Cardiac Output (Pt2): Mechanical events and Stroke Volume

Question 1

systole

Answer 1

ventricular contraction and blood ejection

Question 2

Diastole

Answer 2

ventricular relaxation and blood filling

Question 3

Do the ventricles have the same SV

Answer 3

yes

Question 4

what is the cardiac cycle predominately driven by

Answer 4

Pressure changes in the ventricles (minor part played by atrial contraction)

Question 5

What drives opening/closing of valves

Answer 5

pressure changes in the 4 compartments

Question 6

Systole: isovolumetric ventricular contraction

Answer 6

AV valves closed
Pressure ventricles>atria
Aortic and pulmonary valves closed
Pressure ventricles

Question 7

Systole: ventricular ejection

Answer 7

AV valves closed and pressure ventricles > atria

Aortic and pulmonary valves open and pressure ventricles > arteries

Question 8

Diastole: isovolumetric ventricular relaxation

Answer 8

AV valves closed and pressure ventricles > atria

Aortic and pulmonary valves closed and pressure ventricles < arteries

Question 9

Diastole: ventricular filling

Answer 9

Negative pressure in ventricles (90%):
AV valves open, pressure ventricles < atria
A and P valves closed and pressure ventricles < arteries

Atrial contraction (10%):
AV valves open
A and P closed

Question 10

Pressure and volume changes during the cardiac cycle

Answer 10

During systole, BP rising in ventricles, SL valves open and blood passes out
In diastole pressure in arteries gets higher than in the heart, then SL valves close and heart starts relaxing.
As it relaxes, creates a vaccuum in the bottom of the heart, and the low pressure flips open the AV valves

Question 11

SV=

Answer 11

EDV (end diastolic volume) - ESV (end systolic volume)

Question 12

heart sounds caused by

Answer 12

closure of heart valves

Question 13

1st sound

Answer 13

closure of AV valves

onset of systole (contraction)

Question 14

2nd sound

Answer 14

closure of pulmonary and aortic valves

onset of diastole (relaxation)

Question 15

Regulation of SV

Answer 15

• filling pressure (reload)- starling’s law of the heart
• arterial pressure opposing ejection (afterload)
• contractility: sympathetic nerves, circulating agents

Question 16

what is end-diastolic ventricular volume (pre load) determined by

Answer 16

CVP - central venous pressure

Question 17

What is CVP determined by

Answer 17

skeletal muscle pump (blood squeezed back towards heart leading to incr CVP)
Blood volume (reduced BV leads to reduced CVP)
Gravity (posture)- when standing, gravity leads to pooling in legs and reduces volume and CVP
Sympathetic nerves- contraction of central and peripheral veins leads to incr CVP
Respiratory pump (breathing)- inspiration = incr CVP, expiration = decr CVP

Question 18

frank starling mechanism

Answer 18

ventricles contract with more force (ie incr stroke volume) if it contains more blood (ie incr end-diastolic ventricular volume)

Question 19

What is frank starling mechanism determined by

Answer 19

length-tension relationship in the muscle ie greater stretch = more tension developed in the cardiac muscle

Question 20

What is the main function of the frank starling mechanism

Answer 20

maintains balance between left and RHS of the heart and stops accumulation of blood in lungs

Question 21

How does F-S stop blood accumulating in the lungs

Answer 21

if incr venous return to right ventricle then incr contraction
more blood to lungs
If incr venous return to left ventricle then incr contraction
Incr stroke volume
Blood doesn’t accumulate in lungs

Question 22

Contractility

Answer 22

sympathetic only, not para, controls SV
Symp release noradrenaline, activate B1 adrenergic receptors, incr force and speed of cardiac muscle contraction and incr ventricular contraction at any given end-diastolic ventricular volume

Question 23

arterial pressure opposing ejection

Answer 23

Higher arterial BP, harder heart is to open

Hypertension (high BP) makes it more difficult to open valves and eject blood, leading to heart failure

Question 24

congestive heart failure

Answer 24

reduced CO
tiredness and shortness of breath
Fluid retention via kidneys to incr CO ( venous return)

Question 25

systolic dysfunction

Answer 25

coronary heart disease leading to ischaemic heart disease and heart attack
Heart attack damages heart muscle, decr ventricular contractility so lower SV

Question 26

Diastolic dysfunction

Answer 26

Hypertension
stiffening of ventricular wall - incr ventricular muscle- inr cardiac resistance- incr arterial pressure- high BP/ hypertension

Question 27

Diastolic dysfunction

Answer 27

Hypertension
stiffening of ventricular wall - incr ventricular muscle- inr cardiac resistance- incr arterial pressure- high BP/ hypertension
Also stiffening leads to decr in end-diastolic ventricular volume, leads to decr in stroke volume