Ultrasound Blocks for the Anterior Abdominal Wall
Ultrasound Blocks for the Anterior Abdominal Wall
Ultrasound Blocks for the Anterior Abdominal Wall
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24 | <strong>Ultrasound</strong> <strong>Blocks</strong> <strong>for</strong> <strong>the</strong> <strong>Anterior</strong> <strong>Abdominal</strong> <strong>Wall</strong><br />
2. <strong>Ultrasound</strong> and Regional Anes<strong>the</strong>sia<br />
Gabriele Aletti<br />
Sound Waves<br />
The application of pressure to a medium <strong>for</strong> a given period of<br />
time causes <strong>the</strong> compression of its molecules that will become<br />
closer to <strong>the</strong> subsequent molecules. The pressure energy will be<br />
propagated deeper between adjacent molecules in <strong>the</strong> direction<br />
of <strong>the</strong> compression. The movement of <strong>the</strong> molecules will<br />
propagate in <strong>the</strong> <strong>for</strong>m of a pressure wave. A wave is a<br />
disturbance in a medium traveling through it at a constant<br />
speed. The periodic application of pressure will generate more<br />
waves that will travel through <strong>the</strong> medium.<br />
Sound waves are subsequent and periodic high pressure and<br />
low pressure waves of molecular vibration. They travel<br />
longitudinally through a physical medium determining high<br />
pressure areas (compression) and low pressure areas (rarefaction)<br />
along <strong>the</strong> direction of propagation. Each wave has a frequency<br />
(f) of propagation measured as cycles per unit of time.<br />
The wavelength ( λ) is defined as <strong>the</strong> geometric distance at an in-<br />
stant between two successive high pressure pulses or two<br />
successive low pressure pulses. The wavelength of sound<br />
decreases as frequency increases. The speed of propagation of