21 22 Hemodynamics Flashcards
What kind of vessel has the greatest distribution of blood in vasculature?
Systemic veins
(64% )
- 8% in heart chambers
- 10% in pulmonary circulation
- 2% in aorta
- 10% in arteries
- 1% in arterioles
- 5% in capillaries
What is the Darcy’s law?
What does it suggest?
Flow (Q) = change in pressure / resistance
The higher the pressure gradient, the greater the fluid flow.
What is resistance represented in blood circulation?
Total peripheral resistance: sum of all vascular resistance within systemic circulation
~0.02mmHg per ml/min
What is the Poiseuille’s law?
What does it imply?
Q = pressure change x pie (r)^4 / 8n (change in length)
Flow is directly proportional to the pressure difference, and also to the 4th power of the radius
Flow is also inversely proportional to
- viscosity
- length of vessel
Vessel length do not vary significantly in
healthy people, but increases in _______.
Obese people
Thus have higher resistance, less flow, higher blood pressure
Blood viscosity depends on _________.
Viscosity is raised in _____________ , leading to hypertension,
stroke & heart attacks.
Blood viscosity is reduced in ___________.
haematocrit;
polycythaemia (raised
red cell count)
anaemia
(reduced red cell count).
Decreasing vessel radius (r) dramatically _______
resistance and _________flow (F) at constant prefusion
pressure (P) because flow is proportional to radius
to the ______power.
increases;
decreases;
4th
What is the relationship between cross sectional area and velocity?
Inversely related.
Aorta has a low total cross-sectional area (2.5 cm2)
and a high velocity
• In capillaries, the massive total cross-sectional area
responsible for a low mean velocity blood flow
What is the relationship between velocity, flow rate and cross sectional area in an equation?
Velocity (v) = Flow rate (Q)/ cross sectional area (A)
What are the 2 types of flow?
Laminar flow and Turbulent flow
In laminar flow, blood flows
smoothly in concentric layers parallel with the axis of blood vessel,with the highest velocity
in ________ of the vessel
the center
How is turbulent flow formed?
In laminar flow becomes disrupted in the case of atherosclerotic plagues, it becomes turbulent.
At what sites do atherosclerosis preferentially develop?
at arterial branches and curvatures
Why are arterioles called resistance vessels?
Arterioles have small radius but that is not the reason they are called resistance vessels. The pressure drop after blood passes from one end of arterioles to the other is the greatest. Since flow rate (Q) is constant by definition throughout the vasculature, if deltaP is large, then R must also be large.
Among the various types of vessels, the most resistance is encountered at the arterioles, thus the term resistance vessels.
_____ are considered as pressure reservoir due to its elastic property.
Arteries
_____________ is the
change in volume (ΔV) divided by the change in
pressure (ΔP).
Vessel compliance
Which of the following are true?
A. The compliance of the
venous system can be 10-20 times as large as that of the arterial system
B. The venous system can be expanded to contain more than 100% of the total blood volume.
C. Veins can accommodate a
large changes in blood volume
with only a small change at
lower pressure.
Not B: 75% only
What are the reasons for reduced compliance - stiffness?
Ageing, hypertension, atherosclerosis due to loss of elastic fibers
What is the effect of increased vessel wall stiffness to systolic bp and diastolic bp?
Increase systolic bp
Decrease diastolic bp
Suppose during systole, elastic arteries will extend, but it doesnt > increase bp
Suppose in diastole, elastic arteries will recoil, decrease in diameter but it doesnt > decrease in bp
How can we use an equation to determine distribution of blood flow to various organs?
Q organ = (MAP - venous pressure) / R organ
Taking CVS as a whole, the different types or sizes of
vessels are arranged sequentially or in ______.
series
The vascular beds for the various organs are arranged
in _______with each other.
Thus the equation to derive the TPR is:
parallel
1/R total = 1/R1 + 1/R2 + 1/R3 + 1/R4 … 1/Rn
One of the most important mechanism in maintaining a
constant blood flow to three most important organs,
i.e., heart, brain and kidney.
What are the 2 types of autoregulation to control the diameter of arterioles?
- Metabolic autoregulation
2. Myogenic autoregulation
Which of the following about myogenic control of blood flow is correct?
A. It depends on nerves
B. It is independent of hormones
C. It begins with smooth muscle cell membrane being stretched
D. It involved in the opening of stretch-sensitive cation channels
E. Depolarization is caused by Ca2+ influx only
F. Opening of voltage gated Ca2+ channels causes depolarization
G. Ca2+ influx causes vasoconstriction
All except A and E
A: independent of nerves and hormones
E: Na+ and Ca2+ influx
Decrease in systemic
arterial pressure causes cerebral arteries to _____.
dilate
> maintain adequate blood flow
What does it mean by metabolic regulation in blood flow?
Active hyperemia
Local metabolites increases,
e.g. adenosine (increase in ATP metabolism), increase in H+ (lactic acid), increase in K+ (increase in K+ efflux during repolarization), increase in CO2 (increase metabolism, decrease ventilation)
> All of them are vasodilators
Other than autoregulation of blood flow by myogenic and metabolic regulation, paracrine regulation can be involved.
Give examples of this.
EDRFs increase blood flow
and EDCFs decrease blood flow
Nerve can also control blood flow.
Which receptor and NT are involved in sympathetic control?
Noradrenaline: a1 receptors
How can parasympathetic nerves control blood flow? (not too important in controlling TPR but it’s good to know)
Parasympathetic nerve endings release acetylcholine, which reaches the endothelial cells and bind to M2 receptors to release NO.
NO triggers the release of EDHF
Other than parasympathetic and sympathetic nerves, ______ nerves release vasodilators as blood flow regulators.
Examples of vasodilators are:
Sensory
Calcitonin gene-related peptide (CGRP)
Neurokinin A
Substance P
Hormones as vasoconstrictors x3:
Vasopressin
Angiotensin II
Endothelin
Hormones as vasodilators x3
VIP
ANP
Calcitonin gene-related peptide
What is the normal venous pressure in peripheral veins at heart level?
8-10 mmHg
What is the normal Central venous pressure (CVP)?
0-7 mmHg
What does CVP reflect?
What can it determine?
the amount of blood returning to the
heart and the ability of the heart to pump the blood
into the arterial system
EDV
Which of the following will increase CVP? A. Decrease CO B. Heart failure C. Upright position D. Blood transfusion E. Deep inhalation
A,B,D
A: more blood retained at veins
B: same
D: hypervolemia
C and E: decrease CVP
Peripheral venous volume is highly variable and
influences CVP and stroke volume.
It depends on ________ and ________.
Venous pressure
Venous smooth muscle tone
Venous tone is controlled by __________ nerve.
sympathetic nerves,
( they actively regulates the venous blood volume
in the cutaneous, renal and splanchnic circulations)
At times of psychological stress, veins _______.
the veins constrict
and displace blood into the heart and arteries
What is the impact of inspiration on venous return?
Inspiration causes intra-thoracic pressure to fall while increases intraabdominal
pressure, thus increasing
pressure gradient favoring venous return
Other than respiration, what are the factors affecting venous return (CVP)?
Muscular pump Valves Sympathetic nerves (a1) Gravity Total blood volume
