A patient who has been admitted into the Emergency Room with traumatic blood los

Question

A patient who has been admitted into the Emergency Room with traumatic blood loss is undergoing an assessment. What integrated physiological response is most likely happening to compensate for the blood loss?

a) A decrease in mean arterial pressure (MAP) causes a decrease in baroreceptor activity and decreases sympathetic response/heart rate (HR) and systemic vascular resistance

b) An increase in MAP causes a decrease in vagal activity and a decrease in sympathetic response and contractility

c) A decrease in MAP causes a decrease in baroreceptor activity and an increase in sympathetic response and contractility/HR

d) An increase in MAP causes a decrease in vagal activity and an increase in sympathetic response and systemic vascular resistance

e) None of the above makes physiological sense

Explanation / Answer

Option C) A decrease in MAP causes a decrease in baroreceptor activity and an increase in sympathetic response and contractility/HR

Initially, the loss of volume causes an arterial baroreceptor response. The baroreceptors fire at a certain rate, constantly; as arterial pressure decreases, the firing rate also decreases, and this regulates the central descending control of the autonomic nervous system. Thus with blood loss there is an activation of a normal moment-to-moment control of blood pressure, which causes a reflexive decrease in vagal tone and increase in sympathetic tone. The heart rate rises and the systemic vascular resistance increases. This continues for a while. One can compensate for the loss of 10-15% of blood volume with this mechanism, and the cardiac output will not suffer very much.

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