Cardio Phys Review Flashcards
The ____ interval on EKG represents initial depolarization of the ventricle and increases in conditions such as heart block
PR
The ST segment is isoelectric and represents the period when the ventricles are ________
Depolarized
The resting membrane potential for cardiac action potentials is determined by conductance to _____
K+
[maintanence is by Na/K ATPase]
Phases of ventricular action potential and their associated changes in ion conductance
Phase 0 = Na+ in [depolarization]
Phase 1 = slight K+ out, decrease in Na conductance [initial repolarization]
Phase 2 = Ca++ in, increased K+ conductance [plateau — inward current = outward current]
Phase 3 = K+ out, decreased Ca conductance [repolarization]
Phase 4 = resting potential ~ K+ equilibrium potential [inward current = outward current]
Phases of SA node action potential and their associated changes in ion conductance
Phase 0 = Ca++ in [rapid depolarization]
Phase 3 = K+ out [repolarization]
Phase 4 = Na+ leaks in [slow depolarization]
Phases 1 and 2 not present in SA node APs
Preload corresponds to the _______ volume, which is related to the ______ pressure
End-diastolic; right atrial
[thus when venous return increases, EDV increases and stretches/lengthens the ventricular muscle fibers]
Afterload for the left ventricle is the _____ pressure
Aortic
[increases in aortic pressure cause an increase in afterload on the left ventricle]
Afterload for the right ventricle is the _____ pressure
Pulmonary artery
[increases in pulmonary a. pressure cause an increase in afterload on the right ventricle
_____ length determines the maximum tension or force of contraction in cardiac muscle
Sarcomere
The velocity of contraction at a fixed muscle length is maximal when the afterload is ______
It is ______ by increases in afterload
Zero
Decreased
Increased preload results in a _______ in stroke volume, and thus a _____ in width of the pressure-volume loop
Increase; increase
[opposite is true for increased afterload]
Calculation and normal value for ejection fraction
Ejection fraction = stroke volume/EDV
Normally 55%
Isovolumetric ventricular contraction begins after the onset of the _______ on EKG
QRS wave
The onset of the _______ on EKG marks the end of both ventricular contraction and rapid ventricular ejection
T wave
If the EF increases, there will be a decrease in:
A. Cardiac output B. ESV C. HR D. Pulse pressure E. Stroke volume F. Systolic pressure
B. ESV
When EF increases, a higher fraction of the EDV is ejected in the stroke volume. When this situation occurs, the volume remaining in the ventricle after systole (ESV) will be reduced