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SOM 202 > WEEK 3: PHYSIOLOGY OF CARDIAC FUNCTION > Flashcards

WEEK 3: PHYSIOLOGY OF CARDIAC FUNCTION Flashcards

1
Q

State the functions of the cardiovascular system.

A

*To pump blood through the circulation in so doing distributing blood, gases, nutrients to where they are required.

*To collect metabolic waste products for disposal

*To control blood flow to the skin and extremities

*To distribute body heat

*To distribute hormones to distant organs

*To aid body defense by delivering antibodies, platelets, WBC to affected areas

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2
Q

Describe the simplified pathway of blood circulation in the heart and body.

A

-RV is the pump for the pulmonary circulation (blood flow within the lungs)

-LV is the pump for the systemic circulation

-Systemic circulation carries oxygenated blood from the left ventricle, through thearteries, to thecapillariesin the tissues of the body. From the tissue capillaries, the deoxygenated blood returns through asystemofveinsto the right atrium of theheart.

-Pulmonary circulationtransportsoxygen-poor blood from the right ventricle to the lungs, where blood picks up a new blood supply. Then it returns the oxygen-rich blood to the leftatrium.

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3
Q

Which side of the heart carries oxygenated blood?

A

Left side

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4
Q

Describe the conducting system of the heart.

A

Sino Atrial Node (SAN)
Atrioventricular Node (AVN)
Atrioventricular Bundle (Bundle of His)
Right and Left Bundle Branches
Ventricular walls (Purkinje Fibers)

  • Action potential is passed from one myocardial cell to the other thru gap junctions (points of low electrical resistance).

-AV nodal delay allows the atria to complete contracting and emptying into ventricles

-The AV nodal delay is represented by PR segment on the ECG.

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5
Q

State the characteristics of auto-rhythmic cells.

A

*Unstable and changing resting membrane potential called Pacemaker Potential or Pre-potential.

*Continuous depolarization drifting towards Threshold potential (-40 mV)

*Ca2+ producing rapid rising phase of an action potential

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6
Q

Describe the action potential production of auto-rhythmic cells.

A

Resting membrane state= -60
Threshold = -40mv
Peak =+10mv
NOTE: Works as the membrane potential

The ions involved are Calcium channels and Potassium ions.

*Funny channels open when the membrane becomes more –ve (not +ve as is usually the case). Therefore, as soon as the potential goes below -40mV the funny channels open allowing Na+ to start moving inside cell thereby preparing for the next depolarization.

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7
Q

State the normal rates of action potential discharge for the:
*SA node
*AV node
*Bundle of His and Purkinje fibers

A

SA node=70-80
AV node = 40-60
Bundle of His and Purkinje fibers =20-40

  • The other pacemakers cannot dominate the heart unless everything faster than them becomes non-functional.
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8
Q

Describe the action potential in cardiac muscles.

A

Resting potential: -90mV
Threshold potential= -70mV
Peak= +30mV

REFRACTORY PERIOD= 250ms from the time the sodium channels close to the point where Potassium ions move out of the cell during repolarization after plateau phase.

*Plateau prolongs ventricular contraction.

*80-90% of the Ca+ needed for muscle contraction comes from the SR.

*Refractory period lasts for about 250 msec

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9
Q

Describe the plateau in AP of cardiac muscle.

A

*Voltage-gated Na+ channels open briefly, (Na+ influx)

*Re-polarization begins, (K+ efflux) no marked effects

*Slow Ca2+ Channels open, (ECF Ca2+ influx- 20%)

*Ca2+ from ECF triggers Ca2+ sensitive channels in Sarcoplasmic Reticulum to release more Ca2+ (80%) rising intracellular Ca2+ which prolongs depolarization leading to a plateau.

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10
Q

Describe the features of AP in cardiac muscles.

A

Sharp rise (Depolarization phase)
Plateau
Sharp fall
Prolonged Absolute Refractory Period
Action potential lasts up to 200 ms (compared to 1 – 2 ms in skeletal muscle)
Contraction (tension) last for 200 ms or more (15 – 100 ms in skeletal muscle)

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11
Q

Describe the action potential and contractile response of cardiac muscles.

A

*There is increased contractile response during the plateau phase of AP and the contractile response reduces during repolarization.

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12
Q

What is a cardiac cycle?

A

One cardiac cycle is the period of time from the beginning of ventricular contraction to the beginning of the next ventricular contraction.

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13
Q

State the events in a cardiac cycle.

A

Mechanical (Physical)
Electrical
Audible

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14
Q

What is electrocardiograph?

A

An electrocardiograph (ECG) is a test used to measure the electrical activity of the heart

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15
Q

What is an electrocardiogram?

A

*An ECG or electrocardiogram is a recording that shows the electrical activity of the heart.

It is used to detect heart problems and monitor the heart’s health.

Electrodes are placed on the chest to record the heart’s electrical signals, which cause the heart to beat.

ECG is summation of all action potentials generated by nodal and contractile cells at a given time

Clinically, ECG is measured by 12 leads (3 bipolar, 9 unipolar leads)

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16
Q

What is the difference between electrocardiograph and electrocardiograms?

A

An electrocardiograph is a device used in the diagnosis and detection of heart abnormalities that measures electric potentials on the surface of the body and creates a record (electrocardiogram) of the electrical currents associated with heart muscle activity.

*While electrocardiogram is the visual output that an electrocardiograph produces.

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17
Q

Describe normal ECG.

A

1 cardiac cycle lasts for 0.8s

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18
Q

Describe ventricular systole events. (

A

*Lasts 0.28 sec, accounting for about 35% of the cardiac cycle
-Encompasses time of ventricular contraction
Coincides with R-wave on ECG
-Rapid increase in ventricular pressure
-Closure of AV valves (Tricuspid & Mitral)
-Associated with first heart sound

*Isovolumetric contraction (valves on both ends are closed, no change in volume)

Ventricles contract
Intra-ventricular pressure rises.
Pressure continues to rise, no blood ejected.

*Ventricular ejection
-Rapid (70% of total) ejection is in first 1/3 of phase.
-Slow ejection (30%) coincides with onset of T-wave.

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19
Q

Describe events that occur during Ventricular diastole.

A

*Isovolumetric relaxation

-Ventricles relaxation (early diastole)
-Ventricular pressure drops
-Blood backflow in aorta and pulmonary artery closes semilunar valves.
-Ventricles become closed chambers again because the AV
valves are still closed.

*Ventricular filling
-Rapid filing
-Occurs during the first 1/3 of ventricular diastole
Contributes majority volume to ventricles (about 75%)

*Diastasis
Free flow during the 2nd third of diastole
Contributes about 5% of ventricular volume

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20
Q

Describe events that occur during atrial systole.

A

Occurs during last 1/3 of ventricular diastole
Coincides with P-wave on ECG
Contributes to 20- 25% of end-diastolic ventricular volume

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21
Q

Describe the P-wave of the ECG

A

*Lasts about 0.08 s

*Due to movement of depolarization wave from SAN through atria

*Appears for about 0.1 sec, after its occurrence atria contracts

22
Q

Describe the QRS complex.

A

*0.08s
*Ventricular depolarization
*Precedes ventricular contraction

23
Q

What does an enlarged QRS complex represent?

A

Enlarged QRS-Wave represent enlarged ventricle

24
Q

Describe the T-wave of the ECG

A

*0.16s
Caused by ventricular re-polarization

25
Q

Why is the ventricular re-polarization longer than ventricular depolarization?

A

To allow time for ventricular filling

26
Q

Describe the P-Q interval of the ECG.

A

Sometimes called P-R Interval

Duration from beginning of atrial excitation to the beginning of ventricular excitation.

Lasts about 0.16 s

Include atrial depolarization, atrial contraction and passage of depolarization wave in conduction system.

27
Q

Describe the S-T segment of ECG.

A

*This is the ejection phase
*Occurs when the ventricles are depolarized
*Action potential is in the plateau phase
Lasts approximately 0.12 s
Elevated or depressed S-T segment indicates ischemia.

28
Q

Describe the Q-T interval of ECG.

A

*Duration from ventricular depolarization through ventricular re-polarization

Lasts approximately 0.38 s

Prolonged Q-T interval represents abnormal repolarization (ventricular diastolic dysfunction)- this negatively affects ventricular filling.

29
Q

Describe the normal heart rhythm.

A

SINUS RHYTHM: Sinus rhythm refers to the rhythm of your heartbeat, determined by the sinus node of your heart.

*Is present when the SAN is the pacemaker

*Is assumed if P-wave is followed by a normal QRS complex

*Characterized by normal P – R and Q – T interval
Regular R – R interval (rate)

30
Q

What are arrythmias?
What do they result from?

A

Arrhythmias are a condition characterized by abnormal heart rhythm.

1.Ectopic foci: An ectopic pacemaker, also known as ectopic focus or ectopic foci, is an excitable group of cells that causes a premature heartbeat outside the normally functioning SA node of the heart.

*It is thus a cardiac pacemaker that is ectopic, producing an ectopic beat.

2.Alteration in SAN activity

3.Interference with conduction

31
Q

What causes extrasystoles?

A

Premature ventricular contractions
Result from ectopic foci in ventricles

32
Q

What is atrial flutter?
How does it result in reduced cardiac output?

A

*Atrial flutter is an abnormal heart rhythm in the heart’s upper chambers (atria) that beats too fast.
*Fast, regular depolarization (200 – 380 beats min-1)

Not all atrial impulses pass through AV node. Inadequate ventricular filling reduced cardiac output.

33
Q

What is atrial fibrillation?

A

*Rapid, irregular and uncoordinated depolarization of atria.

*No definite P-wave on ECG, Irregular ventricular rhythm

*QRs complexes normal in shape but occur sporadically

*Heart rates exceed pulse rate (pulse deficit)

34
Q

What are ventricular fibrillations?
Why is it a problem?

A

rapid, Uncoordinated ventricular contractions
Irregular ECG, no detectable pattern

Ventricular filling ineffective and impairs circulation.

35
Q

What is cardiac block?
What causes cardiac block?

A

*It means that the electrical signal from the atria is completely blocked from reaching the ventricles.

*Defects in the cardiac conduction, atria beat regularly.

Impulses between atria & ventricle blocked.
In complete heart block atria & ventricles beat separately

36
Q

Describe the following abnormal heart rates:
*Tachycardia
*Bradycardia

A

*Tachycardia = increased heart rate > 100 beats min-1
*Bradycardia = reduced rate < 60 beats min-1

37
Q

What wave forms are used to determine abnormalities of heart function?

What could the abnormalities be?

A

Abnormalities of heart functions can be determined between TWO consecutive QRS complexes on ECG.

*Abnormalities may be in Rhythm or rate.

38
Q

What is the most commonly used glycosides in the treatment of heart failure?

A

Digoxin is the most commonly used glycosides in the treatment of heart failure

39
Q

State the positive Inotropic effects of Digoxin.

A

1: Inhibit NA+/K+ ATPase
2.Inhibited Na+/Ca2+ exchanger

Net effect
*Muscle fiber shortening and tension.

40
Q

State the chronotropic effects of digoxin.

A

Increased parasympathetic tone to SAN and AVN
Inhibits sympathetic tone to the heart
Reduced vasoconstriction reducing peripheral resistance

41
Q

State the net effects of digoxin

A

Slow SAN depolarization, therefore slow heart rate
Increases AVN refractory period
Slows AVN conduction (Negative chronotropic)
Effective ventricular filling
Enhanced cardiac output

42
Q

What causes heart sounds?

A

Heart sounds are caused by vibrations due to turbulence set up within the walls of ventricles and major arteries during valve closure (Not closing of valves).

43
Q

What are abnormal heart sounds called?

A

Abnormal heart sounds are called Murmurs

44
Q

What are murmurs that are NOT associated with heart diseases are called? (Common in young people)

A

Murmurs that are NOT associated with heart diseases are called Functional Murmurs (common in young people)

45
Q

Describe the first heart sound.

A

*Low pitched, soft and takes longer

*Signifies beginning of ventricular systole when AV valves close (Tricuspid & Bicuspid/mitral)

46
Q

Describe the second heart sound.

A

*High frequency (pitched) and Shorter (0.11 s)

*Signifies beginning of ventricular diastole i.e. Semilunar valve closure. (Aortic & Pulmonary)

47
Q

*Weak rumbling sound
*Occurs during rapid filling of ventricles resulting in oscillation of blood between walls of ventricles during inrush of blood from atria

Common in young people and children
Pathological in adults (overfilling, reduced compliance)
What heart sound is this?

A

third heart sound (S3)

48
Q

Low frequency (20 cycles/sec)
Vibrations of ventricles during last diastole (atrial contraction)
Heard in High output states, reduced compliance, AV Block

What heart sound is this?

A

S4

49
Q

Commonest causes of turbulence is VALVULAR Malfunctions including:
STENOTIC valve
INSUFFICIENT or INCOMPETENT

A

Commonest causes of turbulence is VALVULAR Malfunctions including:

*STENOTIC valve – means stiff, narrowed valves and do not open fully

*INSUFFICIENT or INCOMPETENT – means cannot close completely, blood flows backward as well causing turbulence

50
Q

What is backflow of blood at an insufficient or or incomplete valve called?

A

Such backflow is called REGURGITATION

51
Q

What is backflow of blood at an insufficient or incomplete valve called?

A

Such backflow is called REGURGITATION

SOM 202 (15 decks)

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