Throttling in the _____ line of a centrifugal pump involves the risk of the pump cavitation.A.suctionB.exhaustC.pressureD.discharge

共用题干
Surgery Involving the Heart

1 The heart-lung machine(pump-oxygenator)is a valuable addition to the modern operating room.
This machine has made it possible to perform many operations on the heart and other thoracic organs which
could not otherwise be done.There are several types of machines in use,all of which serve as a temporary
substitute for the patient's heart and lungs.
2 The machine siphons off the blood from the large vessels entering the heart on the right side so that
no blood passes through the heart and lungs.The blood is returned to the general circulation for body
distribution through one of the large arteries.While passing through the machine,the blood is oxygenated by
means of an oxygen inlet,and carbon dioxide is removed by various chemical means.These are the processes
that normally take place between the blood and the air in the lung tissue.While in the machine,the blood is
also deformed to be sure that all air bubbles are removed,since such bubbles could be fatal to the patient by
obstructing blood vessels.An electric motor in the machine serves as a pump during the surgical procedure to
distribute the processed blood throughout the body by means of the artery mentioned above.
3 Diseased valves may become deformed and scarred from endocarditis so that they are ineffective and
often obstructive.In some cases a special small knife can be inserted into the heart chamber and the valve
can be cut so that it no longer obstructs the blood flow. The valve may even become partially functional.In
other cases there may be so much damage that replacement is the only resort. Substitute valves,made of
plastic materials have proved to be a lifesaving measure for many patients.Very thin butterfly valves made of
dacron（涤纶）or other synthetic material have also been successfully used.
4 Artificial hearts or parts of hearts designed to assist the ventricles in their pumping function have not
proved as successful as the artificial valves.However,research continues and it is quite possible that an
effective device may soon be ready for use.More spectacular is the transplantation of a human heart from the
body of a person who has recently died.Tissues of the donor and the recipient should be as closely matched
as possible to avoid rejection by the recipient's antibody mechanism.This rejection syndrome is the most
serious problem related to heart transplants.

Endocarditis may cause valves to be damaged________.
A:and finally they fail to function properly
B:to perform many surgical operations on the chest
C:when it passes through the heart-lung machine
D:and they no longer obstruct the blood flow
E:to match tissues of the donor and the recipient
F: when the ineffective valves are replaced by artificial ones