Acute isometric and dynamic exercise do not alter cerebral sympathetic nerve activity in healthy humans

Abstract

The impact of physiological stressors on cerebral sympathetic nervous activity (SNA) remains controversial. We hypothesized that cerebral noradrenaline (NA) spillover, an index of cerebral SNA, would not change during both submaximal isometric handgrip (HG) exercise followed by a post-exercise circulatory occlusion (PECO), and supine dynamic cycling exercise. Twelve healthy participants (5 females) underwent simultaneous blood sampling from the right radial artery and right internal jugular vein. Right internal jugular vein blood flow was measured using Duplex ultrasound, and tritiated NA was infused through the participants' right superficial forearm vein. Heart rate was recorded via electrocardiogram and blood pressure was monitored using the right radial artery. Total NA spillover increased during HG (P = 0.049), PECO (P = 0.006), and moderate cycling exercise (P = 0.03) compared to rest. Cerebral NA spillover remained unchanged during isometric HG exercise (P = 0.36), PECO after the isometric HG exercise (P = 0.45), and during moderate cycling exercise (P = 0.94) compared to rest. These results indicate that transient increases in blood pressure during acute exercise involving both small and large muscle mass do not engage cerebral SNA in healthy humans. Our findings suggest that cerebral SNA may be non-obligatory for exercise-related cerebrovascular adjustments.

Keywords: Cerebral blood flow; noradrenaline spillover; sympathetic nervous activity.

Figure 1.

Schematic of the experimental protocol. Participants were instrumented with IJV, arterial (i.e., ART), and superficial vein of the forearm (i.e., ANTE) catheters upon arrival to the laboratory. The experimental protocol began with a 45-min infusion of tritiated NA (to steady-state) that continued throughout the entire protocol. The participants were then asked to perform a 2-min isometric handgrip test at 30% of their maximal voluntary contraction, which was followed by a 3-min post-exercise circulatory occlusion test. After a 10-min recovery, participants then performed a submaximal supine cycling exercise test that consisted of three stages for both male (75 W, 100 W, 125 W) and female (50 W, 75 W, 100 W) participants.

Figure 2.

Isometric handgrip exercise on noradrenaline spillover and clearance. Mean ± SD and individual data for total noradrenaline spillover (Panel a; n = 11), total noradrenaline clearance (Panel b; n = 12), and brain noradrenaline spillover (Panel c; n = 10 [Rest], 9 [HG], 9 [PECO]). Statistical comparisons that yielded P < 0.05 are illustrated on the Figure.

Figure 3.

Supine cycling exercise on noradrenaline spillover and clearance. Mean ± SD and individual data for total noradrenaline spillover (Panel a; n = 11 [Rest], 10 [EX1], 9 [EX2], 8 [EX3]), total noradrenaline clearance (Panel b; n = 11 [Rest], 9 [EX1], 9 [EX2], 8 [EX3]), and brain noradrenaline spillover (Panel c; n = 9 [Rest], 7 [EX1], 5 [EX2], 5 [EX3]). Statistical comparisons that yielded P < 0.05 are illustrated on the Figure.