Effects of posture on shear rates in human brachial and superficial femoral arteries

Abstract

Shear rate is significantly lower in the superficial femoral compared with the brachial artery in the supine posture. The relative shear rates in these arteries of subjects in the upright posture (seated and/or standing) are unknown. The purpose of this investigation was to test the hypothesis that upright posture (seated and/or standing) would produce greater shear rates in the superficial femoral compared with the brachial artery. To test this hypothesis, Doppler ultrasound was used to measure mean blood velocity (MBV) and diameter in the brachial and superficial femoral arteries of 21 healthy subjects after being in the supine, seated, and standing postures for 10 min. MBV was significantly higher in the brachial compared with the superficial femoral artery during upright postures. Superficial femoral artery diameter was significantly larger than brachial artery diameter. However, posture had no significant effect on either brachial or superficial femoral artery diameter. The calculated shear rate was significantly greater in the brachial (73 +/- 5, 91 +/- 11, and 97 +/- 13 s(-1)) compared with the superficial femoral (53 +/- 4, 39 +/- 77, and 44 +/- 5 s(-1)) artery in the supine, seated, and standing postures, respectively. Contrary to our hypothesis, our current findings indicate that mean shear rate is lower in the superficial femoral compared with the brachial artery in the supine, seated, and standing postures. These findings of lower shear rates in the superficial femoral artery may be one mechanism for the higher propensity for atherosclerosis in the arteries of the leg than of the arm.

Fig. 1

Effects of posture on heart rate (A) and mean arterial pressure (B). Values are means ± SE. †P < 0.05, significantly different than supine posture; ‡P < 0.05, significantly different than seated posture. bpm, Beats/min.

Fig. 2

Effects of posture on blood flow (A) and conductance (B) in the brachial (black bar) and superficial femoral (white bar) arteries. Values are means ± SE. *P < 0.05, significant difference between brachial and superficial femoral arteries.

Fig. 3

Effects of posture on minimum blood velocity (A), maximum blood velocity (B), mean blood velocity (C), and diameter (D) in the brachial (black bar) and superficial femoral (white bar) arteries. Values are means ± SE. *P < 0.05, significant difference between brachial and superficial femoral arteries; †P < 0.05, significantly different than supine posture; ‡P < 0.05, significantly different than seated posture.

Fig. 4

Effects of posture on minimum (Min) shear rate (A), maximum (Max) shear rate (B), mean shear rate (C), and oscillatory shear index (D) in the brachial (black bar) and superficial femoral (white bar) arteries. Values are means ± SE. *P < 0.05, significant difference between brachial and superficial femoral arteries; †P < 0.05, significantly different than supine posture; ‡P < 0.05, significantly different than seated posture.