Interpretation of Pulmonary Function Tests A Practical Guide, 3. ed

13. When to Test and What to Order

The recommendations for preoperative testing are listed in Chapter 10. Although there are many other situations in which pulmonary function testing is indicated, for reasons that are unclear these tests are underutilized. This chapter describes instances in which testing is warranted and includes the basic tests to be ordered. Depending on the initial test results, additional studies may be indicated.

13A. THE SMOKER

Even if smokers have minimal respiratory symptoms, they should be tested by age 40. Depending on the results and a patient's smoking habits, repeat testing every 3 to 5 years is reasonable. The logic for early testing is shown in Figure 13-1. This shows the typical pattern of development of chronic obstructive pulmonary disease (COPD). Spirometry is the first test to have abnormal results. The innocuous cigarette cough may indicate significant airway obstruction. When confronted with an abnormal test result, a patient can often be convinced to make a serious attempt to stop smoking, which is a most important step to improving health. Figure 13-2 shows the average rates of decline in function in smokers with COPD and nonsmokers. The earlier the rapid loss of function can be interrupted in the smoker, the greater will be the life expectancy.

Test: Spirometry before and after bronchodilator

FIG. 13-1. Progression of symptoms in chronic obstructive pulmonary disease (COPD) reflected by spirometry, arterial blood gas studies, and chest radiographs as a function of age in a typical case. Spirometry can detect COPD years before significant dyspnea occurs. (From PL Enright, RE Hyatt [eds]. Office Spirometry:

A Practical Guide to the Selection and Use of Spirometers. Philadelphia: Lea & Febiger, 1987. Used with permission of Mayo Foundation for Medical Education and Research.)

FIG. 13-2. Normal decline in forced expiratory volume in 1 second (FEV1) with age contrasted with the accelerated decline in continuing smoking in chronic obstructive pulmonary disease (COPD). Smoking cessation can halt this rapid decline. (From PL Enright, RE Hyatt [eds]. Office Spirometry: A Practical Guide to the Selection and Use of Spirometers. Philadelphia: Lea & Febiger, 1987. Used with permission of Mayo Foundation for Medical Education and Research.)

13B. CHRONIC OBSTRUCTIVE PULMONARY DISEASE

Even if the clinical diagnosis of COPD is clear-cut, it is important to quantify the degree of impairment of pulmonary function. A forced expiratory volume in 1 second (FEV1) of50% ofpredicted portends future disabling disease. An FEV1 of less than 800 mL predicts future carbon dioxide retention (respiratory insufficiency).

Repeating spirometry every 1 to 2 years establishes the rate of decline of values such as the FEV1. The FEV1 declines an average of 60 mL/yr in persons with COPD who continue to smoke, compared with 25 to 30 mL/yr in normal subjects and persons who quit smoking.

Tests:

1. Initially, spirometry before and after bronchodilator and determination of the diffusing capacity of carbon monoxide (Dlco). Arterial blood gas studies are recommended when the FEV1 is less than 50% predicted.

2. Initially, if available, static lung volumes such as total lung capacity (TLC) and residual volume (RV).

3. Follow-up testing with spirometry is usually adequate.

13C. ASTHMA

It is important to be sure that the patient with apparent asthma really has this disease. Remember that ''not all that wheezes is asthma.'' Major airway lesions can cause stridor or wheezing, which has been mistaken for asthma. The flow-volume loop often identifies such lesions (see section 2K, page 18).

Testing is also important in patients with asthma in remission or with minimal symptoms. This provides a baseline against which to compare results of function tests during an attack and thus quantify the severity of the episode.

The patient should be taught to use a peak flowmeter. He or she should establish a baseline of peak expiratory flows when asthma is in remission by measuring flows each morning and evening before taking any treatment. Then the patient should continue to measure and record peak flows on a daily basis.

PEARL: It is crucial that the patients be taught to use a peak flowmeter correctly. They must take a maximal inhalation, place their lips around the mouthpiece (a nose clip is not needed), and give a short, hard blast. They should avoid making a full exhalation; the exhalation should mimic the quick exhalation used to blow out candles on a birthday cake.

Having the patient with asthma monitor his or her pulmonary status is extremely important. An exacerbation is usually preceded by a gradual decline in peak flow, which the patient may not perceive. By the time the patient becomes symptomatic and dys- pneic, flows may have greatly deteriorated. A decrease of about 20% from the symptom-free, baseline peak flow usually means treatments should be reinstated or increased and the physician contacted. It should be impressed on the patient and family that asthma is a serious, potentially fatal disease and that it must be respected and appropriately monitored and treated. Marked airway hyperresponsiveness and highly variable function are harbingers of severe attacks.

Tests:

1. Initial evaluation includes spirometry before and after bronchodilator—determination of Dlco is optional. If pulmonary function is normal or nearly so and there is any question about the diagnosis, a methacholine challenge study should be done (see Chapter 5). The eventual role of expired nitric oxide (eNO) is still to be determined (see section 5G, page 60).

2. For monitoring on a daily basis, a peak flowmeter is used.

3. Periodic (annual) monitoring with spirometry and bron- chodilator (more often in severe cases).

13D. ALLERGIC RHINITIS

Allergic rhinitis is often associated with asymptomatic hyperreactive airways. It may evolve into asthma. Thus, establishing a subject's baseline function and airway reactivity is justified.

Tests: Spirometry before and after bronchodilator. If the bron- chodilator response is normal but concerns still exist, a metha-choline challenge study (see Chapter 5) is indicated.

13E. CHEST RADIOGRAPH WITH DIFFUSE INTERSTITIAL OR ALVEOLAR PATTERN

Several disorders can present with these patterns (see Table 12-2, page 115). Pulmonary function tests are performed to answer the following questions: Are the lung volumes decreased and, if so, by how much? Is the diffusing capacity reduced? Is there arterial oxygen desaturation at rest or with exercise? Not infrequently, oxygen saturation is normal at rest but decreases during exercise. The tests are also used to follow the course of the disease and the response to therapy.

Tests:

1. Spirometry before and after bronchodilator, determination of Dlco, and pulse oximetry at rest and during exercise. The bronchodilator is used because a subject with inherent hyperreactive airways might develop one of these disorders.

2. Static lung volumes (such as TLC and RV).

3. Lung compliance and recoil pressure at TLC.

PEARL: Rarely, an interstitial or alveolar pattern is associated with an increased Dlco. This can occur with intra-alveolar hemorrhage, such as in idiopathic hemosiderosis (Goodpasture's syndrome), in which hemoglobin in the alveoli binds to carbon monoxide. The Dlco will decrease as the process improves.

13F. EXERTIONAL DYSPNEA

In almost every case of exertional dyspnea, pulmonary function tests should be performed. This approach applies even if the major abnormality appears to be nonpulmonary. We have seen patients with dyspnea who have received elaborate, and expensive, cardiovascular studies before pulmonary function studies were done, and the lungs proved to be the cause of the dyspnea. Also, exercise-induced bronchospasm, often associated with inhalation of cold air, can be a cause of exertional dyspnea.

Tests: Spirometry before and after dilators and Dlco testing. Determination of oxygen saturation at rest and exercise may be appropriate. For evaluation of exercise-induced bronchospasm, a methacholine challenge test should be done. In difficult cases, cardiopulmonary exercise testing may be helpful (see section 11F, page 109).

13G. CHEST TIGHTNESS

Is the tightness caused by angina or episodic bronchospasm? The distinction is not always easy. Dyspnea is often associated with either disorder. If there is doubt, lung function testing, in addition to cardiac evaluation, is warranted.

Tests: Spirometry before and after bronchodilator. Metha- choline challenge testing is done if bronchospasm remains a distinct possibility.

13H. UNEXPLAINED CHRONIC COUGH

Some patients have cough that is not related to chronic bronchitis, bronchiectasis, or a current viral infection. The cough is usually nonproductive. The most frequent causes are listed in Table 13-1. Obviously, many causes are nonpulmonary. Those in which pulmonary function testing can be helpful are asthma, congestive heart failure, diffuse interstitial disease, and tracheal tumors.

TABLE 13-1. Frequent causes of chronic cough

Postnasal drip Asthma

Gastroesophageal reflux

Congestive heart failure

Diffuse interstitial disease

Postviral tracheitis

Angiotensin-converting enzyme inhibitor use

Bronchogenic carcinoma

Miscellaneous

Tracheal tumors

Temporal arteritis

Oculopharyngeal muscular dystrophy

Ulcerative colitis, Crohn's disease

Foreign body

Tests: Spirometry before and after bronchodilator, Dlco test, methacholine challenge. A flow-volume loop also should be considered.

PEARL: In patients whose cough follows a viral tracheitis, systemic or inhaled steroids may provide relief, presumably by decreasing smoldering inflammation that is stimulating cough receptors.

13I. CORONARY ARTERY DISEASE

Because most patients with coronary artery disease have been smokers, they have an increased risk of also having COPD. A strong case can be made for testing all such patients to assess their lung function. And, as noted in section 12H (page 116), congestive heart failure itself can impair lung function.

Test: Spirometry before and after bronchodilator.

PEARL: In addition to patients with coronary artery disease, those with hypertension may need to be tested, especially if therapy with βadrenergic blockers is planned. Nonselective β-adrenergic antagonists are usually contraindicated in COPD, but selective β1 antagonists are generally well tolerated by patients with COPD and most patients with asthma.

13J. RECURRENT BRONCHITIS OR PNEUMONIA

Not infrequently, asthma is mistaken for recurrent attacks of bronchitis or pneumonia. This mistake can be avoided by appropriate pulmonary function testing.

A subset of patients have recurrent bouts of pneumonia presenting as small pulmonary infiltrates. We have seen several such patients in whom the basic problem was occult asthma. Presumably the bronchoconstriction interfered with mucociliary clearance, thus predisposing to pneumonia. Regular use of inhaled steroids and β-agonists led to correction of the problem.

Tests: Spirometry before and after bronchodilator. Methacholine challenge testing is performed if undetected broncho- spasm remains a possibility.

13K. NEUROMUSCULAR DISEASE

There are two reasons for performing pulmonary function tests, including maximal respiratory pressure tests, in patients with neuromuscular disease. First, dyspnea frequently develops in such patients, and it is important to establish the pathogenesis of the complaint. It might be pulmonary or cardiac in origin. Pulmonary function tests help to answer the question. Second, the tests can be useful for following the course of the disease.

Tests: Spirometry before and after bronchodilator, Dlco test, and determination of maximal respiratory pressures.

13L. OCCUPATIONAL AND ENVIRONMENTAL EXPOSURES

Table 13-2 lists substances and occupations that can produce pulmonary abnormalities reflected in abnormal results of pulmonary tests. Some farsighted industries are monitoring workers' pulmonary function on a regular basis. This testing protects both the worker and the employer.

TABLE 13-2. Occupational and environmental exposures that can lead to pulmonary conditions

Industrial dusts

Coal dust (coal workers' pneumoconiosis)

Asbestos (asbestosis, pleural plaques, pleural effusion, lung cancer, mesothelioma)

Silica, quartz (silicosis)

Cotton dust (byssinosis)

Beryllium (berylliosis)

Talc (talcosis)

Occupational asthma

Plastics

Isocyanates

Animal dander, urine, feces

Enzyme dusts

Tea and coffee dust

Grain dust

Polyvinyl chloride (PVC) fumes

Wood dusts, especially Western red cedar

Hypersensitivity pneumonitis

Farmer's lung

Bird-fancier's disease

Mushroom workers, other moldy dusts

Humidifiers

Tests: Spirometry before and after bronchodilator.

13M. SYSTEMIC DISEASES

Several nonpulmonary conditions are frequently associated with altered pulmonary function. Some of the more common ones are listed below, followed by the commonly abnormal pulmonary function test result(s).

1. Rheumatoid arthritis: Dlco reduction is often the first change. Vital capacity may also be reduced, and airflow obstruction occurs in a few cases.

2. Scleroderma (systemic sclerosis): Reduced Dlco is the first change, caused by minimal fibrosis often not visible by radiography. Later, lung volumes can decrease.

3. Systemic lupus erythematosus: Early decrease in Dlco. Later, volumes may decrease dramatically, producing a ''vanishing lung,''which may be more related to respiratory muscle weakness than to pulmonary fibrosis.

4. Wegener's granulomatosis: Both restrictive and obstructive patterns may be found, as well as major airway lesions.

5. Dermatomyositis: Muscle weakness and interstitial disease with low Dlco (most often nonspecific interstitial pneumonia) often occur.

6. Cirrhosis of the liver: In some cases, arterial oxygen desaturation is found. This is due to the development of arteriovenous shunts in the lungs or mediastinum. In many cases, the saturation is lower when the subject is standing (rather than lying), so-called orthodeoxia.

7. Relapsing polychondritis: Inflammatory degeneration of tracheal and bronchial cartilage can lead to a considerable reduction in expiratory flows, an obstructive pattern.

8. Sjogren's syndrome: As many as half of affected patients have airway obstruction resistant to bronchodilators.



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