Cardiac Cycle Regulation (Hassid)

Front 1

What is the primary determinant of arterial resistance?

Back 1

Radius of resistance vessels

Front 2

True or false. The only regulator of cardiac output is the heart itself.

Back 2

False!
Also depends on VASCULAR FUNCTION because the cardiovascular system is a loop.

Front 3

What does the cardiac function curve define?

Back 3

Ventricular output as a function of ATRIAL pressure.

Front 4

What does the vascular function curve define?

Back 4

Venous return as a function of atrial pressure.

Front 5

What is steady state cardiac output?

Back 5

Ventricular output occurring in the INTACT system (heart and blood vessles operating together) = VENOUS RETURN.

Front 6

THE CARDIAC FUNCTION CURVE DETERMINES _________________AS A FUNCTION OF ________________. THUS, IN THE FORMALLY ISOLATED HEART, ATRIAL PRESSURE IS THE______________ AND __________________ IS THE DEPENDENT VARIABLE. HOWEVER, IN THE INTACT SYSTEM, ATRIAL PRESSURE IS NOT AN _________________, BECAUSE IT IS DETERMINED BY THE SIMULTANEOUS ACTIVITY OF THE VENTRICLES AND THE BLOOD VESSELS.

Back 6

ventricular output
atrial pressure
independent variable
ventricular output
independent variable

Front 7

What is atrial pressure determined by?
Which is determined by....

Back 7

Volume of fluid in the atria
Vascular function (causing blood to return to atria) and by ventricular function (causing blood volume to leave atria)

Front 8

What does this graph show?

Back 8

Ventricular output as a function of right atrial pressure.
The greater the atrial pressure, the greater the ventricular output (up to a certain physiological level).

Front 9

Why is increased atrial pressure associated with increased ventricular output?

Back 9

This is why.

Front 10

What are factors that directly set the cardiac function curve?

Back 10

SYMPATHETIC AND PARASYMPATHETIC ACTIVITY
INTRINSIC VENTRICULAR EFFECTIVENESS
AFTERLOAD (AORTIC PRESSURE)
INTRAPLEURAL (INTRATHORACIC) PRESSURE

Front 11

What is the influence of sympathetic/parasympathetic activity on the cardiac function curve?

Back 11

Sympathetic activity at rest is always greater than zero --> the cardiac curve can move up or down with change in activity
Parasympathetic activity changes the cardiac curve opposite to sympathetic activity via effect on heart rate.

Front 12

What is the influence of intrinsic ventricular effectiveness on cardiac function curve?

Back 12

At any right atrial pressure, the ventricular output can change, based on the change of cardiac function curve. HYPEREFFECTIVE OR HYPOEFFECTIVE

There are degrees of intrinsic effectiveness depicted by the various cardiac function curves.

Note the severely diminished curve in systolic heart failure.

Front 13

What is the influence of afterload on cardiac function curve?

Back 13

Increase in afterload decreases stroke volume.

Front 14

What is the influence of intrapleural (intrathoracic) pressure on the cardiac function curve?

What is the net stretch on a ventricle determined by?

Back 14

Net stretch = intraventricular pressure (end diastolic pressure) minus extraventricular pressure (intrapleural or intrathoracic pressure)

As pressure outside decreases (deep breathing), net stretch is increase = greater ventricular output

*note that flat portion of curve remains the same

Front 15

Why does intrapleural pressure influence the cardiac curve?

Back 15

Net stretching = end diastolic pressure (pressure inside ventricles) - intrapleaural pressure (pressure surrounding ventricles)

Increase intrapleural pressure = decreased ventricular stretch = decrease stoke volume

Front 16

What is the vascular function curve?

Back 16

Defines venous return as a function of arterial pressure

INDEPENDENT OF CARDIAC OUTPUT

Front 17

Draw the vascular function curve and label
Plateau, transitional zone, down slope, mean systemic filling pressure

What sets x-axis intercept?
What sets the slope of the curve?

Back 17

You did it! Yay!

Systemic filling pressure
Resistance to venous return

Front 18

Need some help understanding this one.

Back 18

Maybe it will happen in class?

Front 19

What is filling pressure (why was this put AFTER the graphs)?

Back 19

Pressure required to fill blood vessels BEYOND their intrinsic volume.

THE FILLING PRESSURE SHOULD REALLY HAVE BEEN TERMED THE “OVERFILLING” PRESSURE, BECAUSE IT IS THE PRESSURE REQUIRED TO FILL THE BLOOD VESSELS BEYOND THEIR INTRINSIC CAPACITY i.e. THE UNSTRESSED VOLUME.

Front 20

What is intrinsic volume?

Back 20

"Unstressed volume"
Volume that just fills the blood vessels completely --> doesn't require "stressing" or stretching them

Front 21

How do you measure the filling pressure?

Back 21

THE FILLING PRESSURE CAN ONLY BE MEASURED AT ZERO CARDIAC OUTPUT, BECAUSE IN THE FUNCTIONING SYSTEM WITH A CARDIAC OUTPUT, THERE IS NO UNIQUE VASCULAR PRESSURE AND THE PRESSURE REFLECTS THE FUNCTION OF BOTH VENTRICULAR OUTPUT AND VENOUS RETURN.

Front 22

What components determine filling pressure?

Back 22

Unstressed volume (at zero at this point) = anything beyond is filing pressure
Compliance of blood vessels
Blood volume

Front 23

What is the effect of sympathetic activity?

Back 23

The greater the sympathetic activity, the lesser the unstressed volume --> less the compliance due to stiffer blood vessels
Opposite for decreased sympathetic activity

Review this slide!

Front 24

What are the physiological determinants of vascular function curve?

Back 24

Reproduce this slide!

Front 25

What is the effect of changing systemic filling pressure without changing peripheral resistance on vascular function curve?
Think about the slope.

Back 25

Slope will stay the same because resistance is the same.

If you double filling pressure and keep resistance the same, the flow must double also.

Review Hassid's notes on this also.

Front 26

What is we change the total peripheral resistance? What effect does this have on the vascular function curve?
Think about the slope again --> the slope reflects resistance!

Back 26

Increase in resistance = decrease in slope (counter clockwise rotation)

Review Hassid's notes on this also.

Front 27

What two things can cause venous return to change?

Back 27

Changes in filing pressure and/or TPR

Front 28

What are steady state cardiac output, venous return and atrial pressure (end diastolic volume) determined by?

Back 28

Point of intersection of the cardiac function curve and the vascular function curve.

Review Hassid notes.

Front 29

WHY IS THE INTERSECTION POINT OF CARDIAC FUNCTION CURVE AND VASCULAR FUNCTION CURVE THE STEADY STATE VALUE FOR CARDIAC OUTPUT AND VENOUS RETURN?

Back 29

BECAUSE AT ANY OTHER ARBITRARY VALUE OF ATRIAL PRESSURE, THE VENTRICULAR OUTPUT (AS DETERMINED BY THE CARDIAC FUNCTION CURVE) IS DIFFERENT THAN THE VENOUS RETURN (AS DETERMINED BY THE VASCULAR FUNCTION CURVE) AND THUS, ATRIAL VOLUME WILL CHANGE AND EVENTUALLY REACH THE INTERSECTION OF THE TWO CURVES. AT THE INTERSECTION POINT, VENTRICULAR OUTPUT IS EXACTLY EQUAL VENOUS RETURN, THUS STABILIZING ATRIAL PRESSURE, (END DIASTOLIC PRESSURE) VENTRICULAR OUTPUT AND VENOUS RETURN.

Front 30

What is the effect of moving the ventricular function curve without moving vascular function curve?
From increase in sympathetic nerve stimulation.

Back 30

Sympathetic to the heart, move the cardiac function curve upward. We see an increase in ventricular output at lower atrial pressure (which reflects venous pressure).

Front 31

What does hypervolemia do to the vascular function curve?

Back 31

Moves it to the right due to increased blood volume = slope of the line is not changed (TPR remains constant)

Front 32

Read through this in the notes.

Back 32

Then update

Front 33

What is the influence of atrial pressure on pulmonary edema formation?

Back 33

Edema becomes significant when atrial pressure rises about 20 mmHg

Front 34

What does hemorrhage involve?
Continue making more cards after class!

Back 34

Hypovolemia = loss of blood