Cristine Berry, MD, MHS, College of Medicine, University of Arizona
|TIPS FOR USING PULMONARY FUNCTION TESTS (PFTs) IN OLDER ADULTS
Indications for Measuring Pulmonary Function
Common indications for pulmonary function testing (PFT) in older adults are symptoms that suggest lung disease, such as dyspnea, chest tightness, cough, and wheezing. However, some older patients may not experience these symptoms even in the presence of lung disease because they will instinctively limit their activities to avoid exertion that might cause the symptoms to occur. Thus, their low activity levels may preclude symptoms, even in the presence of significant (but undiagnosed) pulmonary disease. There is also evidence to suggest that older individuals have a diminished perception of bronchospasm compared with younger adults. With these concerns in mind, it is reasonable to have a lower threshold for obtaining PFTs in older adults.
The most common PFT is spirometry, which measures the volume of air exhaled from the lungs during a forced expiratory maneuver. Most older adults are able to successfully complete this test, but potential challenges may affect performance in some individuals. For example, patients must be able to hear the technician and understand instructions, form a tight seal with their lips around the mouthpiece, inhale maximally, and then exhale with sustained maximal effort over several seconds to obtain accurate results.
Spirometric measurements include forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and the ratio of these values (FEV1/FVC). Both FEV1 and FVC decline with age, but the decline in FEV1 is greater (Figure 1). Thus, the FEV1/FVC ratio also declines with age.
The FEV1/FVC ratio is useful in the diagnosis of obstructive lung diseases. However, because it changes over the lifespan, the definition of obstruction in older patients has been controversial.
The Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines indicate that a fixed ratio (FEV1/FVC <0.70) should be used to define obstruction, but there is concern this may lead to over-diagnosis among older patients, all of whom experience a decline in FEV1/ FVC. The American Thoracic Society currently recommends defining obstruction by an FEV1/FVC below the 5th percentile for the adult population (see resource list on back page).
Measurement of Lung Volumes
Lung volumes are commonly measured in response to abnormal spirometry to confirm the presence of a restrictive ventilatory defect or to evaluate for hyperinflation and air trapping due to an obstructive ventilatory defect. Lung volumes, including total lung capacity (TLC) and residual volume (RV) (Figure 2), may be determined using body plethysmography or a gas dilution technique. TLC, which usually remains constant with aging, is reduced in restrictive lung diseases. RV, which increases with age, may be further increased in obstructive lung disorders.
Assessing Gas Exchange
Assessment of gas exchange involves measuring the diffusing capacity of the lungs for carbon monoxide (DLCO) and/or arterial blood gas analysis. DLCO decreases with age, as does resting arterial oxygen tension (PaO2). Reference equations specific for age have been established, but in general, PaO2 <70 mmHg is abnormal. Both DLCO and PaO2 may be further reduced in disorders that compromise gas exchange, including interstitial lung disease, pulmonary edema, pulmonary vascular disease, and emphysema.
Assessing Respiratory Muscle Strength
Respiratory muscle strength decreases with age. Maximal inspiratory and expiratory pressures (MIP, MEP) can be measured in a PFT lab, but the results are dependent on patient effort. Thus, further testing may be needed when results indicate respiratory muscle weakness. Normal values, however, rule out significant weakness.
PFT Interpretation in Older Adults
Typical patterns on PFTs in common conditions affecting lung functioning older adults are shown in the table below. Lung function varies by age, sex, and height, and complex equations incorporate these variables to predict normal PFT values. Measured values are compared with predicted values to determine if they are abnormal. Of note, many of these equations were developed from data sets with age limits (e.g., analysis of NHANES III excluded data from patients of age >80 years when establishing normal PFT values), so caution is advised when interpreting PFTs in older patients.
Decline in height with advancing age can affect PFT predicted values. For patients with kyphosis in particular, arm span (from the tip of one outstretched arm to the other) may be substituted for height to determine predicted values. Normal PFT values are lower in shorter individuals, so using arm span avoids the over-estimation of pulmonary function that can occur if height measurements are "artifactually" short due to kyphosis or other conditions.
References and Resources
- Berry CE, Wise RA. Interpretation of pulmonary function test: issues and controversies. Clin Rev Allergy Immunol 2009; 37: 173-180.
- Cerveri I, Zoia MC, Fanfulla F, et al. Reference values of arterial oxygen tension in the middle-aged and elderly. Am J Respir Crit Care Med 1995; 152: 934-941.
- Enright PL. Aging of the respiratory system. Hazzard's Geriatric Medicine and Gerontology, 6th edition. McGraw-Hill, 2009.
- Global Initiative for Chronic Obstructive Lung Disease. Pocket Guide to COPD Diagnosis, Management, and Prevention. 2013.
- Pellegrino R, Viegi G, Brusasco V, et al. Interpretative strategies for lung function tests. Eur Respir J 2005;26: 948-968.
- Sharma G, Goodwin J. Effect of aging on respiratory system physiology and immunology. Clin Interv Aging 2006; 1: 253-260.