Cardiac output
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Cardiac Output. Which Hearts Are Healthy?. End-diastolic volume. Stroke volume. Left Ventricle Volume (ml). End-systolic volume. Stroke Volume?. A. B. C. D. E. Heart Rate (beats/min). 88. 159. 81. 70. 75. Stroke Volume (ml). 92. 100. 67. 79. 70. Cardiac Output (L/min). 8.1.

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Cardiac Output

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Cardiac Output


Which Hearts Are Healthy?


End-diastolic volume

Stroke volume

Left Ventricle Volume (ml)

End-systolic volume

Stroke Volume?


A

B

C

D

E

Heart Rate (beats/min)

88

159

81

70

75

Stroke Volume (ml)

92

100

67

79

70

Cardiac Output (L/min)

8.1

15.9

5.4

5.5

5.3

Cardiac Output?

HR X SV


What determines the stroke volume?

  • Preload: how stretched the muscle is when it starts to contract.

  • Afterload: the active stress the muscle has to generate in order to shorten

  • Contractility: something else, but what?


fulcrum

Preload


The effect of changing preload

highest preload

lowest preload


Afterload


The effect of changing afterload


Positive inotropism =

contractility

Normal

Negative inotropism =

contractility

Contractility


Cellular Mechanism of Preload Effect on Strength of Contraction

Length sensitivity of cardiac and skeletal muscle result from different mechanisms.


Myosin Heads

ThinFilament

1.0 µm

Length sensitivity of skeletal muscle

Thick Filament

1.6 µm

0.2 µm

Optimum

Overlap


Length sensitivity of cardiac muscle

Skeletal

Cardiac


Stretch Muscle

How does preload affect force of cardiac muscle contraction?

Muscle Length

Force of Contraction

Cytoplasmic [Ca++]

Force of Contraction


Length Sensitivity of Cardiac Muscle

  • Increased Ca++ entry through Ca++L channels

Ca++

  • Increased sensitivity of troponin C to Ca++

Troponin

Complex

Myosin Head

Myosin Binding Site


Preload Afterload& Contractilityin the Working Heart


mmHg

kPa

16

120

12

80

End-diastolic LV pressure

Pressure

8

40

4

0

0

Left Ventricle Volume (ml)

150

100

50

End-diastolic LV volume

0

Preload depends on end-diastolic LV pressure and volume


Preload depends on end-diastolic LV pressure and volume


Right atrial pressure as a measure of preload

PRA

Systole

Diastole


Starling’s Law of the Heart

Ventricular

Function Curve

The inflow equals the output


Increased afterload

LV Systolic ejection pressure

shorter ejection time

reduced stroke volume

Afterload depends on systolic ejection pressure

mmHg

kPa

16

120

12

80

Pressure

8

40

4

0

0

Left Ventricle Volume (ml)

150

100

50

0


mmHg

kPa

16

120

12

80

LV Systolic ejection pressure

Pressure

8

40

4

0

0

Afterload depends on systolic ejection pressure


Contractility

  • Anything that influences stroke volume without acting through preload or afterload

  • Sympathetic Nervous System

  • Health of Heart Muscle

  • Coronary Perfusion

  • Drugs


Contractility

“Squeezability”: How tightly can the ventricle squeeze by the end of ejection.


phosphorylates

L-type Ca++

channel

phosphorylates

SR Ca++ ATPase

to increase

Ca++ reuptake

ß-adrenoceptor influence on contractility

phosphorylates troponin to desensitize actin

Enhanced Relaxation

Enhanced Contraction


EKG

Pressure

Aortic

Left ventricular

Left ventricular volume

Sympathetic Effect on the Heart


Stroke Volume

Ejection Fraction =

End-Diastolic Volume

Measuring ContractilityA. Ejection Fraction

Volume

Left Ventricle

150

(ml)

100

Stroke Volume

End-Diastolic LV Volume

50

0

End-Systolic LV Volume


Stroke Volume

Ejection Fraction =

End-Diastolic Volume

Measuring ContractilityA. Ejection Fraction


mmHg

kPa

16

120

12

Slope = LV dP/dt

80

Pressure

8

40

4

0

0

Left Ventricle Volume (ml)

150

100

50

0

Measuring ContractilityB. LV dP/dt Max


A

B

C

D

E

LV dP/dT

1225

1700

900

1233

1209

Measuring ContractilityB. LV dP/dt Max


Increased contractility

Decreased contractility

Measuring ContractilityC. Ventricular Function Curve

16

12

Cardiac

8

Output

(liters/min)

4

0

0

4

8

12

(mm Hg)

(kPa)

0

1

2

Right Atrial Pressure


100

50

0

Measuring ContractilityC. Ventricular Function Curve

B

A

D

Stroke

E

C

Volume

(ml)

(mm Hg)

0

8

16

3

0

1

2

Left Atrial Pressure

(kPa)


Measuring Contractility

  • Ejection Fraction

  • LV dP/dt max

  • Ventricular Function Curve

  • Maximal Systolic Elastance


Diastolic Pressure-Volume Curve

Left Ventricular Pressure

Left Ventricular Volume (ml)


Eccentric (dilated)

Normal

Stiff Ventricle

Diastolic dysfunction

Pressure Overload

Px r

stress =

2h

stress = P xr

2h

Hypertrophy of Left Ventricle

Left Ventricular Pressure

Left Ventricular Volume (ml)


End-systolic Pressure Volume Curve

Left Ventricular Pressure

End-systolic

(contracted myocardium)

mm Hg

kPa

40

300

30

200

20

Diastolic

(relaxed myocardium)

100

10

0

0

0

50

100

150

200

Left Ventricular Volume

(ml)


elastance

The “time-varying elastance” model

Left Ventricular Pressure

mm Hg

kPa

40

300

Emax

30

200

20

100

10

minimum elastance

0

0

0

50

100

150

200

Left Ventricular Volume

(ml)


Emax

“Afterload”

Preload

Measuring ContractilityD. Emax

Left Ventricular Pressure

mm Hg

kPa

Contractility

(slope of end-systolic PV line)

40

300

30

200

20

100

10

0

0

0

50

100

150

200

Left Ventricular Volume

(ml)


same contractility

same afterload

Increased preload

stroke volume

Left Ventricular Pressure

Increased Preload

Left Ventricular Volume (ml)


same contractility

increase afterload

stroke volume

same preload

Left Ventricular Pressure

Increased Afterload

Left Ventricular Volume (ml)


Preload

increased

Left Ventricular Pressure

Afterload compensation

same contractility

increase afterload

Stroke volume restored

Left Ventricular Volume (ml)


Hypertension and Cardiac Work

Left Ventricular Pressure

External Work

increase afterload

Contraction I

Contraction 3

Left Ventricular Volume (ml)


Hypertension and Cardiac Work

Left Ventricular Pressure

Internal work

increase afterload

Left Ventricular Volume (ml)


stroke volume

Left Ventricular Pressure

Increased Contractility

increased contractility

same afterload

same preload

Left Ventricular Volume (ml)


Left Ventricular Pressure

Decreased Contractility

decreased contractility

same afterload

same preload

Left Ventricular Volume (ml)


Preload compensation

Left Ventricular Pressure

decreased contractility

same afterload

Left Ventricular Volume (ml)


Which Hearts Are Healthy?


Left Ventricular Pressure (mmHg)


Which Hearts Are Healthy?

A. Pregnant

3rd trimester


Which Hearts Are Healthy?

B.Exercising


Which Hearts Are Healthy?

C.Systolic Dysfunction


Which Hearts Are Healthy?

D.Normal


Which Hearts Are Healthy?

E.Diastolic Dysfunction


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