OBSTET-L Mensagens pela Setembro, 2002: Re: US e Gestacao

Re: US e Gestacao

From: Luiz Meira

luizmeira@yahoo.com

Mon, 16 Sep 2002 00:30:23 -0300 (ART)

Deixo mais estes links sobre efeito maléfico do Ultrassom:

--- Maria Helena <mhbastos@uol.com.br> escreveu: > >
> Advance for Imaging and Radiation Therapy Professionals
> January 28, 2002
>
> Loud as a Speeding Train?
> Study finds that ultrasound produces vibrartions that may
> 'sound' as loud as
> a subway train to the fetus
>
> Ultrasound scans are audible to a fetus, researchers
> reported at the Dec. 3,
> 2001, meeting of the Acoustical Society of America in
> Fort Lauderdale, Fla.
>
> Moreover, when the ultrasound probe is pointed in the
> right direction, the
> ultrasound pulse may produce vibrations as intense as a
> train coming into a
> station, said Mostafa Fatemi, PhD, associate consultant
> in the Ultrasound
> Research Laboratory, Department of Biophysics at the Mayo
> Foundation in
> Rochester, Minn., lead author of the study.
>
> If ultrasound is defined as sound that lies beyond the
> range of human
> hearing, how can a fetus hear an ultrasound scan?
>
> "This is really a secondary effect," explained Dr.
> Fatemi. "Ultrasound is
> not audible, but, the ultrasound energy produces a
> tapping force on any
> organ or object that it intercepts. "When that tapping
> force is repeated, it
> produces a vibration similar to that produced by sound.
> As the ultrasound
> beam moves during examination of the fetus, the focal
> point of the beam can
> pass over the fetal head. When this happens, the
> sensitive hearing structure
> of the fetus receives vibrations at a rate equal to the
> number of pulses per
> second from the ultrasound beam. The radiation force of
> these vibrations
> produces a localized "noise" that might range from 85
> decibels to 120
> decibels if it were traveling through air. This is
> equivalent to the level
> of sound produced by an approaching subway train.
> However, because sound is
> focused on a tiny, square-millimeter spot, and the sound
> diminishes rapidly
> from that spot, the fetus could quickly adjust its
> position to avoid the
> loudness.
>
> To measure the pressure produced on the hearing mechanism
> of the fetus by
> the acoustic emanations, the researchers measured the
> intensity of the
> radiation force of the ultrasound probe in water baths
> and in the human
> body.
>
> "Knowing the intensity, we know how much force and
> pressure it will produce
> at a localized point," said Dr. Fatemi. "The 85-120
> decibel equivalent force
> is a typical value that varies from machine to machine
> and setting to
> setting." Unlike sound, however, this force is confined
> to a very sharp
> focal area and even a 1-centimeter change in focus
> significantly reduces the
> acoustic vibrations "heard" by the fetus, he noted.
>
> The purpose of the study was to explain the physical
> principle behind the
> observation from physicians and sonographers that the
> fetus moves more than
> usual in the uterus during an ultrasound exam, said Dr.
> Fatemi.
>
> While the study shows that the acoustic stimulation is
> probably the cause of
> this increased movement, he stressed that the question of
> whether the
> ultrasound vibrations cause any harm to the fetus was not
> a subject of this
> project
>
> -By Joyce Ward, CNMI, RT(N)

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