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Approach to the Patient with Disease of the Respiratory System: Introduction
The majority of diseases of the respiratory system fall into one of three major categories: (1) obstructive lung diseases; (2) restrictive disorders; and (3) abnormalities of the vasculature. Obstructive lung diseases are most common and primarily include disorders of the airways such as asthma, chronic obstructive pulmonary disease (COPD), bronchiectasis, and bronchiolitis. Diseases resulting in restrictive pathophysiology include parenchymal lung diseases, abnormalities of the chest wall and pleura, as well as neuromuscular disease. Disorders of the pulmonary vasculature are not always recognized and include pulmonary embolism, pulmonary hypertension, and pulmonary venoocclusive disease. Although many specific diseases fall into these major categories, both infective and neoplastic processes can affect the respiratory system and may result in myriad pathologic findings, including obstruction, restriction, and pulmonary vascular disease (see Table 1).

TABLE – 1 (Categories of Respiratory Disease).

Category	Examples
Obstructive lung disease	Asthma
COPD
Bronchiectasis
Bronchiolitis
Restrictive pathophysiology—parenchymal disease	Idiopathic pulmonary fibrosis (IPF)
Asbestosis
Desquamative interstitial pneumonitis (DIP)
Sarcoidosis
Restrictive pathophysiology-neuromuscular weakness	Amyotrophic lateral sclerosis (ALS)
Guillain-Barré syndrome
Restrictive pathophysiology-chest wall/pleural disease	Kyphoscoliosis
Ankylosing spondylitis
Chronic pleural effusions
Pulmonary vascular disease	Pulmonary embolism
Pulmonary arterial hypertension (PAH)
Malignancy	Bronchogenic carcinoma (non-small-cell and small cell)
Metastatic disease
Infectious diseases	Pneumonia
Bronchitis
Tracheitis
Abbreviation: COPD, chronic obstructive pulmonary disease.

The majority of respiratory diseases present with abnormal gas exchange. Disorders can also be grouped into the categories of gas exchange abnormalities, including hypoxemic, hypercarbic, or combined impairment. Importantly, many diseases of the lung do not manifest gas exchange abnormalities.

As with the evaluation of most patients, the approach to a patient with disease of the respiratory system begins with a thorough history. A focused physical examination is helpful in further categorizing the specific pathophysiology. Many patients will subsequently undergo pulmonary function testing, chest imaging, blood and sputum analysis, a variety of serologic or microbiologic studies, and diagnostic procedures, such as bronchoscopy. This step-wise approach is discussed in detail below.

HISTORY
Dyspnea and Cough

The cardinal symptoms of respiratory disease are dyspnea and cough . Dyspnea can result from many causes, some of which are not predominantly caused by lung pathology. The words a patient uses to describe breathlessness or shortness of breath can suggest certain etiologies of the dyspnea. Patients with obstructive lung disease often complain of “chest tightness” or “inability to get a deep breath,” whereas patients with congestive heart failure more commonly report “air hunger” or a sense of suffocation.

The tempo of onset and duration of a patient’s dyspnea are helpful in determining the etiology. Acute shortness of breath is usually associated with sudden physiological changes, such as laryngeal edema, bronchospasm, myocardial infarction, pulmonary embolism, or pneumothorax. Patients with underlying lung disease commonly have progressive shortness of breath or episodic dyspnea. Patients with COPD and idiopathic pulmonary fibrosis (IPF) have a gradual progression of dyspnea on exertion, punctuated by acute exacerbations of shortness of breath. In contrast, most asthmatics have normal breathing the majority of the time and have recurrent episodes of dyspnea usually associated with specific triggers, such as an upper respiratory tract infection or exposure to allergens.

Specific questioning should focus on factors that incite the dyspnea, as well as any intervention that helps resolve the patient’s shortness of breath. Of the obstructive lung diseases, asthma is most likely to have specific triggers related to sudden onset of dyspnea, although this can also be true of COPD. Many patients with lung disease report dyspnea on exertion. It is useful to determine the degree of activity that results in shortness of breath as it gives the clinician a gauge of the patient’s degree of disability. Many patients adapt their level of activity to accommodate progressive limitation. For this reason it is important, particularly in older patients, to delineate the activities in which they engage and how they have changed over time. Dyspnea on exertion is often an early symptom of underlying lung or heart disease and warrants a thorough evaluation.

Cough is the other common presenting symptom that generally indicates disease of the respiratory system. The clinician should inquire about the duration of the cough, whether or not it associated with sputum production, and any specific triggers that induce it. Acute cough productive of phlegm is often a symptom of infection of the respiratory system, including processes affecting the upper airway (e.g., sinusitis, tracheitis) as well as the lower airways (e.g., bronchitis, bronchiectasis) and lung parenchyma (e.g., pneumonia). Both the quantity and quality of the sputum, including whether it is blood-streaked or frankly bloody, should be determined.

Chronic cough (defined as persisting for more than 8 weeks) is commonly associated with obstructive lung diseases, particularly asthma and chronic bronchitis, as well as “nonrespiratory” diseases, such as gastroesophageal reflux (GERD) and postnasal drip. Diffuse parenchymal lung diseases, including idiopathic pulmonary fibrosis, frequently present with a persistent, nonproductive cough. As with dyspnea, all causes of cough are not respiratory in origin, and assessment should consider a broad differential, including cardiac and gastrointestinal diseases as well as psychogenic causes.

Additional Symptoms

Patients with respiratory disease may complain of wheezing, which is suggestive of airways disease, particularly asthma. Hemoptysis, which must be distinguished from epistaxis or hematemesis, can be a symptom of a variety of lung diseases, including infections of the respiratory tract, bronchogenic carcinoma, and pulmonary embolism. Chest pain or discomfort is also often thought to be respiratory in origin. As the lung parenchyma is not innervated with pain fibers, pain in the chest from respiratory disorders usually results from either diseases of the parietal pleura (e.g., pneumothorax) or pulmonary vascular diseases (e.g., pulmonary hypertension). As many diseases of the lung can result in strain on the right side of the heart, patients may also present with symptoms of cor pulmonale, including abdominal bloating or distention, and pedal edema.

Additional History

A thorough social history is an essential component of the evaluation of patients with respiratory disease. All patients should be asked about current or previous cigarette smoking as this exposure is associated with many diseases of the respiratory system, most notably COPD and bronchogenic lung cancer but also a variety of diffuse parenchymal lung diseases [e.g., desquamative interstitial pneumonitis (DIP) and pulmonary Langerhans cell histiocytosis]. For most disorders, the duration and intensity of exposure to cigarette smoke increases the risk of disease. There is growing evidence that “second-hand smoke” is also a risk factor for respiratory tract pathology; for this reason, patients should be asked about parents, spouses, or housemates who smoke. It is becoming less common for patients to be exposed to cigarette smoke on the job, but for older patients, an occupational history should include the potential for heavy cigarette smoke exposure (e.g., flight attendants working prior to prohibition of smoking on airplanes).

Possible inhalational exposures should be explored, including those at the work place (e.g., asbestos, wood smoke) and those associated with leisure (e.g., pigeon excrement from pet birds, paint fumes) . Travel predisposes to certain infections of the respiratory tract, most notably the risk of tuberculosis. Potential exposure to fungi found in specific geographic regions or climates (e.g., Histoplasma capsulatum) should be explored.

Associated symptoms of fever and chills should raise the suspicion of infective etiologies, both pulmonary and systemic. Some systemic diseases, commonly rheumatologic or autoimmune, present with respiratory tract manifestations. Review of systems should include evaluation for symptoms that suggest undiagnosed rheumatologic disease. These may include joint pain or swelling, rashes, dry eyes, dry mouth, or constitutional symptoms. Additionally, carcinomas from a variety of primary sources commonly metastasize to the lung and cause respiratory symptoms. Finally, therapy for other conditions, including both radiation and medications, can result in diseases of the chest.

Physical Examination

The clinician’s suspicion for respiratory disease often begins with a patient’s vital signs. The respiratory rate is often informative, whether elevated (tachypnea) or depressed (hypopnea). In addition, pulse oximetry should be measured as many patients with respiratory disease will have hypoxemia, either at rest or with exertion.

Simple observation of the patient is informative. Patients with respiratory disease may be in distress, often using accessory muscles of respiration to breathe. Severe kyphoscoliosis can result in restrictive pathophysiology. Inability to complete a sentence in conversation is generally a sign of severe impairment and should result in an expedited evaluation of the patient.

Auscultation

The majority of the manifestations of respiratory disease present with abnormalities of the chest examination. Wheezes suggest airway obstruction and are most commonly a manifestation of asthma. Peribronchial edema in the setting of congestive heart failure, often referred to as “cardiac asthma,” can also result in diffuse wheezes as can any other process that causes narrowing of small airways. For this reason, clinicians must take care not to attribute all wheezing to asthma.

Rhonchi are a manifestation of obstruction of medium-sized airways, most often with secretions. In the acute setting, this may be a sign of viral or bacterial bronchitis. Chronic rhonchi suggest bronchiectasis or COPD. Bronchiectasis, or permanent dilation and irregularity of the bronchi, often causes what is referred to as a “musical chest” with a combination of rhonchi, pops, and squeaks. Stridor or a low-pitched, focal inspiratory wheeze usually heard over the neck, is a manifestation of upper airway obstruction and should result in an expedited evaluation of the patient as it can precede complete upper airway obstruction and respiratory failure.

Crackles, or rales, are commonly a sign of alveolar disease. A variety of processes that fill the alveoli with fluid result in crackles. Pneumonia, or infection of the lower respiratory tract and air spaces, may cause crackles. Pulmonary edema, of cardiogenic or noncardiogenic cause, is associated with crackles, generally more prominent at the bases. Interestingly, diseases that result in fibrosis of the interstitium (e.g., IPF) also result in crackles often sounding like Velcro being ripped apart. Although some clinicians make a distinction between “wet” and “dry” crackles, this has not been shown to be a reliable way to differentiate among etiologies of respiratory disease.

One way to help distinguish between crackles associated with alveolar fluid and those associated with interstitial fibrosis is to assess for egophony. Egophony is the auscultation of the sound “AH” instead of “EEE” when a patient phonates “EEE.” This change in note is due to abnormal sound transmission through consolidated lung and will be present in pneumonia but not in IPF. Similarly, areas of alveolar filling have increased whispered pectoriloquy as well as transmission of larger airway sounds (i.e., bronchial breath sounds in a lung zone where vesicular breath sounds are expected).

The lack of breath sounds or diminished breath sounds can also help determine the etiology of respiratory disease. Patients with emphysema often have a quiet chest with diffusely decreased breath sounds. A pneumothorax or pleural effusion may present with an area of absent breath sounds, although this is not always the case.

Remainder of Chest Examination

In addition to auscultation, percussion of the chest helps distinguish among pathologic processes of the respiratory system. Diseases of the pleural space are often suggested by differences in percussion note. An area of dullness may suggest a pleural effusion, whereas hyperresonance, particularly at the apex, can indicate air in the pleural space (i.e., pneumothorax).

Tactile fremitus will be increased in areas of lung consolidation, such as pneumonia, and decreased with pleural effusion. Decreased diaphragmatic excursion can suggest neuromuscular weakness manifesting as respiratory disease or hyperinflation associated with COPD.

Careful attention should also be paid to the cardiac examination with particular emphasis on signs of right heart failure as it is associated with chronic hypoxemic lung disease and pulmonary vascular disease. The clinician should feel for a right ventricular heave and listen for a prominent P2 component of the second heart sound, as well as a right-sided S4.

Other Systems

Pedal edema, if symmetric, may suggest cor pulmonale, and if asymmetric may be due to deep venous thrombosis and associated pulmonary embolism. Jugular venous distention may also be a sign of volume overload associated with right heart failure. Pulsus paradoxus is an ominous sign in a patient with obstructive lung disease as it is associated with significant negative intrathoracic (pleural) pressures required for ventilation, and impending respiratory failure.

As stated earlier, rheumatologic disease may manifest primarily as lung disease. Owing to this association, particular attention should be paid to joint and skin examination. Clubbing can be found in many lung diseases, including cystic fibrosis, IPF, and lung cancer, although it can also be associated with inflammatory bowel disease or as a congenital finding of no clinical importance. Patients with COPD do not usually have clubbing; thus, this sign should warrant an investigation for second process, most commonly an unrecognized bronchogenic carcinoma, in these patients. Cyanosis is seen in hypoxemic respiratory disorders that result in more than 5 g/dL deoxygenated hemoglobin.

DIAGNOSTIC EVALUATION

The sequence of studies is dictated by the clinician’s differential diagnosis determined by the history and physical examination. Acute respiratory symptoms are often evaluated with multiple tests obtained at the same time in order to diagnose any life threatening diseases rapidly (e.g., pulmonary embolism or multilobar pneumonia). In contrast, chronic dyspnea and cough can be evaluated in a more protracted, step-wise fashion.

Pulmonary Function Testing

The initial pulmonary function test obtained is spirometry. This study is used to assess for obstructive pathophysiology as seen in asthma, COPD, and bronchiectasis. A diminished forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) (often defined as less than 70% of predicted value) is diagnostic of obstruction. History as well as further testing can help distinguish among different obstructive diseases. COPD is almost exclusively seen in cigarette smokers. Asthmatics often show an acute response to inhaled bronchodilators (e.g., albuterol). In addition to the measurements of FEV1 and FVC, the clinician should examine the flow-volume loop. A plateau of the inspiratory or expiratory curves suggests large airway obstruction in extrathoracic and intrathoracic locations, respectively.

Normal spirometry or spirometry with symmetric decreases in FEV1 and FVC warrants further testing, including lung volume measurement and the diffusion capacity of the lung for carbon monoxide (DLCO). A total lung capacity (TLC) less than 80% of the predicted value for a patient’s age, race, gender, and height defines restrictive pathophysiology. Restriction can result from parenchymal disease, neuromuscular weakness, or chest wall or pleural diseases. Restriction with impaired gas exchange, as indicated by a decreased DLCO, suggests parenchymal lung disease. Additional testing, such as maximal expiratory pressure (MEP) and maximal inspiratory pressure (MIP), can help diagnose neuromuscular weakness. Normal spirometry, normal lung volumes, and a low DLCO should prompt further evaluation for pulmonary vascular disease.

Arterial blood gas testing is often also helpful in assessing respiratory disease. Hypoxemia, while usually apparent with pulse oximetry, can be further evaluated with the measurement of arterial PO2 and the calculation of an alveolar gas and arterial blood oxygen tension difference [(A-a)DO2]. It should also be noted that at times, most often due to abnormal hemoglobins or non-oxygen hemoglobin-ligand complexes, pulse oximetry can be misleading (such as observed with carboxyhemoglobin). Diseases that cause ventilation-perfusion mismatch or shunt physiology will have an increased (A-a)DO2 at rest. Arterial blood gas testing also allows for the measurement of arterial PCO2. Most commonly, acute or chronic obstructive lung disease presents with hypercarbia; however, many diseases of the respiratory system can cause hypercarbia if the resulting increase in work of breathing is greater than that which allows a patient to sustain an adequate minute ventilation.

Chest Imaging

Most patients with disease of the respiratory system will undergo imaging of the chest as part of initial evaluation. Clinicians should generally begin with a plain chest radiograph, preferably posterior-anterior (PA) and lateral films. Several findings, including opacities of the parenchyma, blunting of the costophrenic angles, mass lesions, and volume loss, can be very helpful in determining an etiology. It should be noted that many diseases of the respiratory system, particularly those of the airways and pulmonary vasculature, are associated with a normal chest radiograph.
Fig. I : The normal chest X-ray. Note lung markings consist of branching and tapering lines radiating out from the hila; where airways and vessels turn towards the film they can appear as open or filled circles (see upper pole of right hilum). The scapulae may overlie the lung fields; trace the edge of bony structures to avoid mistaking them for pleural or pulmonary shadows. To check for hyperinflation, count the ribs; if more than 10 are visible posteriorly above the diaphragm, the lungs are hyperinflated.
The ‘plain’ chest X-ray

This is performed on the majority of patients suspected of having chest disease. A postero-anterior (PA) film provides information on the lung fields, heart, mediastinum, vascular structures and the thoracic cage (Fig. I) above. Additional information may be obtained from a lateral film, particularly if pathology is suspected behind the heart shadow or deep in the diaphragmatic sulci. An approach to interpreting the chest X-ray is given in Table A, and common abnormalities in Table B.

Table A : How to interpret a chest X-ray

Name, date, orientation	Films are postero-anterior (PA) unless marked
AP to denote antero-posterior
Lung fields	Equal translucency?
Check horizontal fissure from right hilum to sixth rib at the anterior axillary line
Masses? Consolidation? Cavitation?
Lung apices	Check behind the clavicles
Masses? Consolidation? Cavitation?
Trachea	Central? (Midway between the clavicular heads)
Paratracheal mass? Goitre?
Heart	Normal shape?
Cardiothoracic ratio (should be < half the intrathoracic diameter)
Retrocardiac mass?
Hila	Left should be higher than right
Shape? (Should be concave laterally; if convex, consider mass or lymphadenopathy)
Density?
Diaphragms	Right should be higher than left
Hyperinflation? No more than 10 ribs should be visible posteriorly above the diaphragm)
Costophrenic angles	Acute and well-defined? (Pleural fluid or thickening, if not)
Soft tissues	Breast shadows in females
Chest wall for masses or subcutaneous emphysema
Bones	Ribs, vertebrae, scapulae and clavicles
Any fracture visible at bone margins or lucencies?
Table B : Common chest X-ray abnormalities

Pulmonary and pleural shadowing
Consolidation: infection, infarction, inflammation, and rarely bronchoalveolar cell carcinoma
Lobar collapse: mucus plugging, tumour, compression by lymph nodes
Solitary nodule:
Multiple nodules: miliary tuberculosis (TB), dust inhalation, metastatic malignancy, healed varicella pneumonia, rheumatoid disease
Ring shadows, tramlines and tubular shadows: bronchiectasis
Cavitating lesions: tumour, abscess, infarct, pneumonia (Staphylococcus/Klebsiella), Wegener’s granulomatosis
Reticular, nodular and reticulonodular shadows: diffuse parenchymal lung disease, infection
Pleural abnormalities: fluid, plaques, tumour

Subsequent computed tomography of the chest (CT scan) is often obtained. The CT scan allows better delineation of parenchymal processes, pleural disease, masses or nodules, and large airways. If administered with contrast, the pulmonary vasculature can be assessed with particular utility for determination of pulmonary emboli. Intravenous contrast also allows lymph nodes to be delineated in greater detail.

FURTHER STUDIES

Depending on the clinician’s suspicion, a variety of other studies may be obtained. Concern for large airway lesions may warrant bronchoscopy. This procedure may also be used to sample the alveolar space with bronchoalveolar lavage (BAL) or to obtain nonsurgical lung biopsies. Blood testing may include assessment for hypercoagulable states in the setting of pulmonary vascular disease, serologic testing for infectious or rheumatologic disease, or assessment of inflammatory markers or leukocyte counts (e.g., eosinophils). Sputum evaluation for malignant cells or microorganisms may be appropriate. An echocardiogram to assess right- and left-sided heart function is often obtained. Finally, at times, a surgical lung biopsy is needed to diagnose certain diseases of the respiratory system. All of these studies will be guided by the preceding history, physical examination, pulmonary function testing, and chest imaging.

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