What can be heard during inspiration?

Respiratory sound recording and analysis

Often respiratory sounds are measured concurrently with the videoendoscopy recording. This can be performed using a microphone placed in front of the horse's nostrils, either within a mask or attached to the bridle. The recording of respiratory sounds is useful to relate the sounds being reported by the owner or trainer with dynamic events occurring within the airway. Previously, there was some interest in the use of spectral analysis of respiratory sounds for the diagnosis of upper airway collapse136–138 and repeated recordings have been used to measure changes in respiratory sounds following laryngeal surgery.139,140 However, although it is possible to determine differences between conditions such as laryngeal hemiplegia and DDSP, the technique is not sufficiently sensitive to distinguish between different forms of inspiratory noise or horses with complex forms of dynamic collapse.

23.2.2 A: Airway

The primary goal in examining the airway is to assess its patency. If the patient is breathing freely and without stridor, the airway is not obstructed and further examination of it is not needed. Signs indicating airway obstruction include excitation (due to hypoxia), decreased consciousness, harsh barking, stridor, labored inspiratory movements including those of the auxiliary respiratory muscles, apnea, tachypnea, and cyanosis.

Other Sounds Auscultated in the Thorax

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Normal respiratory sounds include referred sounds from the trachea that are commonly heard over the lungs. Vesicular sounds are due to air moving through the small bronchi and are louder on inspiration. Bronchial sounds are due to air moving through the large bronchi and trachea and are heard best on expiration. Bronchovesicular sounds are the combination of the above two and are heard best over the hilar area.

Abnormal respiratory sounds include attenuated sounds as well as increased, abnormal sounds.

Attenuated bronchovesicular lung sounds are due to thoracic masses, pleural effusion, pneumothorax, obesity, pneumonia, shallow breathing, or early consolidation of the pulmonary parenchyma.

Rhonchi are due to air passing through partially obstructed airways in the bronchial tubes or smallest airways. Rhonchi from the large bronchi are low pitched, sonorous, and almost continuous. They are heard best on inspiration. Rhonchi from the small bronchi are high pitched, sibilant, or squeaky, and are heard best on expiration.

Crackles are interrupted, crepitant, inspiratory sounds heard in many disease conditions and are not pathognomonic for pulmonary edema. They are due to opening of alveoli or airways that are collapsed or partially filled with fluid or bubbles bursting in the airways. They are further defined as fine or coarse in quality.

Other sounds which can be ausculted include pleural friction rubs. Pleural friction rubs are grating, rubbing sounds heard during inspiration and expiration owing to the moving of two relatively dry, roughened pleural surfaces against each other. Pericardial friction rubs are short, scratchy noises produced by pericarditis and heart movement. Pericardial knocks are diastolic sounds that occur in animals with constrictive pericarditis. Wheezes are relatively high pitched, musical sounds and are often a sign of pulmonary pathology.

Clinical Presentation

Methods of Sound Recording

One of the earliest methods of recording respiratory sounds during exercise in horses involves a radio-stethoscope (Attenburrow 1978a,b). Using this technique, a microphone is placed over the ventral wall of the trachea at any point between the fourth and ninth tracheal ring. The microphone is glued to the skin to prevent the skin and microphone from rubbing and thus generating friction sounds. The advantages of this technique are that it is simple, easily used in the field and probably excludes recording extraneous sounds associated with exercise, such as footfall and wind noise. The disadvantage of this technique is that it is difficult for the clinician to relate to tracheal sounds, as a human observer does not hear these sounds directly.

Another method involves placing a small microphone in the nasopharynx (Cable et al 2002). This technique protects the microphone, and the recording of extraneous sounds related to exercise is avoided. However, the nasopharyngeal position of the microphone is slightly more invasive, and there may be interference associated with bumping of the microphone on the walls of the nasopharynx. Furthermore, air rushes past the microphone in this position, creating vibrations and unwanted iatrogenic sounds. Similar to the radio-stethoscope, it is difficult to relate to pharyngeal sounds as the human observer normally hears sounds emanating from the nostrils.

Respiratory sounds in exercising horses have been recorded at the nostrils using a facemask incorporating airflow transducers, an endoscope, and a microphone (Franklin et al 2003). This technique has the advantage that upper airway endoscopy, measurement of upper airway flow mechanics, and sound recording can be performed simultaneously. It is possible, however, that the presence of the mask and flow measurement equipment alters sound recordings. A further disadvantage is that this methodology is not suitable for field use.

In our laboratory we also record respiratory sounds in exercising horses at the nostrils (Derksen et al 2001, Brown et al 2004). A unidirectional microphone with a cardioid pickup pattern is attached via a flexible wand to a cavison (Fig. 17.1). This type of microphone centers the sound pickup toward the front of the microphone, and helps reduce extraneous sounds such as footfall and track noise that originate behind and to the side of the microphone. The microphone is covered with a windscreen, and is placed equidistant between the horse's nostrils, approximately 4 cm from the horse's nose. In this way, the microphone is as close to the source of sound to be recorded as possible, while avoiding placement of the microphone in the respiratory air stream. The microphone is attached to an audio recorder with a compression circuit. This kind of recorder automatically adjusts the gain, decreasing the recording of extraneous noises. The advantages of this technique are that it is easily used in the field and it records respiratory sounds that are also heard by human observers.

Simply listening to the audiotape of respiratory sounds made by exercising horses is revealing. The listener can appreciate factors such as respiratory rate, and consistency, the number of swallows, the frequency of stride lead changes, and whether or not abnormal respiratory sounds are present. Concurrent listening to the audiotape and viewing the spectrogram is an effective method of sound evaluation.

Respiratory sound analysis during exercise

It has long been recognized that the production of abnormal respiratory sounds by horses during exercise is frequently associated with various upper airway obstructive conditions. Respiratory acoustic measurements have shown promise for the investigation of upper airway disorders in man and, more recently, in horses with experimentally-induced obstructions. Franklin et al71 recorded respiratory sounds during exercise on the treadmill using an acoustically insulated subminiature omnidirectional microphone with a flat amplitude response between 50 and 13 kHz. Spectral analysis of the audio signal showed marked differences between control and clinically afflicted horses. Dorsal displacement of the soft palate was characterized by a narrow low frequency (20–80 Hz) peak during expiration. Horses with dynamic laryngeal collapse produced inspiratory sounds characterized by a broad band high frequency spectral component in the range 1.1–2.7 kHz. Spectral analysis of respiratory sounds in horses has potential as a diagnostic technique and this equipment may be used in the field.71

Clinical Symptoms

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Weight loss

Respiratory distress with or without respiratory sounds (rales, clicking sounds, and whistling)

Hepatomegaly, visible through the abdominal wall (Fig. 14-168)

Central nervous signs (up to 20% of affected birds): loss of balance, seizures, circling, nystagmus

Enteritis (enlarged abdomen with dilated intestines, often red colored)

Diarrhea

Mortality (up to 80%), especially in young birds during stressful periods i.e., weaning and molting, sometimes acute deaths without premonitory signs.

Many susceptible hosts necropsied for other reasons often show a few Atoxoplasma spp. merozoites in leukocytes mostly from lung imprints, which suggest that there is a high rate of asymptomatic infections and latency in healthy-looking birds from all age groups.

Thoracic Acoustics

Observations on sound generation in airway models and electronic analyses of respiratory sounds suggest a predominant origin from complex turbulences within the central airways. The tracheal breath sound heard above the suprasternal notch is a relatively broad-spectrum noise, ranging in frequency from less than 100 Hz to greater than 2000 Hz. Resonances from the trachea and from supraglottic airways “color” the sound (Fig. 1.7). The lengthening of the trachea with growth during childhood causes lower tracheal resonance frequencies. A dominant source of tracheal breath sounds is turbulence from the jet flow at the glottic aperture. However, narrow segments of the supraglottic passages also contribute to sound generation. There is a very close relationship between air flow and tracheal sound intensity, particularly at high frequencies. In the presence of local narrowing (e.g., in children with subglottic stenosis), flow velocity at the stenotic site is increased, and so is the tracheal sound intensity. Relating tracheal sound levels to air flow measured at the mouth can provide information about changes during therapy. Auscultation over the trachea will provide some information under these circumstances, but objective acoustic measurements are required for accurate comparisons.

Basic “normal” lung sounds heard at the chest surface are lower in frequency than tracheal sounds because sound energy is lost during passage though the lungs, particularly at higher frequencies. However, lung sounds extend to frequencies higher than traditionally recognized. More recent observations on the effects of gas density indicate that lung sounds at frequencies above 400 Hz are mostly generated by flow turbulence. At lower frequencies, other mechanisms that are not directly related to air flow (e.g., muscle noise and thoracic cavity resonances) have prominent effects on lung sounds, and gas density effects are less obvious. Inspiratory lung sounds show little contribution of noise generated at the glottis. Their origin is likely more peripheral (i.e., in the main and segmental bronchi). Expiratory lung sounds appear to have a central origin and are probably affected by flow convergence at airway bifurcations (Fig. 1.8).

Sound at different frequencies takes different pathways on the passage through the lung. Low-frequency sound waves propagate from central airways through the lung parenchyma to the chest wall. At higher frequencies, the airway walls become effectively more rigid and sound travels further down into the airways before it propagates through lung tissue. This information cannot be gathered on subjective auscultation but requires objective acoustic measurements. A trained ear, however, will recognize many of the findings that are related to these mechanisms. For example, lung sounds in healthy children and adults are not necessarily equal at corresponding sites over both lungs. In fact, expiratory sounds are typically louder at the right upper lobe compared with the left side. Similar asymmetry has been recognized when sound is introduced at the mouth and measured at the chest surface. A likely explanation for this asymmetry is the effect on sound propagation by the cardiovascular and mediastinal structures to the left of the trachea. Asymmetry of lung sounds is also noticeable in most healthy subjects during inspiration when one listens over the posterior lower chest. The left side tends to be louder here, probably because of the size and spatial orientation of the larger airways due to the heart.

Objective acoustic measurements have also helped to clarify the difference between lung sounds in newborn infants and in older children. The most obvious divergence occurs in lung sounds at low frequencies where newborn infants have much less intensity. This may be explained by thoracic and airway resonances at higher frequencies in newborn infants and perhaps also by their lower muscle mass. Lung sounds at higher frequencies are similar between newborn infants and older children (Fig. 1.9).

Adventitious respiratory sounds usually indicate respiratory disease. Wheezes are musical, continuous (typically longer than 100 ms) sounds that originate from oscillations in narrowed airways. The frequency of the oscillation depends on the mass and elasticity of the airway wall as well as on local air flow. Widespread narrowing of airways in asthma leads to various pitches, or polyphonic wheezing, whereas a fixed obstruction in a larger airway produces a single wheeze, or monophonic wheezing. Expiratory wheezing is related to flow limitation and can be produced by normal subjects during forced expiratory maneuvers. The situation is less clear for wheezing during inspiration, which is common in asthma but cannot be produced by healthy subjects unless it originates from the larynx (e.g., in vocal cord dysfunction). Very brief and localized inspiratory wheezes may be heard over areas of bronchiectasis.

Crackles are nonmusical, discontinuous (<20 ms duration) lung sounds. Crackle production requires the presence of air-fluid interfaces and occurs either by air movement through secretions or by sudden equalization of gas pressure. Another mechanism may be the release of tissue tension during sudden opening or closing of airways. Crackles are perceived as fine or coarse, depending on the duration and frequency of the brief and dampened vibrations created by these mechanisms. There may be a musical quality to the sound if a short oscillation occurs at the generation site. This has been called a squawk and may appear during inspiration, typically in patients with interstitial lung diseases but also in some patients with pneumonia or bronchiectasis. Fine crackles during late inspiration are common in restrictive lung diseases and in the early stages of congestive heart failure, whereas coarse crackles during early inspiration and during expiration are frequently heard in chronic obstructive lung disease. Fine crackles are usually inaudible at the mouth, whereas the coarse crackles of widespread airway obstruction can be transmitted through the large airways and may be heard as clicks with the stethoscope held in front of the patient's open mouth. Some crackles over the anterior chest may occur in normal subjects who were breathing at low lung volumes, but they will disappear after a few deep breaths.

Several other abnormal respiratory sounds are not generated in intrathoracic airways. Pleural rubs originate from mechanical stretching of the pleura, which causes vibration of the chest wall and local pulmonary parenchyma. These sounds can occur during both inspiration and expiration. Their character is like that of creaking leather and is similar in some ways to pulmonary crackles. Stridor refers to a more or less musical sound that is produced by oscillations of critically narrowed extrathoracic airways. It is therefore most commonly heard during inspiration. Grunting is an expiratory sound, usually low-pitched and with musical qualities. It is produced in the larynx when vocal cord adduction is used to generate positive end-expiratory pressures, such as in premature infants with immature lungs and surfactant deficiency. Snoring originates from the flutter of tissues in the pharynx and has a less musical quality. It may be present during both inspiration and expiration.

There may also be cardiorespiratory sounds. These are believed to occur when cardiac movements cause regional flows of air in the surrounding lung. Because of its synchronicity with the heartbeat, this sound may be mistaken for a cardiac murmur. It can be identified by its “vesicular sound” quality and its exaggeration during inspiration and in different body positions.

At the boundary between different tissues, reflection of sound may occur and sound transmission may decrease, depending on the matching or mismatching of the tissue impedances. Many of the acoustic signs of the chest are explained on the basis of impedance matching alone. The stethoscope is basically an impedance transformer that reduces sound reflection at a mismatched interface, namely, body surface to air. Because it is the only part of the sound transmission pathway that can be kept constant, it is best to always use the same stethoscope. The choice of a bell- or a diaphragm-type stethoscope depends on individual preference. Diaphragm chest pieces can be placed more easily and with less pressure on small chests with narrow intercostal spaces. Compared with bell-type stethoscopes, they tend to deemphasize frequencies below 100 Hz. Both the bell-type and the diaphragm stethoscopes show some attenuation at frequencies above 400 Hz.

CONCLUSION

Patulous ET can cause autophony of one’s own voice and breathing sounds and aural fullness. When a cause can be identified, correction of patulous ET can relieve the symptoms. A concave defect in the anterior wall of the nasopharyngeal orifice of the ET can be seen in these patients. The lack of tissue in this area prevents normal closure of the ET valve in its resting position. Most patients do not need further treatment other than reassurance. A small subset of patients find their symptoms debilitating to such an extent that they seek medical and surgical attention. Before issuing such interventions, SSCD, inner ear hydrops, or temporomandibular joint dysfunction must be ruled out. Various materials have been injected in the defect to allow for tubal closure, but success is not uniform and is temporary. Complete closure of the ET lumen solves the problem of patulous ET, but patients may need permanent middle ear ventilation via tubes.

PETR with a subocclusive catheter relieves most patients of their symptoms with very mild and temporary side effects. If the catheters fail, PETR with cartilage graft can be placed under a submucoperichondrial flap with generally excellent long-term benefits. Some patients require additional adjunctive procedures over time, suggesting loss of graft volume or ongoing loss of ET valve tissue.

Clinical Signs

HV-infected turtles usually develop respiratory signs, including gasping, harsh respiratory sounds, inability to dive properly, buoyancy abnormalities, and the presence of caseous material on the eyes, glottis, and trachea. In juvenile sea turtles, fibropapillomatosis can develop on the carapace, plastron, eyes, epidermis, and, in severe cases, on the mucosal surface of internal organs. Such neoplastic lesions can regress with time (Machado et al., 2013). In some species, such as some freshwater turtles, infected animals can die acutely, whereas other species develop chronic disease. HVs have been detected in the venom glands of snakes and are associated with decreased venom production (Simpson, 1979). In lizards, HV infection is associated with stomatitis and papillomas.