by Ben Best
The photo at the right shows the basic Cryonics Institute perfusion system as it was in 2008. At the heart of the system is a roller-pump and filter, which are documented in detail at the link. For reservoirs we use a nine liter nalgene rectangular clearboy with spigot that connect to the tubing. The nalgene is polycarbonate. Most of the tubing is 3/8 inch PolyVinyl Chloride (PVC), although some silicone (latex?) tubing is used for the steel cannulae. Specifically, we use 3/8" inner diameter (9.5 millimeters), 3/32" wall thickness (2.4 millimeters) Sorin Standard Perfusion Tubing (Durometer 68 Shore). In 2009 the perfusion system was moved to a specially-modified cart.
The Cobe roller-pump measures flow rate in Liters Per Minute (LPM). Pressure is measured in millimeters of mercury (mmHg with a Medtronic 66000 Pressure Display Box.
A Dideco D 734 Adult 40 micron arterial filter is used to catch air bubbles and large particulate matter (the perfusate is filtered beforehand to 0.2 microns). Air and fluid at the top of the filter is returned to the reservoir through a purge line. Although it seems reasonable to think that the filter would add pressure to the line, my attempts at measuring this addition indicated that no pressure was being added. The top of the Dideco D 734 Adult 40 micron arterial filter can easily became cracked when trying to connect it to the purge line at the top. Epoxy glue can be used to seal the crack and firmly connect the purge line to the top of the filter, thereby eliminating all leaking.
When perfusing directly into the ascending aorta, a single cannula [Elongated One-Piece Arterial (EOPA) Central Arterial Pressure (CAP) cannula] is used, with drainage through the superior vena cava. Otherwise, steel cannulae (arterial tubes) are used, with drainage through the jugular veins. The EOPA CAP cannula has an attachment at the end which is intended to allow for direct determination of patient pressure, as distinct from line pressure. Getting pressure at the outlet of the EOPA CAP cannula is difficult because the tube is so thin and hard to prime, so for this reason we decided that it is easiest and adequately accurate to take pressure readings from the base of the EOPA CAP cannula or the top of the filter (CI uses a tube connection at the top of the filter to get pressure readings). Very little pressure appears to be added by the EOPA CAP cannula at the flow rates used in perfusing a cryonics patient.
steel arterial cannulae (arterial tubes)
come from the The
Embalmers' Supply Company (ESCO).
Stopcocks are to be used with the
cannulae to connect the cannulae to tubing.
The item identification
used by ESCO in the catalog is somewhat irregular. ESCO has
internal identification numbers which they use when making
shipments which may not match those in the catalog. Often,
but not always, adding "49" to the catalog ID
will give the ESCO internal ID. The following is a mapping
beteen ESCO IDs and the catalog IDs for some ESCO
cannulae used by CI. (OD = Outer Diameter)
The steel arterial cannulae are screwed into a steel stopcock much like catalog #70 (page 57) which are connected tothe 3/8" tubing. Typically, CI's funeral director will use a 1/4" OD (Outer Diameter) arterial cannula with a 4" working length (catalog #103, page 80) or a smaller 3/16" OD arterial cannula with a 4" working length (catalog #901-C, page 77) — using no less than two cannulae.
As shown in the above graph for water, increases in flow rate result in
increased line pressure. Normal cardiac output is about 4 to 6 Liters
Per Minute (LPM). But flow rates during a CI perfusion
are typically much less, in part because perfusion solution is more
viscous than water.
Testing 70% CI−VM−1 at freezer temperature (nearly
−20ºC) yielded the following values for pressure added to
the line pressure by two cannulae for given flow rates LPM:
Viscosity increases greatly as temperature drops.
At 2.0 LPM line pressure is increased by 84 mmHg
by the 1/4" OD cannula at freezer temperature,
but only increases by 28 mmHg at room temperature.
Normal perfusion flow rates in a CI cryonics case are
usually 1.0 LPM or less.
|Pressure from cannula||Purge line only on filter|
|Carotid/Vertebral Cannulation||Aortic Cannulation|
|Steel Carotid Cannulae||EOPA CAP Aortic Cannula|