Heart 7 Flashcards

1
Q

Four factors that determine cardiac output

A

Heart rate, afterload, preload, and contractility

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2
Q

Preload

A

The muscle load BEFORE contraction is initiated; dependent on ventricular filling

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3
Q

Afterload

A

Muscle load AFTER contraction initiation; determined by arterial pressure

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4
Q

What is the difference in muscle tension between preload and afterload?

A

Preload will generate passive tension on the heart while the ventricles are filling; afterload will be any force within the heart that resists muscle shortening

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5
Q

Contractility

A

The inherent ability of actin and myosin to form cross-bridges and generate contractile force

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6
Q

What does contractility have to do with preload and afterload?

A

Nothing

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7
Q

What primarily determines contractility?

A

Intracellular calcium concentration

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8
Q

Contraction

A

Process by which muscle generates tension or force

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9
Q

Two types of muscle contraction

A

Isometric contraction and isotonic contraction

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10
Q

Isometric contraction

A

Contraction without shortening; usually occurring when the heart can’t generate enough force to meet the afterload

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11
Q

Isotonic contraction

A

Contraction with shortening and constant force; occurs whenever the heart is able to meet the afterload

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12
Q

Contraction types during a normal cardiac cycle

A

Initially the muscle generates isometric contractions until the semilunar valves blow open, in which case they become isotonic contractions

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13
Q

Length-Tension relationship of cardiac muscle

A

Increase in resting cardiac muscle length will increase contraction strength

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14
Q

Which cardiac factor is related to the length-tension relationship?

A

Preload

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15
Q

Resting tension

A

Amount of tension that develops passively by stretching the muscle (i.e., increasing the preload).

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16
Q

Graphic view of compliance

A

Slope of the resting tension curve is determined by this

17
Q

Active tension

A

Amount of isometric tension that is developed by muscle contraction at a particular muscle length

18
Q

Graphic view of contractility

A

Slope of the active tension curve on the length-tension graph

19
Q

Compliance

A

Change in volume in relation to a change in pressure: primary determinant of resting cardiac tension

20
Q

Which type of muscle has a lower compliance: skeletal or cardiac?

21
Q

What is another word for contractility?

22
Q

What would changes in inotropy do to the length-tension graph?

A

Positive inotropic effect: active curve goes up and to the left
Negative inotropic effect: active curve goes down and to the right

23
Q

How does an increase in preload cause an increase in tension development?

A

Creates more optimal overlap between thick and thin filaments;
increases calcium sensitivity of myofilaments

24
Q

Changes in preload and their effect on muscle shortening

A

Increase in preload: more muscle shortening

Decrease in preload: less muscle shortening

25
Changes in afterload and their effect on muscle shortening
Increase in afterload: less muscle shortening | Decrease in afterload: more muscle shortening
26
Increase in contractility achieved by sympathetic nerve stimulation increases what three things?
Amount of muscle shortening, velocity of shortening, and rate of relaxation
27
Force generated by the muscle determines . . .
velocity of shortening.
28
Index of contractility
Maximal velocity of shortening with no load"
29
Maximal isometric force
When the muscle is unable to meet the afterload
30
Increasing preload has what effect on the force-velocity graph?
It has no effect on Vmax, but will increase the velocity of shortening, moving the X-intercept over to the right
31
Increasing contractility has what effect on the force-velocity curve?
Both increases Vmax and the velocity of shortening, increasing both the X- and Y-intercepts