A perfusion circuit is used for two separate functions:
1. Initial blood washout and cooling.
2. Cryoprotective perfusion.
Alcor's Air Transportable Perfusion kit (ATP) is documented here.
Some case
reports from 20 years ago by Mike Darwin such as 8504 and Fried contain
diagrams of perfusion circuits.
There
does not seem to be any public documentation of the actual Alcor perfusion circuit, although there is
an incomplete photo here. And on page 8, here.
Suspended Animation's Stockert SCPC Mini-Bypass System is documented here.
Ben Best discusses blood washout and perfusion here.
The Cryonics Institute perfusion circuit is documented at phases.html and Perfusion_System.doc.
External cooling is simply not efficient enough. The skin is well insulated and the extremities are poorly vascularized. The cooling curve would be unacceptably
long if only external cooling were used. If the brain is not cooled quickly enough, it will become edematous (swollen). Edema is a very significant problem because it is largely irreversible, and edema sqeezes shut capillaries in the brain which then cannot be perfused later with cryoprotectants. It is absolutely essential to keep the capillaries open.
In addition to cooling, the washout removes the red blood cells (RBC's) and other whole blood components. RBC's become stiff as they get colder and have difficulty passing through capillaries, possibly impairing circulation. Removing RBC's before extensive cooling reduces the risk of impaired circulation of the capillaries in the brain.
This is the replacement of the patient's blood by a mixture of chemicals called cryoprotectants. The
cryoprotectants allow an ice-free cryopreservation. See the Cryoprotectants page for further discussion.
Our perfusion circuit will take a long time to build. A diagram of the planned layout will be posted soon.
1. Bladders with various concentrations of perfusate.
2.
Silastic tubing, 3/8" ID.
3. Pump. Masterflex 7554-80 with 7518-10 heads.
4. Heat exchanger, 30 plate, 3" wide x 7.5" tall x 4" thick, 5 gpm (for less viscous
fluid), 3/4" NPT ports.
5. Ice bath (for heat exchanger) Addition of salt can take the heat exchanger to slightly subzero temperatures
until a chiller can later be added.
6. Pump (for heat exchanger)
7. Arterial filter
8. Sample port
9. Thermocouple (K type)
10. Pressure gauge, 1/4" NPT, mmHg scale, liquid or gas, Ashcroft.
12. Aortic cannula. (similar to the Medtronic
EOPA CAP)
1. Venous cannula
2. Thermocouple (K type)
3. Sample port
4. Waste reservoir
Connector block: The thermocouples (TCs) and manometer are all wired to an NI SCB-68 connector block:
which is then connected using an NI SHC68-68-EP 2m cable:
to an NI card in a laptop.
The temperature inputs will all be tracked by a custom C# program. The
source code will be posted here. If this is used in the field, the thermocouples could instead be connected to the handheld temperature logger.