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