Cardiac Output

Question 1

name the three contributors to altering stroke volume

Answer 1

preload
afterload
contractility

Question 2

how must contractility, preload, and afterload change to increase the SV?

Answer 2

contractility and preload increase

afterload decreases

Question 3

what two things is preload proportional to?

Answer 3

LVEDV and LVEDP

Question 4

where does preload lie on the PV loop?

Answer 4

right at end of diastolic filling and just prior to isovolumetric contraction

Question 5

what really determines the preload of the heart?

Answer 5

the tension in the ventricular walls…laplaces law

Question 6

what physical exam technique can we use to measure the preload and why does this work?

Answer 6

measuring the diastolic jugular venous pressure gives a good estimate of the preload of the RV because the jugular is almost directly connected to the RA and in diastole the RA is about equal in pressure to the RV

Question 7

explain the Frank Starling Mechanism

Answer 7

as you increase the force or load on the muscle…it leads to a better overlap of actin and mysoin..yielding an optimal length that will cause the greatest force in contraction

Question 8

what effect does nitroglycerin have on the vessels?

Answer 8

it is a potent venous dilator

Question 9

when you decrease the venous tone, or dilate the venous system…what effect does this have on preload?

Answer 9

due to the venous system needing constriction to increase flow back to heart, when you dilate the venous system you get a lesser preload of the heart and less oxygen demand

Question 10

name three ways to regulate preload

Answer 10

blood volume
venous tone
body position…gravity plays big role in venous system

Question 11

what is the easiest thing to really compare afterload to?

Answer 11

systemic vascular resistance

Question 12

describe a common way of increasing the afterload of the heart that has to do with valves

Answer 12

aortic valve stenosis…less compliance here leads to higher pressure to overcome for the heart

Question 13

if there is an increase in afterload…what must happen to the isovolumetric line in the PV loop?

Answer 13

it will reach a higher peak since the heart must overcome a higher pressure to begin ejection

Question 14

define afterload in terms of the heart muscle

Answer 14

afterload is the wall tension during contraction of the heart

Question 15

with afterload causing an increase in necessary pressure for ejection, explain how the SV is lessened

Answer 15

the myofibrils and myosin and actin shorten at a decreased velocity and with the finite time for ejection the stroke volume decreases

Question 16

how do we mathematically define afterload?

Answer 16

the SYSTOLIC WALL STRESS

Question 17

what is wall stress equivalent to?

Answer 17

pressure times radius divided by wall thickness times 2

Question 18

if you increase afterload what happens to O2 demand of the heart?

Answer 18

increased

Question 19

which two anti anginal agents decrease the afterload of the heart?

Answer 19

calcium channel blockers and nitrates

Question 20

what class of sympathetic agents increase heart contractility and what is the mechanism?

Answer 20

beta agonists…like dobutamine

increase intracellular calcium

Question 21

does the contractility of the heart depend on the load or stress on the heart?

Answer 21

HELL NO

Question 22

what is contractility truly proportional to?

Answer 22

how many actin and mysoin crossbridges are made…so really intracellular calcium

Question 23

name four determinants of contractility

Answer 23

drugs that increase intracellular Ca (sympathetic tone)
Myosin ATPase activity (catalyzes ATP at higher rate)
ATP levels
number of sarcomeres

Question 24

the line depicting contractility on a PV loop takes what form?

Answer 24

a simple line with y=mx+b slope

Question 25

a tachycardic rate causes what with preload and contractility?

Answer 25

decrease in preload and increase in contractility

less filling time to refill leads to decreased preload

shorter time between beats means more intracellular calcium so increased contractility

Question 26

when exercising, what is the main contributor to increased CO?

Answer 26

HR increase

Question 27

with exercise, what happens to SVR and how does this affect the heart?

Answer 27

decrease in SVR due to arteriodilation of muscular arteries

leads to a decrease in afterload of the heart so increased SV

Question 28

what happens to venous return during exercise? effect this has on heart?

Answer 28

increased venous return,..increased preload…increased SV