A LABORATORY SIMULATION MODEL OF HEART USING A LARGE COLLAPSIBLE BLADDER

Dr Uday Prashant

Why Pulsatile flow

• Development of atherosclerosis is dependant upon the vessel geometries, branching points and fluid flow patterns

• It has been observed that early atherosclerotic lesions develop preferentially in the vicinity of arterial branching and

• curvature where blood flow patterns are complex and multi-directional,

• The most recent such studies implicate oscillatory shear stress on vessel walls in the development of early lesions.

• Although the biological basis of these observations remains to be determined, flow-induced vascular endothelial dysfunction is thought to be involved.

• Therefore, studies of arterial flow fields that aim to generate physiologically relevant flow information need to be based on realistic geometries and

• to incorporate blood flow pulsatility

• There have been several experiments to produce pulsatile flow in laboratory

Requirements of pulsatile flow generators

• It is quite challenging to give more realistic picture of pulsatile flow in heart without resorting to actual humans or animals for better understanding of pathophysiology of atherosclerosis.

• They should be easily manufactured and not very expensive and complicated.

• Should give actual rapid fluid pressure surges as seen in our body.

• Same model should give wide pressure fluctuations seen in various chambers like aorta, ventricles and atria

• Should not damage blood elements

Displacement and Vacuum pulsatile pump but they fail to produce rapid fluid transits seen in vivo

Pulsatile flow generators

Require computer control and actuator pumps

They are huge complicated and consume lot of power

•

• The gear pumps used by Issartier et al., Petersen et al., etc produce cavitation and damage to suspended particles.

• Peristaltic pumps which were developed later to prevent particle damage of gear pumps suffer the drawback of production of only limited subset of waveforms even if they are computer controlled and the systems lack flexibility to operate under wide flow conditions

• Microcomputer controlled piston pumps are very complicated, difficult to set up and cumbersome to operate

BASIC CONCEPTS My discovery involves two basic concepts

1) Flow induced collapse in collapsible tubes

2) Fluid structure interactions in flexible tubes

Method of construction• To a source water that has very negligible head is connected to

collapsing rubber bladder.• This rubber bladder is highly elastic and the lower end is connected

to flexible thin garden hosepipe made of synthetic rubber or PVC. • This flexible rubber tube hangs freely after taking initial ‘U’ shaped

curve.• The distal end is open to atmosphere and all the connections are

airtight.• If the vertical height from the tap to balloon is less than from ground

to the balloon (h1 > ho) and during certain range of flow rates• it exhibits an interesting phenomenon of alternate collapse

(buckling) and opening, along with generation of pulsatile flow of water

Schematic diagram of novel pulsatile flow generator

Other Potential uses

• I postulated seeing the vigor of contractions of each pulsation

• May be it can be used as a novel hydroelectric turbine.

• Did some initial experiments• Awaiting funds for further research.• Mainly used to provoke interest in investors

on this new technology which I developed

Principle of working• Once the bladder and pipes are completely filled & flow is

fully established due to negative atmospheric pressure created by Venturi effect, the rubber bladder collapses and stops the flow.

• The flow is instantaneously reduced. Steady continuous flow is converted to unsteady pulsatile flow by collapsible bladder

• There is large negative pressure “WAVE” generated travelling at speed of sound in water.

• This pressure wave interacts with specially designed flexible tubes with elastic supports and transmits energy.

Types of Coupling

• The most significant mechanism is - the junction coupling others are - Poisson and - friction coupling

• Wiggert D.C, Tijsseling, A. S (2001)- Junction coupling is taken place due to unsupported discrete points of the piping systems such as unrestrained valves, junctions, closed ends, pumps, etc.

• MOC (Method of Charecteristics) and FEM (Finite Element Method) are used to solve structural equations.

100108

180190

217227

250285

300340

3600

20

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140

Flow rate in ml/sec

Frequency of oscillations per minAmplitude of vibrations in mm

Freq

uenc

y an

d am

plitu

de o

f osc

illati

ons

30 50 96 130 150 1650

20

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60

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Variation of frequency with height at constant flow rate of 240 cm^3/sec

frequency of oscillatons

Amplitude of oscillations

Vertical height in cm

fre

qu

en

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an

d a

mp

litu

de

of

os

cil

lati

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s

The figure below shows the deformation of a thin-walled elastic tube which conveys a viscous flow (the direction of the flow is

from left to right).

• In its undeformed state, the tube is cylindrical and the ends of the tube are held open (think of a thin-walled rubber tube, mounted on two rigid tubes).

• As we increase the external pressure [from (a) to (d)], the tube buckles and deforms strongly.

• The reduction in the tube's cross sectional area changes its flow resistance and thereby the pressure distribution in the fluid, which in turn affects the tube's deformation.

• This is a classical example for a large-displacement fluid-structure interaction problem for which many applications exist in biomechanics

• e.g. blood flow in veins and arteries, flow of air in the bronchial airways, generation of wheeze, korokoff sounds during BP measurements

• The photograph below shows the experimental setup used to investigate the viscous flow through elastic tubes:

• Inside a pressure chamber, a thin-walled rubber tube is mounted on rigid tubes.

• A syringe pump at the upstream end pumps highly viscous silicon oil through the tubes.

• The volume flux and the pressure inside the pressure chamber can be controlled independently to induce the tube's collapse.

The figure above shows an example of the two Finite Element meshes used to solve the problem of Stokes flow in an elastic tube.

STEADY FLOW: CHOKING, FLOW LIMITATION AND ELASTICJUMPS

Theory of Waterhammer

• The bladder once collapsed must remain in same state under ordinary conditions.

• But due to ingenious use of flexible tube, the ‘U’ shape bend and elastic supports lead to

• Complex fluid structure interactions which cause the bladder to open automatically and produce pulsatile flow.

• Water hammer effect is produced because during collapse of bladder the velocity of flow changes too rapidly < 4L/C where L is length of tube and C is velocity of sound in water (1200m/sec)

UNDERSTANDING WATERHAMMER

• Water hammer is produced commonly in dams or in houses, hotels, train bathroom taps or valves suddenly opened or closed loud bang is heard with vibrations of pipes mostly at bends and junctions

• Can be as loud as a thunder• Hardly any useful applications described and

mostly engineers interest is to suppress it to maximum extent

Similar to hydraulic ram pump

• A hydraulic ram or impulse pump is a device which uses the energy of falling water to lift a lesser amount of water to a higher elevation than the source.

• Each impulse creates waterhammer which pumps water high much above from which water flows.

• The water hammer and pulsatile flow are created by operation of solid valves but it doesn’t resemble to collapse produced by beating heart

Hydraulic Ram Animation

Liebau Effect: - Valveless impedance pump

The last terms in the Eqs (9B) and (10), modelling friction coupling, depend on the relative velocity V - uz

p/ = 998.2 kg/m3, cr = 1257 m/s and AV = 0.3m/s), but deviates from it when time proceeds

Wiggert DC and Tijsseling AS (2001), Fluid transients and fluid-structure interaction in flexible liquid-filled piping,ASME Applied Mechanics Reviews 54 455-481

• Our model also produces similar pressure tracings depending upon location of pressure recording.

• No need to separately construct different prototypes for mimicking different chambers of heart.

• All can be analyzed in one model and simultaneously

Advantages

• By this model we develop alternative simulative in vitro model for pulsatile flow fluid mechanics in both

heart chambers blood vessels.

These are very cheap and easy to construct than complicated design models shown earlier.

More realistic reproduction of pressure waves than other models without involving complex gears, piston pumps, actuators, micro computers

Does not damage blood elements

Other Uses

• Can be used as micro pump in fuel injection system and drug manufacturing units.

• Can be used in particulate filtration unit where pulsatile flow enhances rate of particulate filtration process.

• Can be used as novel mini hydroelectric turbine.

When something is new, they say "it's not true".

When its truth becomes obvious, they say "it's not important".

When its importance cannot be denied, they reason, "it's not new".

William James

Thank you