's law. Secondly, turbulence increases in conduit arteries with exercise intensity in a dose-dependent manner in both retrograde and antegrade flows during both AX and RX.