Chapter 5- Part 2 Flashcards
What is another term for systemic vascular resistance?
Total peripheral resistance
Define systemic vascular resistance
The resistance to blood flow offered by all of the systemic vasculature excluding the pulmonary vasculature
What will generalized vasoconstriction do to systemic vascular resistance?
Increased systemic vascular resistance
What will generalized vasodilation do to systemic vascular resistance?
Decrease systemic vascular resistance
What equation can be used to calculate systemic vascular resistance?
SVR = (MAP-CVP)/CO
Is systemic vascular resistance determined mean arterial pressure or cardiac output?
Systemic vascular resistance is determined by vascular diameters, length, anatomical arrangement of vessels, and blood viscosity
In this equation(SVR = (MAP-CVP)/CO), which variables are the mathematical dependent and independent variables?
Mathematically systemic vascular resistance is the dependent variable
In this equation(SVR = (MAP-CVP)/CO), which variables are the physiological dependent and independent variables?
Physiologically systemic vascular resistance and cardiac output are the independent variables normally
Mean arterial pressure is the dependent variable
What units can be used to express systemic vascular resistance?
mmHg/mL min-1
What is vascular tone?
A partially constricted state of the resistance vessels
What vessel types exhibit vascular tone?
Resistance vessels
Can vessels that exhibit vascular tone dilate, constrict, or can they do both?
Vessels they exhibit vascular town can dilate and constrict
What extrinsic mechanisms determine the degree of smooth muscle activation?
Sympathetic nerves and circulating hormones
What intrinsic mechanisms determine the degree of smooth muscle activation?
Endothelial-derived factors, smooth muscle myogenic tone, locally produced hormones, and tissue metabolites
Which is most important for maintaining systemic vascular resistance and arterial pressure, vasoconstrictor mechanisms or vasodilator mechanisms?
Vasoconstrictor mechanisms
What would the appropriate response be when an individual goes from a seated position to a standing position?
To maintain arterial blood pressure when a person stands up, vasoconstriction mechanisms are activated to constrict resistance vessels and increased systemic vascular resistance
What would be the appropriate response when a muscle needed additional oxygen, such as during aerobic exercise?
Vasodilator mechanisms will predominate override vasoconstrictor influences
What is venous pressure?
A general term that represents the average blood pressure within the venous compartment
What is central venous pressure?
The blood pressure in the thoracic vena cava near the right atrium
Why is this pressure important?
it determines the feeling pressure of the right ventricle and thereby determines ventricular stroke volume
What equation is used to quantify central venous pressure?
dPv = dVv/Cv
Pv equals CVP
Vv equals blood volume on Venous side
Cv equals Venous compliance
How is equation 5-11 related to equation 5-4?
Compliance equals a change in venous volume divided by a change in the venous pressure
Draw a compliance curve for a vein.
A
How does this curve relate to the shape and geometry of the vessel?
At very low pressures the vein is collapsed in this shows high venous compliance. As pressures increase the vein assumes a more circular cross-section and its walls become stretched reducing compliance
What is significant about this curve at low pressures and volumes?
At very low pressures the vein collapses
What is significant about this curve at high pressures and volumes?
At higher pressures when the venous cylindrical in shape increase pressure can increase volume only by stretching the vessel wall
What anatomical components resist stretching of the vessel wall?
The structure and composition of the wall particularly by collagen and smooth muscle and elastin components
How would this curve change with an increase or a decrease in vessel compliance?
At higher volumes and pressures the change in volume for a given change in pressure is less
What are the effects of sympathetic adrenergic stimulation on this curve?
Change in sympathetic activity can increase or decrease the contraction of venous smooth muscle thereby altering Venous tone
What will a rightward diagonal shift in the venous compliance curve do venous volume and pressure?
decrease in venous volume and an increased venous pressure
What will drugs that reduce venous tone do to venous pressure and volume?
Drugs that reduce Venous tone will decrease venous pressure while increasing venous volume by shifting the compliance curve to the left
What would you expect central venous pressure to be in the supine position?
2 mmHg
What would you expect venous pressure to be in the legs while in the supine position?
4 to 5 mmHg
What would you expect venous pressures in the feet to be when standing still?
Venous pressures in the feet when a person is standing still may reach 90 mmHg because of the increased Hydrostatic pressure owing to the influence of gravity
What will going from sitting to standing do to central venous pressure?
Decreased CVP
Explain the shifts in blood volume that occur when going from sitting to standing
The shift in blood volume from the thorax to the dependent limbs causes thoracic venous volume and CVP to fall
Explain how the shifts in blood volume would affect cardiac output.
reduced right ventricular preload causes left ventricular stroke volume subsequently to fall because of reduced pulmonary venous return to the left ventricle. The reduced stroke volume causes cardiac output
and arterial blood pressure to decrease
What is orthostatic hypotension?
If systemic arterial pressure falls by more than 20 mmHg upon standing
Orthostatic hypotension may cause a feeling of lightheadedness due to cerebral perfusion falling
What protective mechanisms restore normal cardiac output?
Baroreceptor reflexes are activated to restore arterial pressure by causing peripheral vasoconstriction in cardiac stimulation (increased HR and inotropy)
Why does retrograde blood flow not occur in veins?
Veins have one-way valves that permit blood flow toward the heart and prevent retrograde flow
Explain the concept of the skeletal muscle pump.
Deep veins in the lower limbs are surrounded by large groups of muscles that compress the veins when contract. This compression increases the pressure within the veins which closes the upstream valves and opens downstream valves thereby functioning as a pumping mechanism
How can rhythmical contraction of leg muscles counteract gravitational forces?
Rhythmical contraction of the leg muscles also helps to counteract gravitational forces when a person stands up by facilitating venous return and lowering venous and capillary pressures in the feet and lower limbs
What happens to venous pressure in the ankle when a person goes from standing still to walking?
Venous pressure falls to 30 to 40 mmHg after several steps
How would venous incompetence affect this response?
Muscle pumping becomes ineffective and blood volume and pressure increase in the veins of the dependent limbs which increases capillary pressure and may cause edema
What determines venous return to the right atrium from the abdominal vena cava?
the pressure difference between the abdominal vena cava and the right atrial pressure
What will an increase in right atrial pressure do to venous return?
Increasing right atrial pressure impedes venous return
What will a decrease in right atrial pressure do to venous return?
Lowering right atrial pressure facilitates venous return
Define intrapleural pressure.
The pressure and space between the thoracic wall and the lung
It is generally negative or sub atmospheric
What happens to intrapleural pressure during normal inspiration and what effect does this have on the lungs, the atria, the ventricles, and the vena cava?
During inspiration, the chest wall expands, and the diaphragm descends. This causes interpleural pressure to become more negative, causing expansion of the lungs, atrial and ventricular chambers and vena cava.
This decreases the pressures within the vessels and cardiac chambers
What happens to intrapleural pressure during normal expiration and what effect does this have on the lungs, the atria, the ventricles, and the vena cava?
During expiration the opposite occurs although the net effect of respiration is that the increased rate and depth of ventilation facilitates venous return and ventricular stroke volume
What happens to right atrial and ventricular preloads and right ventricular stroke volume with a fall in right atrial pressure during inspiration?
The fall in right atrial pressure during inspiration is associated with an increase in right atrial and ventricular preload and right ventricular stroke volume
How is this related to transmural pressure?
The fall in intrapleural pressure causes the transmural pressure to increase across the chamber walls
Define transmural pressure.
Transmural pressure is the difference between the pressure within the chamber and the pressure outside the chamber
Draw a curve showing the response of intrapleural pressure, right atrial pressure, and venous return during a normal inspiration and a normal expiration at rest.
A
Explain the physiological mechanism of the respiratory pump – how does inspiration/expiration increase cardiac output?
when transmural pressure increases the chamber volume increases which increases sarcomere length and myocyte preload
The net effect of respiration is that increasing the rate and depth of respiration increases venous return and cardiac output
What is the Valsalva maneuver?
Exhaling forcefully against a closed glottis
How does the Valsalva maneuver affect central venous pressure and what is the mechanism to explain it?
Increased central venous pressure
Intrapleural pressure Becomes very positive which causes the transmural pressure to become negative, thereby collapsing the thoracic vena cava. This dramatically increases resistance to venous return and reduces venous return
List and summarize the eight conditions that influence central venous pressure.
1-An increase in total blood volume increases thoracic blood and therefore and therefore CVP
2-a decrease in cardiac output causes blood to back up into the venous circulation as less blood is pumped into the arterial circulation
3-a decrease in systemic vascular resistance by selective arterial dilation increases blood flow from the arterial into the venous compartments. This increases venous volume and CVP, while at the same time reducing arterial volume and pressure
4-reduced venous compliance–construction of per referral veins elicited by sympathetic activation or circulating vasoconstrictors substances causes blood volume to be translocated from peripheral veins into the thoracic compartment thereby increasing CVP
5-postural changes such as moving from standing to a reclining or squatting position diminishes venous pooling in the legs caused by gravity, which increases the rest vitamin CVP
6-valsalva maneuver causes external compression of the thoracic vena cava which increases CVP
7-respiratory pump–increased respiratory activity facilitates venous return into the thorax, thereby helping to maintain CVP when cardiac output is elevated during exercise
8-muscle pump–rhythmic muscular contraction, particularly of the limbs during exercise, compresses the veins and facilitates venous return into the thoracic compartment, which increases CVP
What factors determine venous return from the capillaries?
Venous return from capillaries is determined by the difference between the mean capillary and right atrial pressures divided by the resistance of all post capillary vessels
Explain why under steady-state conditions, venous return equals cardiac output when averaged over time.
Under steady state conditions, venous return equals cardiac output when averaged overtime. This is because the cardiovascular system is essentially a closed system, keeping in mind that merit is fluid exchange throughout
What is the best way to show how/why cardiac output depends on systemic vascular function?
By use of systemic vascular and cardiac function curves
Who is credited with the conceptual understanding of the relationship between cardiac output and systemic vascular function?
Arthur Guyton
Draw a figure that shows the relationship between cardiac output, mean aortic pressure and right atrial pressure.
A
At a cardiac output of 5 L/min, what are mean aortic pressure and right atrial pressures?
Mean aortic pressure of 95 millimeters mercury
Right atrial pressures of 0 mmHg
What happens to mean aortic pressure as cardiac output is decreased?
mean aortic pressure decreases
What happens to right atrial pressure as cardiac output is decreased?
Right atrial pressure increases
When cardiac output reaches 0 L/min what happens to mean aortic pressure and right atrial pressures?
Right atrial pressure continues to rise and mean aortic pressure continues the fall until both pressures are equivalent, when systemic blood flow ceases
Define mean circulatory filling pressure.
The pressure test zero systemic flow
What would you expect a normal mean circulatory filling pressure to be?
about 7 mmHg
Why must baroreceptors be blocked in order to experimentally quantify mean circulatory filling pressure?
Otherwise the value for mean circulatory filling pressure is higher because of vascular smooth muscle contraction and decreased vascular compliance going to sympathetic activation
Explain why right atrial pressure increases in response to a decrease in cardiac output.
Less blood per unit time is translocated by the heart from the venous to the arterial vascular compartment. Decreasing stroke volume
Under resting conditions at a cardiac output of 5 L/min, what would happen to cardiac output if heart rate were suddenly increased? Why?
Cardiac output will not increase much above 5 L per minute because RA pressure falls below zero, which collapses the vena cava at the level of the diaphragm where it enters the thorax from the abdomen
The magnitude of the relative changes in aortic and right atrial pressures from a normal cardiac output to zero cardiac output is determined by what?
The ratio of venous to arterial compliances
What equation is used to quantify the ratio of venous to arterial compliance?
Cv/Ca= dVv/dPv / dVa/dPa
If the heart is stopped, how can this equation be simplified to show this relationship?
When the heart is stops, the decrease in arterial blood volume equals the increase in venous blood volume
What is the normal range for venous to arterial compliance?
10-20
If venous to arterial compliance was 15, how much would a 1 mmHg increase in right atrial pressure decrease mean aortic pressure?
15 mmHg
Draw the systemic vascular function curve.
A
What is another name for this curve?
Venous return curve
On this curve, what is the x-intercept?
The mean circulatory filling pressure
Define mean circulatory filling pressure.
this is the pressure throughout the vascular system when there’s no blood flow
What two factors determine mean circulatory filling pressure?
Vascular compliance and blood volume
Draw a normal systemic vascular function curve; superimpose on this curve a curve that shows the effects of an increase in blood volume, a decrease in blood volume, an increase in venous compliance, a decrease in venous compliance, an increase in systemic vascular resistance, and a decrease in systemic vascular resistance.
A
Explain the physiological mechanisms that contribute to these changes in the curve
Increased blood volume or decreased venous compliance causes a parallel shift of the vascular function curve to the right, which increases mean circulatory filling pressure
Decreased blood volume or increased venous compliance causes a parallel shift to the left and a decrease in the mean circulatory filling pressure
What is the physiological significance of each of these changes?
At a given cardiac output and increase in total blood volume or decreased venous compliance is associated with an increased right atrial pressure
Draw the cardiac function curve; superimpose on this curve cardiac function curves that depict enhanced cardiac function and depressed cardiac function.
a
Why is it important that cardiac output is the dependent variable and right atrial pressure is the independent variable for the cardiac function curve?
Because according to the Frank-Starling relationship, and increased right atrial pressure increases cardiac output
How is the cardiac function curve related to Starling’s curve?
According to Starling relationship, an increase in right atrial pressure increases cardiac output. This relationship can be depicted using the same axis as used in systemic function curves in which cardiac output is plotted against right HR pressure
What factors can cause the cardiac function curve to shift?
Changes in heart rate
With a normal cardiac function curve, what is right atrial pressure at a cardiac output of 5 L/min?
0 mmHg
If cardiac function were enhanced (curve shift upward and to the left), what would cardiac output be at a right atrial pressure of 0 mmHg?
It will increase
Draw a normal cardiac function curve and superimpose on it a normal vascular function curve.
Identify on this curve the operating point under normal resting conditions.
A
Superimpose on this figure a cardiac function curve that demonstrates enhanced cardiac function.
A
Superimpose on this figure a vascular function curve that demonstrates a decrease in venous compliance
A
Superimpose on this figure a vascular function curve that demonstrates both a decrease in venous compliance and a decrease in systemic vascular resistance.
A
What would the operating point be if sympathetic nerves to the heart were stimulated to increase heart rate and inotropy?
Only a small increase in cardiac output will occur accompanied by a small decrease in right atrial pressure. This is point B on the graph
What would the operating point be if sympathetic nerves to the heart were stimulated to increase heart rate and inotropy, and sympathetic activation decreased venous compliance?
Cardiac output will be greatly augmented
What would the operating point be if sympathetic nerves to the heart were stimulated to increase heart rate and inotropy, AND sympathetic activation decreased venous compliance, AND there was a decrease in systemic vascular resistance?
Cardiac output would be further enhanced. This is point D on the graph
Draw combined cardiac and systemic function curves that demonstrate changes in cardiac and systemic vascular function during heart failure.
A
Explain how these changes affect cardiac and vascular function.
Cardiac output would be greatly reduced and right atrial pressure would be elevated
