Alterations in the rheological artery during rhythmic thigh flow profile in conduit femoral muscle contractions in humans

The present study examined the rheological blood velocity profile in the conduit femoral artery during rhythmic muscle contractions at different muscle forces. Eight healthy volunteers performed one-legged, dynamic knee-extensor exercise at work rates of 5, 10, 20, 30, and 40 W at 60 contractions per minute. The time and space-averaged, amplitude-weighted mean ( V-mean) and maximum (V-max) blood flow velocities in the common femoral artery were measured during the cardiosystolic phase (CSP) and cardiodiastolic phase (CDP) by the Doppler ultrasound technique. The V-max /V-mean ratio was used as a flow profile index, in which a ratio of similar to 1 indicates a m m flat velocity flow profile and a ratio significantly > 1 indicates a parabolic velocity flow profile ' At rest, the V-max / V-mean ratio was similar to 1.3 and similar to 1.8 during the CSP and CDP, respectively. The V-max/V-mean ratio was higher (p < 0.01) during the CDP than during the CSP, both at rest and at all work rates. The V-max/V-mean ratio during the CSP was higher Max (p < 0.01) at 30 and 40 W compared to at rest. The V-max/V-mean ratio during the CDP was lower (p < 0.05) at 5 and 10 W compared to at rest. There was a positive linear correlation between blood flow and incremental work rates during both the CSP and CDP, respectively. Thus under resting conditions, the findings indicate a steeper parabolic velocity profile during the CDP than during the CSR The velocity profile during the CDP furthermore shifts to being less steep during rhythmic muscle contractions at lower intensities, but to being reelevated and normalized as at rest during higher intensities. The steepness of the parabolic velocity profile observed during the CSP at rest increased during muscle contraction at higher intensities. In conclusion, the blood velocity in the common femoral artery is parabolic both at rest and during exercise for both the CSP and CDP, indicating the persistence of laminar flow. The occurrence of any temporary slight disturbance or turbulence in the flow at the sight of measurement in the common femoral artery does consequently not induce a persisting disturbed and fully flat plug-like velocity profile. Instead, the steepness of the parabolic velocity profile is only slightly modified, whereby blood flow is not impaired. Thus the blood velocity profile, besides being influenced by the muscle contraction-relaxation induced mechanical impedance, seems also to be modulated by the cardiac- and blood pressure-phases, consequently influencing the exercise blood flow response.