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BMD221 Biomedical Physiology > Week 3 Heart Axis And Cardiac Flow > Flashcards

Week 3 Heart Axis And Cardiac Flow Flashcards

1
Q

What is one lead

A

A set of TWO electrodes

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2
Q

What does a lead measure

A

Records a voltage shift
As waves spread over the heart

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3
Q

How are direction and strength of a signal related in a lead

A

When a wave is parallel (same direction) it sis stronger

Perpendicular - no signal

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4
Q

Why is einthovens triangle formation used

A

A wave travelling in any direction will be parallel to at least one of the three leads

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5
Q

Ground electrode - purpose

A

Acts as a baseline

Looks at the natural voltage of the ground

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6
Q

By convention - what are the ECG directions for depol and repol

A

Depol - positive (up)

Repol - negative (down)

Waves travelling away from the positive electrode - opposite ^

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7
Q

Why is lead 2 normally used in a single lead trace

A

Lead 2 has the strongest response to a healthy heart

Several issues can be detected on lead 2 - other leads can then be assessed

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8
Q

Q of QRS

A

Depolarisation in the direction of the negative electrode - downward slope

small magnitude

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9
Q

Upwards slope R of QRS

A

Ventricle is being depolarised

Happens in the direction of lead 2

Huge wave in the positive direction

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10
Q

Downward slope R of QRS

A

Ventricle is still depol
But wave points less at the positive electrode
So is seen returning to 0

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11
Q

S of QRS

A

Opposite direction to positive electrode
Wave travels toward atria
Small magnitude
Trace is negatice

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12
Q

What is the heart axis

A

The mean vector
Describing direction of voltage in the heart

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13
Q

Heart axis calculation

A

Calculates mean of each mean electrical wave
Normal is 0-90 degrees

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14
Q

what causes ventricular fibrillation

A
  • AP keeps circling back on itself
  • or cardiomyocytes are repeatedly contracting
  • or contracting irregularly so ventricle is out of synch
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15
Q

when to use a defibrillator

A
  • not for a flatline
  • is used for ending FIBrillation
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16
Q

how does a defib work

A

depolarises all cardiac cells at once

to create a fresh signal from myogenic pacemaker cells

to bring back synchrony in beating

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17
Q

what are the two valves

A

mitral/bicuspid - 2 cusps
tricuspid - 3 cusps

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18
Q

what is the wiggers diagram

A

a method to visualise several aspects of the heart at once

19
Q

systole

A

period of contraction of the ventricles

20
Q

diastole

A

relaxation of heart muscle + then chamber fills with blood

21
Q

phases of systole

A
  1. isovolumetric contraction
  2. rapid ejection phase
  3. slow ejection phase
22
Q

phases of diastole

A
  1. isovolumetric relaxation
  2. rapid filling phase
  3. slow filling phase
  4. atrial contraction
23
Q

what phase of diastole is the P wave

A

atrial contraction / depol

24
Q

what phase of systole is QRS

A

ventricular contraction

25
Q

what phase of systole is the T wave

A

ventricular relaxation / repol

26
Q

aortic pressures in
1) diastole
2) ejection phase
3) isovolumetric phase

A

1) diastole - 80mmHg
2) ejection phase - 120
3) isovolumetric relaxation - aortic valve closes, causes dicrotic notch

27
Q

ventricular pressure
1) isovolumetric contraction
2) ejection phase
3) isovolumetric relaxation

A

1) ventricle contracts, closed chamber so pressure increases

when ventricular pressure crosses (is higher) the aortic pressure, the aortic valve opens

2) ejection phase is the top peak ◠ curve

when VP decreases and drops below the aortic pressure, the aortic valve closes

3) isovolumetric relaxation starts - pressure decreases - slope downwards

when VP falls below atrial pressure (1-7 mmHg) - mitral valve opens - rapid and slow filling ventricle phase starts

28
Q

Atrial pressure

A

starts high than VP

mitral valve closes when ven pressure raises -> raises atrial pressure

ejection phase - atrium is filled + pressure rises

when pressure is higher than VP - mitral valve opens and filling phase of ventricle starts

29
Q

ESPVR

A

end systolic pressure volume relationship

the max pressure of left ventricle at any volume

a measure of cardiac contractility

30
Q

EDPVR. passive filling curve of the left ventricle during diastole and is a measure of passive chamber stiffness

A

end diastolic pressure volume relationship

passive filling curve of the left ventricle during diastole

measure of passive chamber stiffness

31
Q

factors affecting cardiac output:

A
  1. preload
  2. frank starling mechanism
  3. afterload
  4. compliance
  5. inotropy
32
Q

what is cardiac output

A

amount of blood that the heart pumps in a minute

33
Q

what is preload

A

how much blood is in the chamber at the end of diastole

more blood entering heart = more preload
so heart increases stroke volume

34
Q

stroke volume

A

The volume of blood pumped out of the left ventricle of the heart during each systolic cardiac contraction

35
Q

factors that increase preload

A

these factors increase ventricular filling time

  1. increased atrial contractility
  2. increased central venous pressure
  3. decreased heart rate
36
Q

frank starling mechanism

A

when the heart is stretched
the heart contracts more
so end systolic volume is maintained

more contracting = more preload = increased stroke volume

37
Q

afterload

A

the pressure the heart has to pump to push blood out during ventricular contraction (systole)

38
Q

aortic pressure

A

the pressure at the root of the aorta

caused by blood pushed from the LV to the aorta

39
Q

how does afterload determine end systolic volume

A

increased aortic pressure - increased afterload

  1. higher aortic pressure = aortic valve closes earlier
  2. less ventricular emptying
  3. volume is at the end of systole
40
Q

what is compliance

A

the inverse of stiffness

ie. MORE stiff, LESS compliant

41
Q

how does compliance contribute to preload

A

it alters EDVPR

hypertrophy:
preload is reduced by having a stiffer heart

ventricle walls do not stretch as far in response to more blood volume

42
Q

what is inotropy

A

increases the speed of contractility
lowers end systolic volume (ESV)
affects ESPVR

43
Q

inotropes

A

make the heart beat with more or less power

44
Q

between which phases does ejection occur

A

spans from the end of isovolumic contraction to the beginning of isovolumic relaxation

BMD221 Biomedical Physiology (6 decks)

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