L2: Coupling of the Heart & Peripheral Circulation

What is important to remember about cardiac output and blood returning to the heart

the amount of blood leaving the heart (CO) MUST EQUAL the amount of blood returning to the heart (venous return)

Where is the heart located in the body? (which region)

Thorax

the pressure in the intrathoracic cavity is ____________

negative (below ATM)

What are the 2 forces important in returning blood back to the right side (venous side) of the heart?

1. Peripheral venous pressure

2. Central venous pressure

Describe Central venous pressure (CVP)

measure of the pressure in the venous system as it enters the right atrium or Vena Cava... NOT THE VENTRICLE

* determines how much blood can flow back to the heart

2/3 of the blood volume exists in the _________ circulation

venous

What 4 major factors determine cardiac output (CO)?

1. Preload: length of ventricle before contraction

2. Afterload: aorta resistance the heart must overcome

3. Contractility: actin, myosin, Ca2+, ATP

4. Heart Rate

CO = SV * HR

On a regular basis, we move up and down the Starling curve all the time (exercising, laying down, standing up, etc.)... when does a problem occur?

problems occur when preload, afterload, contractility, and HR are not functioning

* starling curve CHANGES and still move up and down the curve... but move to a LOWER starling curve with a lower SV

Central Venous Pressure (CVP) is also called __________

ventricular filling pressure

Describe Arterio-venous coupling

pump --> CO into arteriole circulation through capillaries --> arterioles control resistance and pressure --> blood collected by small venules --> blood returns to heart

blood travels from a ______ pressure to a ______ pressure

higher pressure --> lower pressure

* venous gradient = high --> low

Describe what occurs when the pump is off when it comes to cardiovascular function

pump off --> pressure is static (7 mmHg)

in the cardiovascualr system, pressure is determined by ______________

how much volume there is and the stiffness of vessels

if pressure is the same downstream as it is upstream.. flow = ____

ZERO

Describe what occurs when the pump is on when it comes to cardiovascular function

pump on --> transferring fluid from venous side to arteriole side --> arteriole pressure increases --> venous pressure decreases

(moving fluid from one compartment to another compartment)

As heart rate increases (30-60) pressure becomes __________

normalized and CO increases while venous pressure decreases

When the heart is beating... how is blood being transferred?

from venous side to arteriole side and must have a gradient to move blood forward

Describe the venous function curve

if central venous pressure increases --> venous return decreases --> decreases CO

once central venous pressure = peripheral pressure (7 mmHg) = ________

no driving force

when you inhale what happens to pressure?

inhale --> pressure becomes NEGATIVE (less positive) --> helps to drive blood back to the heart

decreased peripheral resistance = _______ Venous return

increases

increased peripheral resistance = ________ Venous return

decreases

increase venous return = _______ CO

increase

increased blood volume -->

increased pressure --> increased venous return --> increased central venous pressure

decrease blood volume -->

decrease pressure --> decrease venous return --> decrease central venous pressure

increase systemic filling pressure --->

increase venous return to heart

decrease systemic filling pressure --->

reduce venous return to heart

the veins below the heart (except for the vena cava) have _______

valves

What is the key characteristic of the valves in our veins below the heart

ONE WAY VALVES

* allow blood to only travel in ONE DIRECTION... not the opposite direction because the valves close

Small veins are embedded in __________

muscle

Contract skeletal muscle --> _________

contract skeletal muscle --> blood is pushed UP back to heart and won't go back into the periphery

* unless have varicose veins where valves are compromised

Explain the Skeletal muscle pump

contraction of skeletal muscle compresses intra-muscle veins that propels blood toward the heart

*skeletal muscle contraction --> increase systemic filling pressure --> increases venous return

What happens to venous return if a person is standing still without contracting muscles?

venous return is impaired

In a STEADY STATE... what must the relationship between venous return and cardiac output be?

venous return and cardiac output MUST be equal

If systemic filling pressure (7 mmHg) is equal to central venous pressure = ________

NO FLOW

if decrease central venous pressure = _________ venous return

increases

With an increased blood volume/venous tone... how does the venous return curve shift?

shifts to the right

* increase systemic filling pressure --> increase venous return --> increase central venous pressure

With a decreased blood volume/venous tone... how does the venous return curve shift?

shifts to left

* decrease systemic filling pressure --> decrease venous return --> decrease central venous pressure

decreasing resistance to flow = ________ venous return

increased

increasing resistance to flow = ________ venous return

decreased

When standing up... what pressure is acting on our bodies?

gravity (holding us down and affecting hydrostatic column)

In the supine position:

arterial pressure

heart level = ____ mmHg

ankle and head level = ____ mmHg

venous pressure

heart level = ____ mmHg

ankle and head level = ____ mmHg

arterial pressure

heart level = 100 mmHg

ankle and head level = 95 mmHg (slightly lower)

venous pressure

heart level = 2 mmHg (Right atrium or vena cava)

ankle and head level = 5 mmHg (slightly higher)

In the standing/upright position

arterial pressure

heart level = ____ mmHg

ankle = ____ mmHg

venous pressure

heart level = ____ mmHg

ankle = ____ mmHg

arterial pressure

heart level = 100 mmHg (same as supine)

ankle = 185 mmHg

venous pressure

heart level = 0 mmHg

ankle = 85 mmHg

Why is the arterial pressure the same (100 mmHg) at heart level in both supine and standing positions?

have pressure exerted by heart and peripheral vessels that propels blood... but also have GRAVITY in standing position that increases the hydrostatic pressure on vessels

with muscular contraction, hydrostatic column is minimized because squeezing blood back to the heart... what is the venous pressure in the ankles if contracting muscle?

15 mmHg

what happens when we inspire air?

inspiration --> creates a more NEGATIVE intrathoracic pressure and more POSITIVE intra-abdominal pressure

* opposite occurs during expiration

inspiration = ______ stroke volume

decrease SV

expiration = _______ stroke volume

increase SV

What are the 2 ways to help venous return back to the heart?

1. contracting skeletal muscle

2. inspiring air (deeper breath you take --> more negative intrathoracic pressure gets --> increased venous return)

at 5 liters/minute (equilibrium) what are the same?

cardiac output and venous return are the same

What does exercise do to cardiac output?

increase CO to deliver more blood flow to muscle

increase ventricular function --> ___ cardiac output --> ___ CVP --> ___VR

increase CO, decrease CVP, increase VR

What is the Fick principle and what is its importance?

Fick principle: rate of O2 consumption, arterio-venous (A-V) difference in O2 content

It is used to measure cardiac output (CO)

CO = O2 consumption (ml/min) / arterio-venous O2 difference (ml/L)

is pressure slightly higher in the legs or chest?

pressure in the legs MUST be slightly higher than the pressure in the chest in order to drive blood back to heart