Chapter Nine — Regulation of Plasma Osmolality
Highlights
- CFTR Chloro Channel
Summary:
The average sodium content in human sweat ranges from 10 to 90 millimoles per liter. Does anybody know what the sodium is in cystic fibrosis, the sweat sodium level? I know it's elevated. Is it 70, 80? It's about chloride, but sodium must follow too. The only way to prevent it would be to have salt water and which is 3% and no one's going to drink that.
Transcript:
Speaker 1
Yeah, absolutely. Any, any of that stuff is too bad, but you're right. The only way to prevent it would be to have salt water and, which is 3% and no one's going to drink that.
Speaker 3
Yeah. No, I completely agree, Roger, about the lack of, of benefit from sports drinks or proven benefit by, by any sort. In fact, you know, I often have patients with chronic side age that come for a follow up clinic and they tell me very proudly that, dog, I'm drinking Gatorade. So you should be proud of me. And I'm like, no, I'm not proud of you. That's a lot of water. Stop doing that. So yeah, to me, it was just the connection of a concentration of sodium and sweat that allows me to remind the connection with Gatorade.
Speaker 2
Does anybody know what the sodium is in cystic fibrosis, the sweat sodium level? I know it's elevated.
Speaker 1
Is it 70, 80? It's about chloride, but sodium must follow too. I do. I'll bet it is.
Speaker 4
It's above 60 to 70 is the cut off. So half normal or above? Half normal or above. Excellent.
Speaker 5
The average sodium content in human sweat ranges from 10 to 90 millimoles per liter, which is similar to chloride, an important determination of the final sodium and chloride concentration in sweat are driven by the sodium potassium ATPase, which is influenced by ottostrone and cystic fibrosis transmembrane conductors regulator, Chloro channel, the CFTR Chloro (Time 0:26:38)
- Is It Fibrosis?
Summary:
High sweat chloride can be helpful to diagnosis of fibrosis in a patient with symptoms, but there are some healthy individuals who do have more than 60. These are sometimes termed, quote unquote, salty sweaters in the literature. Confirm torch and testing is recommended.
Transcript:
Speaker 5
Conductors regulator, Chloro channel, the CFTR Chloro channel. As is it fibrosis, high sweat chloride can be helpful to diagnosis of fibrosis in a patient with symptoms, but because there are some healthy individuals who do have a sweat chloride more than 60, these are sometimes termed, quote unquote, salty sweaters in the literature. Confirm torch and testing is recommended. There was one seminal study looking at the sweat electrolyte differences in patients with cystic fibrosis, paired to healthy controls, and they showed that the sweat chloride in controls was at an average of 23 millimoles per liter compared to 93 millimoles per liter in patients with cystic fibrosis. And so although the normal range of sweat chloride in humans is 10 to 90, a sweat chloride less than 30 is considered normal. Okay.
Speaker 2
So then he talks about the regulation of plasma osmolality. He says normal osmolality is 275 to 290. But the next sentence is what I love is that you have this range from 270 to 290 says but in individuals, it really only varies from 1 to 2%. So what we have is you have a bell curve where a lot of different people have different osmolalities, but in any one individual, it's going to be much tighter regulated than that full range of 275 to 290 may imply, which I thought was actually pretty cool. So the average among people (Time 0:27:55)
- Osmolality
Summary:
In any one individual, it's going to be much tighter regulated than that full range of 275 to 290 may imply. So the average among people is that but the average for one person is more tightly regulated. And we've talked a little bit about this that we've detect the osmolality and specialized cells in the hypothalamus.
Transcript:
Speaker 2
2%. So what we have is you have a bell curve where a lot of different people have different osmolalities, but in any one individual, it's going to be much tighter regulated than that full range of 275 to 290 may imply, which I thought was actually pretty cool. So the average among people is that but the average for one person is more tightly regulated, which is going to be within with five points essentially is what it sounds like.
Speaker 3
Or even smaller, right? You look back at old labs in your patients and it's 141, 141, 141, 142, 142, 141, 141, 141, 141, right?
Speaker 2
And Melanie's talking about sodium. They're not osmolality, but yeah. No, no, no, I just want to, I don't want anybody to think that, you know, an osmolality 140 is normal. That's not, you know, profoundly ill at 140, right? And that, and we've talked a little bit about this that we've detect the osmolality and specialized cells in the hypothalamus and that the body responds to these changes. And then he kind of goes through an example. So what happens when you get a water load and that's going to suppress ADH and that he says that the ADH has a half life. And so your peak diuresis will be 90 to 120 minutes following your water load because you need to metabolize the pre existing ADH.
Speaker 1
So I was thinking about that and, you know, I've got non-nephrologist friends that talk about exact phenomena when they go out (Time 0:28:58)
- How the Body Responds to an Osmolar Load
Summary:
He says, there is so much urine-production potential that hyponatremia only occurs when there's an impairment in renal water excretion. And he says, this is more about water intake than kidney changes. He really could have gotten for an endorsement deal here. I think that really would have made this.
Transcript:
Speaker 2
As evidence that there's, you know, performance enhancing drug clearance is actually- And this line comes up a couple of times, but he really lays the smackdown later, but he does tease here. He says, there is so much urine-production potential that hyponatremia only occurs when there's an impairment in renal water excretion. I don't want to get, I don't want to lean into that statement yet, because he really focuses in on that later and we'll get to that later. And then he flips the script. So that's how the body responds to a water load, and then he talks about how the body responds to an osmolar load, and one guess on what is an example of an osmolar load, Burton Rose's favorite osmolar load.
Speaker 1
Potato chips. Potato chips. Probably K-Pods don't know if this is typically safe at all.
Speaker 6
K-Pods potato chips. It doesn't mention it, but we can infer. We can dream, right?
Speaker 4
We can infer. He really could have gotten for an endorsement deal here. I think that really would have made this. And he says, this is more about water intake than kidney changes.
Speaker 2
And then he does talk about the normal sodium in DI, and then he says, this is the perfect evidence that though we have two ways to defend against hyponatremia, which is the use of ADH and thirst, thirst is so much more important, because even if you completely remove ADH, which would be central diabetes, or I think he thinks the example he likes to use is nephrogenic diabetes precipitous. (Time 0:33:41)
- Polydipsia
Summary:
I read this kind of a sequence that says there's much creation of excess sodium or responsive mediated reduction in release of aldosterone. And then first you increase water intake and then it lowers the plasma osmolarity toward normal and then further expands the volume. So I guess my question is so expanding the volume, even though there is that reduction in aldosterone, the water intake is still increasing the volume in that moment. Yeah. It's a little bit of volume, but I didn't love this paragraph because it's kind of mixed volume and osmolarities together. He's not wrong. I just, I hate. Well, that's what's confusing.
Transcript:
Speaker 1
I read this kind of a sequence that says there's much creation of excess sodium or responsive mediated reduction in release of aldosterone. And then first you increase water intake and then it lowers the plasma osmolarity toward normal and then further expands the volume. So I guess my question is so expanding the volume, even though there is that reduction in aldosterone, the water intake is still increasing the volume in that moment. I think that's what's implying. Yeah, it's a little bit of volume, but I didn't love this paragraph because it's kind of mixed volume and osmolarity together. And I just think it's so much better to separate those two. He's not wrong. I just, I hate. Well, that's what's confusing. Yeah. To people when you say, well, water is not volume and you're like, well, except when you're drinking water because you're thirsty and hyper as molar. And then it is volume, right?
Speaker 3
In this scenario. Absolutely.
Speaker 6
This is what trips up people when they're thinking about this and when you say this, because you're saying, oh, I just drank a liter of this and you were trying to, and then we say like, oh, well, there's still you will even or like in situations of polydipsia, right? Hypotentremia from polydipsia. Technically, it's under you. Believe it. How can you be you believe if you drank in excess of I don't know, 10 liters, right? And so I think I agree that I also agree. I don't really like this part because it's this part is confusing.
Speaker 5
But I mean, water is volume (Time 0:36:53)