Medical Lecture 1

8/9/2019 Medical Lecture 1

1/27

Physics in Medicine

PH3708

Dr R.J. Stewart


2/27

Scope of Module

ardio!"ascular syste#

$%luid flow in pipes& circulation syste#& pressure

Me#'ranes

$(s#osis and solute transport

)rans#ission of electrical si*nals

$+er"es& ,-

(ptical %i'res and ,ndoscopy


3/27

Scope of Module

ltrasound

$/#a*in* and Doppler #easure#ents

Radioisotope i#a*in* and radiolo*y

!ray *eneration and i#a*in*

+MR i#a*in*


4/27

Module Resources

1e' Pa*e2$ http2www.rd*.ac.u4physicsnetunits3ph3708ph3708.ht#

5oo4s2$ -ood *eneral 'oo4s2

6Physics of the 5ody& a#eron& S4ofronic4 and

-rant

6Medical Physics& J.. Pope$ (ther #ore specialised 'oo4s are *i"en in the unit

description and will 'e referred to where necessary


5/27

ardio"ascular Syste#

Physics of the Body, Cameron, Skofronick

and Grant, Ch. 8

/n considerin* the circulation of 'lood& one

essentially considers the flow of a "iscous

fluid throu*h pipes of different dia#eters

Define2$9iscosity2 arises fro# frictional forces associated

with the flow of one layer of li:uid o"er another


6/27

9iscosity

onsider a circular cross section pipe2

$%low throu*h pipe due to pressure difference

$ssu#e2 flow at walls of pipe ; 0& #a=rv


7/27

9iscosity

)he slower #o"in* fluid outside the central =shaded> re*ion e


8/27

9olu#e %low Rate

)he a"era*e flow fro# the heart is the

stro4e "olu#e =the "olu#e of 'lood eected

in each 'eat> < nu#'er of 'eats per second.)his is E F0 =#l'eat> < 80 ='eats#in> ;

G800 #l#in


9/27

9olu#e %low Rate

Poiseulles ,:uation

$9olu#e flow rate& Q& related to pressure

difference P& len*th land radius a'y2

l

a

P1 P2

P P1! P2

Qa

lP=

G

8


10/27

9olu#e %low Rate

(ften con"enient to define a resistance, "

to flow& such that PQ"

P1 P2 P#

"1 "2 "#

P P1$ P2$ P#Q"1$Q"2$Q"#Q"

""1$"2$"#

Series Parallel

"1,Q1

"2,Q2QQ1$Q2P%"1$P%"2P%"

1/"1%"1$1%"2


11/27

Resistance R

)he resistance decreases rapidly as a

increases

R ; ?PI ; 8 l B AaG)he units of R are Pa #!3s

narrowin* of an artery leads to a lar*e

increase in the resistance to 'lood flow&'ecause of aGter#.


12/27

9olu#e %low Rates

,ffect of restrictions and 'loc4a*es2

$Series& whole flow is reducedstopped

$Parallel& flow partially reduced& increased in

other parts of the networ4


13/27

)ransport Syste#

closed dou'le!pu#p syste#2

Syste#ic

irculation

Kun*

irculation

Keft side of heart

Ri*ht side of heart


14/27

)ransport Syste#

Structure of the Heart

/nferior "ena ca"a

=fro# lower 'ody>

Superior "ena ca"a

=fro# upper 'ody>

orta


15/27

)ransport Syste#

5ranchin* of 'lood "essels

$teries 'ranch into arterioles& "eins into

"enulesrteries

rterioles

apillaries

9enules

9eins

Heart


16/27

)ransport Syste#

apillaries

$%ine "essels penetratin*

tissues$Main route for *asnutrient

e


17/27

)ransport Syste#

5lood is in capillary 'ed for a few seconds

* of #uscle has a "olu#e of a'out

0F##3=density of #uscle E*#c#3or

000 *#3>& hence there are a'out

L04# of capillaries with a surface area of

E@ #@assu#in* a typical capillary is@0m in dia#eter.


18/27

Pressures

Kar*e pressure "ariations throu*hout the

syste# =note 4Pa ; 7.3N ## H*>

$7 4Pa =@N ##H*> after left "entricle

$@ 4Pa =N ## H*> after syste#ic syste#

$3.G 4Pa =@N ##H*> after ri*ht "entricle

5lood pressure #onitor on ar# #easures@0 ##H* systole and 80 ##H* diastole for a

healthy youn* person


19/27

Pressure


20/27

Pressure

,ffect of *ra"ity on pressure

$Density of 'lood E .0G


21/27

Pressure

onse:uences

$9aricose "eins

+or#ally =e.*.& durin* wal4in*> #uscle action helpsreturn "enous 'lood fro# the le*s

(ne!way "al"es in le* "eins to pre"ent 'ac4ward

flow

Defecti"e "al"es #eans poolin* of 'lood in le*"eins


22/27

Pressure

cceleration

$onsider upward acceleration& a! au*#ents *ra"ity

$effecti"e *ra"ity ; aO&$Pressure difference ; =aO&>h

Pressure at head reduced.

,.*.& a; 3*

Pheart!head; .0G


23/27

Rate of 'lood flow

5lood lea"es heart at E 30 c#s

/n capillaries& flow slows to E ##s

$Surprisin* ! continuity should i#ply hi*her

flow

$Recall indi"idual capillaries only E@0# in

dia#eter& 'ut "ery #any hence total crosssection e:ui"alent to a tu'e 30 c# in dia#eter

usin* esti#ate of @@N < 0Fcapillaries in 'ody


24/27

,ffect of onstrictions

5ernoulli effect

$+arrowin* of tu'e *i"es increased "elocity& 'ut

reduced pressure

/ncreasin* "elocity at o'struction leads to a

transition fro# la#inar to tur'ulent flow


25/27


)ransition fro# la#inar to tur'ulent flow

characterised 'y"eynold's ()m*er, +

%low

rate

Pressure

Ka#ina

r

)ur'ulen

t

Qc

$ritical "elocityc Qc

$c;+"

$%or #any fluids&+E000

$e.*& in the aorta

="-c#>& cE 0.G#s


26/27


pparent that one can *et a rapid increase

in flow as a function of pressure in the

la#inar re*ion& 'ut relati"ely slow intur'ulent re*ion

$Durin* e


27/27

%urther Readin*

ll inPhysics of the Body, Cameron,

Skofronick and Grant, Ch. 8,

Measure#ent of 'lood pressure

$Section 8.G

Physics of heart disease

$Section 8.0

Documents

Medical Lecture 1