Cassi, the key word is "interrupted" and so is considered a continuous flow without stopping so the WTS doesn't considered it stored. Notice the Talmudic comments in the 1989 article.
Blood Brochure p. 27 Jehovah?s Witnesses?The Surgical/Ethical Challenge
Many will allow the use of (non-blood-prime) heart-lung, dialysis, or similar equipment if the extracorporeal circulation is uninterrupted.
w89 3/1 pp. 30-31 Questions From Readers
In a somewhat different process, autologous blood can be diverted from a patient to a hemodialysis device (artificial kidney) or a heart-lung pump. The blood flows out through a tube to the artificial organ that pumps and filters (or oxygenates) it, and then it returns to the patient?s circulatory system. Some Christians have permitted this if the equipment is not primed with stored blood. They have viewed the external tubing as elongating their circulatory system so that blood might pass through an artificial organ. They have felt that the blood in this closed circuit was still part of them and did not need to be ?poured out.?
What, though, if the flow of such autologous blood stopped briefly, such as if a heart-lung machine is shut down while the surgeon checks the integrity of coronary-bypass grafts?
Actually, the Biblical emphasis is not on the issue of continuous flow. Even aside from surgery, a person?s heart might stop briefly and then resume. His circulatory system would not have to be emptied and his blood disposed of just because blood flow had stopped during the cardiac arrest. Hence, a Christian having to decide whether to permit his blood to be diverted through some external device ought to focus, not primarily on whether a brief interruption in flow might occur, but on whether he conscientiously felt that the diverted blood would still be part of his circulatory system.?Galatians 6:5.
What about induced hemodilution? Some surgeons believe that it is advantageous for a patient?s blood to be diluted during surgery. Thus, at the start of an operation, they direct some blood to storage bags outside a patient?s body and replace such with nonblood fluids; later, the blood is allowed to flow from the bags back to the patient. Since Christians do not let their blood be stored, some physicians have adapted this procedure, arranging the equipment in a circuit that is constantly linked to the patient?s circulatory system. Some Christians have accepted this, others have refused. Again, each individual must decide whether he would consider the blood diverted in such a hemodilution circuit to be similar to that flowing through a heart/lung machine, or he would think of it as blood that left him and therefore should be disposed of.
A final example of autologous blood use involves recovering and reusing blood during surgery. Equipment is used to aspirate blood from the wound, pump it out through a filter (to remove clots or debris) or a centrifuge (to eliminate fluids), and then direct it back into the patient. Many Christians have been very concerned whether in such salvage there might be any brief interruption of blood flow. Yet, as mentioned, a more Biblical concern is whether the blood escaping into a surgical wound is still part of the person. Does the fact that the blood has flowed from his circulatory system into the wound mean that it should be ?poured out,? like the blood mentioned at Leviticus 17:13? If an individual believes so, he would probably refuse to permit such blood salvage. Yet, another Christian (who also would not let blood flow from him, be stored for some time, and later be put back into him) might conclude that a circuit with recovery from a surgical site and ongoing reinfusion would not violate his trained conscience.
As we can see, there is a growing variety of equipment or techniques involving autologous blood. We cannot and should not try to comment on each variation. When faced with a question in this area, each Christian is responsible to obtain details from medical personnel and then make a personal decision.