Reactive bradycardia with fever-
**Core Concept**
Reactive bradycardia is a physiological response to certain stimuli, such as fever, stress, or pain, where the body's parasympathetic nervous system dominates over the sympathetic nervous system, leading to a decrease in heart rate. This response is mediated by the vagus nerve and involves the release of acetylcholine, which acts on the sinoatrial (SA) node to slow down the heart rate.
**Why the Correct Answer is Right**
During fever, the hypothalamus acts as the body's thermostat, increasing the body temperature set point. To counteract this, the body's parasympathetic nervous system is activated, leading to a decrease in heart rate as part of the body's attempt to conserve heat. The vagus nerve releases acetylcholine, which acts on the SA node to decrease the heart rate, resulting in reactive bradycardia.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe a physiological response to fever. Bradycardia is not a direct result of the fever itself, but rather a compensatory response to the increased body temperature.
**Option B:** This option is incorrect because it implies that the heart rate increase is a direct result of the fever, which is not the case. Fever actually leads to a decrease in heart rate, not an increase.
**Option C:** This option is incorrect because it does not specify the underlying mechanism of reactive bradycardia, which involves the parasympathetic nervous system and the release of acetylcholine.
**Clinical Pearl / High-Yield Fact**
Reactive bradycardia can be a normal response to fever, stress, or pain, and is not necessarily a cause for concern. However, if the heart rate remains persistently low or is accompanied by other symptoms such as hypotension or altered mental status, further evaluation is warranted.
**Correct Answer:** C.