Question

Which of the following is true

Select one:

a. Vasomotor syncope may occur when you lie down after standing up for a long time

b. Vasomotor syncope is caused by increased venous return, which causes excessive stimulation of the baroreceptor reflex

c. Vasovagal syncope occurs in response to a disturbing situation that causes over-stimulation of the SNS

d. Contraction of the lower leg muscles helps to prevent vasomotor syncope because it increases the pressure gradient from the peripheral veins to the right atrium

Answer 1

Question

Which of the following is true?

Select one.

Answer: d) Contraction of lower leg muscles helps to prevent vasomotor syncope because it increases the pressure gradient from the peripheral veins to the right atrium.

Explanation: Syncope is sudden loss of consciousness for a brief duration of time due to decreased blood supply to the brain. It is not associated with any neurological deficit. This transient decrease in the blood supply to the brain is due to sudden fall in the blood pressure.

Contraction of lower leg muscles like gastrocnemius and soleus ( calf muscles) during locomotor activities like running and walking pumps the venous blood against the gravity with sufficient pressure to the right atrium of the heart, maintaing the venous return and subsequently the blood pressure of the body. Thus, contraction of the calf muscles helps to prevent the vasomotor syncope by maintaining venous return and the blood pressure to optimum levels. Hence, calf muscles particularly the soleus is known as the "peripheral heart" of the body.

Other options:

a) Vasomotor syncope may occur when you lie down after standing up for a long time.

This is an incorrect statement as vasomotor syncope may occur when you suddenly stand up after lying down for a long time as the blood pressure suddenly drops when you stand up instantly from lying down position. This sudden fall in the blood pressure decreases the blood supply to the brain causing syncope.

b) Vasomotor syncope is caused by increased venous return, which causes excessive stimulation of the baroreceptor reflex.

This is an incorrect statement as vasomotor syncope is caused by decreased venous return which causes firing of nerve signals from the baroreceptors located in the right atrium which sends signals to the vasomotor center of the medulla of brain stem. From the medulla of the brain stem inhibitory signals are send to the blood vessels decreasing the sympathetic vascular tone which causes vasodilatation and sudden drop in the blood pressure which might lower down the blood flow to the brain causing syncope.

c) Vasovagal syncope occurs in response to a disturbing situation that causes over-stimulation of the SNS.

This is an incorrect statement as vasovagal syncope occurs in response to disturbing situation that causes under- stimulation of the SNS (sympathetic nervous system). Disturbing situation like any sudden emotional shock or potentially any emotional and overwhelming situation can stimulate the brain stem to cause over stimulation of parasympathetic nervous system ( vagal tone ) or under stimulation of sympathetic vascular tone.

Over-stimulation of parasympathetic nervous system (vagal tone) decreases the heart rate and contractility of the heart causing sudden fall in the blood pressure. Under-stimulation of sympathetic vascular tone causes vasodilatation which again causes sudden fall in the blood pressure. Thus, the sudden fall in the blood pressure due to increased vagal and decreased sympathetic vascular tone causes decreased blood flow to the brain causing syncope.