for perfusion students

1. Pulsatile Perfusion
Vs
Non-Pulsatile Perfusion
Nahas N
NIMS

2. Pulsatile vs non- pulsatile (Continuous)
Flow
• Why use pulsatile flow?
Inherently more physiologic (simulates the human heart).
• What is flow like in our vessels??
• Is there a difference between pulsatile and non-pulsatile flow?
• Theories behind pulsatile perfusion
• Effects of pulsatile perfusion
• Benefits
• Systems delivering pulsatile perfusion
• Setting pulsatile mode in HLM
• Conclusion

3. Pulsatile Flow in Vessels

4. • Pulsatility is an intrinsic aspect of the human cardiovascular systems,
as the beating heart generates periodically alternating blood pressure
and flow.
• Pulsatility is emerging as the preferred perfusion method for CPB.
• Clinical evidence show better cardiac, renal, and pulmonary outcomes
in patients receiving pulsatile perfusion
• Better cytokine, endothelin, and hormone levels and a higher
respiratory index are shown in pulsatile perfusion modes compared
with non-pulsatile perfusion modes

5. Theories of Pulsatile Flow
• Energy Equivalent Pressure
• Capillary Critical Closing Pressure
• Neuroendocrine reflex mechanisms effected
by baroreceptor discharge

6. • Pulsatile flow lacks a universal definition, and quantification of
arterial pressure and pump flow-waveforms is imprecise.
• Adequate quantification depends on an energy gradient rather than a
pressure gradient.

7. Energy Equivalent Pressure
• EEP can be used to calculate the total hemodynamic energy (THE),
and, in conjunction with the mean arterial pressure (MAP), the surplus
hemodynamic energy (SHE).
• SHE represents the extra energy generated caused by pulsatility.
• Theoretical advantage that the production of pulsatile flow depends
not on a pressure gradient, but on an energy gradient.
• EEP formula, which precisely quantifies hemodynamic energy, is
defined as the ratio between hemodynamic work during time (∫fpdt)
and the volume of blood pumped in that same period of time (∫fdt).

8. In 1966, Shepard et al. introduced pulsatile blood flow in terms of
energy equivalent pressure (EEP).
• EEP represents the energy content of the pulsatile arterial wave.
EEP = ∫pfdt/ ∫fdt
P = pressure (mmHg)
f = flow rate (ml/sec)
dt =change in time at a specific point
• Using this formula it was determined that the energy needed to deliver
pulsatile flow was up to 2.3 x that required to produce non-pulsatile
flow for the same levels of mean pressure and flow.

9. • SHE values correlate with the existence of pulsatility.
• If the pump flow were completely nonpulsatile, then the SHE values
would be zero.
• What does this extra energy mean?
- The extra energy generated by a pulsatile or nonpulsatile device
is the difference between the mean arterial pressure and EEP.
- Thought to be available to the tissues by capillary patency
- Increased lymph flow
- Oscillatory movements at the cell level

10. Surplus Hemodynamic Energy

11. Capillary Critical Closing Pressure
Studies have suggested a reduction in capillary blood flow and a
significant reduction in cerebral capillary diameter with non-pulse as
opposed to pulsed flow.
(1) Suggests that capillary patency is preserved longer by the
peaks of systolic pressure.
(2) That non-pulsatile flow produces more microcirculatory
shunting and reduced capillary perfusion

12. Windkessel Principle

13. Capillary Critical Closing Pressure: (although never seen under
microscope) The belief that when the pressure in the capillary
system goes below a certain point the capillaries will
close…reducing the gas exchange between the blood and the
tissues

14. Endocrine reflex mechanism effected by baroreceptor discharge
• Transition from pulsatile to non-pulsatile flow results in:
Marked increase in discharge frequency from baroreceptor in
carotid sinus
-This may initiate reflex neuroendocrine responses which
remain operative throughout the non-pulsatile phase.

15. Release of
baroreceptors in
aorta and carotid
artery
Critical Closing Pressure
Neuroendrocrine reflex
mechanism

16. EFFECTS OF PULSATILE PERFUSION

17. Hemodynamic Effects of Pulsatile Flow
• Non-pulse flow is associated with progressive elevation in SVR
- Renin angiotensin activation
- Continues into the post CPB period
• Pulsatile perfusion is associated with significantly lower levels of
vascular resistance in all regional vascular beds
Benefits:
- Improved tissue perfusion
- Lower afterload for ventricle at the end of the perfusion
period

18. Effect on Microcirculation , lymph flow and Metabolism
• Improves microcirculation and tissue metabolism
• Inhibits edema formation by increasing lymph flow
• Lactate production is reduced as a result of aerobic
metabolism.

19. Metabolic Effects of Pulsatile Flow
• Cellular level
Pulsed flow is associated with higher rates of oxygen consumption and
reduced metobolic acidosis
- ??enhanced energy may maintain microcirclatory patency and
optimize tissue perfusion.
• Organ Level
- Kidney: Improved kidney function is the result of better gas
exchange at the capillary level together with the maintenance of
normal lymph flow.
- Brain: reduced cerebral acidosis/markers of brain injury
- Hepatic, gut, pancrease: functions better preserved possibly because
of reduction of mucosal ischemia which can induce endotoxemia

20. Effect on Brain:
• Better preservation of regional cerebral blood flow causing reduction
in cerebral acidosis
• Pulsatile flow reduces cerebral vascular resistance by as much as
25%. The improvement in regional blood flow distribution causes
reduced cerebral lactate production .
• Anaerobic metabolism is suppressed with pulsatile blood flow,
particularly during the critical cooling and rewarming phases.
• No difference in cerebral oxygen saturation.

21. Effect on Pancreas & Liver:
• Preserves pancreatic function better than nonpulsatile CPB.
• Reduced incidence of elevated amylase levels in patients undergoing
CPB with pulsatile flow.
• Hepatic function is also preserved as reflected in postoperative SGOT
level. Hepatic blood flow shows a vasoconstrictive response to
nonpulsatile CPB with decrease in hepatic oxygen consumption.

22. Pulsatile blood flow and the gut;
• Postoperative gastrointestinal morbidity occurs in undergoing CPB. The
cause is mesenteric hypoperfusion leading to ischemia CPB associated
with endotoxemia which in turn cause increase in gut permeability.
• Pulsatile blood flow results in improved blood flow to the gut ,reducing
mucosal ischemia by increasing oxygen delivery.

23. Systems Producing Pulsatile Flow
• Roller Pump
Pump-head accelerates in systolic phase and decelerates during
diastole
- Sub-optimal waveform
• Centrifugal pumps
- EEP and SHE is very minimum.
- Heat generation is more
- Afterload dependance makes them unreliable for this
purpose.

24. • Physiologic pulsatile pumps create the most
hemodynamic energy levels whereas some roller
pumps produce only a quarter of the hemodynamic
energy generated by these physiologic pumps, and
non-pulsatile pumps do not generate adequate SHE at
all.
• Pulsatile flow is a more complex procedure for
minimal benefits.

25. VENTRICULAR PUMPS
Physiologic method for generating
pulsatile blood flow
Operate in a similar manner to the
ventricle of the heart.
Consist of compressible sac and
two one-way valves permitting
blood to flow into and out of the
ventricle in only one direction.

26. COMPRESSION PLATE PUMPS
A length of tubing of known diameter is placed on a rigid back plate and
compressed by a moving plate that descends for a preselected stroke length,
thereby ejecting a volume of perfusate from the tube .The direction of blood
flow is ensured by valves positioned at the inlet and outlet of the ventricle
or sac.

27. The Natural Pulse

28. What the Natural Pulse Does
• Steep front (blood acceleration) induces a pressure wave
• Pressure wave creates a wave phenomenon which:
- expands walls of blood vessels, allowing more blood flow to
move with lower pressure
- reinforces muscles of blood vessels
- removes obstacles inside the blood vessels
- pushes blood through tiny capillaries

29. PULSATILE ASSIST DEVICE
• Is an intermittent occlusive device that employs an intraaortic balloon
pump apparatus to produce pulsatile blood flow in the arterial line of
the CPB circuit.
• The pulse is generated by occluding the arterial line of the circuit under
flowing conditions, thereby creating a large pressure and volume delay
within the arterial side of the circuit. On deflation of the balloon in the
arterial line, the pressure and volume are released in the aorta to the
patient as a pulse.

30. PULSATILE PUMPING CURVE

31. • Base flow -- continuous flow without the pulsatile component
• Start time -- time when the pump flow starts from the base flow
• Stop time -- the time when the flow returns to base flow.
• Start and stop time points reflect the time between the two R waves of
ECG, must be atleast 20% of cycle.
• Internal frequency --70 to 80
PEDIATRIC CIRCULATORY SUPPORT
- LOW BASE FLOW AND SHORT SYSTOLIC PERIOD PRODUCES
BETTER PULSATILITY.
- Hemolysis and GME is a concern.

32. BASE FLOW, FREQUENCY, WIDTHSETTINGS OF HLM:

34. • Beneficial in
- elderly patients
- high risk group
- patients with pre existing renal disease.
- Cardiac surgery in pregnancy

35. Release of GME
Comfort level with
non pulsatile flow
Difficult to understand the
pressure curves and energy
generated
Fear of shear stress/
hemolysis/intimal damage
Diminished
pulsatility

36. Pulsatility over CPB circuit components
• In developing a model that can best predict the behavior of pressure-
flow waveforms in the ECC,
- component design must be first optimized.
• The ECC presents an entirely different hemodynamic environment
than human circulation.
• Because blood is pumped through the oxygenator, the arterial filter,
and several feet of arterial tubing, significant pressure drops occur.
• It is important to select satisfactory circuit components, so that
energy loss is minimized.

37. Obstacles to Transmitting Pulsatile Flow
• Length of tubing
• Resistance and damping of the:
- Membrane
- Arterial line filter
- Cannula
The small size of the aortic cannula creates the equivalent
of AS resulting in circuit stresses and possibly hemolysis

38. Clinical Outcomes of Pulsatile Perfusion
• Facilitate aerobic metabolism due to increases in vital organ blood
flow and microcirculation
• Increases renal, cerebral, pancreatic flow
• Increase capillary perfusion
• Increase RBC transit
• Increase in Lymphatic function
• Positively affect the recovery process, by reducing
- systemic inflammatory response syndrome
- inotropic support
- intubation periods
- duration of hospitalization.

39. • Reduced markers of endothelial damage
• Decrease release of baroreceptor reflex hormones, limiting
vasoconstriction
• Attenuation of hormonal responses :
Catecholamine,
Renin Angiotensin Aldosterone,
Antidiuretic hormone,
Cortisol,
Thromboxane,
Prostacyclin.
• Improved gastric mucosal oxygenation

40. THANK
YOU