CHAPTER 25 VENOUS HEMODYNAICS Flashcards
What is intraluminal pressure?
Pressure exerted on the venous wall from WITHIN THE VEINS.
What is interstitial pressure?
The pressure exerted on the venous walls from OUTSIDE THE VEINS.
What is transmural pressure??
The difference between intraluminal and interstitial pressure.
intraluminal-interstitial = transmural
How is transmural pressure related to intraluminal pressure.
Directly
What is known as “across the wall” pressure?
Transmural
What does transmural pressure determine?
The cross-sectional shape of the veins.
Elliptical or dumbbell shape vein has what 3 things?
- Lower blood volume
- Lower intraluminal pressure
- Low transmural pressure
Does an elliptical shaped vein have a higher or lower resistance?
Higher resistance
A circular shaped vein has what 3 things?
- higher intraluminal pressure
- Higher blood volume
- Higer transmural pressure
Does a circular shaped vein higher or lower resisant?
Lower resistant
How are volume and transmural pressure related?
directly
What does compliance within the veins allow for?
Maintains pressure gradient for blood to flow.
Allows for an increase in blood without an increase in blood pressure.
What is hydrostatic pressure?
Pressure within a column of fluid extending from the heart to the level where the pressure is being measured.
What is the formula for hydrostatic pressure?
Hp=pgh
What is the hydrostatic pressure of a supine individual?
0mmHg
What is the hydostatic pressure at the ankles of a standing individual?
100mmHG
Above the heart, what is hydrostatic pressure?
Negative
In calves with competent venous valves which way will blood flow?
One way, or unidirectional.
With an effective calf muscle pump, how much of the blood will be ejected?
> = to 60%
In calves with incompetent venous valves, what way will blood flow?
antegrade and retrograde
Incompetent valves will have increased what?
- pressure
- pooling
Incompetent venous valves will have decreased what?
- venous return
- cardiac output
Veins at rest (post contraction) act as what?
reservoirs for blood collection, with competent valves, maintain unidirectional movement of blood.
What is referred to as the “venous heart”
Calf muscles
During inspiration the diaphragm does what?
Descends
During inspiration there is a decrease in what?
intrathoracic pressure (in the arms, head and neck).
* Blood loves to go the way of less pressure
During inspiration there is an increase in what?
intra-abdominal pressure
During inspiration, blood increases where?
in the arms, head, and neck veins.
During expiration, there is an increase where?
in the intra-abdominal pressure
During expiration, there is a decrease in what?
intrathoracic pressure
During expiration, blood flow increases where?
in the lower extremity
Portal vein flow has what 2 qualities?
- minimially phasic
- almost no variation with respiration
What does a valsalva maneuver cause?
- increased intrathoracic pressure
- increased intra-abdominal pressure
During a valsalva maneuver what is halted?
Venous return is halted.
What is normal venous flow called?
spontaneous
What is flow with alternating respirations?
Phasic flow
Visible flow with hand compression is what?
augmentable
Vessels close to the heart are what?
- Pulsatile
- bidirectional
