Dark story How scientists use goats to solve bends

Dark story How scientists use goats to solve bends

In 1905, a Scottish physiologist tested a method to help divers avoid bends. Some goats were lost in the process.

When the autopsy was performed on the diver in 1900, they found bubbles in the brain and heart. There were so many bubbles, in fact, that when the examiners raised their hearts, he was gurgling with foam. The cause of death was decompression sickness. And while doctors knew the cause of the state, they desperately needed a way to prevent it. For the Scottish physiologist in charge of finding a solution, it would take multiple tests - and 85 goats - to find a method to avoid the atrocious state.

Anyone working under compressed air is prone to decompression sickness-this is especially true for divers who, in order to dive deep need to breathe higher levels of compressed air in order to overcome the pressure of the sea room. As the divers on the bottom blow the compressed air, they do not notice anything-the air seems the same as it would on the surface. However, as the plunger surfaces and the water pressure decreases, the compressed air gases the plunger soaked come out of the solution forming bubbles, much the way a bottle of soda water does when the hood is open.

From the various gases inside the bubbles, the oxygen is easily absorbed by the body, the carbon dioxide is easily expelled, but nitrogen bubbles linger. These travel through the body and lodge in the joints, spine and organs. Those suffering from decompression sickness experience a variety of symptoms including dizziness, double vision, severe pain, blindness and paralysis. Death was frequent. The decompression sickness was also known as diver's paralysis and caisson's disease, as it was diagnosed for the first time among the workers who built the Brooklyn Bridge under compressed air. But it is most commonly referred to as elbows, because of the twisted position that victims often took.

At the beginning of the 20th century, there was no known way to prevent turns. If the divers surfaced and showed symptoms, they were often sent down or placed in a recompression chamber, dubbed a "diver's oven," to breathe the compressed air that forced the nitrogen bubbles into their body. to recover in solution. Then they were decompressed by trial and error. The most common tip of the day was to gradually lift a diver through a pressure atmosphere every 20 minutes, which almost never worked.

In 1905, the British Admiralty commissioned Scottish physiologist John Scott Haldane to solve the problem. Haldane at that time was known for his experiments in the fight against harmful gases in mines and his studies on breathing. Not one to shy from practical experimentation, he and a colleague sealed themselves in an airtight box, they nicknamed the "coffin" and recorded their reactions as they ran out of breathable air. The motto of the Haldane family was "to suffer".

Haldane coordinated test dives with the Royal Navy, reviewed the medical literature and interviewed divers. He learned that decompression sickness never occurred when a diver stayed above 33 feet. The compressed air that was delivered to the divers at this depth was at a pressure of about two atmospheres, double the air pressure on the surface. Haldane reason that if a diver can surface after being exposed to doubling air pressure without adverse effects, then any man could withstand an immediate drop in air pressure by half, no matter how deep.

For example, if a diver goes down to 300 feet, the volume of compressed air needed to overcome the pressure of the water is a little over 148 pounds per square inch (psi). Instead of coming gradually, a diver can climb immediately to 134 feet where the pressure is 74 psi, half. Then, after waiting a while to allow the body to adjust and dispel the bubbles, the diver can climb to 51 feet, where the pressure is a little over 37 psi, wait, and so on until that he could surface. Haldane has dubbed his theory decompression.

To test his hypothesis, Haldane ordered experiments at the Lister Institute of Preventive Medicine in London by Lieutenant Guybon Damant of the Royal Navy, an expert diver and amateur scientist, and the physiologist Edwin Arthur boycott. The researchers first experimented on mice, rats, guinea pigs and an old hen by placing them in a large experimental air tank, filling it with compressed air and then venting the air. The results were inconclusive as these smaller creatures traded gases faster than humans.

Researchers have considered alternatives such as monkeys, dogs and pigs. But these were either too small, difficult to obtain, or had very different respiratory rates from humans. Finally, they settled on the goats they calculated had a respiratory exchange rate 1.7 times that of a human adult male.

A herd of 85 goats was assembled to list for some sinister experiences. The researchers put groups of up to eight goats inside the chamber, delivered compressed air, waited, then normalized pressure before releasing them into the Institute's courtyard for observation.

As in humans, goats had different types of symptoms indicating curvature. Some refused the food. Others bleated in pain. Some have become paralyzed (temporary and permanent). Others have shown injuries in the knees (a common occurrence of elbows as the bubbles lodged in the joints). Some suffered from shortness of breath and labored breathing. Others are dead. The researchers were not completely devoid of compassion. They tried to limit the experiments to what they felt did not kill the goats, and those who were in great distress were euthanized. At the end of all these experiments, there was a surviving goat, which was adopted by Lieutenant Damant as a pet. This is how researchers confirmed that goats that were decompressed did not suffer from bends.

The next step was the human tests. Lieutenant Damant and Warrant Officer Andrew Catto, an expert diver, volunteered for the position. Like the goats, they entered the experimental chamber and submitted to compressed air episodes up to a little over 94 psi from which they were staged uncompressed. After repeated attempts, there were no signs of turns. Now, it was time for real-world experiences.

At the end of August 1906, Haldane, Catto and Damant sailed the HMS Spanker torpedo boat to the deep waters of Loch Efforçn, a finger off the Firth of Clyde. Damant and Catto fit into the bulky diving dress that in the air weighed nearly 200 pounds. The divers were physically connected to the spanking by an air hose and a lifebuoy, the last of which was threaded with a copper wire that allowed telephone communication with the surface.

Trial dives were conducted by Catto and Damant who were kneeling deep in the Loch mud for one hour. When the weather came up, Damant, which went down to 90 feet, was raised to 30 feet which was calculated to be the most superficial depth he could safely unpack. He held a shot line and agitated about his limbs vigorously with the idea that this would help disperse nitrogen bubbles faster. Five minutes later, he was transported to 10 feet. He waited another 10 minutes before being raised to the surface. There was no sign of the turns.

The tests continued for more than a week, but not all went as planned. On the afternoon of August 28, Catto dipped to 180 feet and worked to attach a weight to a bullish for 12 minutes to simulate realistic conditions. As he climbed, he found that his line of life had become entangled. It was not a terrible entanglement, but it was at an unprecedented depth and the pumps, which were cranked, had trouble delivering the proper amount of air. This made Catto particularly sluggish.

Catto was finally able to unravel his line. By the time he was unraveled, he had been on the bottom for 28 minutes. No human had ever been exposed to these levels of compressed air (over 90 psi) under real conditions for so long. During the elevation of Catto, the researchers took great care and the scene decompressed him with nine stops. It took Catto 90 minutes to reach the surface. The diver showed no sign of elbows, just exhaustion. Catto Dove the next day, and three days later, Damant descended to an unprecedented depth of 210 feet, a world record. He surfaced without any signs of decompression sickness.

The tests were a total success. Haldane published a series of dive tables that were quickly adopted by Great Britain and soon after by divers from all over the world. These charts formed the basis of the essential rules for safely raising divers on the high seas.

Staged decompression is still used today. On September 18, 2014, the Egyptian diver Ahmed Gabr Dove 332.35 meters (1 090 feet) in the Red Sea, setting a world record for scuba diving on the high seas. The ambient sea pressure was over 472 psi. While it took Gabr 14 minutes to reach this depth, he spent 13.5 hours decompressing to the surface.

الوسوم: history