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DudoVene t1_iu4hu5o wrote

notably : no. pH in physiological fluids in mammals is very stable and involves many biochemical process in order to. for example, blood pH roughly vary for less than 0.2 ph unit in normal conditions. Any larger variation in this value will lead to conformationnal changes in circulating proteins and also on exhibited proteins (like receptor on the cell surface) and finally strong metabolic issue.

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Existing_Thought5767 t1_iu4nofz wrote

This is the right answer. pH should not change in your body unless you have some really serious problems. Even pH in water is relatively consistent when talking about bodies of water. If pH drops in water then it leads to coral bleaching and kills off living things that would need a stable pH. Many things adapt to the pH in their environment.

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ELI-PGY5 t1_iu4vi1s wrote

It’s not really the right answer. Because we test the pH of bodily fluids pretty regularly, and it’s clinically useful. Just not useful in CSF in standard practice, and it definitely not a standard test in Alzheimer’s.

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NergalMP t1_iu536tk wrote

It’s clinically useful because pH outside the normal range is indicative of a significant problem. Mammalian physiology operates in a pretty narrow pH range with many processes maintaining it.

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ELI-PGY5 t1_iu56p3o wrote

  1. pH changes in bodily fluids are often clinically useful
  2. I don't really care about pH in CSF.
  3. I doubt it's a good test for Alzheimers, as we would presumably all be doing it if a $20 investigation could detect the condition. The linked article isn't very relevant to everyday clinical medicine.
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NergalMP t1_iu5l91f wrote

Sorry, I meant it can be clinically useful outside the specific CSF/Alzheimer’s question. I’m sure it’s irrelevant to that.

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MeshColour t1_iu54qhd wrote

We test blood oxygen level pretty regularly too, which is also clinically useful?

That's unrelated to the fact that for a healthy person that it should not vary

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Existing_Thought5767 t1_iu5gzml wrote

It is 100% the right answer. Just because you are checking pH in blood doesn’t mean it suppose to change when you get sick or something. As people in this have said .2 pH is the most change you will see in the human body, anything more than that change you body literally cannot function. Cells would be destroyed very quickly.

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ELI-PGY5 t1_iu5i898 wrote

That’s gibberish. pH of blood changes in specific disease states. Checking blood pH is a common, useful pathology test.

As for 0.2 = “cells destroyed very quickly” “body would literally not function” - you’re exaggerating. A drop of 0.2 (7.4 to 7.2) would not even count as a severe acidosis.

So I rate your comment 3.2% the right answer, not 100%.

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Daguvry t1_iu5zvmw wrote

Run blood gases all the time working in Respiratory. That's how we monitor correct vent settings and most COPD patients on BIPAP. I can swing blood pH by more than .2 in less than hour with tidal volumes and respiratory rates.

Out of control diabetics can get really low pH values but that's a metabolic issue, not a respiratory issue. I've seen plenty of diabetics under 7.0 pH where the normal pH values are 7.35-7.45

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ELI-PGY5 t1_iu7lm1h wrote

Yeah, I was think of a guy I saw recently with DKA, pH 6.9, not crisp but his cells were also not all dead.

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gasdocscott t1_iu8ox4x wrote

I've treated patients with pH less than 6.7 (or lower- the gas machine doesn't go lower). Often DKA, which is remarkably responsive to treatment even at those extremes.

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DidjaCinchIt t1_iu4xwvz wrote

People: “But, but, but what about alkaline water? It’s good for you!”

Stomachs: LULZ

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minion_is_here t1_iu7981d wrote

That's kind of a separate issue. Chronic acidosis is a big problem in the U.S. (probably due to our diets + stress), so you may say the stomach's self-regulation will always keep the proper pH, that is just not true. Alkaline water doesn't treat the root cause, though. It may help some people with symptoms because it's like taking a weak antacid. You could probably get a better result with tums.

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fastspinecho t1_iu5aua4 wrote

That doesn't really answer the OP's question.

It's entirely possible that pH is both "stable" (i.e. small standard deviation in normal people) AND significantly different in Alzheimer's.

In fact, the more "stable" it is normal people (i.e. the smaller the standard deviation), the smaller a change needs to be in order to be significantly different in Alzheimer's.

For example, if all healthy people have pH between 7.36 and 7.44, then pH of 7.33 would be evidence of pathology.

That said, I don't believe there is any good evidence that the pH of CSF is significantly in Alzheimer's and controls.

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ELI-PGY5 t1_iu4v6gs wrote

The normal range for pH is 5 times that. And we see sick or sick-ish people outside that range pretty regularly. Pretty much everyone at my local hospital who gets blood drawn gets their pH checked.

But as to OPs question - my answer is no. We don’t have any simple tests for Alzheimer’s. MRI and PET provide decent info. But if pH on an LP was different, we’d suddenly have a simple, cheap-ish test for the condition.

pH isn’t a useful test on CSF in normal circumstances btw. We do care about pH in other fluids - pleural fluid, vaginal samples, blood etc.

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mirrim t1_iu4wf9y wrote

This is not true. Normal blood pH is 7.35-7.45. A pH of 6.4 or 8.4 would be fatal. The instruments in my lab can't even read lower than 6.8.

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Grogfoot t1_iu50dpc wrote

"Fluids" is pretty broad, and would include things such as urine, which can be quite variable. But, OP and the thread is referring to fluids that would likely be those continuous with blood and would definitely not vary by an entire pH unit!

Typical pH values of blood are ~7.3. A blood pH less than 6.8 wouldn't even be incompatible with life let alone "normal range".

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ELI-PGY5 t1_iu5ei09 wrote

Sorry, it’s 2am and I misread. The guy I was responding to is too high not too low. Normal range for blood pH is .1 unit, I would disagree that pH varies by 0.2 in normal conditions, 7.2 to 7.4 is a pretty massive difference as you presumably know.

But that’s largely irrelevant to my point, which is that pH is not so stable that it can’t be used for diagnostic purposes. It’s just that it’s not used for the diagnostic purpose that the OP asked about, and the behaviour of tau proteins etc as noted in the reference doesn’t lead me to think that it is likely to be.

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