[AlphBravo (OP)]

Recently I sprained my ankle, and was somewhat immobilised as a result, but during my convalescence, I noticed due the changing weather my ankle would start aching and  noticed these aches were not due to any movement of the ankle but possibly the changing air pressure so why do joints ache due to air pressure?
Also do plants flower as a result of these changes?
 

[tangoblue]

your joints ache because of the air pressure because as the air pressure changes you joints contrast and expand.

[Bored chemist]

Tangoblue, do you have any idea how small the changes in air pressure are and how little the body (which is mainly water) would contract and expand in response to those changes?

The compressibility is about 50 ppm per atmosphere, and air pressure changes are not generally as large as 0.1 atmospheres so the change in volume would be something like 5 parts in a million.
If you look carfuly, under some circumstances you can see the movement of veins etc with the person's pulse. That's a massively bigger effect and yet it doesn't generally get the blame for painful joints.

I suspect that the weather changes with air preessure and the colder, or perhaps wetter, air is responsible for the pain.

[tangoblue]

Hmm, ill take your word for it.

[maffsolo]

"Intraarticular pressure

Intraarticular pressure is about -4 mmHg in the resting, normal knee, and this pressure falls farther when the quadriceps muscle contracts. The difference between atmospheric pressure on overlying tissues and subatmospheric values within the joint helps to hold the joint members together and thus provides a stabilizing force. In a pathologic effusion, however, the resting pressure is above that of the atmosphere and it rises farther when surrounding muscles contract. Thus, reversal of the normal pressure gradient is an additional destabilizing factor in joints with effusions"

Some people can almost predict the weather like a built in barrometer.

[tommya300]

My mom had bad knees she could tell within a few days, that it was going to be stormy weather

[Geezer]

My wife complains of pains in her joints and thinks they might be related to changes in atmospheric conditions. I was sort of thinking it could be related to changes in air pressure too, but I realize now that is highly unlikely.

If changes in air pressure were the cause, she'd be screaming blue murder every time she went in a plane, or went up and down mountains in a car, but I've never heard her complaining in those situations.

[RD]

Tangoblue, do you have any idea how small the changes in air pressure are and how little the body (which is mainly water) would contract and expand in response to those changes?

There is CO₂* gas dissolved in synovial fluid ... http://en.wikipedia.org/wiki/Synovial_fluid

(* probably not as much as in coca-cola though [] )

[Bored chemist]

"There is CO2* gas dissolved in synovial fluid"
And it is likely to stay there since the concentration will not get high enough for it to bubble out of solution.

[RD]

"There is CO2* gas dissolved in synovial fluid"

And it is likely to stay there since the concentration will not get high enough for it to bubble out of solution.

It does when joints are "cracked" ...

The volume of synovial fluid within the joint is insufficient to fill the expanding volume of the joint and gases dissolved in the synovial fluid (mostly carbon dioxide) are liberated and quickly fill the empty space, leading to the rapid formation of a bubble. This process is known as cavitation. Cavitation in synovial joints results in a high frequency 'cracking'

http://en.wikipedia.org/wiki/Synovial_fluid#Cracking_joints

[Geezer]

"There is CO2* gas dissolved in synovial fluid"

And it is likely to stay there since the concentration will not get high enough for it to bubble out of solution.

It does when joints are "cracked" ...

The volume of synovial fluid within the joint is insufficient to fill the expanding volume of the joint and gases dissolved in the synovial fluid (mostly carbon dioxide) are liberated and quickly fill the empty space, leading to the rapid formation of a bubble. This process is known as cavitation. Cavitation in synovial joints results in a high frequency 'cracking'

http://en.wikipedia.org/wiki/Synovial_fluid#Cracking_joints

Good points RD. I can make my neck do a super "crack' from time to time. I hope my head doesn't fall off.

But, but, but, how would we explain the apparent lack of the effect in aircraft etc.? Perhaps it has to be very slow changes in pressure, but that does seem a bit counterintuitive.

[Bored chemist]

That's a rather bigger, faster pressure change than the weather manages (unless you happen to be rather close to a thunderbolt).

[Geezer]

That's a rather bigger, faster pressure change than the weather manages (unless you happen to be rather close to a thunderbolt).

Exactly. And yet the only effect I'm aware of on planes etc. is on people's ears, but not their joints.

I suppose it's not impossible that our joints somehow manage to equalize internal with external pressure when the external pressure changes rapidly, whereas if the external pressure changes very slowly the equalization does not happen? That would only make sense if there was some sort of differentiating mechanism involved during equalization.

Another off the wall thought - could there be any connection between this and "the bends"? I seem to remember that can produce excruciating pain in joints.

[RD]

That's a rather bigger, faster pressure change than the weather manages (unless you happen to be rather close to a thunderbolt).

But the "cracked" joint must have a gas bubble knocking about in it, which will change in size according to atmospheric pressure.

how would we explain the apparent lack of the effect in aircraft etc.?

Pressurised  aircraft ?  …

Cabin pressurization is the active pumping of compressed air into an aircraft cabin when flying at altitude to maintain a safe and comfortable environment for crew and passengers in the low outside atmospheric pressure.

http://en.wikipedia.org/wiki/Cabin_pressurization

[Geezer]

Pressurised  aircraft ?  …

Cabin pressurization is the active pumping of compressed air into an aircraft cabin when flying at altitude to maintain a safe and comfortable environment for crew and passengers in the low outside atmospheric pressure.

http://en.wikipedia.org/wiki/Cabin_pressurization

Don't fall for it! If I remember rightly, you are at a pressure that's equivalent to about 10,000 feet. If they kept you "at sea level", they would wear out the airframes much faster. The added advantage of keeping you at high altitude is that the lack of oxygen makes you sleepy, so you are less likely to get into a brawl with your fellow passengers or the crew.

[tommya300]

Pressurised  aircraft ?  …

Cabin pressurization is the active pumping of compressed air into an aircraft cabin when flying at altitude to maintain a safe and comfortable environment for crew and passengers in the low outside atmospheric pressure.

http://en.wikipedia.org/wiki/Cabin_pressurization

Don't fall for it! If I remember rightly, you are at a pressure that's equivalent to about 10,000 feet. If they kept you "at sea level", they would wear out the airframes much faster. The added advantage of keeping you at high altitude is that the lack of oxygen makes you sleepy, so you are less likely to get into a brawl with your fellow passengers or the crew.

Well mom did not have the fortune of testing it at different altitude. Good to know it isn't the cause.
But she never missed a storm, Why I ask?

Is that  how cabin fever is controlled now? I thought that they secretly pumped Nitrous Oxide into the vents...   [)]

[Geezer]

I exaggerated a bit - sorry. It's quite a bit less than 10,000 feet, but still quite high. According to Wiki -

"At a cruising altitude of 39,000 feet, a Boeing 767's cabin will be pressurized to an altitude of 6,900 feet"

[Bored chemist]

"But the "cracked" joint must have a gas bubble knocking about in it, which will change in size according to atmospheric pressure."

Not for long, it will redissolve.