Tuesday 26th April 1:37 pm
The beautiful act of vomiting
Tuesday 3rd November 2015 11:56 am
Vomiting may be one of most disgusting experiences you can have, but the physical processes behind it are actually beautifully choreographed.
Even seeing another person vomit can make an otherwise well bystander start vomiting.
So why would a medical doctor work with biological scientists and engineers in North Carolina to build a vomiting machine – in fact, a projectile vomiting machine? They wanted to understand how Noroviruses spread through the air.
Vomiting is an involuntary and forceful expulsion of whatever happens to be in your stomach out through your mouth – and sometimes your nose.
There seems to be a vomiting centre in your brain known as the Area Postrema. Various nerves connect to it, such as Cranial Nerve VIII (which deals with balance) and Cranial Nerve X (which among things, deals with your gut). The vomiting centre also has receptors for chemicals such as dopamine, serotonin, opiates and so on.
Believe it or not, vomiting is a beautifully choreographed act.
In the lead up to the actual act of vomiting, your lungs will take a deep breath (which minimises the chances of getting vomit into your lungs) and you’ll start salivating (which helps protect your tooth enamel from the stomach acids which can cause dental erosion).
You then generate higher pressure in the abdomen (as your tummy muscles contract) and lower pressure in the chest (as you try to breathe in against a closed larynx). These two effects combine to propel the contents of the stomach into your oesophagus – and through your mouth, and out. Sometimes, people can vomit so forcefully and for so long that their tummy muscles get sore.
There are many causes of vomiting.
Looking at the gut, vomiting can be set off by gastritis, food poisoning, overeating, food allergies, lactose intolerance in children and many other conditions.
Considering the sensory system and the brain, vomiting can be caused by motion sickness, concussion, migraine, brain cancers and more. Other causes include metabolic disturbances (altered levels of calcium, urea, glucose, etc), pregnancy, drugs (such as opiates, alcohol, etc) and yes, infectious agents such as “Norovirus”.
Norovirus, which used to be called Norwalk Virus and Norwalk Agent, can be nasty. Each year, it infects about a quarter of a billion people, and kills 200,000 of them. But in most cases, people recover fully within a few days, even though the symptoms are unpleasant.
These symptoms include nausea, projectile vomiting, tummy pain, watery diarrhea, headache and a low-grade fever. Norovirus is classically associated with gastroenteritis outbreaks on cruise ships, aircraft, hotels, schools and public gatherings.
Norovirus can survive for up to 12 days on contaminated clothing, weeks on hard surfaces, and months or perhaps years in contaminated still water.
It is spread by contaminated food or water, direct person-to-person contact, and yes, through the air – which is where vomiting comes in.
Here’s a typical story: it involves 126 people at a function eating at a restaurant, which had 6 tables.
One person had already been infected with Norovirus, and they quietly vomited onto the floor. (Yes, nasty.) The staff quickly and efficiently cleaned it up, and everybody continued eating.
But from that one vomit, the Norovirus particles travelled through the air – and over the next few days, 52 of the 126 people got sick.
The infection rate was related to the distance from the vomit epicentre. At the same table as the unfortunate vomiter, over 90% got infected. At a nearby table, the infection rate was 70%. And way on the other side of the restaurant, even there, 25% got Norovirus.
The projective vomiting machine
Until the North Carolina team got together to build a projectile vomiting machine, nobody really understood how much virus was released during a typical vomiting episode. This was why they built a one-quarter scale Simulated Vomiting Device, and loaded it up with a well-studied and relatively harmless virus known as Bacteriophage MS2.
Their device had a simple hand pump to pressurize it, various valves to let the pressure build up and be suddenly released, and a clay face mask wrapped around the output pipe giving a suitable expression of misery.
In a full-scale human vomit, the maximum volume is around 800 ml, including some 50-200 ml of air. This air contributes to turning some of the wet vomit into tiny aerosols in the air. Now vomit varies in consistency, so the experimenters used both watery artificial saliva, and thick gluggy vanilla instant pudding.
They found that the number of virus particles released from the mouth of their Simulated Vomiting Device ranged from 36, right up to 13,000.
And how many Norovirus particles do you need to get infected? Just 20.
That’s a (w)retchedly small amount that can set off a huge vomit …
This blog first appeared on Dr Karl's Great Moments in Science
© 2017 Karl S. Kruszelnicki Pty Ltd