Transcript AV shunt

Vascular Physiology
Qiang XIA (夏强), PhD
Department of Physiology
School of Medicine
Tel: 88206417, 88208252
Email: [email protected]
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Hemodynamics（血流动力学）
• Blood flow
Q= DP/R = (P1-P2)/R
Q= PA/R
Q: cardiac output, 5 L/min
R: total peripheral resistance
PA: aortic pressure
Resistance of blood flow
Poiseuille Law: Q=pDPr4/8hL
h: viscosity
r: radius of the vessel
L: length of the vessel
R= 8hL/pr4
Q= DP/R
Jean Louis Marie Poiseuille \pwä-'zəi\ (April 22, 1799 - December 26, 1869) was a French
physician and physiologist.
Poiseuille was born in Paris, France.
From 1815 to 1816 he studied at the École Polytechnique in Paris. He was trained in
physics and mathematics. In 1828 he earned his D.Sc. degree with a dissertation
entitled Recherches sur la force du coeur aortique. He was interested in the flow of
human blood in narrow tubes.
r: main determinant of blood flow
Arterial blood pressure（动脉血压）
Arteries
Blood pressure measurement
1. Direct (invasive) measurement technique
2. Indirect (non-invasive) measurement technique
Systolic pressure (SP，收缩压):
the maximum arterial
pressure reached during
peak ventricular ejection
Diastolic pressure (DP，舒张压):
the minimum arterial
pressure just before
ventricular ejection begins
Pulse pressure (PP，脉压): the
difference between SP and
DP
Mean arterial pressure (MAP，
平均动脉压): the average
pressure in the cardiac cycle
(=DP+1/3PP)
Mean arterial pressure (MAP)
To estimate systolic and diastolic pressures, pressure is
released from an inflatable cuff on the upper arm while
listening as blood flow returns to the lower arm.
查DynaMed
JNC8高血压管理指南要点（2014）
The joint National Committee on Prevention, Detection, Evaluation, and Treatment
of High Blood Pressure
• 2014 Hypertension Guideline
Management Algorithm
• http://jama.jamanetwork.com/artic
le.aspx?articleid=1791497
我国四次高血压患病率调查结
果
引自中国高血压防治指南（2010）
中国高血压防治指南（2010）
Factors affecting arterial blood pressure
• Stroke volume
• Heart rate
• Peripheral resistance
• Elastic vessels
• Blood volume
Ventricular ejection
Q= PA/R
Q: cardiac output (CO)
R: total peripheral resistance (SVR)
PA: aortic pressure (MAP)
MAP = CO  SVR
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1
2
4
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The blood moved in a
single heart contraction
stretches out the arteries,
so that their recoil
continues to push
on the blood, keeping it
moving during diastole.
Movement of blood into and out of the arteries during
the cardiac cycle
Arterial pulse（动脉脉搏）
In response to the pulsatile contraction of the heart:
pulses of pressure move throughout the vasculature,
decreasing in amplitude with distance
Arterial pulse
recorded in different
vessels
Arterial pulse
recorded under
different conditions
Clinical Application of Arterial Pulse
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Systematic examination of pulses:
Which and what order?
1. Radial artery
Where and how?
Why?
•Radial side of wrist.
•With tips of index and middle fingers.
•To assess rate and rhythm.
•Simultaneously with femoral to detect
delay.
•Not good for pulse character.
2. Brachial artery
•Medial border of humerus at elbow medial to biceps
tendon.
•Either with thumb of examiner's right hand or index
and middle of left hand.
•To assess pulse character.
•To confirm rhythm.
3. Carotid artery
•Press examiner's left thumb against patient's larynx.
•Press back to feel carotid artery against precervical
muscles.
•Alternatively from behind, curling fingers around side
of neck.
•Best for pulse character and, to some
extent, left ventricular function.
•To detect carotid stenosis.
•At resuscitation (CPR).
4. Femoral artery
•Patient lying flat and undressed.
•To assess cardiac output.
•Place finger directly above pubic ramus and midway •To detect radiofemoral delay.
between pubic tubercle and anterior superior iliac spine.•To assessperipheral vascular disease.
5. Popliteal artery
•Deep within the popliteal fossa.
•Compress against posterior of distal femur with knee
slightly flexed.
•Mainly to assess peripheral vascular
disease.
•In diabetics.
6. Dorsalis pedis (DP) and tibialis
posterior (TP) arteries (foot)
•Lateral to extensor hallucis longus (DP).
•Posterior to medial malleolus (TP).
•As above.
7. The abdominal aorta
•With the flat of the hand per abdomen, as body habitus •In peripheral vascular disease.
allows.
•To detect aneurysmal swelling.
From: http://www.patient.co.uk/
Microcirculation（微循环）
Function:
Transfer of substances
between blood & the tissues
Structure of microcirculation
A-V shunt
3 pathways
• Circuitous channel (Nutritional channel)（营
养通路）
2
1
3
A-V shunt
4
5
• Thoroughfare channel（直捷通路）
2
1
3
A-V shunt
4
5
• Arteriovenous shunt (A-V shunt)（动-静脉短路）
2
1
3
A-V shunt
4
5
Arterioles（微动脉）
Two major roles:
• To be responsible for determining the
relative blood flow in individual organs at
any given MAP
• To be a major factor in determining MAP
Arterioles
•
•
•
•
•
•
Small precapillary resistance vessels (10-50 μ) composed of an
endothelium surrounded by one or more layers of smooth muscle cells
Richly innervated by sympathetic adrenergic fibers and highly
responsive to sympathetic vasoconstriction via both α1 and α2
postjunctional receptors
Represent a major site for regulating systemic vascular resistance
Rhythmical contraction and relaxation of arterioles sometimes occurs
(i.e., spontaneous vasomotion)
Primary function within an organ is flow regulation, thereby determining
oxygen delivery and the washout of metabolic by-products
Regulate, in part, capillary hydrostatic pressure and therefore influence
capillary fluid exchange
Dynamic adjustments in the blood distribution to the
organs is accomplished by relaxation and contraction
of circular smooth muscle in the arterioles.
Local Control of Blood Flow
• The mechanism independent of nerves or
hormones by which organs and tissues alter their
own arteriolar resistances, thereby self-regulating
their blood flows
– Active hyperemia（主动充血）
– Flow autoregulation（血流自身调节）
– Reactive hyperemia（反应性充血）
– Local response to injury（对损伤的局部反应）
Local control of organ blood flow
Active hyperemia and flow autoregulation differ in their
cause but both result in the production of the same
local signals that provoke vasodilation.
• Reactive hyperemia – When an
organ or tissue has had its blood
supply completely occluded, a
profound transient increase in its
blood flow occurs as soon as the
occlusion is released
• Response to injury – Tissue injury causes a
variety of substances to be released locally
from cells or generated from plasma
precursors. These substances make
arteriolar smooth muscle relax and cause
vasodilation in an injured area
Extrinsic Control
• Sympathetic nerves（交感神经）
• Parasympathetic nerves（副交感神经）
• Noncholinergic, nonradrenergic autonomic
neurons (NO or other noncholinergic
vasodilator substances)（NANC）
• Hormones (epinephrine, angiotensin II,
vasopressin, atrial natriuretic peptide)
Sympathetic stimulation of alpha-adrenergic receptors cause
vasoconstriction to decrease blood flow to that location.
Sympathetic stimulation of beta-adrenergic receptors lead to
vasodilation to cause an increase in blood flow to that location.
Renin-angiotensin system（肾素-血管紧张素系统）
ANGII can be produced
directly by conversion of
angiotensinogen by the tissue
plasminogen activator (tPA),
cathepsin G and tonin or by
hydrolysis of angiotensin I by
chymase and cathepsin G.
CAGE = chymostatin-sensitive angiotensin
II-generating enzyme
Robert Toto & Biff F.
Palmer. Am J Nephrol
2008;28:372–380
Vasopressin（血管升压素）
Endothelium-derived vasoactive substances
•Vasodilator factors
•PGI2 – prostacyclin（前列环素）
•EDRF (endothelium-derived relaxing factor, nitric oxide)
•EDHF (endothelium-dependent hyperpolarizing factor)
The 1998 Nobel Prize in Physiology or Medicine
Nitric oxide as a signaling molecule in the
cardiovascular system
Louis J Ignarro
Ferid Murad
Robert F Furchgott
Sildenafil, the prototypical PDE5 inhibitor
A phosphodiesterase type 5 inhibitor, often shortened to PDE5 inhibitor, is a drug used to block
the degradative action of phosphodiesterase type 5 on cyclic GMP in the smooth muscle cells
lining the blood vessels supplying the corpus cavernosum of the penis. These drugs are used in
the treatment of erectile dysfunction, and were the first effective oral treatment available for the
condition. Because PDE5 is also present in the arterial wall smooth muscle within the lungs,
PDE5 inhibitors have also been explored for the treatment of pulmonary hypertension, a disease
in which blood vessels in the lungs become abnormally narrow.
•Vasoconstrictor factors – Endothelin-1（内皮素-1）
Major factors affecting arteriolar radius
Diversity among signals that influence contraction/relaxation
in vascular circular smooth muscle implies a diversity of
receptors and transduction mechanisms.
Capillaries（毛细血管）
• Main function:
Exchange of
nutrients and
metabolic end
products
Capillaries lack smooth muscle, but contraction/relaxation of circular
smooth muscle in upstream metarterioles and precapillary sphincters
determine the volume of blood each capillary receives.
Capillary walls
are a single
endothelial cell
in thickness.
The capillary is
the primary
point exchange
between the
blood and the
interstitial fluid
(ISF).
Intercellular
clefts assist the
exchange.
Structure of capillary wall
Structure of the capillary wall
•Continuous: found in muscle, skin, lung, central nervous
system
•Fenestrated: found in exocrine glands, renal glomeruli,
intestinal mucosa
•Discontinuous: found in liver, spleen, bone marrow
Relationship between total cross-sectional area
and flow velocity
Six balls in per minute
mandates six balls out per minute.
Therefore, the velocity of the balls in the smaller tubes is slower.
There are many, many capillaries, each with slow-moving
blood in it, resulting in adequate time and surface area
for exchange between the capillary blood and the ISF.
• Diffusion
• Pinocytosis
• Filtration and
Reabsorption
Movement of fluid and solutes out of the blood is called filtration.
Filtration
Absorption
Movement of fluid and solutes into the blood is called absorption.
Net filtration pressure (or Effective filtration pressure)
EFP + Filtration
EFP -  Reabsorption
Pc
EFP
Effects of arteriolar vasodilation or vasoconstriction on capillary
blood pressure
Dynamic changes in vasodilation/vasoconstriction in the
arterioles regulate downstream pressures and flow rates.
Venous pressure
and venous return
（静脉血压与静脉回流）
• Venous pressure
– Peripheral venous pressure（外周静脉压）──
the pressure in the peripheral veins
– Central venous pressure (CVP，中心静脉压)──
the pressure in the thoracic vena cava & the right
atrium 4~12cmH2O
Central venous pressure measurements were obtained for
three astronauts (indicated by different colors). Notice the
dramatic CVP changes that occurred during launch as well as
when the astronauts arrived in space.
Measurement of central venous pressure
Jugular venous pressure is a clinical measure
of central venous pressure. It is the height of
the pulsating column of blood in the great
veins draining into the right atrium and, in
malaria, is a useful measure of over- or underhydration (hyper- or hypovolaemia).
Jugular venous pressure is the vertical distance, measured in cm, between the venous pulsation in the neck and the sternal angle (junction of
the second rib with the sternum) when the patient is propped up on pillows at 45 to the horizontal. In this position, the sternal angle marks the
level of the right atrium. The height of the jugular venous pressure is normally 4–5 cm. In order to measure it, the patient should be made as
comfortable and relaxed as possible. It is difficult or impossible to identify venous pulsation if the neck muscles are contracted. Try to achieve
good (oblique) lighting of the neck. Look for the jugular venous pulse in the internal jugular vein or its external jugular tributaries on both sides
of the neck with the patient's chin tilted up and slightly away from you. The following characteristics help to distinguish jugular venous pulsation
from carotid arterial pulsation. The jugular venous pulse:
•has two waves for every single carotid artery pulsation; make this comparison by gently palpating the carotid pulse on the opposite side of the
neck;
•falls with inspiration and rises with expiration (except where there is cardiac tamponade);
•can be obliterated by pressing firmly but gently with the back of the index finger placed horizontally just above the clavicle at the root of the
neck;
•may be visible only when the patient is lying flat (in cases of hypovolaemia) or when the patient is sitting upright at 90 (for example, in severe
congestive cardiac failure);
•is usually impalpable.
At rest, approx. 60% of the
total blood volume is in the
veins. Sympathetically
mediated venoconstriction
can substantially increase
venous return to the heart.
Determinants of venous pressure
• Contraction of venous smooth muscle
– Sympathetic neurons
– Hormonal and paracrine vasodilators
and vasoconstrictors
• Skeletal muscle pump
• Respiratory pump
Venous valve
Varicose vein（曲张静脉）
Varicose vein
great saphenous vein
Venous flow is assisted by the skeletal muscle pump
mechanism working in combination with one-way valves.
Respiratory activity (Respiratory pump)
Alterations in “venous return” alter end-diastolic volume (EDV);
increased EDV directly increases stroke volume and cardiac output.
The Lymphatic System
（淋巴系统）
• The lymphatic
system is a network
of small organs
(lymph nodes) and
tubes (lymphatic
vessels) through
which lymph flows
Lymphatic fluid, formed
by the slight mismatch
between filtration and
absorption in the
capillaries, returns to
the blood in the veins.
Terminal lymphatics
Lymphatic pump
Relation between
interstitial fluid
pressure and lymph
flow
Significance of lymphatic return
• Absorption of proteins
• Transportation of fat and other nutrients
• Balance between plasma and interstitial fluid
• Protection
Elephantiasis
（象皮肿）
Chronic, often extreme
enlargement and hardening
of cutaneous and
subcutaneous tissue,
especially of the legs and
external genitals, resulting
from lymphatic obstruction
and usually caused by
infestation of the lymph
glands and vessels with a
filarial worm.
Elephantiasis
Also known as lymphatic filariasis, this condition
occurs when parasitic worms (any of several
types of filaria worms) infest the lymphatic
system. The filaria are transmitted by
mosquitoes to the blood and can build a
population in the lymph nodes, blocking fluid
drainage from arms, legs, genitals, or
breasts. It is called elephantiasis (literally,
"elephant condition") because in extreme
cases, the arms and legs look like the limbs of
an elephant. Elephantiasis affects over a 100
million people around the world. However, most
cases are not as extreme as in this photo!
(丝虫病)
A summary of dynamic changes in MAP and TPR.
Blood loss causes a
reduction in MAP, which, if
left unchecked, would
result in rapid and
irreversible damage to the
brain and the heart.
The End.