Medical ventilator, as an important part of medical equipment, has gradually evolved from a simple assisted ventilation tool to a highly intelligent device with multiple functions and modes after years of research and development and innovation.
"Bible • Genesis" said that God created man out of clay, and breathed life into his nostrils, so man gained life. According to research, "Genesis" originated from the Hebrew "Old Testament" written around 1000 BC, which has a history of more than 3,000 years. People at that time had clearly realized the importance of breathing.
Several ancient civilizations in the world have attached great importance to breathing. In our China, Zhuangzi in the Warring States Period (about 369 BC - about 286 BC) had a health preservation method of "exhaling and breathing, exhaling the old and absorbing the new" ("Zhuangzi·Deliberate"). There are also special breathing methods in Indian yoga.
The Belgian physician Andreas Vesalius was the first to study breathing scientifically. He was a famous doctor at that time and served as the royal physician to the king and the pope. He was also one of the founders of anatomy. He carefully studied the structure of the lungs and larynx, and described the mechanism of sound production in detail.
It was the Spaniard Michael Servetus who first discovered the alveoli. Michael Servetus' father was a government official and came from a well-to-do family. He began to study law, during which he also studied theology, and later went to Paris to study medicine.
At that time, religions in Europe were facing great changes. John Calvin created a new fatalism sect, which confronted the traditional Trinity theory of the Vatican, and the two sides were already at war.
Servetus believes that there is no Trinity in the Bible and advocates monotheism. He wrote two critical articles and corresponded with Kelvin. But Kelvin thought his thinking was out of line with his own, a dangerous alternative.
In 1553, the Holy See arrested him and tried him publicly. Thanks to the help of his friends, he escaped with "insufficient evidence". He fled to the Protestant place of Kelvin for refuge, but was arrested and imprisoned, tortured, and finally burned in public. Later generations respected him as the founder of the monotheistic sect.
In his writings Servetus described the alveoli (approximately 0.2 mm in diameter) that are difficult to see with the naked eye. But since his writings were mainly theological, his remarks on the alveoli were not noticed until more than a hundred years later.
The Italian doctor Realdo Colombo also discovered alveoli during the same period. He succeeded Andreas Vesalius as the professor of anatomy at Padua University in Italy, which was founded in 1222 and is one of the earliest universities in the world.
Colombo carefully described the structure of the lungs and alveoli, but failed to discover the mechanism of respiration.
Colombo also discovered the law of friction: when a heavy object moves on a plane, the coefficient of friction is equal to the ratio of thrust to pressure. This law is one of the fundamental laws in mechanical engineering.
In 1628, British physician William Harvey discovered blood circulation, but failed to discover the relationship between blood circulation and breathing.
The famous Robert Hooke also studied breathing. He did an animal experiment:
Attach the dog's windpipe to a jar that can be ventilated or closed. His experiments proved that even without breathing, the air flowing through the trachea could sustain life, but the absence of fresh air was fatal.
By the mid-18th century, the structure of the lungs had been clarified and oxygen was discovered. But still no one has cracked the secret of breathing.
Until 1904, the Danish scientist Christian Bohr studied the physiology of fish together with his doctoral supervisor. They found that the amount of oxygen in the swim bladder was much higher than in the blood vessels of the fish.
So where did the oxygen go?
Bohr conducted in-depth research and proposed the Bohr effect: the decomposition of oxygen is related to the concentration of carbon dioxide and the pH of the environment. This important finding links animals' inhalation of oxygen with exhalation of carbon dioxide. Bohr is handsome, and his son Niels Bohr is the founder of quantum mechanics and won the Nobel Prize in 1922.
Grandson Aage Bohr discovered the laws of particle motion and won the Nobel Prize in 1975.
In 1908, Christian Boll returned to teach at the University of Copenhagen, Denmark. He hired the Danish scientist August Krogh. Crowe, the son of a shipwright, studied medicine and physiology at the University of Copenhagen. Krogh's wife, Marie Jorgensen Krogh, was a classmate of his. Mary had nine siblings, but only four survived to adulthood. So she decided to study medicine. Crowe and his wife shared the same goals, played harmoniously, and made many outstanding contributions.
Under Ball's tutelage, Crowe began to study gas exchange in the human body and the flow of oxygen throughout the body. He discovered that oxygen flow is regulated by capillaries. When the body is at rest, many capillaries close; during exercise, the capillaries open, allowing more oxygen to be delivered to the muscles. This discovery completes the cycle of oxygen and carbon dioxide in the human body.
In 1914, Mary further demonstrated that the oxygen transport mechanism discovered by Crowe was sufficient to maintain the body's metabolism under a wide variety of conditions.
Crowe won the Nobel Prize in 1920.
In 1922, when the Crows visited Canada, they noticed the newly discovered insulin. Mary suffered from type 2 diabetes, so they immediately bought the patent for the production and sales of insulin in Europe. After returning to Denmark, Crowe set up the company with his friends. The company is still operating successfully, benefiting Mary and countless diabetic patients for life.
Today, we have a clear understanding of the principle of breathing. Human breathing is dominated by the automatic control system of the cerebral cortex (voluntary control), and is also affected by other receptors (receptors), including:
Respiratory nervous system (acting through the medulla, pons, and spine);
· Lung stretch receptors;
Stimulus receptors in the lungs and trachea;
· Muscle and joint receptors;
Central biochemical receptors (response to increases in carbon dioxide (CO₂ ↑), hydrogen ions (H⁺ ↑));
Peripheral biochemical receptors (response to decreased oxygen (O₂ ↓), increased carbon dioxide (CO₂ ↑), increased hydrogen ions (H⁺ ↑));
·Other sensory and emotional receptors, other sensory perception includes pain, cold and heat, etc. Emotions include happiness, anger, fright, excitement, subjective ideas, etc. These receptors all act through the hypothalamus.
The respiratory system includes the trachea, lungs, and thoracic cavity. The lungs are enclosed in the pleura and diaphragm of the chest cavity. The ribcage includes the thorax, sternum, thoracic vertebrae, ribs, and intercostal muscles. The pleura is connected to the intercostal muscles, with the pleural cavity and pleural sac in between.
The breathing process is divided into three steps:
In the first step, the nervous system drives the intercostal muscles to expand the chest cavity, and the lungs expand accordingly, creating negative pressure to draw in fresh air.
In the second step, the fresh air mixes with the blood in the alveoli, sends oxygen into the blood, and then sends the oxygen-rich blood to the whole body through the heart through the arterial blood, and then releases oxygen through the capillaries to supply various tissues and organs. The carbon dioxide produced by the metabolism of various tissues and organs is absorbed by the capillaries to form blood with high carbon dioxide content, which is returned to the heart and lungs through the veins, and finally the carbon dioxide in the blood is absorbed and precipitated by the alveoli.
In the third step, the nervous system drives the intercostal muscles to restore the lungs to their original shape, squeeze out the air, and expel the carbon dioxide-rich gas in the alveoli.
Humans breathe about 12-20 times per minute. This frequency is similar to that of ocean waves. Therefore, when we walk on the beach and listen to the sound of the waves, it will resonate with our hearts and feel particularly comfortable.
The respiratory system works day and night, day after day, year after year, whether it is sitting, lying, running, jumping, eating, drinking, waking up, feeling excited, usually able to self-regulate well. But there are also times of illness. There are several types of lung disease, including
Infectious lung disease (bacterial infection, viral infection, fungal infection, etc.);
·Diseases related to air pollution and smoking;
Occupational-related diseases;
· Immune-related diseases;
・Diseases related to heredity;
Lung tumors, etc.
When you are sick, you need to rest, take medicine, get an injection, or even have an operation. When the condition is serious and it is difficult to breathe spontaneously, a ventilator must be used (life is very tenacious, and the patient can gradually withdraw from the ventilator after overcoming difficulties and slowly resume spontaneous breathing).
In the 1930s, polio was epidemic in the United States. Most of the victims were children, US President Franklin Roosevelt. Many patients experience paralysis of the respiratory system as a result.
In order to save these patients, Harvard Medical School invented the "iron lung" ventilator. The ventilator is a rectangular metal box in which the patient lies, with only the head exposed. The ventilator has two vacuum air pumps, one for pumping air and one for inflating, so that the pressure inside the box expands and relaxes like the breathing process. Over the next 30 years, the iron lung became one of the main treatments for polio.
In 1939, the National Polio Foundation began distributing iron lungs on a large scale, at a price of about $1,500 each (the average price of a house at the time).
Today's ventilators use tubing to supply and exhaust air directly to the breathing system. The ventilator is divided into two steps: inhalation and discharge. During inhalation, the vacuum pump exhausts, thereby bringing in fresh air, which is pushed through the inspiratory valve into a humidity-controlled chamber and then to the patient, at which point the expiratory valve is closed. When discharging, the vacuum pump pumps air, but the suction valve is closed, and the gas exhaled by the patient is discharged through the discharge valve and filter. Ventilators also typically monitor breathing and heartbeat and adjust the air pressure and speed of inhalation and exhalation.
Since the outbreak of the new coronavirus Covid-19 around the world, ventilators have been widely used and have saved countless lives.
The development history of medical ventilators has fully demonstrated the power of medical technology innovation. From the initial simple mechanical device to today's intelligent and networked high-tech products, medical ventilators have been constantly evolving and growing on the road to saving the lives of critically ill patients. It is believed that with the continuous advancement of technology, medical ventilators will continue to bring more surprises and hopes to the medical industry in the future. 
