L11 Cardiac Muscle Mechanisms

Question 0

Isometric contraction

Answer 0

Contracting without shortening; what the heart does right before ejection when it is meeting the afterload

Question 1

The 4 determinants of Cardiac Output:

Answer 1

Heart Rate: determines output bc higher HR brings in more Ca which boosts contractility

Contractility: based off of Ca . If having contractility problems, give diuretic to lower volume pumped out of heart

Preload: force placed on the muscle before contraction; filling of the heart with blood stretches the cell and generates tension (EDVolume)

Afterload: load on the muscle that prevents it from shrinking; what inhibits the heart from ejecting blood (ie: arterial pressure, hypertension)

Question 2

Isotonic contraction

Answer 2

Shortening of the muscle; what the heart does when it has met the afterload and is actively ejecting blood

Question 3

Resting Diastolic tension

slope = compliance

Answer 3

tension from stretching the muscle before in shortens
Higher resting tension comes from higher Preload and is influenced by Compliance
Higher compliance = more stretchy
Lower compliance (from ischemia) shifts the curve up, increases slope

Higher tension leads to higher higher pressure, which means more blood ejected (Length-Tension relationship)
more stretch = more contraction upon ejection

Question 4

Active Systolic tension

slope = contractility

Answer 4

The isometric tension created when a muscle contracts with a certain preload.
Represents Stroke Volume (kind of, bc SV = EDV-ESV) and is influenced by contractility.
Larger slope = more contractility

heart failure - reduced contractility - shifts curve DOWN, same length change generates less pressure

Question 5

How does preload affect tension development in cardiac muscle:

Answer 5

More preload means the muscle is stretched farther apart before contracting. This creates more optimal overlapping space between thick/thin filaments so contraction is stronger

Question 6

Compliance

Answer 6

Definition: the change in volume in relation to the change in pressure
∆V/∆P -OR- ∆L/∆Tension

a muscle that has a very low compliance (the heart) will change slightly in length but DRASTICALLY in tension, meaning that a little stretch goes a long way

Question 7

Effects of preload on contraction

Answer 7

more preload, stronger contraction

Question 8

Effects of afterload on contraction

Answer 8

more afterload, less shortening

Question 9

Effects of Contractility on contraction

Answer 9

INDEPENDENT OF PRELOAD AND AFTERLOAD
determined by intracellular Ca content

more contractility = increases peak isometric tension (greater potential for contraction), and enhances relaxation time

more contractility = allows the muscle to shorten to a *shorter level than normal, so more shortening and stronger contraction

Question 10

Force-Velocity relationship

Answer 10

higher force = lower velocity –> higher force could be more afterload

Preload:
if you increase the preload, you stretch the muscle more so the velocity INCREASES

Afterload:
if you increase the afterload, you make it harder to contract, so the velocity DECREASES

Contractility:
if you increase contractility, you increase max isometric force, which gives more potential for contraction, so velocity INCREASES