Heart as a Pump

Question 1

what is cardiac output?

what happens if different cardiac outputs occur in the ventricles?

Answer 1

cardiac output: Cardiac output (CO) is the amount of blood pumped by the heart minute and is the mechanism whereby blood flows around the body, especially providing blood flow to the brain and other vital organs

different cardiac outputs: blood will gradually accumulate in a ventricle and be removed by the other

Question 2

Mean arterial pressure (MAP) is the product of ? and ?

Answer 2

Mean arterial pressure (MAP) is the product of cardiac output (CO) and total peripheral resistance (TPR):

MAP = CO × TPR

Question 3

what is the difference between BP in systemic and pulmonary circulation? why?
what does this mean as a consequence for anatomy? (2)

what controls the level of blood flow to an organ?

Answer 3

• BP in systemic circulation high to give efficient distribution of blood to different organs
• needs thick, muscular arteries: prevents aneurisms
• needs thicker ventricles

- blood flow to organs is normally determined by state of constriction of muscles around the small arteries feeding that orgran

Question 4

why is pulmonary artery pressure lower than systermic artery pressure?

Answer 4

total vascular resistance in the pulmonary vascular bed is much lower than in systemic circulation (so lower pressure is needed)

there is no need for high pressure because only the lungs are involved

Question 5

what is BP (systolic and diastolic) of systemic and pulmonary circ in:

a) normal / starts?
b) arterioles?
c) capillaries?
d) right atrium

Answer 5

a) normal: 120/80 mmHg
b) arterioles: 30 mmHg
c) capillaries: 10mmHg
d) right atrium: 2mm Hg

normally: 120/80 mm Hg

• *pulmonary circ:**
  a) normal: 25/8 mmHg
  b) capillaries: 8-12 mmHg
  d) left atrium: 5 mm Hg

Question 6

normal BP in the lungs is X mmHg or about Y of rest of bodies BP?

Answer 6

Normal blood pressure in the lungs is 15 -25 mmHg, or about 1/5th the bodies blood pressure.

Question 7

what is starlings law of the heart?

what is the limit to starlings law? what does this result in?

Answer 7

- ventricular contractile force is proproportional to end diastolic volume (aka ventricle will pump out however much blood is delivered to it by atria - more blood: more strongly pumped)

• if more blood is delivered: ventricle expands to a greater diameter & contracts more strongly

limit to starlings law:

• If the preload is too great and the ventricle expands beyond a certain volume, the mechanism fails: ventricle contracts more weakly
• this is a tipping point: beyong which heart failure starts to occur

Question 8

what is preload?

what is preload directly proportional to?

Answer 8

• *pre-load:
• **volume of blood at end of diastolic filling - stretch
• the difference between end diastolic and systolic volumes called: preload. determined by the volume of blood delivered to heart by IVC and SVC

(another way of looking at preload is: the degree of stretching experienced by the ventricle during diastole is called the preload)

Question 9

preload determines X of the ventricles?

what does this ^ in turn determine in the heart?

Answer 9

• preload determines the end diastolic volume (EDV) of the ventricles
• in turn, determins the stroke volume: (the volume of blood pumped out heart per beat)

Question 10

what is stroke volume? what is it normally in healthy human?

what is end-diastolic volume? how does it differ to stroke volume?

what is residual volume? what is normally in healthy

Answer 10

stroke volume: the volume of blood pumped out of heart per beat - usually 70ml

end diastolic volume: the amount of blood that is in the ventricles before the heart contracts.

differ because: there is always some blood left in the ventricle at end of systole: residual volume (ESV)

Question 11

what is EDV and ESV?

what is EDV and ESV values in healthy heart?

Answer 11

ventricular end-diastolic volume (EDV) and the end-systolic volume (ESV).

The EDV is the filled volume of the ventricle prior to contraction

ESV is the residual volume of blood remaining in the ventricle after ejection.

EDV: 120 ml

ESV: 50 ml

(120 - 50 = 70 ml = stroke volume!)

Question 12

how do u calculate stroke volume?

Answer 12

EDV-ESV

Question 13

why is an enlarged heart a bad sign?

what does larger end diastolic volume produce ^?

Answer 13

• enlarged heart = enlarged ventricles
• enlarged ventricles will not have corresponding increase in ventricular wall thickness, so will contract more weakly than a smaller heart
• this is bc the heart fibres are stretched to point where Starling mechanism no longer works

larger end diastolic volume produces a smaller stroke volume: heart failure

Question 14

what is the mechanism underlying starlings law?

Answer 14

at low EDV: there is less overlap of cross bridges (of actin and myosin): weak contraction

at high EDV: more overlap of cross bridges stronger contraction

increasing the overlap of active region of A & M increases the force of contraction

Question 15

what is afterload?

what does afterload depend on ? (2)

Answer 15

This is the effective flow impedance (dyanmic resistance) of the aorta and large arteries (resistance left ventricle must overcome to circulate the blood)

Afterload depends on the diameter & elasticity of the tissue

Question 16

what is the reciprocal of impedence?

what does a higher ^ of aorta do to afterflow?

Answer 16

compliance

higher compliance of aorta = lower afterload = less work the heart has to do for cardiac output

Question 17

what effect does altering afterload have on the cardiac workload?

Answer 17

increasing afterload = increasing cardiac workload

Question 18

what is inotropy?

which factors increase inotropy?(7)

Answer 18

inotropy: the contractility (force of contraction) of the ventricular muscle

factors that increase inotropy:

Increased blood calcium levels
Beta adrenergic agonists (such as adrenaline - increases contractility)
Excess thyroid hormone
Drugs which stimulate calcium entry into the myocardium, e.g. levosimendan
Cardiac glycosides (e.g. digoxin)
Insulin (increases inotropy)
Glucagon

Question 19

Answer 19

Question 20

Answer 20

Question 21

the atrioventricular valves are controlled by which muscles?

the atrioventricular valves are kept in position by what?

Answer 21

AV valves are controlled by papillary muscles

AV valves are kept in positon by chordiane tedinae

Question 22

Right atrio-ventricular valve is the X (due to the X valve leaflets)

Left atrio-ventricular valve is the X valve (or X valve, has X valve leaflets)

Answer 22

Right atrio-ventricular valve is the tricuspid valve (due to the 3 valve leaflets)

Left atrio-ventricular valve is the mitral valve (or bicuspid valve, has 2 valve leaflets)

Question 23

which are first muscles to contract during systole?
what does this cause to happen?

Answer 23

• papillary muscles contract first during systole
• pull on the chordinae tendianeae and pull the valves closed

Question 24

explain the pressure profiles in the left atrium, left ventricle and the aorta for a single cardiac cycle, using the diagram below

Answer 24

• start at the point marked ’mitral valve opening’. The left ventricle is at its minimum volume having just completed systole
• As the ventricle fills we travel up the lower slope ‘a’ from ESV (end systolic volume) to EDV (end diastolic volume).
• The ventricle starts to contract and the pressure rises steeply along the vertical line ‘b’.
• At point ‘1’ the mitral valve closes as the ventricle has started to contract.
• Initially the ventricular pressure rises due to ventricular contraction but the volume stays constant as the aortic valve is closed. This the isovolumentric contraction phase, hence line ‘b’ is vertical.

- When the pressure in the ventricle is greater than that in the aorta the aortic valve opens (point 2)

• Now the ventricular volume decreases as it ejects blood into the aorta; note the humped appearance of the curve ‘c’.
• At some point beyond ‘c’ the ventricle stops contracting; now the pressure drops until it is below that in the aorta and the aortic valve closes (point ‘3’). The pressure in the ventricle drops rapidly at a constant end systolic volume (ESV).
• Eventually we return to point ‘4’ where the ventricular pressure drops below that in the atria, the mmitral valve opens and the cycle repeats.

Question 25

explain the mechanism of the cardiac cycle

Answer 25

_Atrial systole:_ - **atria contract** during the **start of the P wave**, and the **contraction of ventricles is delayed by AV node.** They push **blood** down **through AV** valves **into the relaxed ventricles.** _Atrial diastole_ occurs as the **atria relax**. _Ventricular systole_ - papillary muscles contract and close AV valves - **Isometric contraction** is when the pressure is rising in the ventricles, yet not enough for the aortic/pulmonary valves to be pushed open. - **Valves open when the pressure in the ventricles rises above _80_** - As the pressure rises above 80, the **semilunar valves open and blood is ejected - ** after 1/10S, contractility of ventricle wanes, pressure decreases and back pressure closures valves * *- Ventricles relax as pressure drops, semilunar valves close** Blood will begin to flow into the **relaxed atria** *_isovolumetric relaxation phase occurs in ventricles_ ventricles relax, but dont change their volume until finally AV valves open and cycle starts again*

Question 26

what does the area inside graph show?

Answer 26

shaded area hows the **work** done by the heart per cycle

Question 27

why is it not life threatening if atrial systole does not occur?

Answer 27

the relaxed ventricle will **receive blood from the atria as it sucks it in due to pressure differences (**but the decrease in cardiac output occurs) / (the **elastic recoil of the ventricular walls** as they enlarge due to diastole sucks blood in)

Question 28

in a pressure volume diagram - how can we see differences in stroke volume? what does a decrease in preload do to stroke volume? what does an increase in preload to to stroke volume?

Answer 28

**stroke volume is the difference between the two vertical lines** an _increase_ / **decrease** in preload _increases_ or **decreases** diastolic filing and get a larger or **reduced** stroke volume

Question 29

what is atrial fibrillation? how do u spot it on ECG? why is atrial contraction needed during exercise?

Answer 29

**- Atrial fibrillation** (asynchronous contraction of atria) is a common condition in the over 60s, and is often detected only by the patient feeling dizzy or breathless during exercise. - AF (atrial fibrillation) is easy to spot in an ECG as there is an **absence of P waves,** but normal QRS waves - Atrial contraction is **necessary to fill the ventricles during exercise, as diastole is shortened with the increased heart rate.** The atria give the blood an extra ‘push’ which helps fill the expanding ventricles.

Question 30

what happens to each of the valves during cardiac cycles & when? what ensures that mean ventricle and aortic pressures do not completely match?

Answer 30

At the **start of systole** as the left ventricle starts to contract, the **mitral valve close**s then as pressure rises above diastolic the **aortic valve opens.** At the **end of systole**, the pressure in the ventricle decreases and **aortic valve closes.** Finally, when the **pressure is near zero** the **mitral valve opens again**. There is a s**imilar sequence in the right side of the heart.** _Impedance properties mean ventricle and aortic pressure do not completely match_

Question 31

label which valves are open / closed

Answer 31

Question 32

what causes the 'lubb' and 'dupp' sounds of heart? what are s3 & s4 sounds? who has them?

Answer 32

_lubb_**: closure of AV valve**s followed by the **opening of the aortic and pulmonary artery valve**s is the first heart sound. This is known as **S1**. _dupp:_ **closure of the aortic and pulmonary artery valves** followed by the **opening of the AV valves** is the second heat sound, known as **S2** _S3:_ faint low-pitched sound is heard in about 1**/3 of the way through diastole in many children and young adults**. It coincides with the **period of rapid ventricular filling and is due to turbulent flow during the filling**. A third heart sound may also be heard in **adults with heart disease**, and is usually a sign of serious heart damage, possibly damaged heart valves. _s4:_ sometimes heard **immediately before the first heart sound.** It is due to **turbulent flow** in the ventricle and **rarely occurs in normal adult**s. Because of their cadence or rhythmic timing S3 and S4 are called gallops. Gallops are low frequency sounds that are associated with diastolic filling. To investigate heart sounds in detail, they can be recorded and amplified to give a phonocardiogram

Question 33

what are s3 & s4 aka? & what part of cardiac cycle are they asssociated with? how do u investigate heart sounds in detail?

Answer 33

- S3 and S4 are called **gallops**. - Gallops are low frequency sounds that are **associated with diastolic filling**. - To investigate heart sounds in detail, they can be recorded and amplified to give a **phonocardiogram**

Question 34

what is the jugular venous pulse? how does it occur? what are the 3 peaks in venous pulse? why do they occur?

Answer 34

- There are no valves between the vena cava and the right atrium, or the pulmonary valves and the left atrium - As there are no valves, when the **right atrium contracts a back pressure occurs in the jugular vein.** This can be felt as a faint pulse, the **jugular venous pulse.** _There are three peaks in the venous pulse: a, c, and v:_ - **a pulse** is due to **atrial contraction just before the tricuspid valve closes** - **c wave** is due to **pressure rising in the atrium just after the tricuspid valve closes** before the **valve bulges back into the atrium,** - **v wave** corresponds to **venous filling when the tricuspid valve is closed**

Question 35

Answer 35

Question 36

what happens to JVP if the heart is not dealing with preload?

Answer 36

JVP rises and large venous pulse can be seen

Question 37

Venous return to the heart is mediated by which three main factors?

Answer 37

**One way valves in the veins.** As muscles in the limbs and abdomen contract they _squeeze the blood in the veins and it is propelled upwards to the hear_t. The one-way valves themselves help prevent the backflow of blood as it is under such low pressure that without valves it could easily flow back away from the heart. **Muscular pumps:** The contractions of muscles in limbs squeeze veins, and in conjunction with the one way valves, this propels blood back to the heart **Thoraco-abdominal pump.** During inspiration, pressures in the thoracic cavity are reduced, pulling blood into the inferior vena cava. On exhalation, thoracic pressure increases and this blood is forced into the right atrium

Question 38

what happens in exercise to venous return to heart to match cardiac output ? why is it more important to repiar arterial supplies than venous? (2)

Answer 38

all three factors (one way valves, muscular pumps and thoraco-abdominal pump) work together to increase and match cardiac output. - **Veins have many anastomoses** (parallel channels) to **enable alternative pathways for blood to return to the hear**t. - Small veins can also **enlarge rapidly to cope with a greatly increased flow**. - Whatever blood gets to an organ can normally be drained away

Question 39

what do the QRS, ST phase & T phase of an ECG correspond to in the cardiac cycle? what stages of ECG do you hear the heart sounds?

Answer 39

- **QRS complex** occurs during the **isovolumetric contraction phase of muscle** - **ST phase** corresponds to **ejection phase** - **T phase** corresponds to the **isovolumetric relaxation phase** _Heart sounds:_ * *LUBB / SI:** after QRS * *DUPP / S2**: after T phase

Question 40

what does this show?

Answer 40

atrial fibrillation