In an earlier post I suggested there was a connection between ladies' corsets and Henry's Law. A general statement of Henry's Law is that the solubility of a gas in a liquid depends on the pressure of the gas above the liquid. An everyday example is soda. A can of soda is pressurized by exposing it to carbon dioxide having equivalent of about 2.5 times atmospheric pressure at room temperature. When you quickly lower the pressure of carbon dioxide over the liquid, say by opening the can, the solubility decreases and the gas adjusts by rapidly coming out of solution. Fizzing results (and eventually the soda goes flat).
When a diver dives the pressure of the gases breathed increases, and the amount dissolved in the blood increases. Diving to just 50 feet increases the total pressure to roughly that of the carbonated soda! Rapidly ascending reduces the pressure, just like opening the can of soda, and the gas rapidly comes out of solution - the diver's blood can "fizz". Bubbles in the blood and body tissues are clearly not a great thing, and the physiological effects range from the relatively minor (bubbles in the skin layers) and joint pain, to potentially lethal embolisms in the brain and lungs.
This phenomenon was first observed by Robert Boyle in 1670 who noted the formation of bubbles in the eyes of a snake that had been placed in a high pressure environment, then rapidly decompressed. "I once observed a viper furiously tortured in our exhausted receiver… that had manifestly a conspicuous bubble moving to and fro in the waterish humour of one of its eyes." Before the effects was widely understood, many construction workers suffered from "caisson workers' disease" while working in pressurized environments (caissons) under rivers.
Dive tables - a schedule for ascending from a dive that reduces the chance of decompression sickness - were first created for use by British Navy divers in the early 20th century. How do whales and dolphins cope without dive tables? Half-mile deep, hour long dives are not uncommon - and a rapid ascent from depth could cause a massive case of the bends. They may not be immune - recently researchers have found evidence for chronic decompression injuries in sperm whales. The whale bone in the photo above shows evidence of dysbaric osteonecrosis (bone death caused by rapid decompression).
What does this all have to do with ladies' corsets? In the 1870s tight corsets and big bustles were all the rage. The posture forced upon women wearing these fashionable undergarments was called the Grecian Bend. As decompression injuries caused a similar posture, workers on the Brooklyn Bridge christened the syndrome "the Grecian bends", soon shortened to "the bends".
The photograph of the whale bone is by Tom Kleindinst, Woods Hole Oceanographic Institution and is used with permission.
The image of the Grecian Bends is from the Library of Congress
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