When sympathetic nerve fibers are stimulated, which vital sign is elevated?

When sympathetic nerve fibers are stimulated, the heart rate is elevated primarily due to the activation of the sympathetic nervous system, which is part of the body's "fight or flight" response. This system releases catecholamines such as epinephrine and norepinephrine, which act on the heart to increase the rate of contraction and thereby raise the heart rate.

Increased heart rate can also occur alongside elevated blood pressure and respiratory rate; however, the question specifically asks about the vital sign that is most directly and consistently elevated due to sympathetic stimulation. While blood pressure may also rise due to increased cardiac output and vasoconstriction, and respiratory rate may increase to meet heightened oxygen demands, heart rate is the most directly linked response to sympathetic activation.

Temperature does not typically rise as an immediate response to sympathetic stimulation; instead, it is more influenced by metabolic processes and other factors. Thus, selecting heart rate reflects the most accurate physiological change when sympathetic nerves are activated.