Things you always wanted to know the answer to [Vol. 5]
Discussion
C n C said:
Jordie Barretts sock said:
Currently getting over a chesty cough.
Why is it when you have a bad coughing fit, your vision starts to go and you feel dizzy? I thought it might be oxygen starvation to the brain, but generally I can hold my breath for longer than a coughing fit and not feel dizzy.
I'm a long way from an expert, but it could well be a combination of a couple of factors:Why is it when you have a bad coughing fit, your vision starts to go and you feel dizzy? I thought it might be oxygen starvation to the brain, but generally I can hold my breath for longer than a coughing fit and not feel dizzy.
1. Rapid movement of your head when coughing repeatedly (similar to sneezing), where the brain impacts the inside of your skull which can cause generation of synaptic impulses potentially affecting signals from the optic nerves, and balance. In effect this is similar to a very mild concussion.
2. When coughing, the rapid expansion/contraction of the lungs can cause short but significant variation in blood pressure. This could easily affect the signals from the optic nerve (vision), and also affect the receptors in the inner ear (balance/dizzyness).
3. Rapid changes in the air pressure in the lungs/thoat/mouth would also affect your ears (think ears popping when ascending/descending in a plane), which may also have some effect on your inner ear/balance/dizzyness. The air pressure in your synapses may also have an impact on your vision.
I am not a doctor, so just my layman's suggestions.
Final thought re. holding your breath and oxygen starvation - if you hold your breath, your heart is still pumping blood normally, and it is still carrying oxygen to your brain. When you are forced to breath again (can't hold your breath any longer), this impulse is driven by the increase in CO2 in the blood, and not the lack of O2, so holding your breath wouldn't cause oxygen starvation.
It is possible that in point (2) above, changes to your blood pressure with a coughing fit may well affect the flow of blood to the brain, so I guess a slight oxygen supply issue could well be a result. Possibly a very mild version of Cough Syncope which is far more extreme.
Edited by C n C on Wednesday 15th May 16:01
It's true that respiratory drive is controlled by your blood CO2 levels, not O2 levels (except in a particular group of COPD patients but that's irrelevant at this point).
A short period of breath holding isn't enough to significantly decrease pO2 (partial pressure of oxygen) or SaO2 (arterial oxygen saturation), and a coughing fit wont make a blind bit of difference to either of those. However, oxygen is important.
Brain is dependent exclusively on aerobic respiration, i.e., oxygen utilising energy generation. Unlike pretty much all other tissues, e.g., muscles, it can't utilise anaerobic respiration. Furthermore, it also can't use any substrates other than glucose delivered freshly by blood; it has no emergency reserves or stores. Therefore, cutting off or reducing its blood supply affects consciousness very quickly. This can manifest as dizziness, visual changes, fainting etc.
With those as our starting points, next we need to look at what happens when you cough. During a single cough, there is a sudden contraction of chest wall muscles, intercostal muscles etc., all of which results in a big spike in intrathoracic pressure. It's that sudden, massive rise in intrathoracic pressure that expels whatever the body is trying to get rid of from the lungs; the lungs don't have a way of generating that pressure themselves to that extent. They have some elastic recoil, but for that to work, you'd need to induce a pneumothorax.
Now, under normal circumstances that's just a momentary increase and doesn't have much of an effect. However, if you have a coughing fit where you're coughing continuously for a period, then your intrathoracic pressure will remain elevated as it will not have the chance to return to normal between each cough. The reason why this is important is because return of venous blood to the heart from the rest of the body is dependent on intrathoracic pressure being very low, negative, in fact. Therefore, a prolonged period of increased intrathoracic pressure reduces blood return back to the heart. The first consequence of this is that there's no blood to pump out to the lungs to re-oxygenate. The follow on consequence is that there's no oxygenated blood to pump around the rest of the body, including the brain. The rest of the body can cope, but the brain starts to suffer within seconds if its blood supply is disrupted. The other consequence of preventing blood returning back to the heart to continue circulating round the body is that you get venous congestion which becomes more apparent where it's more visible - face. Venous blood is a much darker colour than arterial blood and venous congestion results in the typical purple/blue appearance as a result.
The effects of a coughing fit are similar to the effects of a Valsalva manoeuvre, which, if done extremely powerfully, can cause loss of consciousness (including in the middle of a med school physiology experiment where one may have been the subject...) where intrathoracic pressure is raised by taking a deep breath, closing the glottis and breathing out against it.
In short, the dizziness and similar effects caused by a coughing fit arise as a result of the changes it induces in intrathoracic pressure and the consequent reduction in blood flow to the brain. The more reduction, the worse the dizziness and purple face, they are directly correlated.
QuickQuack said:
Lots of really interesting medical stuff
Wow - thanks for this - really appreciated and equally as interesting!This is one of the things I love about PH - one can post some of the most obscure questions and another PH'er with genuine expertise in the subject will respond with a very detailed, but also understandable answer.
Many thanks!
QuickQuack said:
The effects of a coughing fit are similar to the effects of a Valsalva manoeuvre, which, if done extremely powerfully, can cause loss of consciousness (including in the middle of a med school physiology experiment where one may have been the subject...) where intrathoracic pressure is raised by taking a deep breath, closing the glottis and breathing out against it.
That's really interesting - it reminds me of a craze that swept through school in the late 70s / early 80s where kids would take really deep breaths in and out a few times then put their thumb in their mouth and blow hard against it and faint. Cue lots of "yeah yeah he's just pretending", "no he's really gone look.>" etc. Absolutely no idea where the craze came from or why we did it. Quite bizarre.
Granadier said:
Going back to gears, bicycles often have gear shifters on both handlebars, but they work in opposite directions, I think. Pushing the left shifter forward gives you a lower ratio, while pushing the right one forward gives a higher ratio, and vice versa when pulling them back.
That is to do with gravity the distance your thumb has to travel on the shifter in each case.-For the rear derallieur moving the chain down gives you a higher gear, gravity / the spring in the mechanism is on your side so a simple release of a ratchet does the job
-For the front the opposite is true, moving downwards (toward the frame) gives a lower gear so the click / ratchet release does the job.
In both cases it is ergonomically better for the lower lever to carry out the longer travel
BigBen said:
That is to do with gravity the distance your thumb has to travel on the shifter in each case.
-For the rear derallieur moving the chain down gives you a higher gear, gravity / the spring in the mechanism is on your side so a simple release of a ratchet does the job
-For the front the opposite is true, moving downwards (toward the frame) gives a lower gear so the click / ratchet release does the job.
In both cases it is ergonomically better for the lower lever to carry out the longer travel
Yes, this. However there did used to be derailleurs that work the opposite way around; the spring tension is pulling the mechanism onto the lowest gears. These are called 'low normal' types and were very unusual 15+ years ago, and are probably now extinct -For the rear derallieur moving the chain down gives you a higher gear, gravity / the spring in the mechanism is on your side so a simple release of a ratchet does the job
-For the front the opposite is true, moving downwards (toward the frame) gives a lower gear so the click / ratchet release does the job.
In both cases it is ergonomically better for the lower lever to carry out the longer travel
Clockwork Cupcake said:
Do Opticians (Boots, specifically) have a policy that absolutely every member of staff must wear glasses even if they don't need glasses, or does it just seem like it?
I don't know about Boots, but it certainly policy in Vision Express. They wear clear lenses if they don't need a prescription. Jordie Barretts sock said:
I don't know about Boots, but it certainly policy in Vision Express. They wear clear lenses if they don't need a prescription.
InterestingI had an eye test in Boots Opticians today, and every member of staff had glasses on. But then I popped into SpecSavers to have a look at their frames and one member of staff wasn't wearing glasses which suggests that it's not policy there.
Mr Penguin said:
Do dogs (or any other animal besides human) engage in paedophilia? If so what is the reaction from other animals in the pack (assuming social animals)?
You'd need to be more specific. Any animal (humans excepted) deem it acceptable to procreate with any of their species old enough. An old dog will try to mount a young bh in her first season. Roughly equivalent to a 70yo bloke having it away with a 12yo? Never really thought about it to be honest.
Mr Penguin said:
Do dogs (or any other animal besides human) engage in paedophilia? If so what is the reaction from other animals in the pack (assuming social animals)?
With some bees and wasps the males mate with the females as soon as they emerge from the cell.Not sure you can cite this as a legal defence though ...
WrekinCrew said:
With some bees and wasps the males mate with the females as soon as they emerge from the cell.
Not sure you can cite this as a legal defence though ...
M'Lud I identify as a bee, hence the striped tie.Not sure you can cite this as a legal defence though ...
Are those able to reproduce? I suppose my question is more aimed at animals who are too young to reproduce rather than hebephilia.
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