At the fundamental level, all hearts are pumping mechanisms, but their design varies significantly between various groups of organisms. An insect's heart is extremely simple compared to a human heart and is in essence a modified dorsal blood vessel. The abdominal portion of this blood vessel, the insect's "heart" is divided into chambers separated by small valve-like openings called "ostia," through which blood enters the heart. Each chamber has a pair of alary muscles which expand and contract to facilitate the flow of blood through the heart. The section of the dorsal vessel after the heart does not possess valves or musculature but is instead simple tube called the aorta which facilitates transport of the blood to the head (anterior end), where it empties into the body cavity.
The design of (implantable) artificial hearts is modeled after that of the human heart and for all practical purposes function in a similar manner. As in the human heart, blood flow is regulated by the volume of blood that fills the various chambers of the heart and the pumping rate (the rate at which the chambers fill and drain with blood).
Most modern artificial hearts use energy from either the internal or external batteries. Since the external battery pack is small and portable, you can go places and be fairly active. The internal battery is an emergency battery. It is kept charged continuously by the external batteries. Without input from the external battery, the internal battery can typically only run for approximately 30 minutes. Power is sent from the external batteries to the internal pump through the skin, using coils. One coil is implanted inside you and the other is external. When you put the external coil over the implanted coil, power moves through your skin to the internal coil without any wires actually penetrating the skin. For brief periods, you can remove the external coil (transmitter) and be free of all external parts - the internal batteries supply the power for up to 30 minutes this way.
Anything implanted into the human body can run the risk of being rejected whether it be of biological origin or not. While metals such as titanium in general tend to be fairly biocompatible, the implants are often sites for serious infections to start. A great deal of research is involved with the design of special coatings for implantable materials to prevent these problems from occurring.
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