Cardiac ouput Flashcards
Quantity of blood pumped into the aorta each minute by the heart
Cardiac output
quantity of blood that flows through the circulation
Cardiac Output
Sum of all the blood flows to all of the tissues of the body
Cardiac output
Cardiac output per square meter of body surface
Cardiac index
What is the cardiac index of a normal human being
70kg
body surface area= 1.7 square meters
Cardiac output=5L
Cardiac index=5/1.7 square meters= 3 L/min/m^2
is the quantity of blood flowing from the veins into the right atrium each minute
Venous return
Venous return and cardiac output must equal one another except
for a few heartbeats at a time when blood is temporarily stored in or removed from the heart and lungs
What 4 factors directly affect cardiac output
the basic level of body metabolism
whether the person is exercising
the person’s age
the size of the body
Cardiac index peaks around age ___ and then
10 (about 4 L/min/m^2) and then declines to about 2.4 L/min/m^2 at 80
What happens to the cardiac output and cardiac index as the oxygen consumption (during exercise increases)
They both increase at the same rate as increased oxygen consumption
What is normal cardiac ouput
about 5 L/min
What is the limit of cardiac output
about 13 L/min about 2.5 times the normal cardiac ouput of 5 L/min
A normal human heart, functioning without any special stimulation, can pump a venous return up to about ____ time the normal venous return before the heart becomes a limiting factor in the control of cardiac ouput
2.5 times
What are two factors that cause a hypereffective heart
- ) nervous stimulation
2. ) hypertrophy of the heart muscle
The flick principle of blood flow is used to calculate what
blood flow through an organ
what is the equation for flick principle
Cardiac output= Oxygen consumption/ (oxygen in pulmonary vein - oxygen in pulmonary artery)
What is the equation for stroke volume
stroke volume= cardiac ouput/HR
What is the determining factor that controls how much blood the heart pumps out?
The heart is a “demand” pump
the heart pumps out whatever blood comes back into it from the venous system
It is the amount of blood returning to the heart that determines how much blood the heart pumps out
The cardiovascular system consists of ______ pumps and _____ circuits connected in series
two, two
What are the two pumps of the heart
The left and right ventricles
What are the two circuits of the cardiovascular system
pulmonary and systemic circuits
Because the two circuits of the cardiovascular system are connnected in series
flow must be equal in the two circuits
cardiac output and rate of the two circuits are equal
all pressures are higher in the systemic circuit
chemical composition of pulmonary venous blood is similar to that of systemic arterial blood
chemical composition of venous blood entering the right atrium is the same as the composition of pulmonary arterial blood
What is the normal cardiac output for a young, healthy male
5.6 L/min
What is the cardiac output of a woman
4.9 L/min
What is the cardiac output of a resting adult
5.0 L/min
Control of cardiac output is primarily due to what
Venous return
What is the Frank-Starling Law
Heart automatically pumps whatever amount of blood that flows into the right atrium
Stretching of the heart causes what
the heart to pump faster and with more force
Stretching of the right atrium initiates what reflex
Bainbridge reflex
Under most normal non-stressful conditions, the cardiac output is controlled almost entirely by
Peripheral factors that determine venous return
What is ohm’s law in turn of cardiac ouput
any time the long-term level of total peripheral resistance changes the cardiac output changes quantitatively in exactly the opposite direction.
What are the most important controllers of cardiac ouput
Peripheral factors
Both the _____ and the ______ reflexes control heart rate
Bainbridge and baroreceptor reflex
Stretching the Sinus node in the wall of the right atrium has a direct effect on the rhythmicity of the node to increase the HR as much as
10 to 15 percent
The bainbridge relex (atrial stretch relex) responds to what
changes in blood volume as detected by stretch receptors in the right atrium, signals are sent form the right atria up the vagus nerve to the medulla, a signal is then sent back down to increase HR and contractile force. This is to prevent damming of blood in the heart and pulmonary system.
What is the main difference between baroreceptor relfex and Bainbridge relfex
baroreceptors are due to atrial pressure and Bainbridge is due to atrial stretch
The bainbridge reflex is not significant in humans except when
at birth when a large volume of the uteroplacental blood returns to the mother’s circulation and results in tachycardia.
What happens to cardiac output as total peripheral resistance increases
it decreases
what is the equation for cardiac output
cardiac output= arterial pressure/ total peripheral resistance
What are three factors that cause hypereffective heart
Nervous stimulation
Hypertrophy of heart
Exercise via the nervous system
- intense increase in metabolism in active skeletal muscles
- This allows more blood into these arterioles
- Brain sends motor signals to the muscles and to the ANS centers of the brain to excite circulatory activity
- This causes a large vein constriction
- This leads to increased heart rate, and increased contractility of the heart
Factors that cause a hypoeffective heart
Increased arterial pressure (i.e. Hypertension)
Inhibition of nervous excitation of the heart
pathological factors causing abnormal heart rhythm/rate
Coronary artery blockage
Valvular heart disease
Congenital heart disease
Cardiac Hypoxia
In demonstration of the frank-starling mechanism as ventricles fill in response to higher atrial pressure, each ventricular volume and strength of cardiac muscle contraction
increases and results in an increase in an increase in cardiac output
Factors causing that decrease cardiac ouput
severe blood vessel blockage ----> MI Severe valvular disease Myocarditis Cardiac Tamponade Cardiac metabolic arrangements
Beriberi
Insufficient quantity of the vitamin thiamine (Vitamin B1) in the diet. Leads to nutrient lack in tissues and Vasodilation
This leads to increase in cardiac output and venous return, often twice the normal
Atriovenous fistula effect on Cardiac ouput
connection between a major artery and major vein, decreases peripheral resistance, venous return, and cardiac ouput
Hyperthyroidism effect on cardiac output
Metabolism of most tissues of the body becomes greatly increased. oxygen usage increases, and vasodilator products are released from the tissues. Venous return and Cardiac output often increase to 40 to 80 percent above normal
Anemia effect on cardiac output
Two peripheral effects greatly decrease total peripheral resistance.
1.) reduced viscosity of the blood- from decreased RBCs
2.) diminished delivery of oxygen to the tissues, which causes vasodilation.
thus cardiac output greatly increases
Conditions that cause low cardiac output fall into what two categories
- ) Abnormalities that decrease pumping effectiveness of the heart
- ) Those that decrease venous return
How does decreased tissue/muscle mass effect Cardiac Output
decreases the total oxygen consumption and blood flow needs of the muscles, resulting in decreases in skeletal muscle blood flow and cardiac output
How does hypothyroidism effect cardiac ouput
tissue metabolic rate is reduced thus oxygen and nutrition needs of tissues will also decrease, thus leading to reduced cardiac output
Non-cardiac factors that decrease cardiac ouput
Decreased blood volume acute venous dilation obstruction of large veins decreased tissue mass (esp. muscle mass) Decreased metabolic rate of tissues
Cardiac ouput=
arterial pressure/total peripheral resistance
If all nervous circulatory reflexes are prevented form acting, venous return decreases to zero when the right atrial pressure rises to about
+7Hg
If right atrial pressure is -2mm Hg then venous return reaches
a plateau, caused by collapse of veins entering the chest
Venous return is affected by what 3 factors
right atrial pressure, degree of filling of the systemic circulation (measured by the mean systemic filling pressure)
Resistance to blood flow between the peripheral vessels and the right atrium
what is mean systemic filling pressure
booth arterial and venous pressures come to equilibrium when all flow in the systemic circulation ceases at a pressure of 7mmHg
What is mean circulatory filling pressure
When heart pumping stops, blood flow ceases
The mean circulatory pressure is the pressure that is constant throughout the body
The greater the volume of blood the ____ the mean circulatory filling pressure
greater
at 4 liters what is the mean circulatory pressure
about 0
What is the mean circulatory pressure with 5 liters of blood
about 7 mmHg
sympathetic nervous stimulation has what effect on the mean circulatory filling pressure
increases it
The greater the difference between the mean systemic filling pressure and the right atrial pressure, the greater the
venous return
The difference between the mean systemic filling pressure and the right atrial pressure equals
pressure gradient for venous return
Venous return equals
(mean systemic filling pressure- Right atrial pressure)/resistance to venous return
(note that the numerator is pressure gradient for venous return)
about ___of the resistance to venous return is determined by arteriolar and small artery resistance
1/3
The normal resistance to venous return is
1.4 mm Hg per L/min of blood flow
factors that affect venous return
right atrial pressure, mean systemic filling pressure (Psf), and blood flow resistance between peripheral vessels and right atrium
What factors increase mean systemic pressure (Psf)
- Increase vascular volume (this can be done by inusion or activation of renal-angiotensin-aldosterone system)
- Decrease venous compliance (this can be done through sympathetic stimulation, muscle pump, exercise, lying down)
An increase in Psf has what effect on the vascular return curve
shift the curve to the right
enhances filling of the ventricles
Factors that decrease mean systemic pressure (Psf)
- Decrease vascular volume (hemorrhage, burn trauma, vomiting, diarrhea)
- Increase venous compliance (inhibit sympathetics, alpha block, venodilators, standing upright)
Decrease in Psf has what effect on the venous return curve
it shifts to the left
Thus reduces filling of the ventricles
sympathetic (positive inotropic effect) can increase Psf, venous return, and cardiac ouput while maintaining the same right atrial pressure. How?
Because the increase in stroke volume
Large blood flow during skeletal muscle activity is due mainly to
chemicals that act directly on muscle arterioles to dilate them: ex. Reduction of oxygen, adenosine, potassium ion, ATP, Lactic acid, Carbon dioxide
Two ways the nervous system controls blood flow through skeletal muscle
Sympathetic vasoconstrictor nerves: secrete norepiniephrine, which can decrease blood flow to as little as one-half to one-third
Adrenal medullae: secretes epinephrine and norepinephrine
Explain the mass discharge of the sympathetic nervous system during exercise
-heart rate increases
-most peripheral arteries are strongly contracted except
those in active muscles
coronary arteries
cerebral arteries
-Muscle walls of veins are contracted: increases mean systemic filling pressure
How does the sympathetic stimulation during exercise increase arterial pressure
- vasoconstriction of arterioles and small arteries in most tissue
- increased pumping activity of the heart
- increase in mean filling pressure caused mainly by venous contraction
coronary blood flow in the left ventricle during systole
falls to a low value
What is the primary controller of coronary flow
local muscle metabolism
Does Direct ANS stimulation acts on blood vessels themselves
Yes
Indirect ANS stimulation is on the cardiac muscle tissue and
indirectly on the coronary vessels via local control mechanisms
Causes of death caused by coronary occlusion
Decreased cardiac output
damming of blood in pulmonary blood vessels and death resulting form pulmonary edema
fibrillation of the heart
rupture of heart
