Lecture 11 - Cardiac Function Flashcards
What are the 4 determinants of Cardiac Output?
- Heart Rate
- Contractility
- Preload
- Afterload
What is isometric contraction?
contraction WITHOUT change in length (shortening)
What is the load on the muscle BEFORE contraction is initiated?
PRELOAD
- stretches the muscle length and creates PASSIVE tension
- same as END-DIASTOLIC VOLUME
(volume before the LV contracts - exerts wall pressure)
What is the load on the muscle AFTER contraction is initiated?
Afterload
- load on the muscle AFTER contraction is initiated
- ex: arterial pressure reisting LV contraction
What is any force that resists muscle shortening?
AFTERLOAD
- based on arterial BP, heart size, aortic valve)
What is contractility? What is it based on? What is it INDEPENDENT of?
- ability of actin & myosin cross-bridges to form & generate contractile force
- Based on intracellular Ca
- Independent of PRELOAD and AFTERLOAD
If a muscle is unable to create enough FORCE to overcome after load (ex: push aortic valve open) then the contraction is:
- Isometric
- Isotonic
ISOMETRIC (no muscle shortening)
What is ISOTONIC contraction?
contraction WITH muscle shortening but with CONSTANT FORCE (no change)
If a muscle IS able to generate enough force to meet the after load, the contraction is:
- Isotonic
- Isometric?
ISOTONIC
- muscle shortening occurs
During a normal cardiac cycle, what comes first? Isometric or Isotonic contractions?
1st = ISOMETRIC (increasing force, but muscle has not shortened yet)
2nd = ISOTONIC
(muscle shortens at a constant max force)
ex: lifting a 10 lb weight
- first isometric (muscle shortens) then isotonic
An increase in cardiac muscle length will increase or decrease contraction strength?
Increase contraction strength
If you increase the amount of tension that develops passively by stretching the muscle, how does this affect PRELOAD?
Increases preload
ventricular filling volume or end-diastolic volume
The slope of the Resting (Diastolic) Tension graph is determined primarily by what?
COMPLIANCE
change in volume/ change in pressure
(change in length/ change in tension)
- increase tension = LESS compliant
A decrease in cardiac muscle compliance, increases or decreases the slope of the Resting Tension(Diastolic)?
INCREASES the slope (pressure on y-axis & length on bottom)
- Compliance inversely related to pressure
- so once compliance decreases, greater tension/pressure is felt during PRELOAD
- as the tension increases
How can compliance be explained in terms of a bike tire/water ballon analogy?
the bike tire has greater tension and is thus less compliant
- water balloon has less tension and is MORE compliant
Name the term for the following:
The amount of isometric tension that is developed by muscle contraction at a particular muscle length (preload).
AFTERLOAD
In the systolic tension curve, what represents the slope?
CONTRACTILITY
- as contractility increases the line moves UP and to the left
i.e. sympathetics
What has higher compliance, skeletal or cardiac muscle?
SKELETAL
- cardiac is less compliant and developed tension at shorter muscle lengths than skeletal
- higher pressure at a given volume/length
Why do cardiac cells primarily work on the ASCENDING limb of the LENGTH-TENSION graph?
- because they have relatively LOW compliance
In the heart, what does SYSTOLIC tension curve represent?
STROKE VOLUME
BOARDS QUESTION:
How does the infusion of fluid into the venous system increase cardiac output?
- INCREASES THE SARCOMERE LENGTH of the muscle cell
- increases preload and thus contraction & cardiac output
- increases BP
Determine which statement determines Systole & Diastole
- Passive Increase in force
- Actin & Myosin interaction
- Diastole
2. Systole
What is a component in a sarcomere that generates RESISTANCE upon lengthening of the sarcomere ?
TITIN!!
- think of a sarcomere like a rubber band
if you increase end-diastolic volume, is contraction increased or decreased?
INCREASED
What is the inherent ability of actin & myosin to generate tension? This is determined by what?
CONTRACTILITY (inotropy)
intracellular Ca!
(increase Ca = increase contractility)
A positive inotropic affect will shift the length-tension graph where?
UP and LEFT
ex: w/ sympathetics
- able to contract more
How does an increase in preload cause an increase in tension development?
- Increase in Actin-Myosin overlap
2. increase Ca sensitivity of myofilaments
How does one change the slope of the Diastolic tension? Systolic?
- change Compliance
- increase slope by DEcreasing compliance - Change Contractility
- increase slope by increasing compliance
Changing preload on isotonic contractions, changes what?
MUSCLE length
Describe the affects of increasing and decreasing preload on muscle shortening in isotonic contractions.
Increasing preload INCREASES muscle shortening
decreasing preload decreases shortening
less passive force
Describe the affects of increasing and decreasing AFTERLOAD on muscle shortening in ISOTONIC contractions.
INCREASING after load, DECREASES muscle contraction
-as arterial pressure goes up = less shortening, less STROKE VOLUME
decreasing after load, decreases muscle contraction
Increasing contractility does what to the PEAK ISOMETRIC tension and rate of relaxation? How can this affect be achieved?
- Increases BOTh the isometric tension & the rate of relaxation (shifts graph up and left)
- oppostive occurs when contractility is reduced –> graphed pushed further RIGHT and relaxation is slower –> wider curve) - Sympathetic stimulation! (positive inotropic)
At constant after load & preload, does increasing contractility increase or decrease muscle shortening?
INCREASES (greater change in length)
- think of water balloon vs. bike tire
What affect would INCREASING contractility have on the following:
- Muscle shortening
- Velocity of shortening
- Rate of relaxation
- INCREASE shortening
- Increase Velocity
- Increase rate of relaxation
(sympathetic stimulation via SERCA activation & Ca uptake)
Increasing the after load, increases or decreases the velocity of ISOTONIC (same force) contraction?
DECREASES the after load
What is Vmax?
max velocity of shortening with no load
What is the term for when a muscle cannot meet the after load?WHat value does it equal?
MAXIMUM VELOCITY OF SHORTENING
= zero
How does Increasing the preload affect the force-velocity curve in terms of afterload?
Increasing preload increases the velocity
- shifts the line RIGHT
- line is longer –> more force and greater velocity
(at any after load)
Is Vmax changed when preload is changed? What changes Vmax?
NO!
contractility changes max (it increases the maximum velocity!!)
How does increasing CONTRACTILITY affect the force velocity curve?
SHIFTS it UP and and to the right
- increases Vmax
Changes in contractility and preload change what value ultimately?
the MAXIMUM ISOMETRIC FORCE
at zero
Increasing afterload causes what changes to
- Velocity of muscle shortening
- Amount of muscle shortening
DECREASES velocity & amount of shortening
- think of something pushing against a saloon door on 1 side, but you don’t have enough force to push against them and open the door (so velocity and shortening is decreased)
At any given after load
Decreasing:
1. Preload
2. Contractility
changes the velocity of shortening how?
DECREASES the velocity of shortening
When an infarct occurs, is compliance of the tissue increased or decreased?
DECREASED
- slope on length-tension graph is increased
- pressure goes up abnormally & prevents normal filling of blood
What are two mechanisms for rapid relaxation?
- Phospholamban inhibition - therefore SERCA is active
2. lower affinity of Troponin C to Calcium
How is stroke volume affected if velocity of shortening is reduced?
LESS STROKE VOLUME!
- imagine a water balloon squeeze quickly = water shoots up
squeeze slowly = water just flops over (not enough pressure)
What is a clinical case we heard about that the after load is increased so aortic valve is not opening and a “thump” is heard?
PVC
