2 more articles of interest.

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Tadpoles take blame for human hiccups

19:00 05 February 03

Why do we hiccup? It's a question that has vexed great minds for millennia and now, at long last, an international team may have come up with the answer.

Hiccups are sudden contractions of the muscles we use to breathe in. Just after the muscles start to move, the glottis shuts off the windpipe, producing the characteristic "hic" sound. Surprisingly, ultrasound scans reveal that babies in the womb start hiccuping after two months, before any breathing movements appear.

That suggests that hiccups in adults are just the remnant of some primitive reflex, which occur only when this brain circuit is accidentally triggered. Yet the purpose of hiccups during pregnancy remains unclear. One theory is that the movements prepare babies' respiratory muscles for breathing after birth, another that they prevent amniotic fluid entering the lungs.

None of these theories explains all the features of hiccups. If their purpose is to prevent liquid getting into the lungs, points out Christian Straus at Pitie-Salpetriere Hospital in Paris, you would expect the closure of the glottis to be associated with the contraction of the muscles used for breathing out, as in a cough, not those for breathing in.

But there is one group of animals in which the peculiar combination of the contraction of these muscles and the closure of the glottis does serve a clear purpose: primitive air breathers that still possess gills, such as lungfish, gar and many amphibians. These animals push water across their gills by squeezing their mouth cavity while closing the glottis to stop water getting into the lungs.

Brain circuitry

In the latest issue of BioEssays (vol 25, p 182), a team led by Straus proposes that the brain circuitry controlling gill ventilation in these early ancestors has persisted into modern mammals.

There are many similarities between hiccuping and gill ventilation in animals like tadpoles, the researchers argue. Both are inhibited when the lungs are inflated, for example, and by high carbon dioxide levels in air or water. But why do we still hiccup 370 million years after our ancestors began hauling themselves onto land?

If the team is right, hiccupping before birth is just an early stage in the development of suckling, a little like learning to crawl before you can walk. Straus thinks the circuitry that controls the movements of the gills and glottis was conserved during evolution because it formed a building block for more complex motor patterns, such as suckling in mammals. "Hiccups may be the price to pay to keep this useful pattern generator," he says.

He points out that the sequence of movements during suckling is very similar to hiccuping, with the glottis closing to prevent milk entering the lungs.

It is a plausible idea, says Allan Pack, an expert in respiratory neurobiology at the University of Pennsylvania. "But it's going to be very tough to prove."

Straus thinks the real test of theory will be to look at the specific neurons that control hiccups and suckling. If the team is right, he says, most of the nerve cells that are active during suckling should also be active when we hiccup.

Randerson

After Challenger, shuttle safety became a priority. Or did it?

19:00 05 February 03

There is something especially shocking about the death of a shuttle crew. The loss is felt more keenly than seven deaths on the road or even in a plane crash. Cynics may scoff that public reaction is overly sentimental and question the sense of sending people into space, but that doesn't alter the fact that astronauts are courageous people.

Their job is to risk their lives in pursuit of what seems to be a basic human need - to explore beyond our usual frontiers. It was a tragedy when died in Antarctica 90 years ago, and it is again with the deaths of the Columbia astronauts.

The question everyone wants answered is why. What triggered the dramatic rise in temperature in Columbia's left wing that seems so closely linked to its fate? There is every chance that we will find out most of what happened. Shuttles are monitored in far more detail than aircraft. Every second, hundreds of instruments, from gyroscopes to temperature sensors, send readings back to Earth.

These readings, combined with the condition of shuttle debris and maps of where it fell, should give NASA's accident investigators an excellent chance of piecing together Columbia's final minutes. Whether they will identify the precise trigger - the initial failure - is more difficult to tell.

Tile damage

Already some potential triggers are looking like they will stay low on the list of probabilities. A fuel tank explosion seems unlikely, since the crew were on the radio after Columbia began behaving erratically.

Data released so far show that Columbia's attitude was correct as it returned to Earth. This suggests that its reaction control thrusters - used to manoeuvre the shuttle in space - were working properly. Likewise, the elevons - which manoeuvre the craft inside the atmosphere - seem to have tried to restore stability. For this reason, a failure of Columbia's computerised flight controller looks unlikely, though it has yet to be entirely ruled out.

So attention has turned to the ceramic tiles that protect the shuttle from the heat of re-entry - and specifically to the possibility that they were damaged during launch. Shortly after lift-off on 16 January, something fell from the central fuel tank and hit the shuttle's tiled underbelly. It was first thought to be a piece of insulation weighing little more than a kilogram. But NASA investigators are now studying the possibility that it was frozen solid, making it far heavier.

If this event turns out to be the fatal trigger, it invites suspicion that NASA has learned little from the investigation into its last great tragedy, the Challenger disaster in 1986. In that investigation, the late Nobel laureate Feynman pointed out a dreadful flaw in NASA's method of risk assessment.

NASA managers already knew that during lift-off, exhaust gases corroded rubber "O-ring" seals in the solid rocket boosters. These seals were not designed to be eroded, nor was the process of erosion understood. But instead of seeing this as a warning that something was wrong and in need of thorough investigation, the managers took the success of previous launches as evidence that the next one would be safe. It was a fatal inference.

Warning sign

Has that mistake been repeated? In 1992, during a previous lift-off, a piece of insulation fell from a fuel tank and gouged a hole in Columbia's wing. The tiles there are not designed to withstand impacts. But instead of seeing this as a warning sign, NASA cited the success of the 1992 mission as a reason to assume that this latest one was not in danger.

Repeated impacts by blocks of frozen insulation of different weights hitting the shuttle at different places, speeds and angles, might do all kinds of damage to the vehicle's structure. Did NASA managers know the full range of possibilities?

We are, of course, at the start of the investigation, so this line of reasoning may turn out to be wrong. Nevertheless, once investigators have identified the most likely sequence of events, they would do well to broaden their inquiry. There have been several warnings of poor communications between NASA managers and contractors, and high-profile statements that budget cuts, job freezes and loss of trained staff are compromising safety. Anything that diminishes NASA's strict safety culture needs to be removed.

As courageous as astronauts are, they are not reckless. They deserve to know that their safety is the first priority of every engineer, accountant and administrator.

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