What does it mean if your FEV1 is low?

Forced Expiratory Volume Over Time.

The FEV1 is the measurement of dynamic volume most often used in conjunction with the FVC in analysis of spirometry (Fig. 25-4). The measurement incorporates the early, effort-dependent portion of the curve and enough of the midportion to make it reproducible and sensitive for clinical purposes. Forced expiratory volume (FEV) measurements taken at 0.5, 0.75, 2.0, and 3.0 seconds add little information to the FEV1 measurement. The forced expiratory volume exhaled in 6 seconds (FEV6) is useful, however, because it closely approximates FVC, has been shown to be a valid alternative to the conventional FEV1/FVC, and is easier for patients with severe airflow obstruction to attain.14 In addition, the end of the test is more clearly defined, permitting more reliable correspondence between measured and referenced values.15 Furthermore, as demonstrated by Swanney and associates,15 the degree of airflow obstruction, reflected in the FEV1/ FEV6 obtained from spirometry, can serve as an independent predictor of subsequent decline in lung function; it may therefore be used to detect smokers at higher risk for developing chronic obstructive pulmonary disease (COPD).15

1.3.4 Forced Expiratory Volume 6

Forced Expiratory Volume after 6 seconds (FEV6) is one of the spirometry parameter. According to GOLD guidelines, FEV1/FVC and %FEV1 denote the COPD severity. Swanney et al. (2000) analyzed the ratio FEV1 and FEV6 in obstructive respiratory disease. They suggested FEV6 is better in terms of accuracy, less physically demanding and reproducible. Bhatt et al. (2014) compared the ratio of FEV1 and FEV6 with the ratio of FEV1 and FVC in COPD diagnosis. It is concluded that; FEV1/FEV6 could be substituted to FEV1/FVC and predict COPD better. Vandevoorde, Verbanck, Schuermans, Kartounian, and Vincken (2006) has determined the static cut-off values for FEV1/FEV6 as an alternative tool for existing spirometry methods. Limitations of COPD diagnosis using FEV6 are: it overdiagnoses the restrictive patterns in elderly subjects in addition it carries all limitations of spirometry. The altered respiratory dynamics put the subject at a mechanical difficulty which eventually leads to the development of symptoms of COPD. FEV6, IOS, and FOT give good results for COPD diagnosis. However, these methods are unable to consider the respiratory dynamics and hence have restricted use.

New techniques like IOS and FOT, provides information related to the resistive properties of the respiratory system throughout silent breathing. Brashier and Salvi (2015) observes that; in asthmatic patients, IOS and spirometry results show a good correlation. IOS and FOT methods are new technologies. Kolsum et al. (2009) stated that; as of now, these methods lack definitive predictive equations, are nonportable, costly and cannot be used as a point of care modality. Spirometry, IOS, and FOT don’t consider respiratory dynamics, and places the respiratory system at a mechanical difficulty which progress towards COPD.

In COPD, respiratory muscles play an essential role. The survey is conducted to find the significance of the respiratory muscles in COPD. Many researchers have also studied COPD using respiratory muscles. Researchers have studied activations of Parasternal, Intercostal, Diaphragm, Sternomastoid and Abdominal muscles in COPD. Muscles can be analyzed using Electromyography (EMG), Vibromyography (VMG), and tissue oxygen saturation. There is a need for extra hardware for muscle analysis using VMG and tissue oxygen saturation, while EMG machine is readily available in hospitals. Muscle analysis using EMG reduces the need for additional equipment and also leads to the COPD diagnosis. Table 1.2 compares the recent trends in COPD diagnosis.

Table 1.2. Review of literature survey finding gaps between existing technology.

TechniqueMethodologyAdvantagesCOPD gradeLimitationsSpirometryMeasures the flow of air to and from lungs during respirationWell known recommended by GOLDYesTough to execute with critically ill patients, subjective, slow, leads to the progression of symptoms of COPD.FOTObserve the flow response of the respiratory system by passing external pressure signalsA significant correlation between spirometryYesCostly, nonportable, different results for the same pathophysiological event.IOSSound waves are superimposed on the normal breathingSimple tidal breathing, less cooperation, effort independentYesCostly, nonportable, steep theoretical background and upcoming technologiesFEV6Force expiratory volume after 6 secondFEV6 is more repeatable, small physical demands compare to spirometryYesTough to execute with critically ill patients, over diagnosis in elderly patients.EMGRespiratory muscle analysisEasy to use, noninvasiveNoLimited features, stationary analysis, and small data set.

Fig. 1.10 shows the flow of literature survey leading to the identification of EMG analysis technology for the diagnosis of COPD.

Spirometry (FEV6) is difficult to perform and time-consuming. IOS and FOT are upcoming technologies and has a steep theoretical background. Thus, development of an easy to perform and physiologically accurate method to assess pulmonary mechanics is needed in COPD patients. The surface EMG technique is noninvasive, doesn’t require insertion of needle and analyses the muscle conditions effectively. EMG is easy to use and the hardware required is already available in hospitals. Therefore, by studying the gaps and limitations of existing methods, the EMG analysis technique has been selected for this research in the diagnosis of COPD. Surface EMG analysis of respiratory muscles can lead to useful technique for the analysis of respiratory mechanics in COPD.

Predicted Postoperative Forced Expiratory Volume in 1 Second

ppoFEV1, which is estimated on the basis of the number of functioning, nonobstructed segments to be removed during an operation, traditionally has been used to stratify respiratory risk in candidates for lung resection. The following equations can be applied to estimate the residual lung function.

For candidates for pneumonectomy, the perfusion method is used with the following formula:

ppoFEV1=preoperativeFEV1×(1−fractionoftotalperfusionfortheresectedlung)

A quantitative radionuclide perfusion scan is performed to measure the fraction of total perfusion for the resected lung. For candidates for lobectomy, the anatomic method is used with the following formula:

ppoFEV1=preoperativeFEV1×(1-a/b)

The number of functional or unobstructed lung segments to be removed is represented by a, and the total number of functional segments is represented by b.22

The findings of bronchoscopy and computerized tomographic scanning should be used to assess and estimate the patency of the bronchus and segmental structure.

Many studies have investigated the role of ppoFEV1 in predicting postoperative complications and in selecting patients for surgery. Olsen et al.23 were the first to suggest a safety threshold value of 0.8 L as the lower limit for surgical resection. However, Pate et al.24 found that patients with a mean ppoFEV1 of as low as 0.7 L tolerated thoracotomy for the resection of lung cancer. The main limitation of those early studies is that they used an absolute value of ppoFEV1. This method might prevent older patients, patients of small stature, and female patients, all of whom might tolerate a lower absolute FEV1, from having a potentially curative resection for the management of lung cancer.

Markos et al.25 were the first to propose using a percentage of the predicted value as the cutoff value. They found that half of the patients with a ppoFEV1 of less than 40% of the predicted value died in the perioperative period. Other authors confirmed that perioperative risk increases substantially when the ppoFEV1 is less than 40% of the predicted normal value.26-32 The predictive role of ppoFEV1 recently was challenged in investigations that showed an acceptable mortality rate among patients with prohibitive FEV1 or ppoFEV1 values who underwent lung resection.33,34

Alam et al.35 demonstrated that the odds ratio for the development of postoperative respiratory complications increased as the ppoFEV1 and ppoDLCO decreased (with a 10% increase in the risk of complications for every 5% decrease in predicted postoperative lung function). Brunelli et al.33 showed that ppoFEV1 was not associated with an increased risk of complications in those with FEV1 less than 70%.

These findings may be partly explained by the so-called lobar volume reduction effect, which can reduce functional loss in patients with airflow limitations. In candidates for lobectomy with lung cancer and moderate-to-severe COPD, resection of the most affected parenchyma may determine an actual improvement in the elastic recoil, a reduction of the airflow resistance, and an improvement in pulmonary mechanics and ventilation–perfusion matching, similar to what happens in typical candidates for lung volume reduction surgery with end-stage heterogeneous emphysema.

In this regard, many studies already have shown the minimal loss or even improvement of pulmonary function after lobectomy in patients with obstruction, calling into question the traditional operability criteria that are primarily based on pulmonary parameters.36–43

Brunelli et al.42 recently found that patients with COPD had significantly lower losses of FEV1 and DLCO compared with patients without COPD at 3 months after lobectomy for the management of lung cancer (8% compared with 16% and 3% compared with 12%, respectively). In that series, 27% of patients with COPD actually had improvement in FEV1 and 34% had improvement in DLCO at 3 months after the operation.

This lobar volume reduction effect takes place very early after lung resection. In fact, 17% of patients with airflow limitation who undergo pulmonary lobectomy actually may have improvement in FEV1 at the time of discharge as compared with preoperative measurement.44

The early lobar volume reduction effect was confirmed by Varela et al.45 who showed that the percentage loss of FEV1 on the first postoperative day after lobectomy was lower in patients with a higher degree of COPD. These findings indicate that ppoFEV1 may not work properly in patients with obstructive disease and cannot be used alone to select patients for surgery, especially those with limited pulmonary function.

Although many studies have shown that ppoFEV1 is fairly accurate for predicting the definitive residual FEV1 at 3 months to 6 months after surgery, Varela et al.46 recently demonstrated that it substantially overestimates the actual FEV1 in the first postoperative days, when most complications occur. On the first postoperative day, the actual FEV1 was measured to be about 30% lower than predicted.46 This finding may have serious clinical implications whenever ppoFEV1 is used for patient selection and risk stratification before surgery.

Restrictive Versus Obstructive Patterns and Disorders

The FEV1 to FVC ratio is particularly useful in distinguishing restrictive from obstructive patterns on pulmonary function tests (Table 13-1). These patterns correlate with primary pulmonary obstructive and restrictive diseases, but restrictive patterns may also point toward other extrapulmonary processes, such as respiratory muscle weakness or kyphoscoliosis.

Normal patients usually have an FEV1 and FVC that are at least 80% of the predicted values obtained from a normal population, and normal subjects can usually expire 80% of their FVC in 1 second. The FEV1 to FVC ratio normally is 0.70 or greater. With restrictive disorders, there is a decrease in both the VC and air flow because of limitations in lung and chest wall expansion, for example, from pulmonary fibrosis, vascular disease, mass lesions compressing the pulmonary space, kyphoscoliosis, or ankylosing spondylitis. Moderate to severe respiratory muscle weakness is another important cause of a restrictive pattern. In restrictive disorders, the FVC and FEV1 are symmetrically reduced (Fig. 13-3). With respiratory muscle weakness, the FVC also may be significantly lower in the supine position than in the upright position. In some primary restrictive pulmonary diseases associated with increased lung recoil, the FEV1 may actually be elevated. Thus, the FEV1 to FVC ratio generally remains greater than 0.70 in all restrictive disorders. In addition, other lung volumes, including total lung capacity, RV, and FRC, are low in most restrictive disorders. Descending to the RV depends on expiratory muscle strength, so that it may be higher in some patients with neuromuscular disease than in the usual restrictive pattern.

In obstructive disorders in which air expulsion is impeded, the FEV1 is significantly reduced whereas the FVC is preserved or mildly reduced (Fig. 13-3). Therefore, the FEV1 to FVC ratio is less than 70%. In addition, obstructive diseases of pulmonary origin, (e.g., chronic bronchitis) usually are associated with a high RV or FRC. Patients with neuromuscular diseases usually do not manifest this obstructive pattern unless there is an associated pulmonary disease.

Spirometry

Spirometry (FEV1, forced vital capacity [FVC], and FEV1/FVC) should be performed in a non‐acute setting before and after bronchodilator administration. An FEV1 less than 80% of predicted, and an FEV1/FVC ratio of less than 65% are consistent with airway obstruction. Reversibility is present if there is at least a 12% and 200 mL increase in the FEV1. If reversibility is not demonstrated initially, a trial of corticosteroids may be administered, and the test repeated in 2 to 3 weeks.

Spirometry with methacholine (or histamine) challenge may be performed in patients with atypical presentations of asthma, such as isolated cough, or exercise‐induced symptoms. Spirometry is measured at baseline and after nebulized saline. If there is no change in the FEV1, methacholine is administered in increasing doses until either a 20% decrease in FEV1 is noted (positive test) or the highest concentration of methacholine is reached (negative test). Although a positive test is not specific for asthma, a negative test rules out asthma with approximately 95% certainty.

Patients with a history highly suggestive of asthma but negative spirometry testing should be evaluated with either serial spirometry (due to intermittent or diurnal symptoms) or provocation testing.

Spirometry should be repeated every 1 to 2 years to establish new baselines as the disease progresses.

Interpretation of Challenge Studies

Serial measurements of FEV1 over the first 30 minutes after exercise or EVH is used to determine whether the test is positive and to quantify the severity of bronchoconstriction.108 In most cases the nadir in FEV1 occurs within 5 to 10 minutes of cessation of exercise, but occasionally is not reached until 30 minutes.109 The presence of EIB is defined by plotting FEV1 as a percent decline from the preexercise baseline FEV1 at each postexercise interval. Some accept a decrease of 10% or greater from baseline FEV1 as an abnormal response,109-111 but the specificity is higher with a criterion of 15% from baseline. The basis of these recommendations are three studies in normal children that demonstrate an upper 95% confidence limit of the FEV1 fall as 8.2%, 10%, and 15.3%.112,113 A method to quantify the overall severity of EIB is to measure the area under the curve (AUC) for time multiplied by the percent fall in FEV1.

AGING, FORCED EXPIRATORY VOLUMES, AND PEAK FLOW: IMPLICATIONS FOR COUGHING AND CLEARANCE OF AIRWAY SECRETIONS

Forced expiratory volumes and peak expiratory flow show an age-related linear decrease, probable reflecting structural changes, and chronic low-grade inflammation in peripheral airways (Enright et al., 1993). Indeed, for a male subject with a height of 180 cm, between the ages of 25 and 75, forced expiratory volume in 1 sec (FEV1) drops by 32%, forced vital capacity (FVC), by 24%, and peak expiratory flow (PEF), by 22% (Quanjer et al., 1993). In the very old, both the decrease in forced expiratory flow rates and in lung elastic recoil may compromise the efficacy of clearing airway secretions by coughing. Critical values for PEF have been reported, under which the risk of pneumonia markedly increases (Tzeng et al., 2000). In patients with neuromuscular disorders, a PEF below 270 L/min is associated with an increase in risk of pulmonary infection, and at PEF values < 160 L/min, cough is ineffective for clearing secretions from the airways (predicted PEF for an 80-year-old woman, measuring 160 cm, is 300 L/min). Coughing requires a precise coordination of laryngeal and respiratory muscle function: after a rapid inspiration, airways are submitted to a compression phase in which active glottic closure and abdominal contraction are critical, before the “explosive” expiratory phase. A decrease in expiratory muscle strength may thus compromise the efficacy of the cough reflex. The efficacy of glottic closure depends on the integrity of laryngeal muscle function and complex integrated reflexes that may be altered in the elderly by transient or permanent neurological disorders (cerebro-vascular disorders, extra-pyramidal, or cerebellar disorders). Indeed, ischemic stroke increases markedly the risk of pneumonia: in a large series of 13440 patients, pneumonia was the most frequent and serious complication, causing 31% of all deaths (Heuschmann et al., 2004). Glottal gap related to unilateral vocal cord paralysis is a potentially reversible sequel of acute cerebro-vascular events that may also increase the risk and frequency of aspiration (Fang et al., 2004).

Mucociliary clearance (progression of mucus layer lining the tracheal and bronchial epithelium) is also affected by the aging process. Even in the healthy nonsmoking aged population, mucociliary clearance rates are slowed in comparison with the young. Nasal mucociliary clearance and frequency of mucosal ciliary beat are decreased in older subjects; aging also is associated with ultrastructural changes in microtubules of ciliae of the respiratory epithelium. Indeed, both smoking and nonsmoking elderly have reduced tracheal mucus velocity compared with younger individuals (Ho et al., 2001). Dehydration, frequent in older debilitated subjects, may further compromise mucociliary clearance.

28.5.4.3 Small Airways

FEV1 and PEF measurements reflect changes in the caliber of the large airways. Our knowledge of anatomical and physiological changes in the small airways of patients with asthma is based on small case series of resected lung tissue from patients with asthma undergoing surgery for cancer, or on cases of fatal asthma.

These case series have demonstrated that there is significant inflammation present in the small airways (<2 mm diameter) in asthma. Fatal asthma is associated with peripheral airway inflammation and differences in the number of activated eosinophils in the distal lung. Other studies have revealed alterations in the epithelium and smooth-muscle, as well as mucous hypersecretion and distal airway plugging of the small airways. The presence of inflammation in the small airways in asthma may explain why small airways account for up to 50–90% of total airflow resistance in asthma, but only 10% of airflow resistance in normal airways.

Recently, the development of “small-particle” ICS, designed to target the peripheral lung, and the advent of new technologies—nitrogen washout, impulse oscillometry, and hyperpolarized noble gas magnetic resonance imaging, which allows assessment of peripheral lung function—have led to a resurgence of interest in the distal lung. Studies of small-particle ICS have been inconsistent; those comparing small-particle and standard-particle ICSs have failed to demonstrate improved asthma outcomes when administered in clinically comparable doses. Future asthma treatment may yet be stratified by the presence or absence of small airway inflammation.

What diseases would have a low FEV1?

What is FEV1 and what does it tell you about a patient?

What is an abnormal FEV1?

Can FEV1 be improved?