Respiratory System

Jeffrey R. Kovan

James L. Moeller

Asthma

Typically characterized as intermittent narrowing of the airways due to chronic inflammation and bronchial hyperactivity, asthma often is provoked by irritants or “triggers” that come in contact with the bronchi. Airway inflammation appears to be the precipitating factor leading to increased airway reactivity. Wheezing, cough, chest tightness, and shortness of breath are the typical presenting symptoms, but frequently are not found at the time of examination. The prevalence of asthma in children is approximately 6% to 7% in the general population (1). The incidence appears to increase in heavily industrialized areas where potential allergens are the greatest. Chronic asthma is the result of cellular changes within the airway epithelium. Inflammatory cells migrate to the bronchi and chemical mediator alterations occur resulting in airway narrowing and increased permeability of the epithelium. Narrowing of the airways secondary to smooth muscle contraction, edema, and increased mucous production ensues. Many potential allergens have been described, which act as triggers for an asthmatic flare. This appears to be more commonly found in patients with a personal or family history of atopy. A few of these include typical house dusts and molds, environmental pollutants, and food allergens. Other precipitating mechanisms to create an asthmatic response include respiratory tract infections, hot and/or cold exposure, smoke, stress, and exercise (2).

Diagnosis and Management

The previously described symptoms of wheezing, cough, and shortness of breath should alert the physician to the possibility of asthma. Demonstrating reversible airway obstruction is essential in confirming clinical suspicions. Use of peak flow measurements and/or spirometry provides an objective means of confirming the diagnosis. The standard classification of asthma severity by the National Heart, Lung, and Blood Institute, known as the National Asthma Education and Prevention Program (NAEPP), set guidelines in 2002 for the diagnosis and management of asthma, which are listed in Table 11.1.

Exercise-Induced Asthma

Exercise-induced asthma (EIA) is a transient airflow obstruction triggered by physical exertion. Airway narrowing occurs in those with increased airway reactivity, and symptoms similar to those described with asthma occur, but on a transient basis. EIA effects approximately 12% to 15% of the general population and has been found in 90% of asthmatic patients (4). EIA is seen in 40% of allergy or “hay fever” sufferers (5). No apparent age or gender differences are reported. The effects of exercise are not clearly understood, although the type, intensity, and duration of exercise, along with varied environmental conditions such as tobacco smoke, molds, dust, and cold temperatures appear to play a role in triggering a flare.

Pathophysiology

The pathophysiology of EIA is commonly described by two theories (6). “The water loss theory” is based on water loss through the bronchial mucosa following exercise as a means to warm and saturate inspired air. Hyperosmolarity of the airways occurs with a subsequent release of mediators leading to bronchial constriction. A second theory describes “heat exchange” as a means to cool the airways with increased ventilation due to exercise. Once cooling is completed, the bronchial vasculature dilates and engorges to rewarm the epithelium. A rebound effect occurs, with hyperemia of the bronchial vascular beds and ultimately airway narrowing. As described earlier, hyper-reactivity with any of the environmental allergens may stimulate an exaggerated EIA response with even minimal exertion.

TABLE 11.1 Long-Term Management of Asthma in Children

Asthma Classification^a	Symptom Frequency	Lung Function^b	Medications Required to Maintain Long-term Control
Mild intermittent	Daytime: 2 d/wk or less Nighttime: 2 nights/mo or less	PEF or FEV1: 80% or more of predicted function	No daily medication needed
Mild persistent	Daytime: more than 2 d/wk, but less than one time/d Nighttime: more than 2 nights/mo	PEF or FEV1: 80% or more of predicted function	Low-dosage inhaled corticosteroid delivered by nebulizer or metered dose inhaler with holding chamber, with or without a face mask, or by dry-powder inhaler in children 5 yr and younger
Moderate persistent	Daytime: daily Nighttime: more than 1 night/wk	PEF or FEV1: 60%-80% of predicted function	Children 5 yr and younger: low-dosage inhaled corticosteroid and long-acting beta2 agonist or medium-dosage inhaled corticosteroid Children older than 5 yr: low- to medium-dosage inhaled corticosteroid and long-acting inhaled beta2 agonist.
Severe persistent	Daytime: continual Nighttime: frequent	PEF or FEV1: 60% or less of predicted function	High-dosage inhaled corticosteroid and long-acting beta2 agonist
PEF =peak expiratory flow; FEV1=forced expiratory volume in 1 sec.
^a-Clinical features before treatment or adequate control.
^b-Lung function measurements are used only in patients older than 5 years.
Source: Adapted from National Asthma Education and Prevention Program. Expert panel report: guidelines for the diagnosis and management of asthma: update on selected topics, 2002. Bethesda, MD: U.S.
Department of Health and Human Services, Public Health Service, National Institutes of Health, National Heart, Lung, and Blood Institute, 2003; NIH publication no. 02-5074:115; From the Courtney AU, McCarter DF, Pollart SM. Childhood asthma: treatment update. Am Fam Physician 2005;71(10):1959-1968, (3).

Signs and Symptoms

EIA is classically described as wheezing and chest tightness within the first 5 to 10 minutes of strenuous exercise. Typically, episodes will remit 30 to 60 minutes after the completion of exercise. History of the signs and symptoms described here with a strong allergy and/or family history of asthma should heighten suspicion for this condition. These symptoms and the less common complaints of cough, fatigue, the inability to keep up with peers, and recurrent “stomach aches” should also alert the care provider to the possibility of EIA. Physical examination is rarely beneficial when the athlete is at rest. Occasionally, signs of allergies, including allergic shiners, nasal polyps, and less commonly, watery and blood shot eyes will be noted. Respiratory findings are also typically absent at rest. Any suggestion of wheezing at rest should raise suspicion of underlying chronic asthma. In an acute event following activity, respiratory wheezing, cough, and poor inspiratory effort will be evident.

Diagnosis

The diagnosis of EIA begins with identification of irritants that may trigger an attack, followed by simple avoidance techniques. When history and clinical findings suggest EIA, supportive care with a trial of nonsedating antihistamines and minimizing cold exposure may relieve or at least delay symptoms. Alternative conservative measures of submaximal exercise for 15 to 30 minutes before sport participation may provide a refractory period of 1 to 3 hours and help a small percentage of sufferers. Self-reported symptoms for EIA diagnosis in the athletic population will likely yield high frequencies of both false positive and false negative results. Diagnosis should include spirometry using an exercise or environmental challenge in combination with the athlete’s history of asthma symptoms (7).

Pulmonary Function Testing

Pulmonary function testing (PFT) provides an accurate assessment of baseline pulmonary function. PFT at rest provides the pre- and postexercise norms for an individual. The use of an office spirometer allows for determination of forced expiratory volumes (FEV) in 1 second (FEV₁). FEV₁ is typically normal in pre-exercise individuals and roughly 90% to 100% of the predicted norms in those with normal lung function following exertion. In chronic asthmatics, baseline FEV₁ values will often be less than 80% of predicted norms (6). In EIA, the most objective measure
for diagnosis is the pulmonary function test following an appropriate exercise challenge.

Exercise Challenge Testing

Exercise challenge testing requires enough exertion to achieve the desired heart rates at 80% to 90% of the maximum for 5 to 8 minutes. This can be achieved with the use of a treadmill or ergometer, but should be a sport specific exercise challenge in the appropriate environment when possible (e.g., the ice rink for skaters, the swimming pool for swimmers). FEV₁, along with FVC (forced vital capacity) and FEF25–75 (forced expiratory flow 25%–75%) are measured postexercise and frequently thereafter for roughly 20 to 30 minutes. Typically, FEV₁ will be used to assess respiratory response following an exercise challenge. A fall in FEV₁ of greater than or equal to 15% from pre-exercise values is diagnostic (6). Healthy controls will maintain FEV₁ values above 85% to 90% of the baseline. A 15% to 20% fall in FEV₁ suggests mild EIA, whereas a 20% to 30% decline is suggestive of a moderate level. A 30% or greater reduction of FEV₁ from baseline would be classified as severe.

Peak Flow Monitoring

When spirometry is unavailable, peak flow monitoring with hand held devices can serve as a useful tool in assessing respiratory status and adjusting treatment options. It is very important that the exercise challenge is adequate to produce a response. Patients should become quite adept at assessing current respiratory status and therefore adjusting workouts and treatments by this method.

Methacholine Challenge Testing

Less commonly used, but quite advantageous when equivocal results are found on traditional testing measures, methacholine challenge testing can be performed to help facilitate a drop in FEV₁. Nebulized methacholine has been shown to have negative effects in asthmatics, thereby lowering FEV₁

Only gold members can continue reading. Log In or Register to continue