A&P Chapter 20
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What is a normal CO/CI for a 70kg individual?
- 5 liters/min
- 3 liters/min/m2
What are 4 things that affect CO?
- 1) Basal Metabolic Rate
- 2) Increased energy requirements (exercise)
- 3) Age (decreases with age after 10 yo)
- 4) Body habits (directly related)
At what age does cardiac function peak? What is responsible for the decline?
- 10 yrs old
- dependent on decreases in metabolic activity and muscle mass
What is responsible for the primary control of CO?
peripheral circulatory factors that affect flow of blood from the veins into the heart
As a tissue's metabolic needs increase, CO _____
CO and total peripheral resistance are _______ related. This is a form of what physics principle?
inversely. Ohm's law.
What is Frank-Starling's Law?
- Increased blood to the heart -->
- increased stretching of ventricular walls -->
- increased force of contraction -->
- more blood being ejected from heart/increased CO
What is the Bainbridge reflex?
- Increased venous return -->
- stretching of the RA/SA node -->
- afferent signal via vagus nerve -->
- vasomotor center in the medulla -->
- efferent signal to RA -->
- reduction in vagal tone (increased HR by 10-15% and increased strength of contraction)
How much can venous return increase before the heart is a limiter on cardiac output?
What 2 things can cause a hyper effective heart?
- 1) Nervous Stimulation (increased SNS, decreased PNS)
- 2) Hypertrophic Heart (to a point)
What 8 things can cause a hypoeffective heart?
- 1) Increased arterial pressure (htn)
- 2) Inhibition of SNS
- 3) abnormal heart rhythm and rate
- 4) coronary artery blockage
- 5) valvular heart disease
- 6) congenital heart disease
- 7) myocarditis
- 8) cardiac hypoxia
What happens during exercise? (blood vessels and ANS)
- increased metabolism of skeletal muscles -->
- peripheral vasodilation (decreased resistance) -->
- hypotension if not for SNS but SNS increases outflow --> large vein constriction, increased HR, increased contractility --> BP maintained or increased
What is Beriberi?
- Insufficient B1 (thiamine) -->
- diminished ability of the tissues to use nutrients -->
- localized vasodilation to increase blood flow -->
- increased CO
How does an AV fistula affect CO?
- shunting of blood from artery to vein -->
- decreased nutrients at capillary level -->
- local vasodilation/ decreased peripheral vascular resistance -->
- increase in venous return and CO
How does hyperthyroidism affect CO?
- increased metabolism/o2 demand -->
- release of local vasodilating substances -->
- decrease in total peripheral resistance -->
- increased venous return and CO
Can increase up to 80%
How does anemia affect CO?
- decreased viscosity and O2 delivery -->
- peripheral vasodilation -->
- increased venous return and increased CO
What are the 2 general causes of decreased CO?
- 1) reduced pumping effectiveness
- 2) reduced venous return
What are 5 things that decrease CO via reduced pumping effectiveness?
- 1) coronary stenosis --> ACS --> cardiogenic shock
- 2) severe valvular heart disease
- 3) myocarditis
- 4) cardiac tamponade
- 5) cardiac metabolic derangements
What are 5 things that decrease CO by decreased venous return?
- 1) decreased blood volume (hemorrhage)
- 2) acute venous dilation (loss of sympathetic tone)
- 3) obstruction of large veins (pregnancy)
- 4) decreased tissue mass (aging, sedentary)
- 5) decreased metabolic rate of the tissues (hypothyroidism)
What two curves are combined to quantitatively analyze CO regulation?
cardiac output and venous return
A rise in intrapleural pressure shifts the cardiac output curve ______ (left or right)?
right, so an increased RAP is required to maintain CO in the presence of increased intrapleural pressures
What are the 3 principle factors that affect venous return?
- 1) RA pressure (impedes return)
- 2) degree of filling of the systemic circulation (facilitates return)
- 3) resistance to blood flow between the peripheral vessel and the RA
The venous return curve shows.....
as the pumping ability of the heart decreases, RAP increases which impedes and decreases venous return
According to the venous return curve, what is an ideal CVP?
What is mean systemic filling pressure? (conceptually and numerically)
When arterial and venous pressure come to equilibrium, all flow in the systemic circulation ceases. 7mm Hg
Why does a slight increase in RAP cause a drastic decrease in venous return? How do the arterioles and small arteries help overcome this?
the venous system is highly distensible --> pooling of blood in the venous system
arterioles and small arteries increase their pressure 30x which forces some blood back into the RA
Describe how the respiratory cycle influences venous return
- chest wall expands and diaphragm descends -->
- intrapleural pressure more negative -->
- expansion of the lungs, cardiac chambers, and SVC/IVC = increased venous return
What is the Oxygen Fick method?
CO = o2 absorbed by the lungs/AV O2 difference
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