cardiac output

Question 1

CO equation

Answer 1

CO = HR X SV; amount of blood pumped by heart per min

Question 2

how is peripheral resistance decreased?

Answer 2

resistance from sympathetic stimulation (releases NE and E which bind to alpa-adrenergic receptors and cause vasoconstriction)–> gives rise to transient ischemia (loss of blood flow); adenosine (metabolite) generated during TI causes vasodilation; known as metabolic autoregulatory phenomena

Question 3

Metabolic autoregulatory phenomena then lead to a reduction in total peripheral vascular resistance

Answer 3

ya

Question 4

SV eq’n

Answer 4

SV = EDV-ESV; EDV normally 120 mL, ESV normally 50 mL–> normal SV is 70 mL

Question 5

ejection fractin eq’n

Answer 5

is a measure of ventricular pumping efficiency

Where EF = SV / EDV

Question 6

what are the factors that can influence SV?

Answer 6

preload (related to EDV); afterload (wall stress to the ventricles); contractility (inotropy)

Question 7

what is preload affected by?

Answer 7

the degree of stretching of the cardiac myocytes prior to contraction and therefore related to the sarcomere length at the end of diastole

Question 8

how else can preload be defined?

Answer 8

Can be defined as the end diastolic circumferential ventricular chamber length just before the onset of the ventricular contraction

Question 9

End-diastolic circumferential ventricular chamber length is directly related to the end diastolic ventricular blood volume (LVEDV)
Preload is also indirectly related to ventricular end diastolic pressure (LVEDP)

Answer 9

ya

Question 10

how is preload related to SV?

Answer 10

proportionally; increase in PL causes an increase in SV

Question 11

what is preload determined by?

Answer 11

ventricular compliance; venous return; length tension relationship; HR (to a lesser extent)

Question 12

what is ventricular compliance?

Answer 12

Compliance is defined as the change in
volume divided by the change in pressure i.e.) ΔV / ΔP = compliance
Or ΔP / ΔV = stiffness

Question 13

what is the venous return?

Answer 13

amount of blood returning from systemic circulation to the heart

Question 14

what happens when venous return increases?

Answer 14

–>stretches the myocytes
–>increases force of contraction
–>higher SV
(Frank-Starling mechanism
or Starling’s law–↑ LVEDP (↑ venous return) ↑ SV)

Question 15

what does the FS mechanism ensure?

Answer 15

the outputs of both the ventricles are matched over time and to prevent the shifting of blood between pulmonary and systemic circulations

Question 16

describe the length tension relationship

Answer 16

Length-tension relationship is the biophysical basis for the Starling’s law of the heart
Changes of the initial length of a myocyte (preload) could affect the contractile force (tension) being developed by that muscle
When the cardiac myocytes is stimulated at the increased preload, there will be a larger increase in active tension