快猫短视频

SLOW internal bleeding is one of the most dangerous injuries that can affect
people in traffic accidents and soldiers in battle. Left unchecked, it can be
fatal, yet doctors often fail to spot the condition until it鈥檚 too late. But now
an ultrasound technique is on the way that lets emergency doctors check for
haemorrhages quickly at a patient鈥檚 bedside.

鈥淪ometimes it鈥檚 hard to be sure if they鈥檙e bleeding or not,鈥� says Xuegong Shi
at ATL Ultrasound in Bothell, Washington, who recently left the University of
Washington in Seattle. 鈥淵ou can think they鈥檙e stable, but they might be slowly
bleeding to death.鈥�

While ruptured arteries are relatively easy to spot, blood leaking from veins
is much tougher to identify and locate, says Shi. The problem is that the blood
pools in the body鈥檚 natural cavities, where the red cells coagulate into
clumps.

These clotted blood pools are extremely difficult to detect, says Shi. Unlike
blood flowing through veins, coagulated blood strongly reflects the ultrasonic
waves. This makes it indistinguishable from organs and other tissues that
reflect ultrasound.

Patients who are well enough to be moved can be injected with a chemical that
shows up on an X-ray image. As well as highlighting blood flow this also shows
any blood that is leaking. But sometimes seriously injured patients need to be
examined on the spot.

Shi says ultrasound can do the trick. He was able to detect the signs of
internal bleeding simply by turning up the power on a portable Doppler
scanner.

While standard ultrasound scanners simply measured the time it takes for
reflected sound waves to return, the Doppler scanner also looks at how the
wavelength of the reflected wave changes. If it has become shorter, for example,
the surface it bounced off must be moving towards the scanner. The faster the
surface is moving, the more the wavelength changes.

With the scanner at high power, the sound waves force the clumps of red blood
cells to flow in the leaked pools of blood. Because the ultrasound doesn鈥檛 make
any surrounding organs move, the pools of blood stand out in a Doppler scan. The
researchers successfully tested the technique on small bags of blood implanted
in pigs.

The effect requires a power level of 20 watts per square centimetre, which is
more than 25 times normal intensity. This level is still safe, Shi says, and far
below the energies used in experiments to cauterise tissues with ultrasound
(快猫短视频, 3 June 2000, p 11).

Because the method is so quick and easy, Shi says it should be useful on
battlefields where severly injured soldiers need to be checked quickly with a
minimum of diagnostic equipment.