8-24 Cardiovascular Pathology Review Flashcards
What is laminar blood flow?
concentric layers of blood, with the slowest layer near vessel walls and the fastest near the middle
Turbulence is minimized -> happens more in straight, long vessels
What is the (mechanical/physiological) advantage of laminar flow?
decreased energy losses, minimized viscous interactions between adjacent layers of blood or vessel wall
Physiologically -> pretty sure blood is less likely to clot
What is turbulence in regards to blood flow?
disrupted laminar flow leading to chaotic flow
When does turbulence happen?
large aa at branch points
diseased/stenotic aa
across stenotic heart valves
How does turbulence change the energy required to drive blood flow? What is the relationship between perfusion pressure, turbulence, and flow?
Increased demand for energy, due to:
friction –> generates heat
turbulence increases perfusion pressure needed to drive a given flow
- or -
at a perfusion pressure, turbulence leads to decrease in flow
Does turbulence happen gradually?
Turbulence happens when flow is high enough to break laminar layers
- happens when Reynold’s number is exceeded
What is Reynold’s number, and what relationship do the different terms of it have with each other?
Re = Vdp/n
V = mean velocity
d = diameter
p/rho = blood density
n = blood viscosity
Reynolds number/threshold for turbulence proportional to velocity, diameter, blood density. Blood viscosity increase will decrease Re/turbulence threshold, vice versa.
What frequent scenarios reduces Re/turbulence threshold?
anemia - makes blood less viscous
high velocity
increased diameter - aneurysm
blood density - increasing RBCs w/ Epo
How is velocity and vessel diameter related?
As diameter of a vessel increases, velocity drops
flow = mean velocity * area(πr2)
How can turbulence be appreciated?
Loss of energy as sound waves = murmurs or bruits
sound energy/murmurs intensify as flow increases
What can increase the sound of murmurs?
Elevated CO - can result in physiological murmurs in pregnant women, or pathological murmurs
What is often the cause of pathological murmurs heard in the heart cycle?
Turbulence of blood flow across a stenotic valve, or movement of blood between heart chambers or into large outflow vessels
Murmurs tend to be low frequency sounds
What are the 2 general classification schemes for murmurs? Give 2 examples of each.
Based on origin:
- Caused by valve defects
- Caused by interchamber defects - cause an abnormal flow of blood between chambers
Based on timing in heart cycle:
- Systolic
- Diastolic
What is the effect of gravity on venous return prior to compensation?
gravity acts on vascular volume and causes pooling in lower extremities or low points of body
- partly possible due to large compliance of venous vessels
Shift in blood volume decreases thoracic venous blood volume,
decreases right ventricular filling pressure/preload,
decline in venous return
What is the effect of gravity on CO before compensation?
Venous return will decrease
Thoracic blood volume will decrease
Cardiac preload will decrease in right atrium
CO will decrease
What is the effect of gravity on BP before compensation?
Since preload in R atrium is lower, there’s also less venous return from lungs, creating decreased L ventricular output and decreased CO
Decreased CO will decrease MAP in absence of HR increase
What is the response of the autonomic nervous system that is initiated by increased baroreceptor firing rate?
Less pressure on baroreceptor reflexes will cause increased firing on the SNS, which will increase systemic vascular resistance
decrease stroke volume and preload
increased heart rate
How is Posieuille’s law important in hemodynamics? What factors have a big influence on resistance?
Posieuille’s law states that resistance is directly porportional to the length & viscosity of the blood, inversely porportional to radius to the 4th power
Whereas vessel length and viscosity do directly influence resistance, these are often fairly fixed entities that don’t change much
Radius is under the influence of the ANS, and is subject to change
- 2x increase in radius = 16x decrease in resistance
What is Ohm’s law and how does it impact hemodynamics?
change in pressure is proportional to flow * resistance
Pressure change across stenotic arteries and valves will be much larger due to more resistance
Increased flow can also increase velocity, leading to turbulence and murmurs
What variables can influence vascular resistance?
intrinsic - local blood flow regulation mechanisms
- i.e. myogenic, NO, endothelin, histamine, bradykinin, arachadonic acid metabolites, hypoxia by-products
extrinsic - originate from outside of tissue, tends to regulate systemic vascular resistance . Tends to be ANS activated or ang II mediated.
What is mean arterial pressure? What relationships does it have with other variables?
MAP = (CO * SVR)/CVP
- CVP is central venous pressure, often near 0
Realistically MAP = CO * SVR
What are the 2 most efficient ways to change MAP?
Changes in CO or SVR
All variables regarding MAP are interdependent, changing one will change the rest
In the real world, how is MAP determined?
MAP = Pdias + 1/3(Psys - Pdias)
What affects SVR?
Anything that affects systemic vascular resistance - changing blood viscosity, changing vessel diameter