Question

While walking to work, Mio has a sudden onset of dizziness and feels faint. In addition, she experiences diaphoresis (excessive sweating) and palpitations (rapid, fluttering heart). When she arrives at her office, her concerned colleagues call an ambulance.

In the emergency department, the nurse and doctor make the following notes in Mio’s record:

55-year-old female, blood pressure = 162/110 mm Hg, on metoprolol, furosemide, propafenone.

Blood pressure dropped upon standing to 102/65 mmHg, and palpitations were observed.

After receiving a 1L fluid infusion, Mio is discharged with the following patient plan: metoprolol adjusted to twice a day, discontinued furosemide and propafenone. Prescribed meclizine.

However, over a period of six weeks, Mio’s symptoms become progressively worse. Mio experiences an increased number of dizzy spells, and the degree of dizziness she experiences worsens. In addition, Mio falls several times. After her last fall at the grocery store, she is admitted to the hospital.

Since Mio’s primary symptom is dizziness, her doctors must take into account several body systems that may influence/cause Mio’s dizziness symptoms.

Part A

Five days after being released from the hospital, Dr. Dorff contacts Mio to see how she is doing. Mio indicates her dizziness persists during attempts to stand. Upon hearing Mio’s response, Dr. Dorff indicates he will do some research and be in touch. Dr. Dorff consults with a thirty-year-practicing neuroendocrinologist to attempt to find some answers. Together, the doctors review Mio’s symptoms (hypertension, tachycardia, palpitations and diaphoresis) and treatments. The neuroendocrinologist immediately identifies a potential cause for Mio’s symptoms, but does not say anything because he recognizes a teaching moment for Dr. Dorff.

“Dr. Dorff, let’s review the mechanism by which the sympathetic nervous system maintains appropriate blood flow to the brain during attempts to stand. A lack of blood flow to the brain may explain Mio’s dizziness,” says Dr. Rodriguez.

Place the sequence of events in the appropriate order to demonstrate the mechanism by which the sympathetic nervous system contributes to normal blood flow to the brain upon standing.

Reset Help Norepinephrine binds beta-1 receptors on Concentration of norepinephrine released to the heart and blood vessels by sympathetic nervous neurons Upon standing blood drops to Increased heart rate Sympathetic activity increases and parasympathetic Beta-1 and the lower portionsthe heart cells and and contractility and vasoconstriction of alpha-1 receptors of the body; blood alpha-1 receptors increases; acetylcholine blood vessels (except in activate pressure to the on smooth muscle activity decreases. brain decreases. release to the heart by parasympathetic neurons decreases. the legs) is observed cells lining the blood vessels Increased cardiac output and peripheral resistance resulting in increased blood pressure is observed Arterial baroreceptors decrease the frequency of action potentials conducted to the cardiovascular control center A reclined person stands up Blood perfusion to the brain is normal

Answer 1

1. Upon standing, blood pressure drops, BP to brain decreases
2. Arterial baroreceptors decrease the action potential frequency in CVS control centr e
3. Sympathetic activity increases, parasympathetic decreases
4. Concentration of NE to heart and blood vessels increases, Ach decreases
5. Beta 1 and alpha 1 are activated
6. NE binds beta 1 on heart, alpha 1 in smooth muscles
7. Increased heart rate and contractility
8. Increased cardiac output and increased BP