All about the Wiggers Diagram Flashcards
Define: Cardiac Output
CO is the flow of blood into the aorta from the heart
What transmitter do sympathetic nerves use on the heart? On what type of receptor does it act? What happens to the second messenger? What results from stimulation?
Norepinephrine acts on B1 adrenergic receptors. This increases cAMP and increases the HR and contractility of the muscle
What transmitter do parsympathetic nerves use on the heart? On what type of receptor does it act? What happens to the second messenger? What results from stimulation?
Acetylcholine which acts on M2 receptors to decrease cAMP, decreasing HR and contractility
What are some intrinsic mechanisms that can regulate CO?
EDV (increased preload) and a change in the membrane potential
How is cardiac output related to oxygen consumption?
Directly. Increased O2 consumption increases CO
What are some factors that increase CO?
Exercise, fever, anxiety, greater body weight, pregnancy, hyperthyroidism, anemias
What are some factors that decrease CO?
Sleep, aging, severe anoxia, hemorrhage, heart disease
How does exercise affect cardiovascular function? Give specific mechanisms
Mechanically, muscle contractions enhance venous return which increases EDV and thus CO. Chemically, lower blood O2 levels with higher blood CO2 levels stimulate local vasodilation which decreases MAP. Baroreceptors respond to this by stimulating an increase in CO
In a normal ECG, what does the P wave represent? What about the PR interval? The QRS complex? The ST segment? The T wave?
P wave- atrial depolarization PR interval- atrial contraction QRS complex- ventricular depolarization (and atrial repolarization) ST interval- ventricular contraction T wave- ventricular repolarization
How do the different waves and intervals of the EKG correspond to the phases of the cardiac cycle?
QRS complex- Phase 0 (inward Na current)
ST interval- Phase 2 (plateau, inward Ca and outward K currents)
T wave- Phase 3 (outward K current)
TP segment and P wave- Phase 4 (iK1 channel and outward K current)
When does most ventricular filling occur? What is the significance of atrial contraction?
Early in diastole (before atrial contraction). Atrial contraction is at the end of diastole and contributes to a small change in ventricular pressure
Why does LV volume increase but pressure decreases at the beginning of diastole?
The forward momentum of the blood expands the ventricles upon filling, causing an increase in volume and a decrease in the ventricular pressure
Why does blood get ejected from the LV? Is this always true?
P (LV) > P (aorta) during rapid ejection of blood
During slow ejection of blood, P (aorta) is greater and blood moves into the aorta because it has enough forward momentum to keep moving forward while the ventricle relaxes
What do the waves in jugular pulse represent? (A, C and V)
A- atrial contraction
C- closure of tricuspid valve
V- atrial filling and emptying
What does the S1 heart sound correspond to? What about the S2 sound? S3? S4?
S1- “lub”, mitral valve closure (end of diastole)
S2- “dub”, aortic valve closure (end of systole)
S3- diastolic filling “gallop.” recoil of ventricles that have limited compliance
S4- Atrial contraction “gallop.”
Describe what occurs to form the dichotic notch
In the aortic pressure curve, pressure drops slightly at the end of systole then rises a bit. This is because when the aortic valve closes, some blood moves against it towards the ventricle. The valve catches it and drives it forward, increasing the pressure in the aorta slightly
Which atrium contracts first? Which ventricle?
Right atrium is first. Left ventricle is first
Which valve is open for a longer period of time: mitral or tricuspid? How about aortic or pulmonic?
Tricuspid and pulmonic are open longer
Why does the left ventricle undergo isovolumic contraction and relaxation?
It needs to exceed P (aorta) to pump the blood into it. But it also needs to be less than P (LA) so it can receive blood in diastole. The isovolumic contraction and relaxation allow it to change in pressure to do these things
On a pressure-volume loop, how would you define ventricular stroke work?
The area inside the loop
What are some factors that influence stroke volume?
Increase SV: increased contractility, increased EDV, increased ventricular compliance, increased filling time
Decreased SV: Increased afterload, increased HR, increased atrial filling pressure
Define: ejection fraction. How would you calculate it?
EF= SV/EDV. The proportion of blood ejected by the ventricle in 1 contraction. In a normal person, is about 55%
