Emergency Medical Technician (EMT) Intermediate Practice Exam

What physiologic response causes tachycardia in a patient experiencing shock?

1. Increased blood volume

2. Sympathetic nervous system activation

3. Beta1 receptor stimulation

4. Pain response

The correct answer is: Beta1 receptor stimulation

The physiological response that causes tachycardia in a patient experiencing shock is primarily due to sympathetic nervous system activation. During shock, the body recognizes a critical drop in blood flow and oxygen delivery, triggering the sympathetic nervous system as a compensatory mechanism. This activation releases catecholamines, such as adrenaline (epinephrine) and norepinephrine, which stimulate the heart to increase its rate and contractility in an effort to maintain adequate blood flow to vital organs. Increased heart rate, or tachycardia, is a direct result of this activation. The body attempts to compensate for the reduced perfusion and maintain homeostasis by enhancing cardiac output. This response may also prepare the body to respond to potential threats or injuries, effectively redirecting blood flow to essential areas. While beta1 receptor stimulation does contribute to increased heart rate by enhancing cardiac contractility, it is more of a downstream effect of the overall sympathetic nervous system activation, not the primary trigger in response to shock. The increase in blood volume is not typically present during shock, especially in cases of hypovolemic shock where blood volume is actually decreased. Although pain can influence heart rate, it is not the primary physiologic response in the context of shock.