Wikipedia:Reference desk/Archives/Science/2014 November 20

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November 20

Can it be a case that diastolic pressure higher than systolic pressure?

5.28.158.161 (talk) 00:59, 20 November 2014 (UTC)

No, since it's defined as diastolic=lower. DHeyward (talk) 01:50, 20 November 2014 (UTC)

No, that's not how it's defined. Diastolic is from dilation, when the heart refills, and systolic is from contraction, when the heart squeezes. I can't imagine any method where squeezing would result in a lower pressure downstream, but I am not an expert in the topic. Ariel. (talk) 02:41, 20 November 2014 (UTC)

Hmmm, that seems true, yet the way blood pressure is typically measured, at an arm cuff, doesn't actually test for the phase of the pulse relative to the heart. The highest pressure and the lowest are measured, that's all. Which is appropriate, since there is at least some delay for the pulse to spread from the heart through the arteries (pulse wave velocity) - this is pretty fast, normally 7 m/s or so, but over 12 if arteries have stiffened. [1] It wouldn't make sense to define the pulse pressure in a way that varies depending on the degree of atherosclerosis, but not on the actual force with which the blood is transmitted, and to a different extent depending on which part of the body is measured and how far it is from the heart. But if you did it that way, and someone had really really elastic arteries, maybe it could be delayed by 50% of a pulse and you would measure a 'negative' pulse pressure (without actually going through the zero pulse pressure, zero circulation, death etc. in the middle). Wnt (talk) 03:40, 20 November 2014 (UTC)

Regardless, the diastole process of refilling the heart is not necessary the same as the definition diastolic pressure which is always the low number. People with compromised cardiac performance still have a blood pressure and the low number is defined the diastolic pressure regardless of how poorly the ventricles are performing. --DHeyward (talk) 04:33, 20 November 2014 (UTC)

This can happen when Intra-aortic balloon pumps are used, but that is a specialized case of an external pump out of phase with the heart. In general, just measuring blood pressure on the arm, no, I don't think this can happen. --Mark viking (talk) 05:08, 20 November 2014 (UTC)

Can you explain me why in this case it can be- please? 5.28.158.161 (talk) 00:09, 21 November 2014 (UTC)

Shape of the fauces at high- and low-pitched voices

Why does the shape of the fauces change with respect to the change of the voice pitch? High-pitched voices make the fauces opening narrow, and low-pitched voices make the fauces opening wide. 140.254.226.219 (talk) 17:00, 20 November 2014 (UTC)

I can't find anything to back this up but logic would suggest that the fauces help to produce the sound of the voice, and, like a musical instrument such as an organ pipe, the resonation of a larger diameter tube produces a lower note. Richerman (talk) 15:38, 21 November 2014 (UTC)

In Python, where does the return output go, if you don't care about it?

(...Moved to Computing Desk)

Crying

Why do babies and small children cry so loudly? I understand the "alert parents to pain or distress" explanation, but the slight advantages of an ear-splitting bawl over a quieter mew seem to me to be massively outweighed in evolutionary terms by the disadvantages (alerting nearby predators that there's a helpless and tasty infant nearby, scaring off nearby game, potentially drawing the attention of hostile tribes, disrupting the sleep of everyone in the vicinity). I'm no expert, but as far as I'm aware there's no other species whose young makes quite so much noise so routinely. Has anyone ever come up with an evolutionary (or even creationist) explanation for why this is? Our crying article doesn't seem to shed any light on the matter. Mogism (talk) 17:59, 20 November 2014 (UTC)

I'm guessing you haven't been to Australia and heard a baby magpie there. HiLo48 (talk) 18:28, 20 November 2014 (UTC)

My assumption is that the disadvantages of loud crying are exaggerated. First, humans are very seldom to predation, and I don't know the extent to which earlier hominins were subject to predation, or were already able to defend themselves against predators. Second, as to scaring away nearby game, in humans, and likely in earlier hominins, the game isn't nearby. The males hunt in groups while the females care for the young. Third, as to drawing the attention of hostile nearly tribes, the tribes are not close enough together that a crying baby would get their attention, and besides tribes in camp, unlike armies in camp or on the move, do not have deliberate silent stand-down, and are relatively noisy anway. As to disrupting the sleep of everyone, that is the whole point. Waking up multiple adults is a small price compared to a sick or injured baby. I think that the advantage to an ear-splitting bawl is not a "slight advantage", but it outweighs the other arguments. I haven't checked the reliable sources. Maybe there should be research, but that is my explanation. Robert McClenon (talk) 18:34, 20 November 2014 (UTC)

OR, but I have seen it with my niblings, mothers get to be pretty good at interpreting different types of crying from loneliness, hunger or colic. As they get older, the attention crying at bedtime becomes more of an outraged scream. I'll email my sister and get back with a reference. μηδείς (talk) 19:40, 20 November 2014 (UTC)

But if the ear-splitting bawl is an advantage, wouldn't you expect it to be common behaviour in infants of other species with a similar niche to hominids? A puppy, monkey etc doesn't shriek at the same volume when it's hungry as it does when in pain. Do baby chimps, which are probably the closest thing to "wild humans", cry in the same way? User:HiLo48, I agree about baby birds, but those are nesting in trees and presumably the whole "risk of attracting predators" dynamic is different. From the experience of living next to a lake, ground-dwelling ducklings and goslings make a much noisier cry when they're in pain or under attack, than they do when they're hungry. Mogism (talk) 20:14, 20 November 2014 (UTC)

Australian magpie chicks keep up the raucous yelling long after they leave the nest. HiLo48 (talk) 20:27, 20 November 2014 (UTC)

Indeed. Here in the USA the young grackles, jays and starlings also make quite loud begging noises after the have fledged. SemanticMantis (talk) 22:10, 20 November 2014 (UTC)

• The book my sister used was a previous edition of Solve Your Child's Sleep Problems By Richard Ferber, known as the cry-it-out method. It is controversial and criticized as cruel, but it was very successful for her, and she did quickly learn the difference between an attention, pain and hunger cry. I am not sure how much that is covered specifically in the book.

As for human-dog comparisons, they just don't apply. The mother is milk laden, and the puppies do not need to beg to be fed. Until they start walking they just make very soft quiet mew-yelps, and in the wild they would be in a den, not out in the open. In primitive human societies, infants ar almost constantly with their mothers, in physical contact and given to suckle almost immediately on crying.

There is also a tension between the mother and child, see parent-offspring conflict. μηδείς (talk) 23:13, 20 November 2014 (UTC)

In primitive human societies, chances are several mothers will be suckling at any given time, so if the child's mother is missing, for whatever reason, another can step in. See Wet nurse. Loud crying can help facilitate this. HiLo48 (talk) 23:45, 20 November 2014 (UTC)

Part of the explanation likely has to do with how helpless a human baby is. Even very young puppies and kittens can stumble about a bit and try to help themselves. A human baby has no such option - if it can't get the help it needs through screaming, it won't get help and babies are very vulnerable. The same situation is also true of many baby birds, which are also altricial. Matt Deres (talk) 15:21, 21 November 2014 (UTC)

It has been found that our brains are hard-wired to respond strongly to the sound of a baby's cry so it probably just sounds particularly loud to us. "The sound of a baby cry captures your attention in a way that few other sounds in the environment generally do, said Katie Young of the University of Oxford, who led the study looking at how the brain processes a baby's cries".[2] And if you ever spent a night in a tent near a field of sheep or cattle (which are prey animals) you will know that mothers and babies constantly make a noise to keep in touch with each other that would compete with any sound a baby makes. Generally the bigger the animal the louder the sound they are capable of making. Richerman (talk) 15:51, 21 November 2014 (UTC)

I am curious whether this is affected by whose baby it is? I notice from experience that while some people will get upset at another person's child crying, and the parents almost always apologize with embarrassment, it doesn't seem to bother me or my sister, whereas with her own children it was definitely an almost irresistible call to action of some sort. μηδείς (talk) 20:17, 21 November 2014 (UTC)

You've stumbled onto the great difficulties of nature: you can always look back and see what was selected, but not look forward to see what will be selected. The truth is only that what is here today has been selected and nearly every conceivable outcome could be argued. There are a lots of inheritance experiments that can be conceived and proved in our lifetime. Not many natural selection ones can be condeucted so people are able to make the argument that all variations are preferred or not preferred. In other words, there is no scientific answer as to why, only the observation as to what. P.S. put a lactating mother next to a crying baby (any baby) and watch involuntary lactation start - as a good a reason as any to cry. --DHeyward (talk) 23:31, 21 November 2014 (UTC)

• As a follow-up to my above comment, my sister said she identified four types of crying by their character and circumstances: hunger, loneliness, pain, and crankiness--being overly tired. She could not attribute this to Ferber, but didn't want to claim it didn't come from another source or sharing with other mothers. μηδείς (talk) 02:13, 22 November 2014 (UTC)

To answer your question above it does say in the article "None of the study participants was a parent or had any particular experience of looking after babies, yet they all responded in the same way, after 100 milliseconds, to the baby cries. "This might be a fundamental response present in all of us, regardless of parental status," said Parsons". Incidentally, I was concerned about your comment above about your "niblings" - I hope you haven't eaten any of them :-) Richerman (talk) 18:58, 22 November 2014 (UTC)

Why does standing up for a long time cause low blood pressure?

5.28.158.161 (talk) 19:43, 20 November 2014 (UTC)

• Your blood and lymph pools in your lower extremities if you don't contract your leg muscles. μηδείς (talk) 19:45, 20 November 2014 (UTC)

In a healthy person it shouldn't. Moving from a sitting to s standing position may cause a temporary reduction in blood pressure but the heart rate should increase to compensate. [3] If a person has a damaged heart they may suffer low blood pressure from standing as the heart has to work harder to pump the blood to the brain against gravity. If they sit or lie down the heart doesn't have to work as hard as the brain is nearer to the level of the heart. If the legs are raised as well, the blood in the lower extremities does not have to be pumped "uphill" back to the heart. Richerman (talk) 23:10, 20 November 2014 (UTC)

The question was "standing up for a long time". Fainting in very fit military troops standing at attention is a common enough occurrence. See orthostatic intolerance. They are taught to flex their leg muscles in place to avoid this. μηδείς (talk) 23:16, 20 November 2014 (UTC)

Ah yes, I wasn't thinking of enforced standing for a long time. However, I think the reason that the blood and lymph pool is because of the increase in gravity as compared to sitting. Richerman (talk) 00:10, 21 November 2014 (UTC)

Yes, the downward pumping away from the heart via the arteries is helped by gravity, whereas the upward pumping via the veins is against gravity. μηδείς (talk) 01:16, 21 November 2014 (UTC)

Read about Congestive heart failure. And beware of the rule against giving medical advice, as we're getting into that neighborhood. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:14, 20 November 2014 (UTC)

The OP has asked a general question with a well known cause we have an article on. He's not said that he suffers from anything. μηδείς (talk) 23:20, 20 November 2014 (UTC)

That's why I said we are merely "in the neighborhood". A question such as that posed by the OP suggests, but does not necessarily demonstrate, personal experience. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:27, 20 November 2014 (UTC)

Whenever biology, chemistry or electricity is involved, we're in the same hood. Just above, someone's looking to score some cheap melanine, another's baby won't stop crying and Alex Sazonov is been (quite possibly) building a deathray. Comes with the territory. InedibleHulk (talk) 01:14, 21 November 2014 (UTC)

I'd like to take credit for Inedible's last comment. μηδείς (talk) 03:16, 21 November 2014 (UTC)

And I'd like to sell it to you, but it's been irrevocably released to the CC-BY-SA zone. Lousy freedom. InedibleHulk (talk) 17:12, 21 November 2014 (UTC)

Actually, that was a rhetorical "I'd like" as in, "I'd like to thank the academy. μηδείς (talk) 20:12, 21 November 2014 (UTC)

Well, you definitely get an assist for steering the conversation. InedibleHulk (talk) 21:11, 21 November 2014 (UTC)

Diapers

I saw a diaper commercial/advert about a brand of diapers that claim up to 12 hours of dryness, but surely 12 hours in a wet or messy diaper would cause irritation to the skin? Also, isn't encouraging parents not a change a kids diaper for 12 hours a really bad idea? --SolliGwaa (talk) 20:24, 20 November 2014 (UTC)

If I'm to believe other diaper commercials, they use various combinations of fabrics to wick moisture away from the layers of fabric that are in contact with the skin. Therefore the baby doesn't have as great a sense of being wet with a wet diaper. Dismas|^(talk) 20:40, 20 November 2014 (UTC)

And, because the incentive of the discomfort of a wet bum is removed, it takes a lot longer for kids to stop wearing nappies. HiLo48 (talk) 21:29, 20 November 2014 (UTC)

Yes. To properly train your child, wrap them in plastic and make them sit in it for a few hours to teach them to not enjoy it. (How about we stick to the actual topic?) --Onorem (talk) 03:26, 21 November 2014 (UTC)

Modern single-use diapers in the USA have something like Water_gel_(plain) in them, separated from the skin by a wicking fabric. It doesn't totally stay dry to the touch from the inside, but much drier than e.g. a traditionally cotton diaper. (as a side note, the absorbing polymer is also why many people don't like to use them - they aren't exactly great stuff to be littering all around the environment, see Polyacrylamide#Environmental_effects.) HiLo's comments are often repeated and make some sense, but of course we'd need a proper reference to back it up. SemanticMantis (talk) 22:08, 20 November 2014 (UTC)

Google has jazillions of hits for feel wet diaper but it looks all either anecdotal (but at least there's "lots of conventional wisdom" saying it and parents using it as a toilet training technique) or promotional for products that keep enough wet feel without actually being a leaky mess. But SemanticMantis is right; in keeping with WP:RS, the plural of anecdotes and PRspeak is not "usable data". DMacks (talk) 04:51, 21 November 2014 (UTC)