Добавил:

Sekretar kiopkiopkiop18@yandex.ru Вовсе не секретарь, но почту проверяю Опубликованный материал нарушает ваши авторские права? Сообщите нам.

Вуз:

Ростовский Государственный Медицинский Университет

Предмет:

Медицина общая

Файл:

5 курс / Пульмонология и фтизиатрия / Principles_of_Pulmonary_Medicine_S_E_Weinberger.pdf

Скачиваний:

Добавлен:

24.03.2024

Размер:

13.99 Mб

Скачать

☆

<<< < Предыдущая 16 17 18 19 20 21 22 23 24 25 26 2728 / 9828 29 30 31 32 33 34 35 36 37 38 39 40 > Следующая >>>

Upper airway disease

The obstructive diseases considered so far primarily affect the airways below the level of the main carina —the bronchi and bronchioles. In contrast to disease of these lower airways, a variety of other disorders affect the pharynx, larynx, and trachea and produce what is termed upper airway obstruction. The discussion of these disorders includes a brief consideration of representative etiologic factors and some of the tests used to make the diagnosis. In particular, use of the flow-volume loop to define the location of upper airway obstruction is considered.

Etiology

The upper airway can be affected by either acute problems or those following a more subacute or chronic course. On an acute basis, the larynx is probably the major area subject to obstruction. Potential causes include infection (epiglottitis, often due to H. influenzae), thermal injury and the resulting laryngeal edema from smoke inhalation, aspiration of a foreign body, laryngeal edema from an allergic (anaphylactic) reaction, or physical trauma associated with endotracheal intubation.

On a chronic basis, the upper airway may be partially obstructed by hypertrophy of the tonsils, by tumors (particularly of the trachea), by strictures of the trachea (often resulting from prior instrumentation of the trachea), or by vocal cord paralysis. Tracheomalacia, another chronic condition that may be congenital or acquired, is characterized by flaccidity of supporting airway cartilage and results in upper airway narrowing, especially on forced exhalation. The entity of obstructive sleep apnea, which is considered further in Chapter 18, is characterized by recurrent episodes of upper airway obstruction during sleep, resulting from anatomic factors and/or abnormal control of upper airway musculature.

Pathophysiology

The resistance of a tube to airflow varies inversely to the fourth power of the radius; hence, even small changes in airway size may produce dramatic changes in resistance and in the work of breathing. There are three pathophysiologic categories of upper airway obstruction which depend on the rigidity and site of the obstruction (intrathoracic vs. extrathoracic). A fixed obstruction occurs when the involved airway is rigidly narrowed, without any change in the size of the lumen during the respiratory cycle. In this case, inspiration and expiration are impaired by the same amount, and the flow rate generated during inspiration is essentially identical to the flow rate during expiration.

On the other hand, if airway diameter changes during the respiratory cycle, the greatest impairment to airflow occurs when the airway diameter is smallest. This type of obstruction is termed a variable obstruction. If the obstruction is located within the thorax, changes in pleural pressure during the respiratory cycle affect the size of the airway and therefore the magnitude of the obstruction. During a forced expiration, the positive pleural pressure causes airway narrowing, making the obstructing lesion more critical. In contrast, during inspiration, the airways increase their diameter, and the effects of a partial obstruction are less pronounced (see Fig. 3.22).

The location and respiratory variability of an upper airway obstruction affect the appearance of the flow-volume curve and the findings on physical examination.

In contrast, if the obstruction is located above the level of the thorax (i.e., outside the thorax), changes in pleural pressure are not directly transmitted to the airway in question. Rather, the negative airway pressure during inspiration tends to create a vacuum-like effect on extrathoracic upper airways, narrowing them and augmenting the effect of any partial obstruction. During expiration, the pressure

generated by the flow of air from the intrathoracic airways tends to widen the extrathoracic airways and decrease the net effect of a partially obstructing lesion (see Fig. 3.22).

Clinical features

Patients with upper airway obstruction may have dyspnea or cough. On physical examination, they may have evidence of flow through narrowed airways. If the lesion is variable and intrathoracic, the primary difficulty with airflow occurs during expiration, and patients demonstrate expiratory wheezing. If the lesion is variable and extrathoracic, obstruction is more marked during inspiration, and patients frequently manifest inspiratory stridor, a high-pitched, monophonic, continuous inspiratory sound often best heard over the trachea. With acute upper airway obstruction, such as that seen with inhalation of a foreign body, anxiety and respiratory distress often are apparent, signaling a medical emergency. In patients with epiglottitis, respiratory distress often is accompanied by sore throat, change in voice, dysphagia, and drooling.

Diagnostic approach

In the evaluation of suspected disorders of the upper airway, radiography and direct visualization provide the most useful information about the macroscopic appearance of the airway. Lateral neck radiographs or CT scans of the upper airway may reveal the localization, extent, and character of a partially obstructing lesion. A CT scan may offer particularly useful information by providing a cross-sectional view of the airways from the larynx down to the carina. Direct visualization of the upper airway may be obtained by laryngoscopy or bronchoscopy, which may reveal the presence of edema, vocal cord paralysis, or an obstructing lesion such as a tumor. However, direct visualization of the airways by these techniques includes some risk. The instrument used occupies part of the already compromised airway and may induce airway spasm or swelling that further obstructs the airway. This is especially true in cases of suspected epiglottitis, in which direct visualization should not be attempted unless the examiner is prepared to perform an emergency tracheostomy.

Because the functional consequences of a fixed versus a variable obstruction and an extrathoracic versus an intrathoracic obstruction are quite different, functional assessment of the patient with presumed upper airway obstruction can be useful in quantifying and localizing the obstruction. To recognize these distinctions, the flow-volume loop and the principles discussed in the pathophysiology section must be understood. This type of physiologic evaluation is appropriate for chronic upper airway obstruction, not for acute life-threatening obstruction.

When a fixed lesion is causing a relatively critical obstruction, maximal flow rates generated during inspiration and expiration are approximately equal, and a “plateau” marks both the inspiratory and expiratory parts of the flow-volume curve. When the lesion is variable, the effect of the obstruction depends on whether the lesion is intrathoracic or extrathoracic. With an intrathoracic obstruction, critical narrowing occurs during expiration, and the expiratory part of the flow-volume curve displays a plateau. With an extrathoracic obstruction, the expiratory part of the loop is preserved, and the inspiratory portion displays the plateau. A schematic diagram of the flow-volume loops observed in these types of upper airway obstruction is shown in Fig. 3.23.

Treatment

Because many different types of disorders result in upper airway obstruction, treatment varies greatly depending on the underlying problem, particularly its acuteness and severity. In acute severe upper airway obstruction, an emergency procedure such as endotracheal intubation or tracheostomy may be necessary to

maintain a patent airway. A procedure such as bronchoscopic laser therapy or airway stenting also may be

Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/

used. Discussion of each disorder and further consideration of management can be found in other textbooks and in some articles listed in the Suggested Readings.

Upper airway disease

Suggested readings