biophysics-Anesthesia

1. -BIOPHYSICS
Dr Nisar Ahmed Arain
Assistant Professor
Anesthesia/Critical care/ER

2. -DEFINATION OF FLOW
-FLOW OF FLUID
--It is the quantity (Q) “volume of Mass” of fluid i.e gas or liquid
passing across a point in unit time (t)
F = Q/t
FLOW OF FLUIDS MAY OCCUR THROUGH
--A) A tube of a constant diameter
--B) A tube of a variable (Non – uniform) diameter
--C) An orifice
FLOW OF FLUIDS ACROSS A TUBE OF A CONSTANT DIAMETER
In order to drive a fluid through a tube, a pressure difference must
be present across both ends of tube i.e (P1 – P2)

3. CHARACTERISTICS
--1-It occurs when a flow passes through a smooth uniform tube.
--2-The fluid moves in a steady regular manner
--3-The flow is silent
--4-It occurs when the flow moves with a velocity below a critical
velocity
--5-The flow of fluid varies directly with the pressure difference i.e
the relationship between the flow and the pressure is linear
and the resistance ® is constant
FACTORS AFFECTING THE LAMINAR FLOW
These factors determine the Hagen – Poiseuille formula
As Q =P / R
The resistance R is affected by:-
--1-Velocity of Fluid (q) The resistance is directly proportional to the velocity
--2-Length of the tube (L) The resistance is directly proportional to the length
--3-Radius of the tube ® The resistance is inversely proportionate to the power
of 4 of the radius i.e R = 1/r4
-THE LAMINAR FLOW

4. --1-TO INCREASE THE RATE OF TRANSFUSION OF FLUIDS
Through an intravenous line, It is more important to increase the
radius of the cannula instead rather than increase the pressure,
as flow is proportional to the pressure i.e an increase in the
pressure increases the flow by the same ratio but the flow is
proportional to the power of 4 of the Radius i.e an increase in the
radius produces an increase in the flow by 16 times (if r = 2 so 24 = 16)
--2- Resistance to breathing is much greater when a tracheal tube of a small
diameter is used as in Pediatrics
-CLINICAL APPLICATIONS

5. CHARACTERISTICS
--1-It occurs when a flow passes through a smooth uniform tube with
a constriction, an orifice, a sharp bend or some other irregularity
--2-The fluid moves in an irregular manner
--3-The flow is noisy i.e it creates sounds e.g
a-Carotid Bruit
b-Murmurs
--4-It occurs when the flow moves with a velocity above a critical velocity
--5-The resistance is higher than that for the same Laminar flow
--6-The flow is not directly proportional to the pressure difference i.e the
relationship between the flow and the pressure is not linear
FACTORS AFFECTING THE TURBULANT FLOW
--The onset of turbulent flow occurs when the Reynolds number is > 200
--Reynolds number = (velocity X Density X Radius) Viscosity
--NB:- Critical velocity occurs when the Reynolds number is >2000
--If the Reynolds number is < 2000, Laminar flow occurs
-THE TURBULENT FLOW

6. --1-DURING BRONCHEAL ASTHMA:-Broncho – constriction occurs, therefore the velocity
of flow is increased above the critical velocity and the flow becomes turbulent where
the resistance is very high
When the helium is used (It has very low density) with oxygen, the density of the
inhaled flow is decreased, therefore, the Reynolds number falls below 2000 and the
flow returns back to the Laminar flow with a low resistance
--2-FLOW OF AIR IN THE RESPIRATORY TRACT IS A MIX BETWEEN
LAMINAR AND TURBULANT FLOW
a-In the wider parts as the Nose, Nasopharynx, and trachea, the flow is more Laminar
b-In the branches of the bronchial tree, the flow is more turbulent
c-In the lower respiratory tract as the surface area is large, the velocity is low so the flow
is more
Laminar again. Any pathology as spasm or infection increases the turbulent flow
--3-DURING ANESTHESIA:-
Reduction of the resistance to flow can be achieved by avoiding the angle piece
connector and making the internal surface of the breathing circuit smooth
-CLINICAL APPLICATIONS

7. DIFFUSION
The movement of a substance from a high concentration
to a low concentration
OSMOSIS
The movement of WATER across a semi permeable membrane
due to difference in non diffusible solute concentration
between the two sides.
CONCENTRATION GRADIENT
The difference in concentration between a region of high
concentration and a region of lower concentration
-DIFFUSION, OSMOSIS AND
CONCENTRATION GRADIENT

8. --1- PASSIVE TRANSPORT
--Does not require cell energy
--Examples:-
a-Diffusion
b-Facillitated diffusion and
c-Osmosis
--2- ACTIVE TRANSPORT
--Requires cell energy
--Example:-
a-Carrier mediated active
transport
b-Endocytosis and
c-Exocytosis
-PASSIVE AND ACTIVE TRANSPORT

9. DIFFUSION
--The random movement of particles of a solute from an area
of higher concentration to an area of lower concentration
a-Particles always move with (Down) a concentration gradient
(the difference in concentration across a membrane)
b-Passive Transport
-METHODS OF TRANSPORT

10. OSMOSIS
--The diffusion of water through a selectively
permeable membrane
a-Passive transport
b-Water molecules move from a higher
concentration OF WATER to a lower
concentration OF WATER
c-Water will move to where there is a
greater amount of solute because
there is less water there
-METHODS OF TRANSPORT

11. FACILITATED DIFFUSION
--1-Particles always move with (Down)
a concentration gradient
--2-Uses Transport / channel proteins
--3-Passive Transport
--4-Usually for specific molecules such as Glucose
--5-Facilitated Diffusion stops at Equilibrium
-METHODS OF TRANSPORT

12. It requires energy in the form of ATP
--1-It is capable of moving solute particles against the concentration
gradient (from low concentration to high concentration)
--2-Uses Transport / Carrier proteins (Protein pumps) embedded in
the plasma membrane
--3-Carrier proteins are specific for the molecules that they allow
through. The carrier protein changes shape which requires energy
(ATP)
-METHODS OF TRANSPORT
ACTIVE TRANSPORT

13. --A- ENDOCYTOSIS
--a process of taking material into the cell by means of “infoldings” or
pockets, of the cell membrane (usually putting them into a Vacuole)
a- PHAGOCYTOSIS “Cell Eating”
--Non specific molecules
--Intake of solids
b- PINOCYTOSIS “Cell Drinking”
--Non specific molecules
--Intake of small droplets of liquid
-METHODS OF TRANSPORT
ACTIVE TRANSPORT

14. -METHODS OF TRANSPORT
ACTIVE TRANSPORT
-EXOCYTOSIS (Reverse Endocytosis)
-This is a process in which the membrane of the
vacuole surrounding the material fuses with the
cell membrane, forcing The contents out of the cell

15. -EXOCYTOSIS and ENDOCYTOSIS