The researchers made their discovery by accident while studying cytochrome P4501A2, one of a large family of enzymes that break down toxic chemicals. Cytochrome P4501A2 specifically attacks caffeine and a few other chemicals, and the researchers were testing men and women to see how quickly they metabolised caffeine. Such experiments usually use college-age volunteers, so most of the women in the sample have never been pregnant. But this time the subjects happened to include a large number of women who had been pregnant.

The researchers found that women who had never been pregnant broke down caffeine only 70 per cent as quickly as men or those women who had been pregnant (Cancer Epidemiology, Biomarkers & Prevention, vol 4, p 529). “We knew that activity levels for this enzyme were low during pregnancy – women who continue to drink coffee during pregnancy would suddenly find themselves wired, and have to cut back – and that men usually have higher activity levels,” says Neil Caporaso, an epidemiologist at the National Cancer Institute who is one of the authors. “What was a surprise is finding that after pregnancy, enzyme activity rebounds to levels higher than for women who have never been pregnant.”

Physicians may need to consider this difference when prescribing drugs, says George Lambert of the University of Medicine and Dentistry of New Jersey, another member of the team. For example, theophylline, which is also metabolised by P4501A2, is a bronchodilator that is used to control asthma. If women who have been pregnant clear drugs from their bloodstream more quickly, then they may need higher doses than women who have not been pregnant.

The researchers presume that the change in metabolism is a result of the general restructuring of a woman’s body and hormonal system that occurs during pregnancy. However, no one knows what happens in detail, or what evolutionary pressures might lead women who have not given birth to have lower levels of detoxifying enzymes, says Caporaso.

Whatever the reason for the difference, researchers may need to take it into account when selecting subjects for drugs trials. “It is obvious that physicians need to pay more attention to differences between men and women, and to be sure to include women who have given birth, as well as the younger, never pregnant women most frequently used in most past studies,” says Caporaso.

There may be even more important implications for the genetics of cancer, Caporaso believes. Cytochrome P450 enzymes metabolise many compounds important in cancers, including oestrogens, which have a big impact on breast cancer, heterocyclic amines, which are implicated in colon cancer, and the aromatic amines that cause bladder cancer. “It is likely that individual variations in activity levels for the cytochrome P450 enzymes play an important role in determining who gets these cancers,” says Caporaso.

Randy Doblar, a manager at ATK, believes the firm’s system would have
helped Noel Fitzpatrick, a British tourist who strayed into a crime-ridden
area of Washington during the summer, and was shot in a deserted alley.
‘If anyone did hear that shot, they did not report it, and as a result,
the killer remains at large and Fitzpatrick bled to death before being found
hours later,’ says Doblar. ‘If a sensor network had been in place there,
it would have detected the shot instantly, and relayed the location to
police and medical units within a few seconds.’

With revenues of more than $1 billion, ATK is the 14th largest contractor
working for the US Department of Defense, and has previously provided the
US Navy with sonar equipment and signal-processing software for detecting
submarines above the noise of oceans. But with the Cold War over, it is
turning towards civil applications – targeting, in particular, urban gun
crimes, the ‘uniquely American epidemic’. The possibility of death by gunshot
is 90 times higher in the US than in any other country, and every two minutes
someone in the US is injured by a gun.

ATK would install a network of units on top of utility poles at each
road intersection in high-crime neighbourhoods. Each unit would contain
a microphone to pick up noises, analogue and digital circuitry – similar
to the navy systems – to distinguish gunshots from other sounds, and a modem
and radio to relay reports to a local command centre. ‘Each report will
arrive at the centre with the unit’s location, the time, and the strength
of the signal. The centre’s computer will combine reports from as many units
as hear each shot, and use the variations in strength and arrival time to
precisely locate the shot,’ says Doblar.

ATK recognises that there are several problems with its proposal: differentiating
gunfire from cars backfiring and other loud, sudden sounds; dealing with
echoes in built-up city streets; making units cheap enough to install at
every corner, yet durable enough to need no maintenance. ‘We think, based
on our decades of experience in locating submarines, that it is possible
to distinguish gunshots – which have special pitch and duration characteristics
– from other noises,’ says Doblar.

The system would need to be ‘tuned’ to deal with echoes, but ATK handled
similar challenges in defence acoustics, says Doblar. He believes the system
would actually save money. According to the Centers for Disease Control
in Atlanta, in 1988 gunfire-related injuries cost the US $16.2 billion
in medical care and lost productivity. Washington alone estimated its hospital
costs from gun injuries at $11 million in 1989. ‘We believe we could cover
the entire city for between $10 and $20 million dollars – but of course
the city would probably choose to put sensors only in high-crime neighborhoods,
at a much lower cost,’ says Doblar.

Some problems that ordinarily dog sensor systems will not actually affect
the new network, he says. ‘People worry about a gunman shooting out a unit,
like shooting out streetlights, before committing a crime. But if someone
did manage to destroy a unit, the last thing the unit would do would be
to report that shot – it can detect a shot before the bullet reaches the
microphone.’ Silencers are no worry as only a tiny percentage of street
crimes involves them. But ATK is also testing microphones that could detect
the acoustical signature of a silenced pistol.

The Amazon: A Satellite’s Eye View* documents the tremendous changes
that settlers, miners and – above all – ranchers and hydroelectric dams
have made. Each two-page spread of this magnificently printed book contains
two images: a false-colour photograph from space with blue rivers, green
forests and pink wastelands created by burning away the trees and a picture
of the same area from the ground. Terrestrial images range from a stunningly
beautiful photograph of water lilies to a grim shot of a settler’s oxcart
amid the ashes of a recently burned clearing.

Liana John, a Brazilian journalist and photographer contributes a short
caption for each set of photographs and an essay to introduce each of the
volume’s three sections. She is always evenhanded, her tone is never strident,
even when the images denounce incredible human folly.

*Amazonia: Olhos de Satelite, Editoracao Publicacoes e Communicacoes
Ltads, Sao Paulo, Brazil, pp 143, $100, in Portuguese, English and French.
Order copies from: Ana Gomes Ferreira, Rua Moura, Brazil, 50, Sao Paulo,
SP Brazil 05507.

Fax 55-11-815-2667.

In shoulder dystocia, a baby’s shoulder becomes impacted against the
mother’s pelvic bone after its head has emerged. This may cause the baby
to suffer fractures, brain damage or even death. If dystocia occurs, as
it does in about one in 100 births in developed countries, the baby must
be delivered within about five minutes, otherwise it will asphyxiate and
die. Unfortunately, any midwife or obstetrician who pulls and twists a baby
to bring it through the pelvic inlet may fracture the baby’s humerus – the
bone between the shoulder and the elbow – or its collar bone. The brachial
nerves in the neck and shoulder may also be torn, paralysing the muscles
of the shoulder and arm.

Dystocia is relatively uncommon, so many health workers are not experienced
in dealing with it. In most cases, there is no injury to the baby and dystocia
is not even reported. But when injury does occur it is often a cause of
injuries and malpractice suits.

Robert Allen, a professor of mechanical engineering at the University
of Delaware, designed the simulator while at the University of Houston.
Jagadish Sorab, one of his graduate students, built a ‘maternal unit’ and
a ‘fetal unit’, as well as providing fingertip sensors that measure the
force that the clinician applies while using the model.

The maternal model closely mimics the size and shape of a typical pelvic
inlet – the space defined by the pelvic bones. In order to measure the force
applied to the pelvic bone as the clinician brings the fetal model through
the pelvic inlet, Sorab put piezoelectric film sensors around the inlet.
These measure force continuously during the ‘delivery’ and send this data
to a computer.

The fetal model is far more complex. It has to simulate the size and
flexibility of a large baby – dystocia is far more common for babies weighing
more than 4 kilograms – yet it must be able to record the various forces
exerted as the neck is stretched and twisted.

A series of potentiometers measures the axial force, or pull, on the
baby’s head, its twisting, and the stretching of the neck around the brachial
nerves. A thin strip of wood anchored at the model’s breastbone mimics the
fetal collar bone. The strip is designed to break under the same amount
of stress as a real baby’s bone would.

Bernard Gonik, an obstetrician in Houston who suggested Allen create
the simulator, wore a ‘tactile sensing system’ – gloves with fingertip stress
sensors – during 24 actual deliveries in order to determine how much force
he exerted on the baby. The births included several ‘difficult’ deliveries,
during which more force was applied than in a normal delivery, and three
involving dystocia. In one case, the baby was injured, and this was the
delivery in which the greatest force was used.

If the simulator is adopted as a teaching tool, doctors and midwives
would also use fingertip sensors to determine exactly, second by second,
how much force they were applying to the baby as they twisted it through
the pelvic inlet.