Cardiac output

Decreasing the rate of a normal resting HR does not decrease the CO until how many bpm?

20

This is the force the ventricle is working against after the force of contraction.

Afterload

Formula for CO

CO = (O2 absorbed per min by lungs ml/min)/([O2]pv - [O2]pa)

What are the 4 main cellular determinants of contractility?

Calcium Kinetics Myosin ATPase activity ATP levels # of cross-bridges

What are the determinants of Ventricular preload?

Central Venous pressure (CVP) Atrial contribution to ventricular filing pericardial sac pressure ventricular compliance

What is the formula for the ejection fraction?

EF = (SV)/EDV x 100%

This is a commonly used measure of cardiac performance.

Ejection fraction

Which principle is directly related with CO?

Fick's

What is the ejection fraction dependent on?

HR, preload, after load, and contractility

This is commonly used to measure CO. With this calculation, you must extrapolate the early down-slope of the curve to the zero point. Dye is used to measure how well oxygenated blood is.

Indicator Dilution Method CO (dl/min) = (mg of dye injected x 60)/(average dye conc per dl of blood mg/dl x duration of curve sec)

If the R ventricle pumps slightly more blood the the L ventricle, how will the heart compensate?

L atrial filling and pressure will ↑, leading to an ↑ in SV

If the SV on the L side rises higher than the R side, how does the heart compensate?

L atrial pressure drops, this decreases L ventricular filling and reduces the L sides SV

What is responsible for the actin-myosin cross-bridge cycling rate?

Myosin-ATPase

This is when ventricular pressure continues to ↑ because the ventricle continues to contract and generate pressure while ejecting blood into the aorta.

Rapid ejection

This is when the ventricular pressure begins to ↓ later towards the end of systole.

Reduced ejection

What is stroke work?

SV x mean arterial pressure

If end-Diastolic volumes at different preloads are about the same, the SV volume will change in proportion to preload. What is this statement saying?

The heart pumps approximately the amount of blood that it receives.

What is the relationship that relates ventricular filling (preload) and ventricular contractile performance referred to?

Ventricular Function Curve or Frank-Sterling Law of the Heart.

How is increased calcium sensitivity observed on a graphical relationship between tension and intracellular free calcium?

a leftward shift

What follows after the closure of the aortic valve?

a period of isometric relaxation

When does the aortic valve close?

after reduced ejection

Stretching associated with increased ventricular filling causes what?

an increase in calcium release from the SR and an increase in calcium sensitivity of the contractile filaments.

If there is a decrease in after load, when will the aortic valve open?

at a lower pressure, resulting in an increased SV

If there is an increase in after load, when will the aortic valve open?

at an increased pressure, resulting in a decrease in SV

When does ventricular volume reach its max?

at the end of atrial contraction

What is the major overall determinant of preload?

atrial pressure

Why is there decreased SV if there is an increase in after load?

because there is a slower shortening velocity and therefore less shortening during systole, resulting in a lower SV

Why can the ventricles dilate beyond the normal limit in heart failure?

because they exhibit increased compliance

How do the sarcomeres adapt to allow the ventricle to dilate, without stretching the sarcomeres beyond their optimal length?

by realigning so that there are more sarcomeres in a series

This is the amount of blood pumped by the ventricle each minute, normally around 5-6 L/min.

cardiac output

The greater the ______ of the ventricular walls, the ______ the ↑ in ventricular pressure with ventricular filling.

compliance; smaller

This is the derivative or rate of the max rate of ventricular pressure rise during the isovolumetric period, and can be easily measured in the clinic. Changes in preload and after load can alter this value.

dP/dtmax

What occurs if there is an increase in after load?

decreased SV

What is the major determinant of after load?

diastolic pressure

What is the normal value for the ejection fraction?

greater than or equal to 55%

When is the contribution of atrial contraction to ventricular filling proportionally greater?

high HR

With age, the aorta and other large arteries lose compliance. what does this result in?

increase in after load on the LV

What occurs if there is a decrease in after load?

increased SV

The dependence of ventricular contractile performance on ventricular filling is what kind of property?

intrinsic property (does not depend on nerves or hormones)

In which way does the aortic valve effect after load?

it usually doesn't - unless it is stenosed.

Cardiac muscle normally functions at what?

less than optimal sarcomere length

What is one cardiac cycle represented by?

one counterclockwise circuit of the P-V loop

This is essentially the amount of ventricular chamber filling.

preload

What is stroke volume dependent on?

preload, after load, and contractility

What does the P-V loop illustrate graphically?

pumping mechanics of the heart

How is the contractility of an intact heart best indicated on the P-V loop?

shift in position of aortic valve closure

This is the difference in the ventricular blood volume at the end of diastole (EDV) and the ventricular blood volume at the end of systole (ESV).

stroke volume

What is cardiac output dependent on?

stroke volume and HR: CO = SV x HR

When the ventricular pressure exceeds the aortic diastolic pressure, what occurs?

the aortic valve opens

In regards to the cardiac cycle, what happens with ↑HR?

the cardiac cycle ↓ which leads to ↓ ventricular filling, leading to ↓ SV

What is after load closely related to?

the mean aortic pressure

With the onset of systole, ventricular pressure ↑. When ventricular pressure exceeds the atrial pressure, what occurs?

the mitral valve closes

At normal systolic arterial pressure, what is CO almost entirely determined by?

venous return to the heart

What are the major physiological determinants of Central Venous Pressure (CVP)?

venous smooth muscle tone(compliance) blood volume body position intrathoracic pressure skeletal muscle pump resistance to blood

What is atrial pressure governed by?

ventricular filling pressure

What does a shift up and to the left on a ventricular function curve indicate about the contractility?

↑ contractility or a ↑ SV

What are the effects of an ↑ in cardiac sympathetic activity, ↑ epi, or ↑ Nepi?

↑contractility and stroke volume

This results in ↑ force of contraction, ↑ SV, and thus an ↑ in CO.

↑ventricular filling/preload

What does a shift down and to the R on a ventricular function curve indicate about the contractility?

↓ contractility