S5 Control Of Cardiac Output Flashcards
Define Afterload
The load the heart must eject blood against (roughly equivalent to aortic pressure)
Define preload
Amount the ventricles are stretched during diastole related to EDV or CVP
Define Total Peripheral resistance
Resistance to blood flow in systemic vasculature.
Where is the biggest drop in blood pressure?
In the arterioles as they exert the most resistance. This drops pressure in venous system but increases pressure in arterial system.
What are the effects of changing the TPR?
If:
TPR decreases, CO unchanged - arterial pressure decreases, Venous pressure increases.
TPR increases, CO unchanged - arterial increase, venous decrease.
CO increase TPR unchanged - arterial increases, venous decreases.
CO decreases, TPR unchanged - arterial pressure will fall, venous pressure will increase.
What changed occur in circulation when there is a need for more blood at tissues?
Precapillary sphincters will dilate
Peripheral resistance falls.
Heart need to pump more so arterial pressure doesn’t fall
Heart detects changes in arterial blood pressure (aBP) and central venous pressure (CVP)
Responds by either intrinsic or extrinsic mechanisms.
How does one calculate cardiac output?
CO = SV x HR
How does one calculate stroke volume?
SV = EDV - ESV
~70ml
Can SV be increased?
Yes - by increases EDV or decreasing ESV. (Regurgitation)
At what Phase do the ventricles fill?
Diastole.
How is Venous pressure related to ventricular pressure?
Higher the Venous pressure, more heart fills
More the ventricle fills, the higher the ventricular pressure.
What is the relationship between venous pressure and ventricular pressure called?
The Ventricular Compliance curve.
What is the Frank-Starling law of the heart?
The more the heart fills, the harder it contracts.(to a point)
The harder it contracts, the bigger the stroke volume.
What can cause increased filling of the ventricles?
Increased Venous pressure.
What does the Starling curve show?
Increasing venous return leads to increased left ventricular end diastolic pressure (LVEDP) and volume (‘increased preload’).
This results in extra blood being pumped out of the ventricle.
