FINAL: Cardiac Physiology

Question 1

Aortic insufficiency

Answer 1

increases pulse pressure and decreases diastolic pressure

Question 2

If systolic pressure is 130 mmHg and diastolic pressure is 82 mmHg an estimate of mean arterial pressure in mmHg is:

Answer 2

98

Question 3

Pulse Pressure is

Answer 3

determined by stroke volume

Question 4

The greatest pressure decrease in the circulation occurs across the arterioles because

Answer 4

they have the greatest resistance

Question 5

The pulmonary circlulation is similar to the systemic circulation is one important respect

Answer 5

the same volume of blood flows through the pulmonary vessels and systemic vessels per unit of time

Question 6

Which of the following structure in the resting subject receives the greatest blood flow per gram of tissue (specific blood flow)?

Answer 6

kidney

Question 7

With a cardiac output of 5.6 L/min and a heart rate of 70 beats/min the stroke volume in mL/beat is:

Answer 7

80

Question 8

If the ventricular Purkinje fibers become the pacemaker of the heart, what is the expected heart rate?

Answer 8

30

Feedback:

If there is a failure in conduction of the S-A nodal impulse to the A-V node or if the S-A node stops firing, the A-V node will take over as the pacemaker of the heart. The intrinsic rhythmical rate of the A-V node is 40 to 60 times per minute. If the Purkinje fibers take over as pacemakers, the heart rate will be between 15 and 40 beats/min.

Question 9

What is the membrane potential (threshold level) at which the S-A node discharges?

Answer 9

-40mV
The normal resting membrane potential of the S-A node is -55 mV. As the sodium leaks into the membrane an upward drift of the membrane potential occurs until it reaches -40 mV. This is the threshold level that initiates the action potential at the S-A node.

Question 10

What is the resting membrane potential of the sinus nodal fibers?

Answer 10

-55mV

Question 11

Which of the following are caused by acetylcholine?

Answer 11

Hyperpolarization of the S-A node

Question 12

Which of the following best explains how sympathetic stimulation affects the heart?

Answer 12

The rate of upward drift of the resting membrane potential of the S-A node increase

Question 13

Which of the following conditions at the A-V node will cause a decrease in heart rate?

Answer 13

Increased potassium permeability

An increase in potassium permeability causes a decrease in the membrane potential of the A-V node. Thus, it will be extremely hyperpolarized, making it much more difficult for the membrane potential to reach its threshold level for conduction. This results in a decrease in heart rate. Increases in sodium and calcium permeability and norepinephrine levels increase the membrane potential, causing a tendency to increase the heart rate.

Question 14

Systemic arterial pressure in the adult is approximately 6-fold that of pulmonary arterial pressure because

Answer 14

systemic resistance exceeds pulmonary resistance
Response Feedback:

Pressure = resistance X flow. Because the flow from the left ventricle approximately equals the flow from the right ventricle, resistance becomes the determining factor. Right and left ventricular stroke volumes are approximately equal.

Question 15

Compared to rest conditions exercise causes the biggest increase in blood flow in:

Answer 15

Muscle and skin

Question 16

he French physician Jean L.M. Poiseuille (1799-1869) defined the factors that regulate the flow of water through a single, rigid cylindrical tube. Which of the following is correct with regard to flow rate as expressed in the Poiseulle equation?

Answer 16

directly proportional to the radius to the fourth power

Question 17

The total resistance offered by three resistances (0.2, 0.4, and 0.2) arranged in parallel would be

Answer 17

0.08 PRU

Question 18

An increase in arteriolar resistance, without a change in any other component of the cardiovascular system, will produce

Answer 18

an increase in arterial pressure

An increase in arteriolar resistance will increase total peripheral resistance (TPR). Arterial pressure=cardiac output X TPR, so arterial pressure will also increase. Capillary filtration decreases when there is arteriolar constriction because Pc decreases. Afterload of the heart would be increased by an increase in TPR.

Question 19

alculate the total peripheral resistance of an individual from the following measured variables:

Mean arterial pressure = 100 mm Hg

Central venous pressure = 0 mm Hg

Cardiac output = 5L/min

In peripheral resistance units (mm Hg/L/min), the total peripheral resistance of this individual is:

Answer 19

20

Question 20

In the figure below, assume that pressure at entrance to segment A is maintained at 100 mm Hg, whereas that at the ends of segments B and C is 0 mm Hg. Assume the numbers listed for each segment represent resistance for the segment in PRUs. Which of the following with increase blood flow through segment C?

Answer 20

Decreasing resistance in segment C to 1 PRU

At constant pressure, the flow through the entire circuit is inversely proportional to resistance. Any factor that decreases total resistance will increase total flow through the system, but flow is diverted through the branches in inverse ratio of their resistances. Option B decreases total resistance and favors flow through segment C over through segment B.

Question 21

The tendency for blood flow to be turbulent is increased by:

Answer 21

PARTIAL occlusion of a blood vessel

Turbulent flow is predicted when the Reynolds number is increased. Factors that increase the Reynolds number and produce turbulent flow are decreased viscosity (hematocrit) and increased velocity. Partial occlusion of a blood vessel increases the Reynolds number (and turbulence) because the decrease in cross-sectional area results in increased blood velocity (v=Q/A)

Question 22

The variable that is most responsible for the change in resistance to blood flow in a healthy individual is the:

Answer 22

radius of the arterioles.

Although all of the factors listed will affect resistance, in the systemic circuit, resistance is varied by controlling the radius of the arterioles.
Resistance is inversely proportional to the fourth power of the vessel radius.