Increased muscle sympathetic nerve activity acutely alters conduit artery shear rate patterns

Abstract

Escalating evidence indicates that disturbed flow patterns, characterized by the presence of retrograde and oscillatory shear stress, induce a proatherogenic endothelial cell phenotype; however, the mechanisms underlying oscillatory shear profiles in peripheral conduit arteries are not fully understood. We tested the hypothesis that acute elevations in muscle sympathetic nerve activity (MSNA) are accompanied by increases in conduit artery retrograde and oscillatory shear. Fourteen healthy men (25 +/- 1 yr) performed three sympathoexcitatory maneuvers: graded lower body negative pressure (LBNP) from 0 to -40 Torr, cold pressor test (CPT), and 35% maximal voluntary contraction handgrip followed by postexercise ischemia (PEI). MSNA (microneurography; peroneal nerve), arterial blood pressure (finger photoplethysmography), and brachial artery velocity and diameter (duplex Doppler ultrasound) in the contralateral arm were recorded continuously. All maneuvers elicited significant increases in MSNA total activity from baseline (P < 0.05). Retrograde shear (-3.96 +/- 1.2 baseline vs. -8.15 +/- 1.8 s(-1), -40 LBNP, P < 0.05) and oscillatory shear index (0.09 +/- 0.02 baseline vs. 0.20 +/- 0.02 arbitrary units, -40 LBNP, P < 0.05) were progressively augmented during graded LBNP. In contrast, during CPT and PEI, in which MSNA and blood pressure were concomitantly increased (P < 0.05), minimal or no changes in retrograde and oscillatory shear were noted. These data suggest that acute elevations in MSNA are associated with an increase in conduit artery retrograde and oscillatory shear, an effect that may be influenced by concurrent increases in arterial blood pressure. Future studies should examine the complex interaction between MSNA, arterial blood pressure, and other potential modulatory factors of shear rate patterns.

Fig. 1.

Original records from 1 representative subject illustrating the elevation in muscle sympathetic nerve activity (MSNA) and the accompanying changes in brachial artery blood velocity at baseline and during lower body negative pressure (LBNP, −40 Torr; A) and cold pressor test (CPT, minute 2; B). AU, arbitrary units.

Fig. 2.

Summary data showing MSNA (A), mean arterial pressure (MAP; B), retrograde shear rate (C), and oscillatory shear index (OSI; D) at baseline (BL), during LBNP, and during recovery (Rec). *Significantly different from baseline; MSNA total activity (F = 11.45; P < 0.0001), MAP (F = 1.36; P = 0.252), retrograde shear rate (F = 10.8; P < 0.0001), and OSI (F = 14.0; P < 0.0001).

Fig. 3.

Summary data showing MSNA (A), MAP (B), retrograde shear rate (C), and OSI (D) at baseline, during CPT, and during recovery. *Significantly different from baseline; MSNA total activity (F = 9.2; P < 0.0001), MAP (F = 41.8; P < 0.0001), retrograde shear rate (F = 5.0; P = 0.005), and OSI (F = 7.0; P = 0.001).

Fig. 4.

Summary data showing MSNA (A), MAP (B), retrograde shear rate (C), and OSI (D) at baseline, during postexercise ischemia (PEI), and during recovery. *Significantly different from baseline; MSNA total activity (F = 13.6; P < 0.0001), MAP (F = 35.6; P < 0.0001), retrograde shear rate (F = 9.3; P < 0.0001), and OSI (F = 10.8; P < 0.0001).

Fig. 5.

Group changes in MSNA (A), MAP (B), and forearm vascular resistance (FVR; C) across all experimental maneuvers and their associations with alterations in retrograde shear rate (top) and OSI (bottom) (n = 10).