The origin of FEV1 and the FEV1/FVC ratio

Over forty years ago when I started to learn about pulmonary function testing I was taught about the nuts and bolts of the tests, not where the tests came from or how they came into existence. Spirometry and the FVC, FEV1 and FEV1/FVC ratio have always appeared to be the core elements of pulmonary function testing and seemed most likely to have been scratched on the wall of the first paleolithic PFT lab cave. I have been reviewing a lot of older research papers lately, including several historical reviews, and was quite surprised to find out how recent both FEV1 and the FEV1/FVC ratio really are.

The first version of the modern spirometer (a counter-weighted volume displacement water seal spirometer) was developed by John Hutchinson in England around 1844. He performed vital capacity measurements on over 3000 people and in 1846 published a paper where he showed (among other things) the linear relationship of vital capacity to height. Different versions of Hutchinson’s spirometer were developed by other researchers in the following decades but even through the 1920’s the only measurement that was ever made with a spirometer remained just the vital capacity.

Wintrich_Spirometer_Fig_19_1854

Wintrich spirometer from 1854

Part of the reason for this has to do with the spirometers of that time. Spirometer bells were usually very heavy and required an equally heavy counterweight. The tubing and the mouthpiece leading into the spirometer was often quite narrow. The combined effects of inertia and resistance made these very poor instruments for measuring expiratory flow. These technology limitations however, also reflect the expectations at that time. Even though spirometers were often equipped with a kymograph drum (first one in 1866) and a lighter spirometer bell could have been made at almost any time the entire concept of measuring a timed vital capacity or of measuring expiratory flow was not on anybody’s horizon.

Fleisch_Pneumotrachograph_1925

Fleisch’s original pneumotachograph from 1925

The first instrument capable of measuring expiratory flow with any fidelity was the pneumotachograph which was developed in the mid-1920’s by Alfred Fleisch. This started to lay the ground work for an appreciation for the importance of expiratory flows and by the 1930’s some researchers had started to note that patients with emphysema took longer to blow their air out than patients with normal lungs. The length of time a patient took to blow out their vital capacity was even proposed as an index of lung disease but at that time the primary attention of most researchers and clinicians was on the Maximum Breathing Capacity (MBC) which was first described in 1933.

Numerous researchers performed the MBC test in both normal subjects and in patients with lung disease over the next several decades and were able to show that there was a relationship between a reduced MBC and lung disease. The range of published normal values for MBC was quite broad however, so one important side effect was that the ability of spirometers to accurately measure MBC (and expiratory flow rates) became important and the concept of spirometer frequency response became much better appreciated.

The MBC test was very strenuous (it was originally performed for 30 seconds) and clinicians were unhappy that most patients were unable to perform the more than a couple times and that training was usually required for the MBC to be performed correctly at all. There was also a certain recognition that a reduced MBC was relatively non-specific.

In 1947, a French researcher, Robert Tiffeneau published the first paper where the FEV1 (which he called the “capacité pulmonaire utilisable à l’effort” or CPUE) was proposed as a replacement for the MBC test. The choice of a 1 second period for a forced exhalation was to a large extent arbitrary and was based on Tiffeneau’s observation that during exercise patients breathed at around 30 breaths per minute so a 1-second maximal exhalation should be able to approximate a patient’s maximum exercise ventilation.

Tiffeneau’s work was not well known outside of France but in 1951 Edward Gaensler of Boston, Massachusetts published a much wider-read paper on the timed vital capacity and included the concept of expressing the FEV as a percentage of the FVC. Research continued on the MBC but an increasingly larger number of researchers began to study the timed vital capacity.

A number of forced vital capacity measurements were proposed during this time by various researchers and include the FEF200-1200 (mean expiratory flow between 0.2 and 1.2 L of the FVC), the FEF25-75 (AKA MMEF, which is the mean expiratory flow between 25% and 75% of the FVC), FEV 0.5 sec, FEV 0.75 sec, the FEV 2.0 and others. A variety of ways of describing the same measurements quickly developed and in 1956 the British Thoracic Society made its recommendations on terminology and the FEV1 and FEV1/FVC ratio as we know it came into being.

I’ve known that Hutchinson developed his spirometer in the 1840’s for quite a while and had always assumed that that the FEV1 and FEV1/FVC ratio dated from that period as well (I mean it’s obvious, isn’t it?) but when compared to diffusing capacity (Krogh, 1910) and lung volumes (Davy, 1800) they are relative newcomers.

As a footnote I will mention that even after the FEV1 became an accepted (and critical) component of the FVC it took a while for spirometer technology to truly catch up. When I started working in a Pulmonary Function lab in the early 1970’s with an almost brand-new testing system it was equipped with a counter-weighted water seal spirometer with a stainless steel bell. The kymograph pen was attached to the counterweight and I remember frequently seeing the chain between the bell and the counterweight go slack during the FVC maneuver. This meant the counterweight and more importantly, the kymograph pen, was not keeping up with the spirometer bell and that the FEV1 I was measuring on the graph paper was being underestimated. That lab didn’t get its first direct-recording spirometer (pen attached to the bell) or pneumotachograph until 1980.

References:

Freedman S. Assessment of airway obstruction. How the subject developed. Proc Royal Soc Med 1971; 64: 1229-1232.

Kingesepp PH. Alfred Fleisch (1892-1973): Professor of physiology at the University of Tartu, Estonia. J Med Biog 2011; 19(1): 34-37.

Yernault JC. The birth and development of the forced expiratory manoeuvre: a tribute to Robert Tiffeneau (1910-1961). Eur Resp J 1997; 10: 2704-2710.  

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