Science Questions

Geoff Blackwell  asked the Naked Scientists:

Given the way breathing helium can make your voice higher pitched, is there a gas that can make it sound lower - just in case you want to sound like Darth Vader, instead of Donald Duck?

Thanks

Geoff


What do you think?

I farted once and a deep gruff voice boomed out, "Was that you?"

Seriously though, any gas denser than air should make your voice sound lower - at the risk of getting choked and poisoned.

Xenon would probably be the best one to use but it's rather rare exoensive and difficult to get but it is being used in light bulbs and flash tubes so it must be available

Yes, have a look at this http://www.youtube.com/watch?v=C40nWXv2Ksg

There is methane and some other heavy gases but you would never know the answer because they would kill you

methane (RMM = 16) is lighter than air and hence would not lower voice timbre. It would anaesthetise you though.

Chris

Cris,

I am sorry of course you are correct, I was thinking about carbon monoxide and heavier gases. Silly me

Alan

Carbon monoxide is practically as dense as air and very toxic- a breath of that might kill you.
The video clip shows that the effect is real so it's hard to see why someone would say "you would never know the answer because they would kill you"
I didn't hear them say what gas it was they were using but I guess it's sulphur hexafluoride.

Methane isn't anaesthetic under normal conditions.

All of these experiments are somewhat risky- the gases are not oxygen and you need oxygen to survive.

Most volatiles, if inhaled, will alter consciousness. People who inhale lighter gas (admittedly this is butane but the chemistry is the same) can testify to this. It may not be sufficient to induce general anaesthesia at low doses, but it can certainly cause cardiorespiratory depression, like nitrous oxide.

Chris

Xenon is an anaesthetic. The chemistry is poorly defined. Methane still isn't anaesthetic.

Methane can behave as an anaesthetic:

"Anesth Analg. 1993 Jul;77(1):12-8.

    Is there a cutoff in anesthetic potency for the normal alkanes?
    Liu J, Laster MJ, Taheri S, Eger EI 2nd, Koblin DD, Halsey MJ.

    Department of Anesthesia, University of California, San Francisco 94143-0464.

Vapor pressures and anesthetizing partial pressures in rats were measured for 10 consecutive normal alkanes, methane through decane. All produced anesthesia as defined by the absence of movement in response to either the application of a tail-clamp or electrical stimulation of the tail. The anesthetizing partial pressure was calculated as the average between the concentrations just permitting and preventing movement. Although nonane and decane did not provide anesthesia when given alone at their saturated vapor pressures, their anesthetic properties could be demonstrated by their ability to decrease the anesthetic requirement for isoflurane (i.e., their anesthetic potencies could be defined by studies of additivity). Anesthetic potency increased (from 9.9 atm for methane to 0.0142 atm for decane) and vapor pressure decreased (from 38.2 atm for ethane to 0.0028 atm for decane) with increasing chain length. The decrease in vapor pressure far exceeded the increase in potency. For nonane and decane, the ratio of the partial pressure required for anesthesia to the saturated vapor pressure was less than 1, being 0.48 and 0.19, respectively. We conclude that no cutoff phenomenon (i.e., no absence of anesthetic effect with longer chain alkanes) exists from n-methane to n-decane, but that larger alkanes have vapor pressures too low to permit their potency to be evident when given alone."

- The difference is that very high MACs (mean alveolar concentrations) are required to drive the anaesthesia. At normal pressure this is insufficient to achieve any anaesthetic effect (which is why they needed 9atm). The same applies to N2O (nitrous oxide / laughing gas), which can help to maintain anaesthesia but at life-compatible MAC cannot induce an anaesthetic effect.

OK, look at what we both posted.
From me
"Methane isn't anaesthetic under normal conditions."
And from you
"Anesthetic potency increased (from 9.9 atm for methane to ..."


Well, unless you spend your time inside a pressure tank at 10 bar or more, I still say I'm right.
Incidentally, if you can let us know what the chemical recation involved with any of these compounds (but particularly the xenon)is I'm sure lots of people would like to know.

Okay, truce!

The chemistry of anaesthesia is poorly understood, but almost certainly relates to cell membrane function, because a feature shared by most anaesthetics is that they are strongly lipophilic; that is, they will dissolve well in fatty / oily substances. This serves two purposes: 1) it means that they penetrate the nervous system very efficiently and 2) they dissolve easily in cell membranes, which are formed from phospholipids (fatty acids linked to a polar phosphate "head").

But once the substances get into the membrane things get a bit blurry. We know that most "general" anaesthetic agents make nerve cells less excitable. This suggests that they probably interact with proteins in the membranes that act as ion carriers or "pores" that are responsible for controlling nerve cell activity. By dissolving in the membrane it's possible that anaesthetic agents can snuggle up with some of these ion channels and change their shape, altering their function.

For instance, depressing the activity of excitatory channels makes a nerve cell less active. At the same time anaesthetics may also potentiate the action of some of the brain's inhibitory transmitter substances, which damp down nerve activity. Alcohol, a well-known CNS depressant, works in this way by making nerve cells much more sensitive to the inhibitory chemical GABA. It's likely that at least some aspects of general anaesthetic agents are attributable to effects like this. Other agents, like ketamine, target specific ion channels and block them.

So what about xenon? Well, owing to its noble gas status, it's unlikely to be reacting with anything so it could just be a size phenomenon. Perhaps a xenon atom is the right size to jam the pores of some of these ion channels I mentioned above and so it competes with the native ion for access to the channel. If the size is a snug fit then the xenon atom might spend much longer in the channel than the native ion, shifting the equilibrium in favour of xenon and thus inducing an anaesthetic effect.

The long and the short of it is, we just don't know how all classes of general anaesthetics work.

Interesting area of science though.
Chris