Lecture 14 - Cardiac Output and Blood Flow in Muscle Tissues

Question 1

Define cardiac output.

(slide 4)

Answer 1

• quantity of blood pumped into aorta each minute
• quantity of blood that flows through circulation
• sum of all the blood flows to all body tissues

Question 2

What is cardiac index?

slide 4

Answer 2

• cardiac output per square meter of body surface
• decreases with age

-normal cardiac index is 3 L/min/M^2

Question 3

What is the main factor that affects cardiac output?

Answer 3

-venous return

Question 4

How does Ohm’s law relate to cardiac output?

slide 15

Answer 4

-long-term peripheral resistance changes cause an inverse change in cardiac output

Question 5

Differentiate between Bainbridge reflex and baroreceptor reflex.

(slide 16)

Answer 5

Bainbridge:
-stretching of the right atrium increases heart rate

Baroreceptor:
-increased pressure in the aorta/carotid increases heart rate

Question 6

How does the Frank-Starling law relate to cardiac output?

Answer 6

-the heart pumps out the amount of blood that flows into the right atrium

Question 7

What factors cause a hypereffective heart? (3)

slide 19

Answer 7

• nervous stimulation
• hypertrophy of the heart
• exercise (large vein contraction which increases venous return)

Question 8

What factors cause a hypoeffective heart? (7)

slide 20

Answer 8

• hypertension
• inhibition of nervous excitation
• pathologic factors
• coronary artery blockage
• valvular disease
• congenital heart disease
• cardiac hypoxia

Question 9

What are cardiac factors that result in decreased cardiac output? (5)

(slide 22)

Answer 9

• severe blockage of blood vessels (MI)
• severe valvular disease
• myocarditis
• cardiac tamponade
• cardiac metabolic derangements

Question 10

What are non-cardiac factors that result in decreased cardiac output? (5)

(slide 22)

Answer 10

• decreased blood volume
• acute venous dilation
• obstruction of large veins
• decreased tissue mass
• decreased metabolic rate of tissues

Question 11

What is the mean systemic filling pressure?

Answer 11

• the pressure of blood flowing into the atrium through the vena cava
• 7 mmHg

Question 12

What is pressure gradient for venous return and what affect does it have on venous return?

Answer 12

• difference between mean systemic filling pressure and right atrial pressure
• high pressure gradient results in increased venous return

Question 13

What is the formula for venous return?

Answer 13

-(mean systemic filling pressure - right atrial pressure) / resistance to venous return

Question 14

What happens to venous return when right atrial pressure is less than -2?
Greater than +7?

Answer 14

• venous return plateaus below -2 because veins in the chest collapse
• venous return is 0 when right atrial pressure is +7 because mean systemic filling pressure is canceled out

Question 15

What affect does strong sympathetic stimulation and complete sympathetic inhibition have on venous return?

(Slide 33-35)

Answer 15

• strong sympathetic stimulation constricts all blood vessels increasing mean systemic filling pressure
• inhibition causes relaxation of all blood vessels and decreases mean systemic filling pressure

Question 16

What factor result in an increase in mean systolic filling pressure? What affect does this have on the venous return curve?

Answer 16

Increase in vascular volume:
-activation of renin-angiotension-aldosterone system

Decrease venous compliance:

• sympathetic stimulaion
• muscle pump
• exercise
• lying down

Shifts venous return curve to the right

Question 17

What factor result in an decrease in mean systolic filling pressure? What affect does this have on the venous return curve?

Answer 17

Decrease vascular volume:

• hemorrhage
• burn trauma
• vomiting
• diarrhea

Increase venous compliance

• inhibition of sympathetic stimulation
• alpha block
• venodilators
• standing upright

Shifts venous return curve to the left

Question 18

What are factors affecting local control of skeletal muscle?

Slide 51

Answer 18

• oxygen
• adenosine
• potassium ions
• ATP
• lactic acid
• carbon dioxide

Question 19

What are nervous controls of blood flow regulation to skeletal muscle?

(Slide 51)

Answer 19

Sympathetic vasoconstrictor nerves:

• secrete norepinephrine
• decrease blood flow

Adrenal medullae:
-secretes norepinephrine and epinephrine

Question 20

What changes to blood flow to skeletal muscle occurs during mass discharge of the sympathetic nervous system during exercise?

(Slide 52)

Answer 20

• heart rate increases
• most peripheral arteries are strongly contracted except: in active muscle, coronary arteries, and cerebral arteries
• muscle walls of vein are contracted

Question 21

In general, blood flow through vessels to a muscle ___________ during contraction and __________ during relaxation.

Answer 21

Decreased; increases

Question 22

What factors affect blood flow in the coronary arteries?

Answer 22

• muscle metabolism of the heart
• ANS stimulation on coronary vessels
• ANS stimulation on the heart