Reflex tachycardia is defined as:

Reflex tachycardia is indeed characterized as a temporary increase in heart rate that occurs in response to a decrease in blood pressure. This physiological response is primarily mediated by the autonomic nervous system, particularly the sympathetic branch, which activates when there is a drop in blood pressure. The body recognizes the need to maintain adequate blood flow and oxygen delivery to vital organs, hence the heart increases its rate to compensate for the reduced pressure.

When blood pressure falls, baroreceptors located in the carotid sinus and aortic arch detect this change. In turn, they send signals to the central nervous system, which triggers the heart to beat faster in an attempt to restore normal pressure levels. This process is a protective mechanism ensuring that blood circulation remains sufficient during episodes such as dehydration, blood loss, or certain medical conditions.

The other options do not accurately capture the essence of reflex tachycardia, as they describe different physiological responses. For instance, a permanent increase in heart rate does not fit the definition, and while stress can elevate heart rate, it is not specifically linked to the mechanism of reflex tachycardia. Additionally, a decrease in heart rate due to increased blood volume does not relate to reflex tachycardia, which is fundamentally about increasing