FEV6

FEV6 (the volume of air forcefully exhaled after 6 seconds) has been proposed as a replacement or surrogate for FVC in spirometry. Given that using FEV6 would simplify and speed up the spirometry test this is a seductive notion.

The use of an expired volume with a fixed expiratory time as a replacement for FVC was proposed at least 25 years ago, although at that time FEV7 was proposed as being slightly more accurate than FEV6. The first reference values for FEV6 however, were not available until the results from NHANESIII study were made available in 1999 and most studies of FEV6 post-date that.

Investigators have noted that FEV6 is less demanding than the FVC, particularly in the elderly or patients with obstructive disease. It has also been noted that the end-of-test is better defined with the FEV6 than it is with FVC and that there is a reduced possibility of syncope.

There is a fair amount of validity to the use of FEV6. FEV6 is more reproducible than FVC and a number of studies have shown that in most cases a reduced FEV1/FEV6 ratio can show airway obstruction as effectively as a reduced FEV1/FVC ratio. Use of FEV6 would simplify and reduce the amount of time that spirometry testing would take and for all these reasons a number of well-known investigators have advocated the use of FEV6. Despite this the adoption of FEV6 into routine clinical practice seems to be limited and I think there are some valid reasons for continuing to use FVC.

One reason I think that FEV6 has not made bigger inroads is partly psychological and that is because it is not the same as FVC. The vital capacity is the maximum amount of air that can possibly be exhaled whereas the FEV6 (or FEV1 or FEV3) is the amount of air that can be exhaled after a specified (and to some extent arbitrary) period of time. Although FEV6 is a useful substitute for FVC it does not reside in the same conceptual space and given the inherent conservatism in many of us this makes it difficult to think of it the same way.

The actual difference between predicted FVC and FEV6 increases with increasing age.

Graph 1 

This means that the FEV1/FEV6 does not decline as rapidly as the FEV1/FVC ratio as patients age.

Graph 2 

The difference between FEV6 and FVC also increases with increasing airway obstruction. When studies compared patients with reduced FEV1/FVC ratios and reduced FEV1/FEV6 ratios there was a high degree of overlap. However a certain fraction of patients have a reduced FEV1/FVC ratio but a FEV1/FEV6 ratio that is within normal limits. This means that the FEV1/FEV6 ratio is less sensitive than the FEV1/FVC ratio for detecting mild airway obstruction. It also means that a reduced FEV1/FEV6 ratio usually only exists when the FEV1 is also below the lower limits of normal.

One goal of spirometry, particularly office spirometry, is to detect airway obstruction when it is in its early stages because early intervention can reduce the long-term severity of lung disease. In this sense the FEV1/FEV6 ratio is not as sensitive as the FEV1/FVC ratio. Having said this, obtaining a quality FVC measurement can be difficult and for office spirometry the FEV1/FEV6 ratio does at least provide a clear signal.

As well as airway obstruction spirometry results are also used to assess possible restriction. For this reason a reduced FVC (with a normal FEV1/FVC ratio) is often used as an indication of a reduced TLC. At first glance it might be thought that FEV6 would be a poorer predictor of restrictive lung disease but it turns out that a reduced FVC and a reduced FEV6 are equally poor predictors of a low TLC. Regardless of the algorithm used, a reduced FVC or a reduced FEV6 (with normal or elevated FEV1/FVC and FEV1/FEV6 ratios) have only about a 50% probability of being associated with a reduced TLC. On the other hand, a normal FVC and a normal FEV6 are equally effective in ruling out restriction.

On the plus side FEV6 is more reproducible and easier to obtain than a FVC. On the minus side the FEV1/FEV6 ratio is not as sensitive an indicator of airway obstruction as the FEV1/FVC ratio. Strictly speaking, however, there is no particular reason that a place can’t be found for both the FEV6 and the FVC.

Obtaining a true, ATS-ERS standard FVC is often difficult with the elderly or patients with obstructive lung disease largely because they will require a prolonged exhalation time. Obtaining a quality FVC and FEV1/FVC ratio is likely most important during an initial visit when an accurate diagnosis is most important. Once airway obstruction has been detected however, there is no reason that a patient cannot be monitored using the FEV6 and the FEV1/FEV6 ratio during follow-up visits. For this reason my recommendation would be to include both the FEV1/FVC ratio and FEV1/FEV6 ratio on spirometry reports and for the physician reviewing the tests to switch back and forth between these ratios based on circumstances.

References:

Akpinar-Elci M, Fedan KB, Enright PL. FEV6 as a surrogate for FVC in detecting airways obstruction and restriction in the workplace. Eur Respir J 2006; 27: 374-377.

Belia V, Sorino C, Catalano F, Augugliaro G, Scichilone N, Pistelli R, Pedone C, Antonelli-Incalzi R. Validation of FEV6 in the elderly: correlates of performance and repeatability. Thorax 2008; 63: 60-66.

Ferguson GT, Enright PL, Buist AS, Higgins MA. Office spirometry for lung health assessment in adults: Consensus statement for the National Lung Health Education Program. Chest 2000; 117: 1146-1161.

Glindmeyer HW, Jones RN, Barkman HW, Weill H. Spirometry: Quantitative test criteria and test acceptability. Am Rev Respir Dis 1987; 136: 449-452.

Hankinson JL, Odencrantz JR, Fedan KB. Spirometric reference values from a sample of the general U.S. Population. Am J Respir Crit Care Med 1999; 159: 179-187.

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Hansen JE, Sun X-G, Wasserman K. Should forced expiratory volume in six seconds replace forced vital capacity to detect airway obstruction? Eur Resp J 2006; 27: 1244-1250.

Jing JY, Huang TC, Cui W, Xu F, Shen HS. Should FEV1/FEV6 replace FEV1/FVC ratio to detect airway obstruction. Chest 2009; 135: 991-998.

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Swanney MP. Jensen RL, Crichton DA, Beckert LE, Cardino LA, Crapo RO. FEV6 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.

Swanney MP, Beckert LE, Frampton CM, Wallace LA, Jensen RL, Crapo RO. Validity of the American Thoracic Society and other spirometric algorithms using FVC and Forced Expired Volume at 6s for predicting a reduced Total Lung Capacity. Chest 2004; 126: 1861-1866.

Vandervoorde J, Verbanck S, Schueermans D, Kartounian J, Vincken W. FEV1/FEV6 and FEV6 as an alternative for FEV1/FVC and FVC in the spirometric detection of airway obstruction and restriction. Chest 2005; 127: 1560-1564.

Vandevoorde J, Verbanck S, Schuermans D, Kartounian J, Vincken W. Obstructive and restrictive spirometric patterns: fixed cut-offs for FEV1/FEV6 and FEV6. Eur Respir J 2006; 27: 378-383. 

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