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
