Biomedical Engineering Reference
In-Depth Information
FIGURE 8-7
Schematic diagram
showing the basic
principles of a
heart-lung machine.
Large veins and arteries are required to insert the large-bore cannulae that will carry the
blood away from the patient to the heart-lung machine and then return the blood from
the machine to the patient as shown in Figure 8-7. Sites for venous access can include
the inferior and superior venae cavae, the right atrium, the femoral vein (in the groin), or
internal jugular vein. Oxygen-rich blood is returned to the aorta, femoral artery, or carotid
artery (Enotes, 2002).
The standard heart-lung machine includes up to five pump assemblies. A centrifugal
or peristaltic pump can be used to drive blood circulation. The four remaining pumps
are roller pumps that provide fluid, gas, and liquid for delivery or removal to the heart
chambers and surgical field:
•
Left ventricular blood removal is accomplished by a roller pump that draws blood
away from the heart.
•
Suction created by a roller pump removes accumulated fluid from the general
surgical field.
•
A cardioplegia delivery pump is used to deliver a high-potassium solution to
the coronary vessels. The potassium stops the heart beating during the surgical
procedure.
•
Finally, an additional pump is available for emergency backup of the arterial pump
in case of mechanical failure.
In peristaltic pumps, also known as roller pumps, the roller assembly rotates and
engages the tubing, PVC, or silicon, which is then compressed against the pump's housing,
propelling blood ahead of the roller head, as shown in Figure 8-8. Rotational frequency
and the inner diameter of the tubing determine blood flow. Because of its occlusive nature,
the pump can be used to remove blood from the surgical field by creating negative pressure
on the inflow side of the pump head.
