Hemodynamics

Question 1

Cardiac output formula

Answer 1

HR x stroke volume

Question 2

CO at rest, CO that can be reached with exercise

Answer 2

5 L/min, 25 L/min

Question 3

Cardiac index

Answer 3

• clinically a more useful measure than CO -takes into account variations in CO related to size
• CI = CO/BSA

Question 4

Regulation of CO

Answer 4

1) Heart rate
- sympathetic and parasympathetic NS
2) Stroke volume
- sympathetic NS
- frank-starling law

Question 5

Frank starling law of the heart (3 principles)

Answer 5

1) heart muscle has intrinsic regulation (ability to regulate contractility independent of sympathetic of parasympathetic input)
2) the strength of contraction is related to the length of the muscle fibers prior to contraction (length-tension relationship)
3) The longer (more stretched) the cardiac muscle fiber is just prior to contraction the stronger the force of contraction (to a point)

Question 6

What is the length of cardiac muscle a function on

Answer 6

-how filled the heart is at the end of diastole (EDV)

Question 7

What is EDV a determinant of

Answer 7

EDP

Question 8

What is the strength of contraction a determinant of

Answer 8

stroke volume ejected from the heart during systole

-total tension developed determines stroke volume

Question 9

Length-tension relationship (i.e. starling curve)

Answer 9

Stroke volume (tension) increases up to a point with increase in LVEDV  (length)
-after peak increase sv fall with further increase in length

Question 10

Heart failure

Answer 10

-by definition characterized by decreased CO and/or volume overload

Question 11

Primary haemodynamic abnormality in patients with heart failure

Answer 11

A decrease in SV is the primary haemodynamic abnormality (so regulation of SV in heart failure is primary site therapeutic intervention)

Question 12

Three determinants of stroke volume

Answer 12

1) Preload
2) Contractility
3) Afterload

Question 13

What represent the preload

Answer 13

LVEDV

Question 14

Heart failure effect on preload vs. stroke volume

Answer 14

Decreased sv with same preload

Question 15

How contractiliy effects graph of SV vs. LVEDV

Answer 15

A change in stroke volume at any given EDV

• increased contractiliy = increased SV at any LVEDV
• decreased contractility = decreased SV at any LVEDV

Question 16

normal ejection fraction

Answer 16

55-75%

Question 17

Calculating Ejection Fraction

Answer 17

Ejection fraction = (EDV-ESV)/EDV X100

Question 18

Definition of systolic dysfunction

Answer 18

LVEF < 40%

Question 19

How to manipulate preload and contractility to help patient in hf

Answer 19

1) decreased preload - give diuretics

2) increased contractility -inotropic therapy

Question 20

pressure volume loops

Answer 20

A to B : ventricular filling
B to C: isovolumetric contraction
C to D: ventricular ejection
D to A: isovolumetric relaxation

Question 21

Effect of increasing preload on pressure volume loop, effect of increasing contractility on pressure volume loop

Answer 21

1) Increase distance A (ESV) – B (EDV) (i.e. SV) by increasing EDV (ESV stays the same)
2) Increase SV by decreasing ESV (EDV stays the same)

Question 22

Afterload

Answer 22

The stress in the ventricular wall necessary to generate the pressure required to eject the stroke volume (approximates the aortic pressure)

Question 23

Wall stress formula

Answer 23

Pxr/ 2xh
P = ventricular transmural pressure (the LDVEDP in most instances)
r = radius of ventricular chamber
h= wall thickness

Question 24

Effect of increasing the afterload on pressure volume loop (2)

Answer 24

Decreases A- B distance (decreased SV) and raises LV pressure at which ventricular emptying occurs (C-D)

Question 25

What determines strength of contraction

Answer 25

-intrinsic property of the myocardium (contractility) + the length-tension relationship (longer a muscle fiber the more tension will generate to a point)