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Cardiopulm > cardiac physiology > Flashcards

cardiac physiology Flashcards

1
Q

Aerobic requirements of the heart (factors)

A
  1. Cardiac tissue metabolically active
  2. Cardiac energy needs met in real time by changes in energy production
  3. Cardiac energy needs can increase 9x from rest to heavy exercise
  4. O2 extraction from blood remains fairly constant regardless of workload
  5. Blood flow increases from 80 to 500 ml/min/100g tissue
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2
Q

Cardiac Myocytes traits

A
  1. Cells are Y shaped
  2. Striated
  3. Contain single nuclei
  4. Limited ability to replicate
  5. Linked together by intercalated disks
  6. Lack distinct fiber types
  7. Do not fatigue
  8. All fibers contract with each beat
  9. all cardiac muscle cells contract regardless of HR/contractility
  10. cardiac muscle cells regulate their force production by regulating availability of CA to sarcomeric proteins

GRADED muscle contractions

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3
Q

Cardiac Excitation Contraction Coupling

A
  1. Ca enters myocyte through channels in T tubules
  2. Triggers release of Ca from SR
  3. Ca induced Ca release
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4
Q

P wave

A

depolarization of atria in response to SA node

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5
Q

PR interval

A

delay of AV node to allow filling of ventricles

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6
Q

QRS complex

A

Depolarization of ventricles, triggers main pumping contractions

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7
Q

T wave

A

Ventricular repolarization

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8
Q

ST segment

A

Beginning of ventricle repolarization, should be flat.

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9
Q

AP of cardiac muscles:

Phase 0

A

Rapid Na+ influx through open fast Na channels

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10
Q

AP of cardiac muscles:

Phase 1

A

Transient K channels open and K efflux returns TMP to OmV

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11
Q

AP of cardiac muscles:

Phase 2

A

Influx of Ca2 through L-type Ca2 channels is electrically balanced by K efflux through delayed K channels

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12
Q

AP of cardiac muscles:

Phase 3

A

Ca2 channels close but delayed rectifier K channels remain open and return TMP to -90mV

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13
Q

AP of cardiac muscles:

Phase 4

A

Na, Ca2, channels closed, open K rectifier channels keep TMP stable at -90mB

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14
Q

Absolute refractory period

A

Stage 0-2

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15
Q

Effective refractory period

A

Stages 0-2 (slightly further than absolute)

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16
Q

Relative refractory period

A

Stage 3

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17
Q

SV=

A

LVEDV-LVESV

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18
Q

EF=

A

SV/EDV x 100

or

[(EDV-ESV)/EDV] x 100

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19
Q

EDV avg

A

110-120 ml

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20
Q

ESV avg

A

40-50 ml

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21
Q

SV avg

A

70 ml

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22
Q

EF (ejection fraction) avg

A

60% is wnl

[(EDV-ESV)/EDV] x 100

23
Q

Atria as a primer

A
  • blood flow into atria is continuous
  • 75% blood flows through atria to ventricles during atrial diastole
  • 25% ejecting during atrial systole
  • Loss of 25% has very limited impact on heart at rest
24
Q

Which period of ventricular diastole has the most rapid filling of ventricles?

A

first 1/3

25
Q

Isovolumetric ventricular contraction phase of systole

A
  • lasts .02-.03 seconds

- No change in volume

26
Q

ejection following isovolumetric phase

A
  • occurs when LV SP > 80 mmHg
  • Period of rapid ejection
  • Period of slow ejection (last 30% in last 2/3 of systole)
27
Q

Ventricular Diastole:

Isovolumetric diastole

A
  • Ventricular pressure < aortic pressure. Aortic valve closes and remains closed; no net blood flow
  • Early part of ventricular relaxation
  • Ventricular pressure is decreasing, AV valves and aortic valve are closed
28
Q

When do the AV valves open

A

Atrial pressure > ventricular pressure

29
Q

T/F: elastic recoil maintains a high aortic pressure during diastole

A

True

30
Q

Incisura

A

back flow just as aortic valve is closing

31
Q

Elevated RV pressure suggests:

A

pulmonary HTN
RV failure
CHF
increased blood volume

32
Q

Pulmonary artery pressure

A

Systolic: 20-30 mmHG
Diastolic: 8-12 mmHg
Mean pulm pressure: 25 mmHg

33
Q

What allows pulmonary circulation to function as a low pressure system

A
  1. RV pumps through shorter length
  2. Pulmonary vasculature more compliant
  3. expansion of lungs = vascular dilation
  4. much lower gravity impact
34
Q

CO

A

HRxSV

4-8 L/min

35
Q

EF

A
  • normally 55-70%

- <40% used to suggest Heart failure

36
Q

Cardiac Index

A
  • Ratio of CO : body surface area

- CO/BSA; units = L/min/m^2

37
Q

preload

A
  • amount of venous return

- degree of myocardial distention prior to contraction

38
Q

afterload

A
  • force that ventricles must overcome to eject blood
  • largely dependent on arterial BP and vascular tone
  • increased afterload like “riding uphill”
39
Q

effects of sepsis:

A
  1. cytokines released during sepsis reduces cardiac contractility
  2. Usually associated with normal or elevated CO
40
Q

Which drugs increase cardiac contractility?

A

positive ionotropic drugs

41
Q

Regulation of HR:

sympathetic NS

A
  1. sympathetic nerves course through atria and ventricles

2. beta blockers trx

42
Q

Regulation of HR:

assessment of SNS

A
  1. resting HR
  2. HR recovery
  3. HR response to standing
  4. HR response to valsalva maneuver
  5. BP response to standing
43
Q

Venous Return:

A

amount of venous blood entering R atria

44
Q

Factors controlling venous return/EDV

A
  1. total blood volume
  2. venous BP
    muscle pump
  3. respiration
  4. gravity/posture
  5. Intrapericardial pressure
  6. R atrial pressure
  7. increased thoracic pressure
45
Q

Pulse Pressure

A 
PP = SP - DP
- normal is 120-80=40
- PP considered abnormally low if it is < 25% of SP or < 30 mmHg
- PP abnormally high if >100 mmHg
PP = SV / arterial compliance
46
Q

Mean Arterial Pressure

A 
MAP= DP + 1/3 (SP-DP)
MAP= CO x SVR (systemic vascular resistance)
47
Q

Normal MAP

A

65-110 mmHg

48
Q

Prolonged decreased MAP leads to

A

ischemia

49
Q

Maintenance of MAP

A
  1. Local control
    - increased NO leads to vasodilation and diminished MAP
    - endothelin released in response to decreased MAP leading to smooth muscle constriction
  2. ANS
    - altered sympathetic and parasympathetic input to vascular smooth muscle
  3. renal regulation of blood volume
50
Q

Law of LaPlace

A

T (LV wall stress) = Pressure x Radius

T=PR

51
Q

T/F:

For a given blood pressure, increasing the radius of the cylinder leads to a linear increase in tension.

A

True

52
Q

T/F: For a given blood pressure, increasing the radius of the cylinder leads to a linear decrease in tension.

A

False (decreasing)

53
Q

Atrial Natriuretic Peptide

synthesized and store/released by atrial myocytes in response to:

A
  1. atrial distension (hypervolemia)
  2. angiotensin II stim
  3. sympathetic stim
54
Q

Atrial Natriuretic Peptide

actions

A
  1. involved in long term Na and water balance, blood volume, and arterial pressure
  2. dilates veins reducing central venous pressure, preload, and CO
  3. Increases diuresis and sodium loss ( decreases blood volume)
  4. Decreases renin release, leading to further diuresis

Cardiopulm (20 decks)

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