6- Cardiac Output Regulation: The Heart

Question 1

Cardiac output (CO)

Answer 1

amount of blood pumped out by heart and into aorta in a period of time (~5L/min)

METABOLISM DRIVES CARDIAC OUTPUT

Question 2

Major factors that affect CO

Answer 2

1. Size of body (bigger people have more CO)/ Cardiac Index
2. Age (CO decreases with age)
3. Level of body metabolish (metabolic disorders have .a large effect on CO)
4. Exercise (any factor that increases metabolism will increase CO, exercise can cause large O2 and nutrient demands)

Question 3

Cardiac Index

Answer 3

• cardiac output per square meter of surface area
• CI ~ 4 L/min per m^2 at age 10 then declines slowly for the rest of your life
• CI ~ 2.4 L/min per m^2 at age 80

Question 4

how are metabolic work, cardiac index, and O2 consumption related?

include preload

Answer 4

all 3 are directly related

• venous return is the sum of all blood flows through all segments of teh peripheral circulation
• in most tissues blood flow increases in proportion to O2 consumption (ex: functional hyperemic response)
• CO is determined by sum of various factors that control local blood flow
• all local blood flows summate to form venous return and heart automatically pumps this blood back into the aorta

PRELOAD determines stroke volume and is based on individual segments constricting and dilating

Question 5

untilization coefficient

Answer 5

(art O2 - ven O2) / art O2

• gives percentage of O2 thats extracted from blood
• you can only extract so much O2 from RBC so when you need more O2 then you have to increase flow as well

Question 6

what primarily determines flow speed

Answer 6

O2 needs since its the most “flow limited” of all the nutrients in the blood/plasma

Question 7

effect of total peripheral resistance on long-term CO level

Answer 7

changes in total peripheral resistance can have a large effect on cardiac output but little effect on arterial pressure

-many mechanisms in place to maintain bp while CO depends mainly on preload of heart

Question 8

Cardiac Output Curves for normal, hypoeffective, and hypereffective hearts

Answer 8

-LOOK AT GRAPH (x: Right atrial pressure (preload for whole heart) // y: cardiac output) , kinda sigmoidal in the order below

• hypereffective (increase contractility) 25L/min
• normal 13L/min
• hypoeffective (decreasing contractility) 5L/min

Question 9

what happens when you increase right atrial pressure (preload for whole heart)

Answer 9

cardiac output increases

-intrinsic mechanism: b/c of the stretch dependent activation of cardiac muscle

Question 10

“effectiveness” of heart as pump can be changed from…

Answer 10

Hyper-effective (stronger contraction at any preload – steeper Starling mechanism)

to

Hypo-effective (weaker contraction at any given preload – flatter Starling curve).

Question 11

factors that cause hypoeffective heart

Answer 11

INCREASE PRELOAD

• inhibition of nervous excitation of heart
• abnormal heart rhythms or rate
• valvular heart disease
• increase arterial pressure (hypertension)
• congenital heart disease
• myocarditis
• cardiac anoxia
• diphtheritic and other types of myocardial or toxicity