Sound in Medicine 23 PDF

Sound in Medicine PART 1 D R. E NTID HAR A LTAEE Topics of the Lecture Characteristics of sound wave.  Refection and transmission  Intensity level ratio.  Applications of sound in medicine  Percussion and Stethoscope General properties of sound A sound wave is the pattern of disturbance cau...

Sound in Medicine PART 1 D R. E NTID HAR A LTAEE Topics of the Lecture Characteristics of sound wave.  Refection and transmission  Intensity level ratio.  Applications of sound in medicine  Percussion and Stethoscope General properties of sound A sound wave is the pattern of disturbance caused by the energy traveling away from the source of the sound (waves transfer energy without transferring matter). Sound, a mechanical disturbance from a state of equilibrium that propagates through an elastic material medium with some definite velocity. In air it can be defined as a local increase (compression) or decrease (rarefaction) of pressure relative to atmospheric pressure.   A sound is a vibration that propagates through a medium in the form of a mechanical wave. The medium in which it propagates can either be a solid, a liquid or a gas. Sound travels fastest in solids, relatively slower in liquids and slowest in gases. In general, the sound speed is given by: 𝜈𝑠 = 𝑓𝜆 Where 𝒇 : frequency λ: the wavelength of the sound waves.  The number of rarefactions and compressions that occur per unit time is known as the frequency of a sound waves. Mathematically, the frequency of a wave is denoted as follows: f=1/T  The distance between the successive compression and rarefaction is known as the wavelength of a sound wave. The wavelength is mathematically represented as 𝑐 follows 𝜆= 𝑓 Homework Q1: Which sound wave will have its crests farther apart from each other - a wave with frequency 100 Hz or a wave with frequency 500 Hz? Q2: If the velocity of sound is 330 meters per second (msˉ¹ what will be wavelength if the frequency is 1 KHz?  Sonic spectrum  Sonic spectrum can be classified (depending on the frequency of the wave) into three frequency ranges: infrasound, audible sound and ultrasound (rarefaction) of pressure relative to atmospheric pressure Sonic spectrum  The human ear can hear sounds in the range of roughly 20 Hz to 20 KHz.  Infrasound: Refers to sound frequencies below the normal hearing range or less than 20Hz. It is produced by natural phenomena like earthquake waves and atmospheric pressure changes. Infrasonic effect on human body: It can travel long distances without losing much power due to its low absorption and large wavelength and also, it can travel through most media, making its effects difficult to minimize. Hence, Intense infrasonic noise is observed to produce clear symptoms including respiratory impairment and aural pain. Other effects may include Fear, Visual Hallucinations, chills.  Infrasonic may also be used in the study of heart mechanical function, revealed by the seismocardiogram (is the measure of the micro- vibrations which are signals in the infrasonic range produced by the heart contraction and blood ejection into the vascular tree.  Ultrasound; Is the frequency range above 20KHz. Ultrasound is used clinically in a number of specialties. It often gives more information than an X-ray and it is less hazardous for the fetus.  Intensity of a Sound Wave  The intensity I of a sound wave is the energy carried by the wave per unit area and per unit time (in units W/𝑚2 ). It may be expressed by the maximum change in pressure; 𝑝 0 as following: 𝑃02 𝐼= 2𝑍 Z acoustic impedance of the medium. Acoustic impedance (Z) = 𝝆𝝂𝒔  Sound Intensity Level [Ratio] The absolute value of sound intensity (I) cannot be measured, instead we can compare it with a reference intensity; (I ) Where 0 𝑰𝟎 = 𝑰𝒎𝒊𝒎 = 𝟏𝟎−𝟏𝟐 (𝑾/𝒎𝟐 ) 𝑰 𝟏 Intensity ratio=𝟏𝟎 𝒍𝒐𝒈 = 𝟏𝟎 𝒍𝒐𝒈 (𝒅𝑩) 𝑰𝟎 𝟏𝟎−𝟏𝟐  Effect the nature of sound on human hearing The human ear can distinguish two characteristics of sound.  Loudness: (or volume) is the degree of sensation of sound produced in the ear. It depends on its intensity.  Pitch: The pitch of a sound refers to whether it is high (sharp).  Sound Reflection and transmission: When the sound wave is applied in a perpendicular way on the interface between two media which have different acoustic impedance (Z1 and Z2) a portion of this wave will pass through and another one reflect (large difference in Z → high reflection ratio. The ratio of reflected; Iref (or transmitted; Itran) and the incident waves (Iin) can be measured as following, If Z1 = Z2 There is no reflected wave and transmission to the second medium is complete. If Z2 ˂ Z1 The sign change indicates a phase change of reflected wave. If ∆Z large High reflection &low transmission Mismatching. Audiogram An audiogram for the normal human ear is given as in the below figure, where:  The lower curve gives the faintest sounds that can be heard (hearing threshold), and  The upper curve gives the loudest sounds that can be heard without pain (pain threshold).  is barely audible at 1000Hz Application s of audible sound in medicine https://youtu.be/1JKXf5osCHE 2. Stethoscope: Stethoscopes are diagnostic instruments that amplify sounds made by the body from the heart, lungs, or other body sites. Modern stethoscope consists of, bell which closed by a thin diaphragm, tubing and earpieces. The bell serves as impedance matcher between body and the air in the tube. This requires that the frequency of the sounds must resonate in the bell membrane. The natural frequency Fres of the bell depends on diameter(d) and tension T of the diaphragm as following: 𝑇 𝐹𝑟𝑒𝑠 ∝ 𝑑 To selectivity pick up certain frequency ranges (low frequency heart murmur, high frequency lung sounds) the appropriate bell size and diaphragm tension must be chosen.