MCQ's: Cardio Physiology

Question 1

At birth:

A. The foramen ovale closes because of a ?

B. The ductus arteriosus closes because of a ?

C. Blood flow in the IVC falls/ rises?

D. Hypoxia will favour what direction of shunt?

E. The first breath generates a negative pressure of about ?

Answer 1

A. reversal of the pressure gradient between the left and right atria

B. exposure to oxygenated blood and reduced prostaglandin-E2 within 24 hours.

C. Falls.

D. A RIGHT TO LEFT SHUNT. Any stimulus increasing Pulmonary Vascular Resistance will favour a right to left shunt and hence a Persistent Fetal Circulation. These stimuli include hypoxia, hypercarbia, acidosis and hypothermia.

E. 50 cm H2O

At birth, pulmonary vascular resistance falls markedly as the lungs expand and fill with air.

This decreases pulmonary artery pressures and increases blood flow to the left atrium. Umbilical vessels constrict and placental circulation ceases resulting in increased systemic vascular resistance and arterial pressure. Left atrial pressure becomes higher than right atrial pressure and this closes the foramen ovale.

Question 2

Hypercalcaemia effect on cardiac relaxation?

Answer 2

Inhibits lusitropy (relaxation)
Catecholamines facilitates rapid myocardial relaxation.

Question 3

What is the Anrep effect?

Answer 3

Afterload is the tension developed in the LV wall during systole.

If afterload increases, SV initially falls. SV is then (partially) restored by an increase in LVEDV. This is known as the Anrep effect.

Question 4

How will afterload be affected in a dilated ventricle?

Answer 4

Using Laplaces law, the increased radius will increase tension so afterload will be high.

Question 5

What fraction of blood supply does the liver recieve from the coeliac axis?

Answer 5

The hepatic artery is a branch of the coeliac axis. There is an inverse ratio of the flow between the hepatic artery and portal vein but under normal conditions 1/3 of hepatic blood comes from the hepatic artery.

Question 6

How does PEEP effect portal blood flow?

Answer 6

PEEP decreases PORTAL blood flow.

Portal blood flow does not autoregulate well. PEEP increases hepatic venous pressure and reduces portal flow.

Question 7

T/F: Arcades of arterioles supplying mucosal villi terminate and branch at the tip supplying well oxygenated blood to the mucosa

Answer 7

False - The countercurrent exchange of oxygen between parallel arterioles and submucosal venules makes oxygen delivery to the tips of mucosal villi poor.

Question 8

Which adrenergic receptors cause mesenteric arteriolar vasodilatation?

Answer 8

BETA 2 adrenergic receptors cause mesenteric vasodilation.

Question 9

Concerning cardiac tissue, calcium within the sarcoplasmic reticulum is released in response to ?

Answer 9

Rising intracellular calcium levels.

Question 10

SA and AV node blood supply is from?

Answer 10

Right coronary artery.

Question 11

During moderate exercise what changes occur in:

1. CBF
2. Central venous pressure
3. Intravascular volume
4. Haematocrit

Answer 11

1. CBF is maintained even with a 7 x increase in CO.
2. CVP - At moderate levels of exercise, increased venous return matched increased cardiac output and thus CVP does not significantly change. CVP does rise at maximal exertion.
3. Decreased intravascular volume due to insensible losses from sweating + capillary filtration.
4. Haematocrit rises due to reduced intravascular volume.

Question 12

Regarding electrolyte changes:

Select true or false for each of the following statements.

A. Hypokalaesmia increases automaticity

B. Hypokalaemia increases the QT interval

C. Hyperkalaemia brings the RMP closer to the threshold potential

D. Hypercalcaemia makes the threshold potential more negative

E. Hypermagnesemia prolongs the PR interval

Answer 12

A. True. Hypokalaemia makes the cardiac muscle RMP more negative, resulting in it being less excitable but with increased automaticity.

B. True.

C. True. Hyperkalaemia makes the RMP less negative.

D. False. Hypercalcaemia makes the threshold potential less negative, decreases conduction velocity and shortens the refractory period.

E. True. Hypermagnesemia delays AV conduction.

HYPER - less negative RMP - more excitable
HYPO - more negative RMP - less excitable but auto

Question 13

How is afterload effected in a failing heart?

Answer 13

Afterload is the tension developed in the LV wall during systole and as such can be related to pressure by Laplaces law.

Thus in the failing heart afterload is likely to be low due to low intraventricular pressure.