Standard pulmonary function tests measure airflow rates, lung volumes, and the ability of the lung to transfer gas across the alveolar-capillary membrane. Indications for pulmonary function testing include assessment of the type and extent of lung dysfunction; diagnosis of causes of dyspnea and cough; detection of early evidence of lung dysfunction; longitudinal surveillance in occupational settings; follow-up of response to therapy; preoperative assessment; and disability evaluation.
Contraindications to pulmonary function testing include acute severe asthma, respiratory distress, angina aggravated by testing, pneumothorax, ongoing hemoptysis, and active tuberculosis. Many test results are effort-dependent, and some patients may be too impaired to make a maximal effort. Suboptimal effort limits validity and is a common cause of misinterpretation of results. All pulmonary function tests are measured against predicted values derived from large studies of healthy subjects. In general, these predictions vary with age, gender, height and, to a lesser extent, weight and ethnicity.
Spirometry (see box, below) and measurement of lung volumes allow assessment of the presence and severity of obstructive and restrictive pulmonary dysfunction. Obstructive dysfunction is marked by a reduction in airflow rates judged by a fall in the ratio of FEV1 (forced expiratory volume in the first second) to FVC (forced vital capacity). Causes include asthma, COPD (chronic bronchitis and emphysema), bronchiectasis, bronchiolitis, and upper airway obstruction. Restrictive dysfunction is marked by a reduction in lung volumes with a normal to increased FEV1/FVC ratio. Severity is graded by the reduction in total lung capacity. A reduced FVC suggests pulmonary restriction but is not diagnostic. Causes include decreased lung compliance from infiltrative disorders such as pulmonary fibrosis; reduced muscle strength from phrenic nerve injury, diaphragm dysfunction, or neuromuscular disease; pleural disease, including large pleural effusion or marked pleural thickening; and prior lung resection. The flow-volume loop combines the maximal expiratory and inspiratory flow-volume curves and is especially helpful in determining the site of airway obstruction (eFigure 9–1).
Representative spirograms (upper panel) and expiratory flow-volume curves (lower panel) for normal (A), obstructive (B), and restrictive (C) patterns.
Spirometry is adequate for evaluation of most patients with suspected respiratory disease. If airflow obstruction is evident, spirometry may be repeated 10–20 minutes after an inhaled bronchodilator is administered. The absence of improvement in spirometry after inhaled bronchodilator in the pulmonary function laboratory does not preclude a successful clinical response to bronchodilator therapy. Measurements of lung volumes and diffusing capacity are useful in selected patients, but these tests are expensive and should not be ordered routinely with spirometry.
Measurement of the single-breath diffusing capacity for carbon monoxide (DLCO), which reflects the ability of the lung to transfer gas across the alveolar/capillary interface, is particularly helpful in evaluation of patients with diffuse infiltrative lung disease or emphysema. The total pulmonary diffusing capacity depends on the diffusion properties of the alveolar-capillary membrane and the amount of hemoglobin occupying the pulmonary capillaries. The diffusing capacity should therefore be corrected for the blood hemoglobin concentration.1
Corrected DLCO = Measured DLCO × (1.7 Hb/(10.22 + Hb),
where [Hb] is the measured hemoglobin concentration (g/dL).
Elevated DLCO is observed in pulmonary hemorrhage and may be seen in acute heart failure and asthma due to an increase in pulmonary capillary blood volume. Reporting the ratio of measured diffusing capacity to alveolar volume (DLCO/VA) is helpful, because a diminished diffusing capacity may only reflect a reduction in the breath taken during the maneuver. In patients with emphysema, the diffusing capacity is characteristically low, the alveolar volume normal or increased, and the DLCO/VA ratio is low. In patients with diffuse infiltrative lung disease, both the diffusing capacity and the alveolar volume are characteristically reduced, and the DLCO/VA ratio is normal or low.
In patients with AIDS, DLCO is a highly sensitive screening test for the presence of pulmonary disease, especially Pneumocystis jirovecii pneumonia, but it lacks specificity. A normal DLCO in an AIDS patient is strong evidence against Pneumocystis pneumonia.
Arterial blood gas analysis is indicated whenever a clinically important acid-base disturbance, hypoxemia, or hypercapnia is suspected. Oximetry provides an inexpensive, noninvasive alternative means of monitoring hemoglobin saturation with oxygen. Oximeters monitor hemoglobin saturation and not oxygen tension. eFigure 9–2 displays the normal relationship between hemoglobin saturation and partial pressure of oxygen in blood. This relationship is not linear. The clinical accuracy of pulse oximeters is reduced in such conditions as severe anemia (less than 5 g/dL hemoglobin), the presence of abnormal hemoglobin moieties (carboxyhemoglobin, methemoglobin, fetal hemoglobin), the presence of intravascular dyes, motion artifact, and lack of pulsatile arterial blood flow (hypotension, hypothermia, cardiac arrest, simultaneous use of a blood pressure cuff, left ventricular assist device and cardiopulmonary bypass). Co-oximetry, a form of oximetry that uses additional wavelengths of light to identify oxyhemoglobin and deoxyhemoglobin, can identify the more common abnormal hemoglobins. The normal arterial PO2 falls with increasing altitude (eTable 9–1).
eTable 9–1.The effect of altitude on PO2 in normal adults. ||Download (.pdf) eTable 9–1. The effect of altitude on PO2 in normal adults.
|Altitude (feet) ||Barometric Pressure (mm Hg) ||Atmospheric1 PO2 (mm Hg) ||Tracheal2 PO2 (mm Hg) ||Arterial3 PO2 (mm Hg) |
|Sea level ||760 ||159 ||149 ||99 |
|2000 ||707 ||148 ||138 ||88 |
|4000 ||656 ||137 ||127 ||77 |
|6000 ||609 ||127 ||118 ||68 |
|8000 ||564 ||118 ||108 ||58 |
|10,000 ||523 ||109 ||100 ||50 |
|15,000 ||426 ||90 ||80 ||30 |
Oxygen-hemoglobin dissociation curve, pH 7.40, temperature 38°C. (Reproduced, with permission, from Comroe JH Jr et al. The Lung: Clinical Physiology and Pulmonary Function Tests, 2nd ed. Year Book Medical Publishers, 1962.)
Nonspecific bronchial provocation testing may aid the evaluation of suspected asthma, when baseline spirometry is normal, and in unexplained cough. The subject inhales a nebulized solution containing methacholine or histamine. These agents cause bronchial smooth muscle constriction in asthmatic patients at much lower doses than in nonasthmatics. If the FEV1 falls by more than 20% at a dose of 16 mg/mL or less, the test is positive. Bronchial provocation testing is 95% sensitive for the diagnosis of asthma. A negative result therefore makes asthma unlikely. Specificity is lower—about 70%—since false positives may occur in several common conditions, including COPD, heart failure, recent viral respiratory infection, cystic fibrosis, and sarcoidosis.
et al. The vital capacity is vital: epidemiology and clinical significance of the restrictive spirometry pattern. Chest. 2016 Jan;149(1):238–51.
et al. Screening for chronic obstructive pulmonary disease: evidence report and systematic review for the US Preventive Services Task Force. JAMA. 2016 Apr 5;315(13):1378–93.
et al. Pulmonary function testing and cardiopulmonary exercise testing: an overview. Med Clin North Am. 2019 May;103(3):565–76.
Cardiopulmonary Exercise Stress Testing
Cardiopulmonary exercise testing is usually performed to evaluate patients with unexplained exertional dyspnea. A bicycle ergometer or treadmill is used. Minute ventilation, expired oxygen and carbon dioxide tension, heart rate, blood pressure, and respiratory rate are monitored. The exercise protocol is determined by the indications for the test and the ability of the patient to exercise. Certain patterns of abnormal oxygen uptake or delivery can be identified and may lead to specific pulmonary or cardiac diagnoses. The test is also used to quantify cardiorespiratory capacity. Complications are rare.
et al. Cardiopulmonary exercise testing: what is its value? J Am Coll Cardiol. 2017 Sep 26;70(13):1618–36.
A. Cardiopulmonary exercise testing: basics of methodology and measurements. Ann Am Thorac Soc. 2017 Jul;14(Suppl 1):S3–11.
Flexible bronchoscopy is an essential tool in the diagnosis and management of many pulmonary diseases. Bronchoscopy is indicated for evaluation of the airway, diagnosis and staging of bronchogenic carcinoma, evaluation of hemoptysis, and diagnosis of pulmonary infections. It allows transbronchial lung biopsy, endobronchial biopsy, bronchoalveolar lavage (BAL), and removal of retained secretions and foreign bodies from the airway. The procedure is contraindicated in severe bronchospasm or a bleeding diathesis. Complications include hemorrhage, fever, and transient hypoxemia. The rate of major complications is less than 1% but increases to about 7% when transbronchial lung biopsy is performed. Deaths are rare. Hospitalization for flexible bronchoscopy is not necessary.
Rigid bronchoscopy is performed for massive bleeding, extraction of large obstructing objects (foreign bodies, blood clots, tumor masses, broncholiths), biopsy of tracheal or main stem bronchus tumors and bronchial carcinoids, and facilitation of laser therapy. Unlike flexible bronchoscopy, which can usually be performed with only topical anesthesia and low-dose conscious sedation (an opioid or benzodiazepine or both), rigid bronchoscopy usually requires general anesthesia.
Advances in techniques including endobronchial laser therapy, electrocautery, tracheobronchial stenting, and endobronchial ultrasound guidance to locate lymph nodes prior to transbronchial needle aspiration biopsy promise to expand diagnostic and therapeutic avenues available to the bronchoscopist significantly. This is an area of rapid technological advancement and emerging clinical research study.
et al. Rigid bronchoscopy. Semin Respir Crit Care Med. 2018 Dec;39(6):674–84.
E. Recent advances in bronchoscopy. F1000Res. 2018 Oct 16;7:1646.
et al. Recent advances in laryngoscopy in adults. F1000Res. 2019 Jun 6;8:797.