Cardiac output

Question 1

what is the LVOT? where is it located?

Answer 1

left ventricular outflow tract - where blood travels from LV, along the leaflet of the mitral valve, and out through the aorta

Question 2

definition: cardiac index

Answer 2

volume of blood ejected from the heart (L) per unit time (min) per unit of body surface area (m2)

Question 3

what are the determinants of SV?

Answer 3

EDV / preload
ventricular contractility
afterload

Question 4

what parameter is a key determinant of ventricular contraction?

Answer 4

ventricular EDV

Question 5

definition: preload

Answer 5

tension exerted on the cardiac venticular muscle when it begins to contract

Question 6

definition: afterload

Answer 6

pressure that the ventricle has to win to produce SV

Question 7

definition: ESV

Answer 7

intraventricular volume at the end of systole

Question 8

what are the determinants of ESV?

Answer 8

preload
ventricular contractility
afterload

Question 9

what is the effect of preload on SV?

Answer 9

within limits, SV increases as preload increases

Question 10

the force of ventricular contraction is a function of what parameter of cardiac output? what is the name of this relationship?

Answer 10

ventricular end diastolic length of cardiac muscle

length dependent activation (frank starling law of the heart)

Question 11

what mechanism explains the balancing of output between the ventricles?

Answer 11

length dependent activation - the length of myocardial sarcomere determines its sensitivity to calcium

Question 12

what is the result of inadequate preload?

Answer 12

decrease in CO

hypotension

Question 13

what is the result of an excessive initial stretch of cardiac muscle?

Answer 13

decompensation

decrease in CO

Question 14

what is the effect of increasing afterload with preload and contractility remaining constant?

Answer 14

SV decreases with increasing afterload

Question 15

what is the ANREP effect? what is the initial response?

Answer 15

when aortic pressure is elevated abruptly, a positive inotropic effect follows within 1 or 2 minutes

initial response - length dependent activation

Question 16

what is the mechanism of the ANREP effect?

Answer 16

increased LV wall tension
increased cytosolic sodium level
increased myocardial cytosolic calcium level
increased myocardial contraction

Question 17

what is the effect of increasing contractility with preload and afterload remaining constant?

Answer 17

increasing increases SV, and vice versa

Question 18

what is the bowditch staircase phenomenon?

Answer 18

an increased HR progressively enhances the force of ventricular contraction (increasing HR intrinsically increases contraction as well)

Question 19

what is the opposing factor of the bowditch staircase phenomenon?

Answer 19

decreased ventricular filling

Question 20

is the effect of the bowditch phenomenon on CO rate-dependent or rate-independent?

Answer 20

rate-dependent

Question 21

what effect does a decreased HR have on the bowditch staircase phenomenon?

Answer 21

decreased HR has a negative staircase effect

Question 22

what is the most clinically common method of measuring CO?

Answer 22

pulmonary artery catheterization (PAC) thermodilution of with bolus injection of cold fluid

Question 23

what is the relationship between thermodilution and CO?

Answer 23

the faster it takes the temperature to equilibrate, the larger the CO

small curve - larger CO