Introduction

Spirometry is the measurement of the volume and flow of air in and out of the lungs. Currently, spirometers can measure lung volumes, such as tidal volume, and lung capacities, such as total lung capacity (see figure 1). Lung function tests date back many centuries, and while the basic principles haven’t changed, the techniques have become more complex and scientists have been able to measure a growing number of variables. Contributions over the years have ranged from determinations of measurements of maximal lung volumes to inventions of new equipment.

Contributions before the 19 th century

The earliest known history of the concept of spirometry goes back to the time of the Roman Empire, specifically between 129-200 AD. Greek doctor and philosopher, Claudius Galen, performed a volumetric experiment on human ventilation. He had a boy breathe in and out of a bladder and discovered that after a period of time, the volume of gas did not change [1].

After this experiment, not much is known about lung function tests until after the 1600’s. Around 1681, Giovanni Alfonso Borelli attempted to measure the volume of air inspired in one breath by sucking a liquid up a tube and measuring its volume [1]. One thing he did that is still performed today is block off the nostrils. Occlusion of the nostrils is important to make sure that no air escapes through the nose while trying to measure the air that enters and leaves the mouth in order to have accurate results.

During the early 1700’s, J. Jurin was the first known scientist to record absolute measurements of air volumes. He measured a tidal volume of 650 mL and also a maximal expiration of 3610 mL. Jurin performed his experiment by blowing into a bladder, and, by following the principles of Archimedes, he was able to measure the air volume in the bladder [1].

During the first half of the 18 th century, Stephen Hales confirmed Jurin’s findings of a maximal expiration of 3610 mL, although it is not known which method he used to take his measurements [1]. According to West [2], Stephen Hales “made many contributions to respiratory physiology” (p. 635), including:

He clarified the nature of the respiratory gases, distinguishing between their free (gaseous) and fixed (chemically combined) forms… demonstrated that rebreathing from a closed circuit could be extended if suitable gas absorbers were included … invented the pneumatic trough for collecting gases… measured the size of the alveoli… calculated the surface area of the interior of the lung… calculated the time spent by the blood in a pulmonary capillary… invented the U-tube manometer… and measured intrathoracic pressures during normal and forced breathing. (p. 635-639)

In addition, Hales is well known for his meticulous measurements and attention to details [2]. This is obviously very important in the determination of the correct absolute measurements of lung volumes and capacities.

John Abernethy, a doctor and teacher of anatomy, physiology and pathology during the late 1700’s, measured a vital capacity of 3150 mL [3]. He collected expired gases over mercury and tried to determine by how much those expired gases had been depleted of oxygen [1]. This concept of depletion of oxygen is essential to understanding lung function and spirometry in that air exhaled will always contain less oxygen than the air inhaled into the lungs because the body needs to utilize the oxygen in order to function.

Contributions during the 19th century

At the beginning of the 1800’s, Sir Humphry Davy used a gasometer (see figure 2) to measure various volumes and capacities. He took his own measurements, which turned out to be a vital capacity of 3110 mL, a tidal volume of 210 mL, and, using a hydrogen dilution method, a residual volume of 590-600 mL [1]. The gasometer he used was “a complex instrument with an ingenious counterweight used to balance the increased weight of the gasometer when the gas enters from the silk bag... [He] would have used the bag to collect expired air” [4]. In addition to making estimates of his own lung volumes and capacities, Davy also “may have been the first person to make successful estimates of his own oxygen consumption and carbon dioxide production”:

Over a series of 20 experiments, he collected his expired air for 1 min. He measured its oxygen and carbon dioxide content, and compared this with the contents of the air that he breathed in… He estimated that his oxygen consumption was 484 ml/min and his carbon dioxide production was 447 ml/min [4].

Davy’s measurements of oxygen consumption and carbon dioxide production are a huge contribution to spirometry because doctors and exercise physiologists rely heavily on them. VO 2, or oxygen consumption, is definitely one of the most important measurements used in exercise physiology because it is an indirect yet very accurate measure of energy expenditure within the body.

Another type of instrument used in the development of spirometry was a “pulmometer.” This piece of equipment was used by both E. Kentish and Charles Turner Thackrah [1]. According to Cleeland and Burt [5], this device was a jar inverted in water used to measure ventilatory volumes. The problem with the pulmometer was that it couldn’t correct for pressure, so the machine not only measured respiratory volumes, but also the power of the expiratory muscles.

An “expirator” (see figure 3) was yet another device, used by Karl von Vierordt in the 1840’s. Vierordt’s focus was on exhaled gases, and through his experiments he was able to come up with very exact determinations of certain volumetric parameters. These parameters, including residual volume and vital capacity, are still used today in modern spirometry [1].

Invention of the spirometer

By the 1840’s, John Hutchinson, a surgeon, had begun his work with spirometers. He invented the spirometer (see figure 4) to measure vital capacity, which he believed to be a powerful indicator of longevity. His spirometer consisted of a calibrated bell inverted in water, which captured exhaled air from the lungs [6]. According to Eckert, “ Hutchinson recorded the vital capacities of over 4000 persons with his spirometer. He classified the persons for example as 'Paupers', 'First Battalion Grenadier Guards', 'Pugilists and Wrestlers', 'Giants and Dwarfs', 'Girls', 'Gentleman', 'Deceased cases'” [1]. This indicates that Hutchinson knew how vital capacity was linked to health. More specifically, “it is useful in identifying patients at risk for many diseases, including chronic obstructive pulmonary disease, lung cancer, heart attack, and stroke” [6]. Hutchinson’s water spirometer is still used today with few alterations, which include the reduction of the mass of the bell and the addition of graphic and timing devices [1].

Modifications of the spirometer

Less than ten years after Hutchinson came out with his spirometer, Wintrich developed a spirometer (see figure 5) that was easier to use. He performed tests on over 4000 people and concluded that the three parameters that determine vital capacity are body height, weight, and age [1].

In 1859, E. Smith developed a portable spirometer, on which he measured gas metabolism. In 1866, Salter added a kymograph to the spirometer in order to record time while obtaining air volumes. T.G. Brodie was the first to use a dry bellow wedge spirometer in 1902, which is the precursor of the Fleisch spirometer used today. Additionally, in 1904, Tissot introduced the closed-circuit spirometer [1].

In the 1920’s, H.W. Knipping and Brauer introduced ergospirometry, which allowed for the testing of performance, instead of just taking all measurements at rest. This was possible due to the development of an ergometer by C. Speck [1]. According to Hollmann and Valentin [7]:

Ergospirometric methods have a certain importance today in research, diagnosis, therapy, rehabilitation, training and sport. Medical special disciplines such as sports medicine, pulmonology, cardiology, occupational medicine, social medicine and physiology of performance and also the fields of biomechanics, clinical pharmacology and biochemistry make use of ergospirometry and owe much new knowledge to it. (p.169)

This concept of measuring lung capacities during physical activity was a huge breakthrough in the scientific world, and it is still used today. It allows exercise physiologists to measure oxygen consumption and energy expenditure during exercise, and therefore gain much information about the fitness and health levels of the individuals performing the tests.

Modern spirometry

Spirometry falls under the broader concept of calorimetry. Calorimetry is the accurate quantification of energy expenditure during rest and physical activity. There are two different methods of measuring calorimetry: directly or indirectly. Direct calorimetry is the assessment of the body’s metabolic rate by direct measurement of the amount of heat produced. Indirect calorimetry is the estimation of heat or energy production based on oxygen consumption, carbon dioxide production, and nitrogen secretion. Two applications of indirect calorimetry are closed-circuit spirometry and open-circuit Spirometry [8].

In closed-circuit spirometry, the individual breathes into a pre-filled container and the exhaled air passes through a canister of soda lime. The soda lime absorbs the carbon dioxide and the oxygen passes back into the oxygen container. A recording drum measures the oxygen removed, which correlates to the amount of oxygen consumed by the individual. This method of spirometry is quite restrictive during physical activity, but is still used in hospitals and labs today [8]. One example of an experiment that used closed-circuit spirometry was that of González-Arévalo et al. [9]. They compared a c losed-circuit PhysioFlex anesthesia machine and the Deltatrac II indirect calorimeter and found that “ the measurement of O 2 consumption obtained with the PhysioFlex anesthesia machine is interchangeable with that obtained by indirect calorimetry” (p. 1680).

Open-circuit spirometry is useful for measuring energy expenditure during physical activity, and three common methods include portable spirometry, bag technique, and computerized instrumentation. In open-circuit spirometry, the individual breathes in ambient air and the exhaled air exits only through a gas meter, which is measured and analyzed. Portable spirometry requires the individual to carry the apparatus similar to a backpack. Expired air passes through a gas meter, which analyzes the air and takes a sample of the ambient air also. Measurements taken will be used to determine oxygen consumption. The bag technique consists of the individual expiring air into a plastic or canvas bag or into a rubber balloon. Like portable spirometry, a meter takes a sample of the ambient air to use when analyzing and determining oxygen consumption. The instruments used in computerized instrumentation include “a system to continuously sample the subject’s expired air, a flow-measuring device to record air volume breathed, and oxygen and carbon dioxide analyzers to measure the expired gas mixture’s composition” [8].

A study performed by Bigoni et al. [10] used a portable ergospirometer, specifically a Metamax 3B Cortex Biophysik, to measure peak oxygen consumption during stress tests. Basset et al.[11] performed an experiment comparing the Douglas bag technique and a computerized system, and found that “a computerized system, using inspiratory or expiratory configurations, permits extremely precise measurements to be made in a less time-consuming manner than the DB technique” (p. 218). Some other spirometers used in past tests have included a computerized Fleisch pneumotachygraphic spirometer [12] and Vitalograph and Jaeger spirometers [13].

Since there really is no “gold standard” for spirometry, all of the above techniques are still used today. All of the techniques are considered accurate, and while there are at times minor discrepancies between different techniques, the differences are not widespread enough to deem a specific technique inaccurate. It appears that the choices for spirometers depend more on what the researchers prefer and on what type of activity the subjects will be performing rather than on the accuracy of the techniques.

Conclusion

This history of spirometry consists of various researchers, concepts, and equipment. It began in the 2 nd century with simple measurements of ventilatory volumes. It progressed through time into more complex measurement of lung functions using a variety of techniques and devices. Now, after years of experiments, it is an extremely accurate way to measure energy expenditure, based on the following simple equation: VO 2 = [volume of O 2 inspired] – [volume of O 2 expired] [14].