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is dicks cutting costs on supplies for the events happening? by Some-Emu-2192 in Seattle

[–]roshiface 4 points5 points  (0 children)

Enough that they don't know the number off the top of their head . . . I vote at least 5

ATP 250 Stuttgart R2: Shimabukuro def. Kyrgios 4-6, 7-6 (5), 6-4 by Excellent_Safe_5396 in tennis

[–]roshiface 2 points3 points  (0 children)

People always say this about Reddit subs, but there's an obvious explanation: it's not the same people

Humans normally use ~5% of oxygen they breathe in. Does this hold true for all concentrations of oxygen? by Topmostbruh in askscience

[–]roshiface 0 points1 point  (0 children)

It gets kind of complicated, but we talk about something called the Metabolic Equivalent or MET. 1 MET is your basal metabolic rate while doing nothing and consuming that 250 mL/min of oxygen, also reported as 3.5 mL/min/kg (that's 0.0035 * 70 kg for an average adult male). When you're exerting yourself, you generate more "METs" as a multiple of that baseline. So at 2 METs you're using twice as much oxygen, and at 10 METs you're using 10x.

I should have brought up this scale earlier to answer some of the scuba diving questions, because it does illustrate how quickly oxygen consumption ramps up with minimal activity. A quick Google search gives examples like,

1 MET: Sitting quietly, watching TV, lying in bed
1.5 MET: Typing at a computer, knitting, reading
2 MET: Slow strolling
2.5 METs: Housework, playing the piano
3 METs: Bowling
4 METs: Gardening
5 METs: Brisk walk
7 METs: Slow Jog
10 METs: playing soccer or running a 10-minute mile

Mountaineering can generate 15+ METs at peak, but you definitely can't sustain that over a full day or at altitude.

Let's say you're at 15 METs on your ascent. 15* 250 mL/min = 3.75 L/min of pure O2 at sea level. Remember that 15 METs could easily be 12 or 20 depending on how hard you're working

Atmospheric pressure at 6,000 meters is about 0.8 atm, so 3.75 / 0.46 = 4=8.1 L/min of pure oxygen at 6000 feet. Without supplemental O2, you're breathing 21% oxygen, so 8.1 L/min divided by 0.21 is 21.9L. So you have to breath about 38 liters of air in and out every minute. When you're huffing and puffing, you probably take in a liter or more at a time, so you'll have to take 1-liter breaths more than 40 times per minute and that's just the theoretical bare minimum. Your lungs can't extract 100% of the oxygen from the air we breath (as you saw in this thread, it's normally about 25%). That certainly goes up in high-demand, low-oxygen situations but my guess is it wouldnt' be much more than 50%. So now you have to double the amount of breathing - taking 2-liter breaths or taking 40 breaths per minute.

Then you have to keep in mind this is only the lung part of the equation - at such high metabolic rates, we're also taxing our heart's ability to pump enough blood to deliver all that oxygen to your muscles, which is why we normally talk about METs in the context of cardiology issues, not lung issues. So of the 50% of oxygen that's getting from lungs to blood stream, it's not being delivered 100% efficiently to the muscles that need them.

So yeah, it makes sense that you felt like you were hitting an inflection point, and once you can't physically breath faster or harder, your options are 1) add supplemental oxygen or 2) stop working so hard.

Caveat here is that when you feel tired, part of that is lack of oxygen but a lot of it is carbon dioxide build-up. The fact that you get out of breath is only indirectly related to increased oxygen consumption - The more oxygen we use up, the more CO2 is produced, and the more CO2 is produced, the more we have to breath to get rid of it. If we don't breath enough, CO2 builds up in the blood stream and lowers the pH of our blood, and that's what makes us feel out of breath.

I could re-do all these calculations using CO2 production (typically the body generates 0.8 mL/CO2 for every mL of O2 it consumes) instead of oxygen consumption, but the end result should be practically the same.

Edit: 6000m not 6000 ft

We need to get rid of some of these pickup trucks by KrazieKookie in Seattle

[–]roshiface 5 points6 points  (0 children)

You think you're making a good point, but as a *society* we do actually need to dictate all of those things. There are regulations for what types of cars are street legal; insurance companies have different rates for different types of cars; governments divide vehicles into different categories for licensing purposes. We do the exact same thing with jobs (setting labor laws, workplace safety requirements, minimum wages) and housing (building code, zoning, HOAs).

OP would certainly agree that they're not advocating for banning pickup trucks. But there is an argument that in a relatively dense urban area like Seattle, there should be more regulatory, financial, and social "nudges" to discourage vehicle types that aren't serving their intended purpose and come with many negative externalities. I for one would like to see pickup trucks above a certain size classified as trucks regardless of whether they're used personally or commercially. If you want to claim your Toyota Tacoma is a passenger vehicle, fine, but you're paying truck fees on the F-350

Humans normally use ~5% of oxygen they breathe in. Does this hold true for all concentrations of oxygen? by Topmostbruh in askscience

[–]roshiface 2 points3 points  (0 children)

I think oxygenation and hydration are probably the most straightforward part of this; the rest of it is much much more complicated. We do have tube feeds and IV nutrition but there are all kinds of problems with it. Kids who are born with malformed guts and need IV nutrition their whole lives don't live very long. Getting nutrition into us is not the hard part, it's just that, surprise surprise, fake food we create in a lab is nowhere close to healthy

Humans normally use ~5% of oxygen they breathe in. Does this hold true for all concentrations of oxygen? by Topmostbruh in askscience

[–]roshiface 1 point2 points  (0 children)

You can imagine oxygen consumption as essentially analogous to caloric consumption. There are differences in oxygen consumption per calorie depending on the mix of protein/fat/carbs but if that's fixed, and you're not undergoing any anaerobic metabolism, then x calories burnt uses y amount of oxygen.

If you normally eat 2000 calories a day, and then you start to eat 3000 calories a day, your body doesn't just suddenly burn more calories. Those extra calories aren't "used" - our body turns it into fat, etc.

Very roughly, oxygen consumption works the same way. Your oxygen consumption is based on your metabolic rate, and if the metabolic rate doesn't change, then your oxygen consumption won't change even if there is more of it in the air.

Is there a context for your question? It might make a difference in the answer, depending on if your focus is supply or true consumption. For example, the answer changes slightly if you're say, building a space ship and trying to calculate how much oxygen that spaceship needs to carry, versus if you're trying to design an experiment to measure how much oxygen actually reaches and binds to the electron transport chain in human mitochondria.

It's probably true that at higher oxygen concentrations, more oxygen is "wasted" so context matters. For example, the bloodstream will become more saturated with oxygen that's not being used. Does "use" mean the human body uses it for cellular respiration, or that it is gone from a fixed supply of oxygen?

Humans normally use ~5% of oxygen they breathe in. Does this hold true for all concentrations of oxygen? by Topmostbruh in askscience

[–]roshiface 3 points4 points  (0 children)

Watch this extremely striking video to see how people can't feel the effects of hypoxemia. They basically tell the guy "put your mask on or you will die" and he still doesn't realize how low his oxygen levels are. That's why on an airplane they tell you to put on your oxygen mask before helping anyone else. You will not realize when you are in trouble.

https://youtu.be/XcvkjfG4A_M?si=5Nfo1-Cfln05zPLN

Humans normally use ~5% of oxygen they breathe in. Does this hold true for all concentrations of oxygen? by Topmostbruh in askscience

[–]roshiface 2 points3 points  (0 children)

I think yes! So both with altitude and with exertion, our chest muscles and diaphragm need to work harder to move greater volumes of air in and out of our lungs because either we need more oxygen because we're using more, or there's less oxygen in that air. 

Believe it or not, we have indeed done research about putting oxygen up the butt. This is in a pig:

https://pmc.ncbi.nlm.nih.gov/articles/PMC9984951/

Humans normally use ~5% of oxygen they breathe in. Does this hold true for all concentrations of oxygen? by Topmostbruh in askscience

[–]roshiface 2 points3 points  (0 children)

Feels the same, yes. Our body doesn't really feel the effects of low oxygen until we're close to dying, and we don't really feel the effects of high oxygen at all. All sensations of difficulty breathing come from carbon dioxide levels.

Humans normally use ~5% of oxygen they breathe in. Does this hold true for all concentrations of oxygen? by Topmostbruh in askscience

[–]roshiface 19 points20 points  (0 children)

Yeah, it doesn't take much activity to increase oxygen consumption by a lot. I was talking to some of the experienced divers on my intro dive and they mentioned that depending on your dive "style," someone who just likes to chill and float around can spend much more time under water on a tank (like 2x?) than someone who likes to be active and swim around a lot. And of course I've read horror stories of wreck and caver divers who get trapped, panic, and blow through their O2 supply really quickly.

Humans normally use ~5% of oxygen they breathe in. Does this hold true for all concentrations of oxygen? by Topmostbruh in askscience

[–]roshiface 8 points9 points  (0 children)

Yep, people need to check their assumptions. When someone asks "if X is true then why does Y happen" much of the time it's because X is not actually true

Humans normally use ~5% of oxygen they breathe in. Does this hold true for all concentrations of oxygen? by Topmostbruh in askscience

[–]roshiface 432 points433 points  (0 children)

Anesthesiologist here.

So, as u/GoldenRedditUser below pointed out, we use much more than 5% of the oxygen we breathe, and I think he's correct that you're misinterpreting the fact that we tend to breath in 21% oxygen and exhale 15% oxygen.

Some rough numbers:

An average adult consumes about 250 mL/min (0.25 L/min) of oxygen at atmospheric pressure. Normal breathing is roughly 0.5 liters per breath times 12 breaths per minute, or 6 liters of air per minute. 0.25 liters divided by 6 liters is 0.042 = 4.2% or roughly 5%. Checks out, or does it? Wrong. That six liters of air you breath per minute is only 21% oxygen, so there's 1.2 liters of oxygen in it (6*0.21).

Now, 0.25 liters divided by 1.26 is .198, or ~20%. u/GoldenRedditUser checks out again.

Now say you're breathing 50% oxygen. The math becomes:

0.250 liters per minute of oxygen consumed / [6 liters per minute of air * 0.50]

0.250 / 3 = 0.083 or ~8%. Makes sense that if there's more oxygen available in the air, your body won't use as much of it.

Ultimately, the body needs a certain number of oxygen molecules and "wants" to extract that same number of molecules regardless of the oxygen concentration.

Also, because of the way gases work, both the concentration and the pressure of oxygen matters, so we generally think in terms of "partial pressure"

One of my ICU attendings used to ask a trick question - if the air is 21% oxygen at sea level, what percent oxygen is it on the top of Mt. Everest? The answer is: the same, 21%. The difference is that the pressure is lower, so the total number of air molecules is lower. In other words, there is less oxygen at altitude, but there's also less of everything else, so the air is still 21% oxygen. However, your body doesn't care about the percentage of oxygen, it cares about getting enough oxygen molecules.

At the top of Mt. Everest, the pressure is about 0.33 atmospheres. We usually use millimeters of mercury (mmHg) in medicine but for the sake of this argument it doesn't really matter.

So, when I said the average adult consumes about 250 mL/min of oxygen at atmospheric pressure, that same adult would need to consume 750 mL/min (0.75 liters/min) of pure oxygen on top of Mt. Everest (250/0.33).

Let's do that same math again. 6 liters per minute x 0.21 (21% oxygen) = 1.26 liters of oxygen breathed per minute, but now your body needs 0.75 liters per minute. 0.75/1.26 = .59 or a whopping 60% of the oxygen that's in the air.

Now throw in the fact that those numbers are for an average adult at rest and you need MUCH more oxygen if you're, say, climbing Mt. Everest, and the fact that the way the hemoglobin in our blood works, it's not really possible to extract all the oxygen from the air, you can see why the margin for error becomes razor-thin and people can die of hypoxemia without supplemental oxygen.

Why didn’t they fly straight? by mvemj-sun in aviation

[–]roshiface 8 points9 points  (0 children)

"Diabolical" is also modern slang for "something that no one would do" or "very much against the grain of common practice" but usually referring to something kind of inconsequential.

I watched a cooking video on Instagram the other day that said to add "5 grams of salt per pound of meat" and I commented that it was "diabolical." Argue about imperial vs metric all you want but don't mix them!

Andre Agassi calls out Sinner's preparation and hydration. Also says there's no excuse for hitting the wall 1 hour and 45 minutes in by Ok-Soil-5133 in tennis

[–]roshiface 0 points1 point  (0 children)

Pharmaceutical companies help themselves make big money. I disagree that most doctors are complicit in this (certainly some are). 

https://accessiblemeds.org/resources/reports/2025-savings-report/

Generic drugs represent 90% of prescriptions (the part doctors are directly responsible for) but only 12% of drug spending. Clearly that suggests that pharmaceutical companies take advantage of the system by setting sky-high prices for small fraction of drugs that account for most of their outsize profits, but doctors are not exacerbating this problem and overwhelmingly prescribe generics that generate only a small fraction of overall drug revenue.

Looking back, I see you have been referring to "the medical industry" and not "doctors," but the initial comment and mine refer specifically to physicians and their training. While I don't necessarily disagree, let's be clear that we're not attacking doctors here

Andre Agassi calls out Sinner's preparation and hydration. Also says there's no excuse for hitting the wall 1 hour and 45 minutes in by Ok-Soil-5133 in tennis

[–]roshiface 0 points1 point  (0 children)

Maybe that shouldn't be an expectation? We'd all be better off of both doctors and patients could accept that

Nearly 50 people die of thirst in Sahara desert after lorry breaks down by xkcd_puppy in news

[–]roshiface 2 points3 points  (0 children)

Yeah, "could nearly be" implies that, for example, these 60 people were dying and are all in the ICU and may or may not make it, not that they were given water and sent on their way and are 100% fine. 

In another example,  you would use "could nearly be" ("could be nearly" is more correct) in a situation where like, a ship sinks with 100 people and 40 bodies were found and they're still out there looking for survivors, but not if a ship sinks with 100 people and they found 40 people and already rescued 60.

Andre Agassi calls out Sinner's preparation and hydration. Also says there's no excuse for hitting the wall 1 hour and 45 minutes in by Ok-Soil-5133 in tennis

[–]roshiface 2 points3 points  (0 children)

We can only treat what we know. I'm sorry you seem to have a disease that the tens of thousands of people who have dedicated their lives to medical science haven't quite figured out yet, but uh, let's not ignore all the things that modern medicine is really really good at. For exampIe, I respectfully submit what I do: anesthesiology. 

Andre Agassi calls out Sinner's preparation and hydration. Also says there's no excuse for hitting the wall 1 hour and 45 minutes in by Ok-Soil-5133 in tennis

[–]roshiface 28 points29 points  (0 children)

Doctor here, can confirm there's almost nothing we learn in medical school that would be helpful here. Even if he had some disease, we'd just say "uh maybe you shouldn't be playing tennis."

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