A New Era for Spirometry

By Thomas L. Petty, M.D.

The author argues that use of spirometry should become as commonplace as testing for blood pressure and cholesterol. Doing so will enable physicians to identify patients in the early stages of pulmonary disorders, when prompt intervention can alter disease course.

Dr. Petty is professor of medicine, University of Colorado Health Sciences Center, Denver, and consultant to faculty, HealthONE Center for Health Sciences Education, Denver. He is a member of the editorial board of IM Internal Medicine. IM September, 1996;59-62, 67,72-75.

The greatest challenge in medicine is prevention or early treatment of diseases in order to avoid premature morbidity and mortality. Hand-in-hand with this aim is avoiding or relieving physician discomfort. The use of spirometry, simple office-based lung function testing, can identify patients who are often asymptomatic but risk suffering or death from disabling or fatal diseases, such as lung cancer,1,2 heart attack,3,4 and stroke,5 as well as premature deaths from all causes.6 Spirometry is especially valuable in early detection of chronic obstructive pulmonary disease (COPD).

This article describes the essential features of spirometry in clinical relevant terms and explains why practicing physicians should make spriometric evaluation an essential part of patient examinations, particularly for those at risk of pulmonary disease. (See "A historical vignette").

Why spirometry is significant

Physicians should begin to think of spirometry measurements in the way that blood pressure is considered today (Table 1) -- as an indicator of a certain level of health. The widespread use of blood pressure measurements to identify asymptomatic hypertensive patients has been a major boost to the nation's health. A combination of antihypertensive medication and methods to lower cholesterol by diet, pharmacologic agents, or both, has resulted in a dramatic reduction in both heart attack and stroke, the first and third most common cause of death in the US.7

Table 1 Sphygmomanometry and spirometry indicators

Sphygmomanometry

Normal reading

Blood pressure, 120/80

Chief factors

Cardiac output

Peripheral resistance

Blood volume

Blood viscosity

Renin, angiotensin axis

Spirometry

Normal reading

Lung function, 3.0 FEV1/4.0 FVC

Chief factors

Elastic recoil

Airways resistance

Large airways

Small airways

Interdependence

Muscular effort and coordination

FEV1 = forced expiratory volume in 1 second;

FVC = forced vital capacity

In the same way that blood pressure and cholesterol numbers have become easy-to-understand yardsticks of complex processes, spirometric measurements can be a benchmark of ventilatory health. Spirometric abnormalities include an impressive list of obstructive and restrictive ventilatory disorders (Table 2). Among these, lung cancer and COPD are related through the common denominator of smoking and possibly other factors. COPD ranks fourth in causes of death, and death rates continue to rise, with more than 100,000 deaths predicted for 1996.8 We are beginning to realize that the earlier spirometric measurements are made -- when the diagnosis of COPD is not even visible on a chest x-ray -- the sooner treatment starts and the greater the improvement in overall survival rates.

Table 2 Common Ventilatory disorders

Obstructive

Restrictive

Common

Asthma

Asthmatic bronchitis

Chronic obstructive bronchitis

COPD

Cystic fibrosis

Emphysema

Uncommon

Bronchiolitis obliterans*

Eosinophilic granuloma

Lymphangiomyomatosis

Sarcoidosis**

Idiopathic fibrosing alveolitis

Interstitial pneumonitis and fibrosis***

Fibrotic residue of disseminated granulomas****

Sarcoidosis

Thoracic deformities

Congestive heart failure

COPD = chronic obstructive pulmonary disease

* May also show mild restrictive defect.

** May show a restrictive defect in advanced fibrotic status.

*** Associated with drug reactions, as in bleomycin, or occupational exposures, including asbestosis.

****For example, tuberculosis and histoplasmosis.

In general, all smokers should have spirometry done at least once, as should anyone with chronic pulmonary symptoms, such as cough, mucus, shortness of breath, or wheeze. If spirometry is normal, it should be repeated, probably yearly, in people who continue to smoke. If spirometry is abnormal, it should be done again after 2 weeks of therapy -- bronchodilators or corticosteroids -- designed to improve airway flow. Spirometry should be performed whenever exacerbations of asthma or chronic bronchitis occur. To monitor the course of restrictive ventilatory disorders, patients with these diseases should have spirometry done every 3 months.

What spirometry measures

Spirometry measures airflow from fully inflated lungs. Flow is a function of pressure and resistance (Figure 1). In ventilatory function, airflow limitation, also called obstruction, can occur through loss of elastic recoil, that is, from the destruction of lung tissue as in emphysema. The result is increased airways resistance, seen in asthmatic bronchitis, chronic bronchitis, or other obstructive disorders.

Expiratory airflow is recorded as volume over time or flow over volume. In Figures 2 to 6, these measurements are compared to the lower limit of normal (listed on the figures). While these methods measure exactly the same thing, the results are displayed differently. I much prefer the volume over time curve because one can directly visualize expiratory time, vital capacity, and forced expiratory volume in 1 second (FEV1). With the flow transducer, only peak flow and forced vital capacity (FVC) can be seen. However, the computer within the spirometer can derive FEV1, the expiratory time, and FEV1 percent of forced vital capacity. Figure 2 is a normal spirogram, Figures 3 to 5 show progressive degrees of airflow obstruction, and Figure 6 presents the pattern of severe ventilatory restriction.

Normal values. Normal values of lung function are based on the patient's age, height, and gender. Younger, taller individuals have higher lung function. Normal values for Caucasian men and women are presented in Figure 7. Men have slightly greater lung function at a given age and height than women, and blacks have predicted normal vital capacities and flows approximately 10% below whites.

Classification of spirometric abnormalities

In obstructive diseases, the FEV1 falls more than the FVC, so that the ratio between FEV1/FVC is 70% to 75% of the lower limit of normal. By contrast, in restrictive diseases, the FVC drops more than the FEV1, and the ratio goes up. Therefore, when the FEV1 percent of FVC is low, and the expiratory time is prolonged (> 6 seconds), physicians are dealing with an obstructive disease. If the expiratory time is short (1 to 2 seconds), and the ratio is high (> 80% to 90%), the condition is a restrictive ventilatory disorder. An algorithm to separate obstructive ventilatory disorders from restrictive ventilatory disorders is presented in Figure 8.

Some overlaps occur, and as COPD worsens in severity, both the FEV1 and FVC decline, sometimes equally. Thus, the ratio is only of value if the FVC is normal or only slightly decreased (note that FEV1 2.0/FVC 4.0 = 50%; FEV1 1.0/FVC 2.0 = 50%, etc.).

Performing spirometric tests

Why not include spirometry as part of the physical examination, just like blood pressure? While spirometry requires coaching by a nurse or a technician in the doctor's office and the patient's cooperation, it's not very difficult.

In spirometry, the patient takes in the largest possible breath, holds it, fills the lungs to the fullest, and pauses for a second, as the mouthpiece of the spirometer is snugly fit to the open mouth and lips. The individual then blasts all the air in one complete effort into the device. The lungs must be squeezed completely empty by patient effort. This is the forced expiratory maneuver. Normal lungs empty in 6 seconds. Expiratory time, the volume, and flow expressed can be accurately measured with simple desktop devices that record the types of curves presented in Figures 2 to 6.

Industry is now producing handheld spirometers (some newer devices are designed to sell for less than $200) that measure FEV1 and FVC. These devices are sufficiently accurate for clinical purposes and can be carried in a doctor's bag or readily used in a physician's office or at the bedside.9

The concept of lung age

Lung age is the age when a person's pulmonary function is normal. Lung age can be calculated from nomogram values (Figure 7).10 If a 46-year-old, 6'-tall male smoker with cough has an FEV1 of 2.6 liters per second (Figure 9), his airflow is that of a normal man at age 80. But, if some reversible component is present and following inhalation of a bronchodilator, the FEV1 elevates to 3.15, the lung age has been "reduced" to 65 years.

The concept of lung age can be used as a strong motivating factor in smoking cessation. We can also project the course of airflow decline over time if this same patient continues to smoke, compared to the probable decline if he stops smoking and regularly uses a bronchodilator, such as an anticholinergic drug.

The validity of these predictors results from the Lung Health Study, which revealed a much slower decline in lung function in those who succeeded in stopping smoking over 5 years, compared with those who continued to smoke. Throughout the study, investigators found that ipratropium was also effective in improving airflow,11 although use of the drug did not change baseline, that is, prebronchodilator lung function.

Peak flow readings insufficient

A history of heavy smoking and a physical examination even with use of a peak flow meter (Figure 10) are not capable of identifying the majority of patients with mild airflow obstruction.12 Peak flow is only a snapshot of flow. It is completely effort-dependent. Peak flow measurements are useful in identifying patients with asthma and in tracking trends in airflow abnormalities and responses to therapy. Peak flow measurements are not so useful in COPD because they may be near normal or even normal in patients with early-to-moderate stages of COPD. This is because COPD is characterized by abnormalities in elastic recoil that are not present in asthma. Elastic recoil may be elevated in asthma due to hyperinflation.

A call for wider use of spirometry

I argue that no physician would use potent antihypertensive agents without measuring blood pressure nor insulin without measuring blood sugar. Who would prescribe warfarin without knowing prothrombin times? I doubt if anyone would prescribe antiarrhythmic agents on the basis of pulse rhythm and rate alone. No longer, than, should physicians threat COPD patients without spirometric testing and, indeed, should perform spirometry on at-risk patients.

A historical vignette

The history of the spirometer merits some mention. Although virtually all students of medicine can name the originator of the x-ray machine (Wilhelm R` ntgen in 1895) and the ECG machine (Willem Einthoven in 1903), virtually no one can recall who developed the spirometer. Even the most recent Encyclopaedia Britannica does not mention John Hutchinson, in contrast to Einthoven and R` ntgen. Hutchinson, a surgeon, also coined the term vital capacity, that is, the capacity for life.

A violinist of some reputation, Hutchinson was known as a very precise man. His exacting observations allowed him to learn that the vital capacity was directly related to the height -- and inversely related to the age -- of the individual. His first paper was published in 1846 and reported on measurements in 2,130 individuals. He recognized that a reduction in vital capacity predicted premature morbidity and mortality. Studies have since proven Hutchinson's recognition -- that the results of spirometric tests predict all-cause mortality. He became a consultant to the insurance industry of London and tried to promote the notion that his vital capacity could be useful for actuarial purposes. Hutchinson's invention was initially acclaimed, "We have no hesitation in recording our deliberate opinion that it forms one of the most valuable contributions to physiological science that we have seen for some time."1

The figure below shows a modification of Hutchinson's first spirometer, is closely reminiscent of the water-filled Collins-type spirometers that are still found in pulmonary function laboratories in some medical schools.

Reference: Hutchinson J: On the capacity of the lungs and the respiratory function with a view of establishing a precise and easy method of detecting disease by the spirometer. Med Chir Trans (London) 1846;29:137.

Lung health initiative

The newly launched National Lung Health Education Program (NLHEP) is sponsored by the National Heart, Lung, and Blood Institute, the American College of Chest Physicians, the American Thoracic Society, and the American Association for Respiratory Care. NLHEP is developing a nationwide program aimed at protection of lung health and early identification of -- and intervention in -- chronic obstructive pulmonary disease and associated disorders. NLHEP recommends that all physicians use spirometric measurements in their daily practices.

Interested physicians should contact NLHEP's Director, Thomas L. Petty, M.D. Professor of Medicine, University of Colorado Health Sciences Center and faculty consultant, HealthONE Center for Health Sciences Education at 1850 High Street, Denver CO 80218 303 839 6755 (phone), 303 832 5137 (fax).

References

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  2. Tockman MS, Anthonisen NR, Wright EC, et al: Airways obstruction and the risk for lung cancer. Ann Intern Med 1987;106:512.
  3. Sorlie P, Lakatos E, Kannel WB, et al: Influence of cigarette smoking on lung function at baseline and at follow-up in 14 years: The Framingham Study. J Chronic Dis 1987;40:849.
  4. Kannel WB, Brand FN: Can a routine lung function test warn of heart trouble? J Respir Dis 1984;5:39.
  5. Strachan DP: Ventilatory function as a predictor of fatal stroke. BMJ 1991;302:84.
  6. Rodriguez BL, Masaki M, Burchfiel C, et al: Pulmonary function decline and 17-year total mortality: The Honolulu Heart Program. Am J Epidemiol 1994;140:398.
  7. Singh GD, Matthews TJ, Clarke SC, et al: Annual summary of births, marriages, divorces, and deaths. United States, 1994. Monthly Vital Statistics Report Vol. 43, No. 13. Hyatsville, MD , National Center for Health Statistics, 1995.

     

  8. Morbidity and Mortality Chartbook on Cardiovascular, Lung, and Blood Diseases. Bethesda, MD, National Heart, Lung, and Blood Institute, May 1994.
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