Blood pumps

Exemples

CHAP. 7- Fluid Machinery…

http://www.youtube.com/watch?v=YqvTKrRJIl8

Jarvik 7 CardioWest TAH• The CardioWest TAH replaces each ventricle with a separate

diaphragm-type pump– Each pump is divided into two chambers by a flexible diaphragm with

blood on one side and air on the other• As air is forced into the device, the diaphragm deforms into the blood

chamber causing blood ejection (systole)• As air is evacuated from the device, the diaphragm deforms into the air

chamber causing blood the enter the device (diastole)– This device is driven pneumatically by an external console attached

to the device by two drivelines that go through the skin– The maximum stroke volume in this device is 70 mL with a flow rate

of 6 to 8 L/min under normal conditions

• This device is currently being used in patients under 67 years old who suffer from biventricular failure and are candidates for transplantation

Nikkiso

• The Nikkiso HPM-15 (Nikkiso Co., Ltd., Tokyo, Japan) is an extracorporeal centrifugal blood pump currently in use in Japan for CPB

– This pump has an impeller with 6 blades

• Extensive simulations of flow and hemolysis have been performed on this device

• According to their website, Nikkiso is presently developing an implantable centrifugal pump

Nikkiso HPM-15 (from Takiura et al., 1998).

HeartQuest VAD

• This device makes use of MagLev technology to magnetically suspend the pump impeller

• Currently, this device has a wearable external battery and controller– Future versions will

make use of TET technology

Upper housing

Outflow cannula

Lower housingImpeller

Figure 5-14. HeartQuest VAD (from Song et al., 2004).

Impella Recover• The Impella Recover (Impella

CardioSystems GmbH, Aachen, Germany) is a catheter-based pump offering short term uni- or biventricular support

– This device is the smallest mechanical circulatory support device in the world

– The Impella Recover can be inserted via the femoral artery or directly into the left ventricle and provides circulatory support for up to 7 days

– A portable console is use to drive and control the pump, thus allowing for easy patient transport

– This device is in use in Europe

Impella Recover Pump (from www.impella.com/bilder/produkte/pumpe_a.jpg).

Fluid System: Heart and vesselsThe Windkessel Model

Fluid Machinery…

Role of the arterial system

The arteries carry blood away from the heart to the tissues.

The aorta branches toward periphery until blood reaches the arterioles and finally the capillaries.

The role of the arterial system is to convert the high velocity (around 1 m/s) pulsatileflow at the level of the ascending aorta to a low velocity (around 0.01 cm/s) steady flow necessary to cellular exchanges.

This is performed using the so called: Windkesseleffect.1473

The Vein Man. Vesalius (1554)

Blood pressure in the circulatory system

Diagram of the cardiac cycle, showing pressure curves of the cardiac chambers, heart sounds, jugular pulse wave, and the ECG.

Blood pressure in the circulatory system

Windkessel Effect• Windkessel: a german word that can be translated as air (wind) chamber (kessel).

• A description of an early Windkessel effect was given by the German physiologist Otto Frank in 1899.

• It likens the heart and systemic arterial system to a closed hydraulic circuit comprised of a water pump connected to a chamber.

• The circuit is filled with water except for a pocket of air in the chamber.

• Water is pumped into the chamber, the water both compresses the air in the pocket and pushes water out of the chamber.

• The compressibility of the air in the pocket simulates the elasticity and extensibility of the major artery, as blood is pumped into it by the heart ventricle. This effect is commonly referred to as arterial compliance*.

• The resistance water encounters while leaving the Windkessel, simulates the resistance to flow encountered by the blood as it flows through the arterial tree from the major arteries, to minor arteries, to arterioles, and to capillaries, due to decreasing vessel diameter. This resistance to flow is commonly referred to as peripheral resistance.

* Compliance is a measure of distensibility, change in length per change in tension or change In volume per change in pressure

Theoretical development of the Windkessel effect

We will consider here the simplest form of the Windkessel effect. This model called Windkessel 2-element considers only the arterial compliance (C) and the peripheral resistance (R).

Hypotheses

1-Unsteady flow.

2-The pressure difference across the resistance is a linear function of the flow rate.

3-The working fluid is incompressible.

4-The flow is constant throughout the ejection phase.

Symbols

P:pressure generated by the heart (N m-2) [mmHg]Q: blood flow in the aorta (m3 s-1) [l mn-1R: peripheral resistance (N s m-5) [dyne s cm-5] C: arterial or systemic compliance (m5 N-1) [ml mmHg-1]t: time [(s)T: period (s) Ts: ejection time (s)

Theoretical development

Conservation of mass

Qcc is the flow to the compliance chamber.

Thus

Hyp: P-Pcv= R×Q1Pcv is the central veinus pressurePcv << P [Pcv≅5 mmHg vs. P≅100 mmHg ])

Hyp: Q=Cte throughout the systolic phase.

Therefore

Then

Systolic phase (valve in open position) 0≤t≤Ts

Finally the equation to be solved for the systolic phase is

Initial condition: P(t=0)=P0

Solving eq. I

a) Particular solution (Q=Cte=0)

Systolic phase (valve in open position) 0≤t≤Ts

Theoretical development

Systolic phase (valve in open position) 0≤t≤Ts

Theoretical development

b) Method of variation of the paramter(α1= α1(t))replace in eq.I

To be replaced in the particular solution

Systolic phase (valve in open position) 0≤t≤Ts

Theoretical development

c) The general solution for the systolic phase is therefore:

To determine the constant α2 we use the initial condition:

Finally, the pressure waveform for the systolic phase can be written as:

Theoretical developmentDiastolic phase (valve in closed position) Ts ≤ t ≤ T

It is same thing as for the systolic phase but with Q=Cte=0

Therefore;

The solution for this equation is under the following form:

Initial condition: P(t =Ts) = Ps(Ts) α3 is determined using the initial condition

Then,

Theoretical developmentDiastolic phase (valve in closed position) Ts ≤ t ≤ T

Finally, the pressure waveform for the diastolic phase can be written under the form:

Theoretical developmentSystolic / Diastolic phase

(valve in open position) / (valve in closed position) 0 ≤ t ≤ Ts / Ts ≤ t ≤ T

To compute the solution, we need to know: P0; Q; R; C; T; Ts.However, it is convenient to use a condition of recurrence to compute P0: P(0)=P(T)

Analysis of the solution

• We can notice from the analytical solution of the Windkessel2-element model the importance of the term (R×C) because it determines the “speed”of the exponential rise or decay. This product is called the characteristic time and is usually noted ().

No resistance Higth resistancecirculation in the veins, venules, capilary

Analysis of the solution

(Stiffer)

dPdVC

Demonstration