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Whitney - Physiology Test 2 > Lecture 12 Cardiac Output and Blood Flow in Muscle Tissues > Flashcards

Lecture 12 Cardiac Output and Blood Flow in Muscle Tissues Flashcards

1
Q

Definitions of Cardiac Output

A

Quantity of blood pumped into the aorta each minute by the heart*
Quantity of blood that flows through the circulation
Sum of all the blood flows to all the tissues in the body

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2
Q

Definition of Cardiac Index

A

Cardiac output per square meter of body surface

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3
Q

Calculation for Cardiac Index

A 
Normal Human Being:
70 kg
Body surface area = 1.7 square meters
Cardiac Output = 5 L
Cardiac index = 5 L/1.7 square meters = 3L/min/m2
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4
Q

Fick Principle of Blood Flow

A

Used to calculate blood from through an organ

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5
Q

Equation used to calculate blood flow through an organ:

A

Cardiac Output = (O2 consumption) / ([O2]pul vein - [O2]pul art)
pul vein = systemic arterial
pul artery = systemic venous

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6
Q

Patient has a resting O2 consumption of 250 mL/min
Systemic arterial O2 content of 0.20 mL O2/mL of blood
Systemic mixed venous O2 content of 0.15 mL O2/mL of blood
Heart rate of 72 beats/min
What is the cardiac output?
What is the stroke volume?

A

Cardiac Output = 250/(0.20 - 0.15) = 5000 mL/min or 5 L/min

Stroke Volume = (5000 mL/min) / (72 beats/min) = 70 mL/beat

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7
Q

What is the determining factor that controls how much blood the heart pumps out?

A

It is the amount of blood returning to the heart that determines how much blood the heart pumps out

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8
Q

The cardiovascular system consists of two pumps and two circuits connected in series:
What are the two pumps?
What are the two circuits?

A 
Pumps = left and right ventricles
Circuits = pulmonary and systemic
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9
Q

Because the two circuits are connected in series:

A

Flow must equal the two circuits
Cardiac output & rate of the two circuits are equal
All pressures are higher in the systemic circuit
Chem. composition of pulmonary venous blood is similar to that of systemic arterial blood.
Chem. composition of venous blood entering the right atrium is the same as the composition of pulmonary arterial blood.

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10
Q

Factors that directly affect cardiac output:

A

Basic level of body metabolism
Whether the person is exercising
Age
Size of the body

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11
Q

Normal Cardiac Output values

A

Young, healthy men: 5.6 L/min
Women: 4.9 L/min
Resting Adult: 5.0 L/min

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12
Q

Control of cardiac output by venous return:

A

Frank-Starling Law
Stretching of heart causes heart to pump faster.
Stretched r. atrium initiates Bainbridge reflex.
Undermost normal non-stressful conditions, the CO is controlled almost entirely by peripheral factors that determine venous return.
Ohm’s Law

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13
Q

Frank-Starling Law (cardiac output)

A

Heart automatically pumps whatever amount of blood that flows into the right atrium… Therefore, peripheral factors are more important controllers of cardiac output

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14
Q

Ohm’s Law (cardiac output)

A

Any time the long-term level of total peripheral resistance changes the cardiac output changes quantitatively in exactly the opposite direction

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15
Q

Bainbridge Reflex (atrial stretch reflex)

A

Responds to changes in blood volume as detected by stretch receptors in the right atrium
Not significant in humans, but does occur after birth

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16
Q

Factors that cause a hypereffective heart

A

Nervous stimulation
Hypertrophy of heart
Exercise via the nervous system

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17
Q

Describe how exercise via the nervous system causes a hypereffective heart

A

Intense inc. in metab. in active skeletal muscles causes muscle arterioles to relax –> Allows more blood into these arterioles –> Brain sends motor signals to the muscles & to the ANS centers of the brain to excite circulatory activity –> Causes large vein constriction –> Leads to increased HR, & increased contractility of the heart

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18
Q

Factors that cause a hypoeffective heart

A

Increased arterial pressure (i.e. hypertension)
Inhibition of nervous excitation of the hear
Pathological factors causing abnormal heart rhythm/rate
Coronary artery blockage
Valvular heart disease
Cardiac hypoxia

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19
Q

Review Ventricular Function Curve

A

Figure 20-5 or slide 22

Cardiac output curves for the normal heart, hypoeffective heart, and hypereffective heart

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20
Q

Cardiac Factors Causing Decreased Cardiac Output

A 
Severe blood vessel blockage --> myocardial infarction
Severe valvular disease
Myocarditis 
Cardiac tamponade 
Cardiac metabolic arrangements
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21
Q

Non-Cardiac Factors Causing Decreased Cardiac Output

A 
Decreased blood volume
Acute venous dilation
Obstruction of large veins
Decreased tissue mass (esp. muscle mass)
Decreased metabolic rate of tissues
22
Q

Factors that affect venous return to the heart from the systemic circulation:

A

Right atrial pressure
Degree of filling of systemic circulation
Resistance to blood flow

23
Q

Right atrial pressure:

A

Venous return –> 0 when r. atrial pressure –> +7 mmHg
= Mean systemic filling pressure
If r. atrial pressure –> -2 mmHg, venous return reaches plateau (caused by collapse of veins entering chest)

24
Q

Degree of filling of systemic circulation:

A

When heart pumping stops:
all blood flow ceases
pressure everywhere in the body becomes equal
= mean circulatory filling pressure
= 0 when BV = 4L
= 7 mmHG when BV = 5L
Almost equal to mean systemic filling pressure

25
Q

The grater the difference between the mean systemic filling pressure and the right atrial pressure, the _______ the venous return

A

greater

26
Q

The difference between the mean systemic filling pressure and the right atrial pressure = ?

A

Pressure gradient for venous return

27
Q

About 2/3 of the resistance to venous return is determined by:

A

Venous resistance (Because of vein distensibility, there is little rise in venous pressure)

28
Q

About 1/3 of the resistance to venous return is determined by:

A

Arteriolar and small artery resistance (Accumulation of blood overcomes much of the resistance)

29
Q

Venous return equation

A

Venous return = (mean systemic filling pressure - right atrial pressure) / (Resistance to venous return)

30
Q

Factors that affect venous return

A

Right atrial pressure
Mean systemic filling pressure
Blood flow resistance between peripheral vessels and right atrium

31
Q

How does right atrial pressure affect venous return?

A

Impedes flow of blood from veins into right atrium

32
Q

How does mean systemic filling pressure affect venous return?

A

Forces systemic blood toward heart

33
Q

What is the mean systemic filling pressure?

A

Pressure when arterial and venous pressures come to equilibrium and systemic circulation flow comes to a stop

34
Q

How do you increase mean systemic filling pressure (Psf)?

A

Increase vascular volume (infusion or activations of renal-angiotensin-aldosterone system)
Decrease venous compliance (sympathetic stimulation, muscle pump, exercise, lying down)

35
Q

Increasing Psf results in:

A

Shift in the vascular return curve to the right

Enhances filling of the ventricles

36
Q

How do you decrease mean systemic filling pressure (Psf)?

A

Decrease vascular volume (hemorrhage, burn trauma, vomiting, diarrhea)
Increase venous compliance (Inhibit sympathetics, alpha block, venodilators, standing upright)

37
Q

Decreasing Psf results in:

A

Shift in the vascular return curve to the left

Reduces filling of the ventricles

38
Q

Large blood flow during skeletal muscle activity is due mainly to chemicals that act directly on muscle arterioles to dilate them:

A 
Reduction in oxygen
Adenosine
Potassium ion
ATP
Lactic Acid
Carbon dioxide 
(All considered local control of blood flow regulation to skeletal muscle)
39
Q

Nervous control of blood flow regulation to skeletal muscle

A

Sympathetic vasoconstrictor nerves

Adrenal Medulla

40
Q

How do sympathetic vasoconstrictor nerves regulate blood flow to skeletal muscles?

A

Secrete norepinephrine

Can decrease blood flow through resting muscles to as little as one-half to one-third normal

41
Q

How does the adrenal medulla regulate blood flow to skeletal muscles?

A

Secrete norepinephrine and epinephrine

Epinephrine also has a slight dilator effect

42
Q

Mass discharge of the sympathetic nervous system:

A

Heart rate increases
Most peripheral arteries are strongly contracted except a few (reviewed later)
Muscle walls of veins are contracted –> increases mean systemic filling pressure

43
Q

During mass discharge of the sympathetic nervous system, what arteries do NOT strongly contract?

A

Those in active muscles
Coronary Arteries
Cerebral arteries

44
Q

Increase in arterial pressure..

Sympathetic stimulation causes:

A

Vasoconstriction of arterioles & small arteries in most tissues
Increased pumping activity of the heart
Increase in mean filling pressure caused mainly by venous contraction

45
Q

Phasic changes in coronary flow during systole:

A

Coronary blood flow in the left ventricle falls to a low value (Opposite to flow in vascular beds elsewhere in the body)

46
Q

Phasic changes in coronary flow during diastole

A

The cardiac muscle relaxes and no longer obstructs blood flow through the left ventricular capillaries

47
Q

Primary controller of coronary flow:

A

Local muscle metabolism

48
Q

Coronary flow increases in direct proportion to:

A

additional metabolic consumption of oxygen by the heart - possible b/c of vasodilators (adenosine?) released by heart muscle cells

49
Q

For blood flow in coronary arteries, direct ANS stimulation acts on:

A

blood vessels themselves

50
Q

For blood flow in coronary arteries, indirect ANS stimulation acts on:

A

the cardiac muscle tissue and on the coronary vessels via local control mechanisms

51
Q

Coronary Occlusion and Death

A

Decreased cardiac output
Damming of blood in pulmonary blood vessels and death resulting from pulmonary edema
Fibrillation of heart
Rupture of heart

Whitney - Physiology Test 2 (8 decks)

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