Which breath sounds would the nurse consider normal select all that apply

Ann Thorac Med. 2015 Jul-Sep; 10[3]: 158–168.

Abstract

Auscultation of the lung is an important part of the respiratory examination and is helpful in diagnosing various respiratory disorders. Auscultation assesses airflow through the trachea-bronchial tree. It is important to distinguish normal respiratory sounds from abnormal ones for example crackles, wheezes, and pleural rub in order to make correct diagnosis. It is necessary to understand the underlying pathophysiology of various lung sounds generation for better understanding of disease processes. Bedside teaching should be strengthened in order to avoid erosion in this age old procedure in the era of technological explosion.

Keywords: Breath sound, bronchial breathing, crackles, rubs, wheeze

The auscultation of the respiratory system is an inexpensive, noninvasive, safe, easy-to-perform, and one of the oldest diagnostic techniques used by the physicians to diagnose various pulmonary diseases. History taking and a detailed physical examination, including the time-honored sequence of inspection, palpation, percussion, and auscultation should be considered an essential part of clinical examination, even in 21st century with explosive advancement in technology related to health sciences. Technologic advancement has led to erosion in the bedside teaching due to overreliance on laboratory testing; therefore, the clinical relevance of auscultation has receded significantly in recent years. It was Hippocrates who began the concept of auscultation by applying ear to the patient's chest to hear transmitted breath sounds and called this procedure as “immediate auscultation”. He described this as a method of direct auscultation. However, with the invention of stethoscope by Rene Theophile Hyac in the Laënnec in 1816; the art of auscultation not only became popular worldwide, but also comfortable for patients and physicians. Laënnec published his seminal work in 1819 in his masterpiece, “A Treatise on the Diseases of the Chest”.[1] Initially; he used rolled paper cone, and later on a wooden tube. Modern stethoscope had undergone several modifications before being molded into the current shape. Auscultation of the lungs includes breath sounds-its character and intensity, vocal resonance, and adventitious sounds. We will discuss the various types of breath sound, adventitious sounds, and vocal resonance; and their clinical importance and pathogenesis.

Physics of Breath Sounds

Breath sound has three characters; frequency, intensity, and timbre or quality; which helps us to differentiate two similar sounds.

Frequency and pitch

Frequency measures the number of the sound waves or vibrations per second and is measured objectively. It is measured in hertz [Hz]. Frequency depends on the number of wavelengths per second. Wavelength is the distance from the peak of one pressure wave to the next pressure wave and is commonly designated by the Greek letter lambda [ë]. Wavelength depends on the speed of the sound waves, the medium through which the sound waves are traversing, and the temperature of the medium. When wavelengths are shorter, there area greater number of sound waves per second, and the frequencies will be higher. On the other hand, with longer wavelengths, the frequencies are lower. Pitch is the subjective perception of sound's frequency. Pitch depends on the frequency and is within 5 Hz of the frequency usually.[2] The human ear can perceive sound waves over a wide range of frequencies, ranging from 20 to 20,000 Hz.

Amplitude or loudness

Amplitude is related to the energy of sound waves and is measured by the height of sound waves from the mean position. Loudness is the subjective perception of amplitude. The range of amplitude is extremely wide, so it is measured on a logarithmic scale and is depicted by decibels [dB]. Sound measured at 10 dB has an increase in sound intensity of 10 times.

Quality or Timbre

Quality or timbre is an important property of sound that differentiates two sounds with the same pitch and loudness. Sound is made up of various frequencies. Fundamental frequency or primary frequency is the lowest frequency of a sound wave and it determines the pitch of the sound. Frequencies higher than the fundamental frequencies are called overtones. Harmonics are overtones whose frequencies are whole number multiples of the fundamental frequency.[3]

Methods of performing auscultation

1. Auscultation should be done in a quiet room, preferably in a sitting position. If the patient cannot assume sitting posture, roll the patient from one side to the other to examine the back.

2. Always warm up the cold stethoscope by rubbing the chest piece in your hands before placing it on naked body. Auscultation should never be done through the clothing.

3. Ask the patient to take deep breaths through the open mouth.

4. Using the diaphragm of the stethoscope, start auscultation anteriorly at the apices, and move downward till no breath sound is appreciated. Next, listen to the back, starting at the apices and moving downward. At least one complete respiratory cycle should be heard at each site.

5. Always compare symmetrical points on each side.

6. Listen for the quality of the breath sounds, the intensity of the breath sounds, and the presence of adventitious sounds.

Mechanism of Breath Sounds Production

The prerequisite for normal breath sound production is the air flow along the trachea-bronchial tree; however, not all types of airflow produce breath sound. Only turbulent and vorticose airflow are responsible for breath sound production.[4] Laminar flow occurs in low flow situations and is silent [Figure 1]. The streams of airflow are parallel to the walls. It is parabolic in shape as air in the central layers moves faster than air in the peripheral layers, with little or no transverse flow. Therefore, there is little mixing or collision between layers of gas. Laminar flow pattern follows the Poiseuille equation, as shown below [Figure 2].

Showing laminar flow pattern

Showing Poiseuille equation

Where Q is the volume flow rate, P is the driving pressure, r the radius, n the viscosity, and l depicts length. Laminar flow is directly proportional to the driving pressure. Small airways [10 ms, and fine crackle as 2CD