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Cardiology > Cardiac Cycle And Output > Flashcards

Cardiac Cycle And Output Flashcards

1
Q

Automaticity

A

Heart muscle is stimulated by nerves and is self excitable

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2
Q

How long is the Cardiac cycle?

A

0.8 seconds (75bpm)

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3
Q

What is the cardiac cycle?

A

Period between the start of one heart beat to the beginning of the next. Systole and diastole

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4
Q

Systole

A

Contraction of heart muscle, blood is pumped into the arteries, approx. 0.1 seconds

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5
Q

Diastole

A

Relaxation of heart muscle, heart filling with blood, approx. 0.7 seconds

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6
Q

What are the phases of the cardiac cycle?

A

Atrial systole > isovolumetric ventricular contraction > ejection > isovolumetric ventricular relaxation > passive ventricular filling

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7
Q

Atrial systole

A

Heart blood pressure is low as blood enters the atria from the pulmonary and systemic circulations and then flows into the ventricles. Approx. 80%, atrial kick forces the remaining 20% (AV valves open, semilunar valves closed)

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8
Q

Ventricular systole

A

Atria relaxes, ventricular pressures rise resulting in AV valves closing

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9
Q

Isovolumetric ventricular contraction

A

The ventricles are completely closed chambers, and pressure in the ventricles increase until the pressure is more than in the aorta/pulmonary trunks

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10
Q

Ventricular ejection

A

Opens semilunar valves

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11
Q

Isovolumetric ventricular relaxation

A

Ventricles relax, ventricular pressure drops. Backflow of blood in aorta and pulmonary trunk closes semilunar valves (dicrotic notch)

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12
Q

Dicrotic notch

A

Brief rise in aortic pressure caused by backflow of blood rebounding off semilunar valves

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13
Q

Passive ventricular filling

A

Blood has accumulated in the atria behind the closed atrioventricular valves passes rapidly into the ventricles

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14
Q

What are the cardiac cycle pressures?

A

Right atrium: 0-4 mmHg, right ventricle: 25 systolic mmHg, pulmonary arteries: 25 systolic mmHg, left atrium: 8-10mmHg, left ventricle: 120 systolic mmHg, aorta: 120 systolic mmHg

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15
Q

What is cardiac output (CO)?

A

The amount of blood pumped by each ventricle in one minute, it is the best indicator of adequate blood flow to the peripheral tissues. Product of heart rate (HR) and stroke volume (SV)

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16
Q

Heart rate

A

Number of beats per minute

17
Q

Stroke volume

A

Amount of blood pumped out by a ventricle with each beat

18
Q

Cardiac reserve

A

Difference between resting and maximal cardiac output

19
Q

The pump at work cardiac output conversion

A

CO=SVxHR

20
Q

Ejection fraction

A

The percentage of blood pumped out of a ventricle with each contraction. Used as a measure of ventricular function.

21
Q

What is the normal ejection fraction?

A

Between 50% and 65%

22
Q

Regulation of stroke volume

A

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

23
Q

End diastolic volume

A

Amount of blood collected in a ventricle during diastole

24
Q

End systolic volume

A

Amount of blood remaining in a ventricle after contraction

25
Q

What are the 4 factors affecting stroke volume?

A

Venous return, preload, contractility, afterload

26
Q

Venous return

A

Amount of venous blood returned to the heart

27
Q

Preload

A

Amount ventricles are stretched by contained blood

28
Q

Contractility

A

Cardiac cell contractile force due to factors other than EDV

29
Q

Afterload

A

Back pressure exerted by blood in the large arteries leaving the heart

30
Q

Critical factor controlling stroke volume?

A

Preload or degree of stretch of the cardiac muscle cells before they contract

31
Q

What increases stroke volume?

A

Slow heart beat and exercise increase venous return to the heart

32
Q

What decreases stroke volume?

A

Blood loss and extremely rapid heart beat

33
Q

Frank-Starling Law

A

More blood in more blood out. The greater the volume of blood in the ventricle, the stronger the contraction. Both increased filling time and increase blood volume = increased SV

34
Q

What are the Extrinsic factors influencing stroke volume that increase contractility?

A

Increased sympathetic stimuli, certain hormones, Ca2+ and some drugs

35
Q

What are the extrinsic factors influencing stroke volume that decrease contractility?

A

Acidosis, increased extra cellular K+, beta blockers and calcium channel blockers

36
Q

Signs and symptoms of decreased cardiac output?

A

Acute changes in BP, acute changes in mental status, cold/clammy skin, colour changes in the skin and mucous membranes, crackles (rales), dyspnea, dysrhythmias, fatigue, orthopnea, restlessness

Cardiology (12 decks)

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