Life-saving artificial heart

For a long time, heart transplantation has been the last option for patients with end-stage heart failure. However, due to the shortage of donor hearts, people have begun to turn their attention to "life-extending machines" - artificial hearts in recent years.

If the heart stops beating... The heart accompanies people throughout their lives. The heart is responsible for blood flow throughout the body, and blood circulation is involved in functions such as metabolism and energy transfer. Once heart function is impaired, human life safety will be greatly threatened. It is reported that approximately 22 million people worldwide suffer from heart failure, and the number is still growing rapidly. Heart failure refers to insufficient heart power to pump enough blood throughout the body, which in turn leads to breathing difficulties, excessive fatigue, and lower limb edema, which seriously affects the patient's daily life and even endangers the patient's life.

How does the heart pump blood throughout the body?

The heart is like a "water pump" that is in charge of "pumping" and "draining". We can imagine the heart as a two-story building with two bedrooms and two living rooms, with the upper floor being the left and right atria, and the lower floor being the left and right ventricles. First, when the ventricles contract, the body's deoxygenated blood will flow from the veins into the right atrium, and then into the right ventricle, and then the right ventricle will pump the deoxygenated blood into the lungs. Deoxygenated blood releases carbon dioxide and absorbs oxygen in the lungs, becomes oxygenated blood, flows into the left atrium, and is pumped to the whole body after passing through the left ventricle. The blood that flows to the whole body produces carbon dioxide and metabolites after cells breathe, and then becomes deoxygenated blood again, and flows back to the heart (right atrium) again... Therefore, the beating of the heart maintains blood circulation throughout the body and brings oxygen and nutrients to other organs. A healthy heart must beat about 100,000 times a day to ensure the normal functioning of the human body.

Currently, among heart failure patients, about 44% rely on cardiotonic drugs to maintain life, and about 23% rely on ventricular assist devices to maintain heart function while waiting for heart transplantation. However, compared with other transplant organs, the shortage of donor hearts is more serious. In order to solve this problem, scientists have turned their attention to the development of artificial hearts.

What is an artificial heart?

An artificial heart is an implantable device that can be divided into two categories: auxiliary artificial heart and complete artificial heart, which is used to replace part or all of the heart's functions. Simply put, the role of an artificial heart is to help or replace the heart's pumping blood, providing a continuous source of power for the whole body blood circulation of patients with heart failure.

At present, the clinical application of artificial hearts is mainly divided into three aspects: first, as a substitute during the transition period waiting for heart transplantation, it buys patients more time to find a suitable donor; second, it provides short-term replacement support for patients with acute heart failure, which will be removed after the heart function recovers; third, it provides long-term replacement for patients with end-stage heart failure, supporting patients to survive with artificial hearts for a long time.

Theoretically, any form of "water pump" can be used as a mechanical artificial heart. However, due to the particularity of the human body, the speed at which the "water pump" drives blood flow, the portability of the "water pump", the immune response caused by the "water pump", and the stability of the "water pump" are all aspects that must be considered.

Based on the above aspects, researchers have developed another fully artificial heart - a fully magnetically levitated artificial heart.

Domestic fully magnetically suspended artificial heart

The principle of the fully magnetically suspended artificial heart is not complicated. It only needs to use magnetic force to suspend the rotor (the rotating part of a rotating machine) in the cavity, and realize the rotation of the rotor by controlling the current. This is similar to the principle of a maglev train, and even no different from a maglev toy. However, as a medical device that coexists with patients for a long time, the operating stability of the fully magnetically suspended artificial heart can meet extremely high requirements. At the same time, its size and biocompatibility have much better effects on the human body than previous artificial hearts.

At present, the new fully magnetically suspended artificial heart developed by the Institute of Artificial Organs of Soochow University is at the world's leading level. It looks like a snail and is mainly made of titanium alloy. The diameter of the device is only 50 mm, the thickness is only 26 mm, and the weight is less than 180 grams. The device uses electromagnets, permanent magnets and rotors to form a pump body to drive blood flow.

The core part of the fully magnetically suspended artificial heart pump is a serrated rotor, with electromagnets and permanent magnets above and below it respectively. The magnetic fields generated by the two make the rotor levitate in the pump body. The magnetic field strength is changed by changing the current of the electromagnet, generating a constantly changing magnetic force to drive the rotor to rotate. The pump body introduces and removes blood through two catheters. Due to the special structure of the rotor, it will apply a negative pressure suction to the blood in the catheter during rotation to "suck" the blood into the pump, and at the same time, it will apply a positive pressure thrust to the blood "sucked" into the pump, so that the blood is pumped out from the other catheter, thereby simulating the pumping process of blood in the heart.

Compared with ordinary rotors, the rotor of the fully magnetically suspended artificial heart also has a certain shock absorption function, which is designed to improve the operating stability of the device when it moves with the human body. In terms of biocompatibility, since the suspended rotor does not require blood as a lubricant for rotation and achieves a much larger suspension gap than a liquid dynamic bearing, it greatly reduces the damage to blood components.

Today, this fully magnetically levitated artificial heart is still in the clinical trial stage. The first person to undergo the transplant trial was a young heart failure patient from Hebei Province. Before the transplant, the patient often felt weak and had difficulty breathing, and basically could only lie in bed to rest every day. In January 2021, the fully magnetically levitated artificial heart was successfully transplanted into the patient. According to the patient's own account, before the operation, he was out of breath after walking 20 or 30 meters. Now he has no problem walking 1,000 meters, and he can go up and down the stairs by himself without the help of others, basically realizing complete self-care.

The combination of a not-so-complicated principle and a highly difficult technology has created a fully magnetically suspended artificial heart. I believe that in the near future, the fully magnetically suspended artificial heart will bring a new "heartbeat" to more heart failure patients.

History of the development of artificial hearts As early as the mid-20th century, scientists began to explore artificial hearts. In 1953, the world's first heart-lung machine achieved 26 minutes of complete respiratory-circulatory support for a heart patient undergoing surgery, preliminarily proving the feasibility of simulating heart function with artificial devices. In 1957, the first artificial heart was introduced. Doctors implanted it into a dog, but the dog only survived for 90 minutes. In 1969, the world's first artificial heart implantation surgery was successfully completed, winning 64 hours of precious time for a patient waiting to receive a human heart transplant, but the patient died of infectious pneumonia 32 hours after receiving a human heart transplant. In 1981, the world's second artificial heart transplant surgery was completed, and the patient who received the transplant received a human heart transplant after surviving for 55 hours. Unfortunately, the patient died of infection, renal failure and lung complications 10 days after receiving a human heart transplant. In 1982, the fully artificial heart was implanted for the first time in a 61-year-old patient, who died 112 days later. In 2004, an improved total artificial heart was introduced. Among the patients who received the transplant, the longest survival time was 1,374 days.

In the 1990s, the fully artificial heart with a pulsatile blood pump as the core was introduced, but it was basically eliminated due to its severe damage to blood components, high incidence of hemolysis (abnormal decomposition and death of red blood cells) and thrombosis in recipients, large size and short service life. After entering the 21st century, rotary blood pumps became the mainstream product in the field of artificial hearts. Among them, the first generation (mechanical contact bearings) and the second generation (liquid dynamic pressure bearings) were also eliminated from the market one after another because of their severe damage to blood components.

The third generation of fully artificial heart uses a fully magnetically suspended blood pump as its core component. Compared with the previous two generations, its advantages are easy control of the rotor, long life, less damage to blood cells (thus reducing the probability of thrombosis and hemolysis), small size (suitable for in vivo transplantation) and low power consumption. The research and development of the fully magnetically suspended artificial heart has brought the field of fully artificial heart to a new stage.