Pulmonary Q&A

On Inspiration and Expiration
THOMAS I. PETTY, MD-Series
Editor University of Colorado

Spirometry: A Key Tool for Every Office Q. How critical—and cost-effective—is in-office . pulmonary function equipment for the primary care practitioner?

A . It is time for the spirometer to take its rightful place alongside the stethoscope, ophthalmoscope, sphygmomanometer, and electrocardiograph. The spirometer is at least as important as any of these other instruments, because spirometric abnormalities are associated with all-cause mortality and indicate an elevated risk of lung cancer, myocardial infarction, and stroke.1 Currently, only about 30% of primary care clinicians use spirometers in their offices; most refer selected patients to pulmonary function laboratories.

Spirometry plays a key role in the workup of dyspnea and chronic cough. Its importance is comparable to that of electrocardiography in a patient with chest pain; unlike electrocardiography, however, Spirometry can identify occult disease in asymptomatic patients. It can detect obstructive lung diseases, such as asthma and chronic obstructive pul- monary disease (COPD), and restrictive lung diseases, such as sarcoidosis and congestive heart failure. Spirometric monitoring is essential—particularly in asthma and COPD—for determining if maximum therapeutic benefit is being achieved and for guiding dosage adjustments.

Keeping it simple. Factors that have delayed the widespread adoption of Spirometry in the primary care office include misinformation about its complexity and costs. Spirometry simply measures the volume of air expired with maximum force after a full inspiratory effort (forced vital capacity [FVC]) and the expiratory flow rate.

Only 2 values are needed in the evaluation—the forced expiratory volume in 1 second (FEV1 [the flow test]) and the FVC (the volume test)—and their ratio. The normal FEV1FVC ratio is greater than 70%. A lower ratio indicates an obstructive disease. Ratios of 85% or more strongly suggest a restrictive disease or ventilatory defect. Because normal lungs empty in 6 seconds or less, the forced expiratory volume in 6 seconds is an excellent surrogate for the FVC and is now the recommended standard.23

Unfortunately, the other "parameters" that engineers have so enthusiastically added to devices that use flow transducers—such as the midexpiratory phase of the forced expiratory flow (FEFgg,25%,75%) and other values—only serve to confuse. These numbers have no special mean- ing and should be removed from spirometers and test reports.

Spreading the word. The aim of the National Lung Health Education Program (NLHEP) is to encourage prima- ry care physicians to use office Spirometry for diagnosis and management of COPD and other diseases. The NLHEP recommends simple 2-parameter office spirometric testing for all smokers and former smokers 45 years or older and for persons who have dyspnea on exertion, chronic cough, mucus hypersecretion, or wheeze.4

In response to requests from the NLHEP, several manufacturers have produced simple, accurate, an^""^- able spirometers that cost less than $1000. Less excessive devices are being developed. Established billing codes are used for reimbursement.

REFERENCES:

1. Petty TL Simple office Spirometry. Clin Chest Med. 2001;22:845-859.

2. Hankinson JL, Odencrantz JR, Fedan KB. Spirometric reference values from a sample of the general US population. AmJResfiir Crit Care Med. 1999;159:179-187.

3. Swanney MR Jensen RL, Crichton DA, et al. FEVg is an acceptable surrogate for FVC in the spirometric diagnosis of airway obstruction and restriction. Am J Respir Crit Care Med. 2000;162:917-919.

4. Ferguson GT, Enright PL, Buist AS, et al. Office Spirometry for lung health assessment in adults. A consensus statement from the National Lung Health Educa- tion Program. Chest. 2000:117:1146-1161.