Apparatus for measuring air volume inspired and expired by the lungs
Spirometer
Spirometer test
Purpose
measuring the volume of air inspired and expired by the lungs
A spirometer is an apparatus for measuring the volume of air inspired and expired by the lungs. A spirometer measures ventilation, the movement of air into and out of the lungs. The spirogram will identify two different types of abnormal ventilation patterns, obstructive and restrictive. There are various types of spirometers that use a number of different methods for measurement (pressure transducers, ultrasonic, water gauge).
A spirometer is the main piece of equipment used for basic Pulmonary Function Tests (PFTs). Lung diseases such as asthma, bronchitis, and emphysema may be ruled out from the tests. In addition, a spirometer often is used for finding the cause of shortness of breath, assessing the effect of contaminants on lung function, the effect of medication, and evaluating progress for disease treatment.[1]
A simple float spirometer being used in a high school science demonstration
Early development
The earliest attempt to measure lung volume can be dated back to the period A.D. 129–200. Claudius Galen, a Roman physician and philosopher, did a volumetric experiment on human ventilation. He had a child breathe in and out of a bladder and found that the volume did not change. The experiment proved inconclusive.[2]
1681, Borelli tried to measure the volume of air inspired in one breath. He assembled a cylindrical tube partially filled with water, with an open water source entering the bottom of the cylinder. He occluded his nostrils, inhaled through an outlet at the top of the cylinder and measured the volume of air displaced by water. Nowadays, this technique is very important in determining parameters of lung volume.[2]
Nineteenth century
1813, Kentish, E. used a simple "Pulmometer" to study the effect of diseases on pulmonary lung volume. He used an inverted graduated bell jar standing in water, with an outlet at the top of the bell jar controlled by a tap. The volume of air was measured in units of pints.[2]
1831, Thackrah, C. T. described a "Pulmometer" similar to that of Kentish. He portrayed the device as a bell jar with an opening for the air to enter from below. There was no correction for pressure. Therefore, the spirometer not only measured the respiratory volume, but also the strength of the respiratory muscles.[2]
1845, Vierordt in his book entitled "Physiologie des Athmens mit besonderer Rücksicht auf die Auscheidung der Kohlensäure" discussed his interest in measuring the volume of expiration accurately. He also completed accurate measures of other volume parameters by using his "Expirator". Some of the parameters he described are used today, including residual volume and vital capacity.[2]
1846 The water spirometer measuring vital capacity was developed by a surgeon named John Hutchinson. He invented a calibrated bell inverted in water, which was used to capture the volume of air exhaled by a person. Hutchinson published his paper about his water spirometer and the measurements he had taken from more than 4,000 subjects,[2] describing the direct relationship between vital capacity and height and the inverse relationship between vital capacity and age. He also showed that vital capacity does not relate to weight at any given height. Hutchinson is regarded as the inventor of vital capacity because he found that with every inch of height vital capacity increased by eight cubic inches.[3] He also used his machine for the prediction of premature mortality. He coined the term 'vital capacity', which was claimed as a powerful prognosis for heart disease by the Framingham study. He believed that his machine should be used for actuarial predictions for companies selling life insurance.[4]
1854 Dr. M. Alton Wintrich developed a spirometer, which was easier to use than Hutchinson's. He did an experiment with 4,000 subjects and concluded that there are three parameters affecting vital capacity: height, weight, and age. His experiment produced results similar to those of Hutchinson's study.
1859 E. Smith developed a portable spirometer, which he used to measure gas metabolism.
1866 Henry Hyde Salter (1823-1871) added a kymograph to the spirometer in order to record time while obtaining air volumes.
1879 Gad J. published a paper entitled "Pneumatograph" that described a machine that allowed the recording of lung volume changes.[2]
Twentieth century
1902, Brodie T. G. was the first to use a dry-bellowed wedge spirometer
1904 Tissot introduced the closed-circuit spirometer
1939 Compton S. D. developed the lungometer for use by Nazi Germany
1959 Wright B. M. and McKerrow C. B. introduced the peak flow meter
1969 DuBois A. B. and van de Woestijne K. P. experimented on humans using the whole body plethysmograph
1974 Campbell et al. refined the previous peak flow meter, developing a cheaper and lighter version[2]
Interpreting Spirometry
Even with the numerical precision that a spirometer can provide, determining pulmonary function relies on differentiating the abnormal from the normal. Measurements of lung function can vary both within and among groups of people, individuals, and spirometer devices. Lung capacity, for instance, may vary temporally, increasing and then decreasing in one person's lifetime. As a result, ideas about what constitutes "normal" are based on one's understanding about the sources of variabilities and can be left to interpretation.
Traditionally, sources of variation have been understood in discrete categories, such as age, height, weight, gender, geographical region (altitude), and race or ethnicity. Global efforts were made in the early twentieth century to standardize these sources to enable proper diagnosis and accurate evaluation of pulmonary function. However, rather than further aiming to understand the causes of such variations, the primary approach for dealing with observed differences in lung capacity has been to "correct for" them. Using results from comparative population studies, attributes are empirically factored together into a "correction factor". This number is then used to form a personalized 'reference value' that defines what is considered normal for one individual. Practitioners may thereby find the percent deviation from this predicted value, known as 'percent of predicted,’ and determine whether someone’s lung function is abnormally poor or excellent.[5]
In particular, 'race correction' or 'ethnic adjustment' effectively has been computer-programmed into the modern-day spirometer. Preconceived notions that 'white' people have greater pulmonary function are embedded in spirometer measurement interpretation and have only been reinforced through this medical stereotyping. In the United States, spirometers use correction factors of 10-15% for those identified as 'black' and 4-6% for those identified as 'Asian.'[6]
Standard Guidelines
In 1960, the European Community for Coal and Steel (ECCS) first recommended guidelines for spirometry.[7] The organization then published predicted values for parameters such as spirometric indices, residual volume, total lung capacity, and functional residual capacity in 1971.[8] The American Thoracic Society/European Respiratory Society also recommends race-specific reference values when available.[9] Even today, the National Institute for Occupational Safety and Health’s Spirometry Training Guide that is linked to the Centers for Disease Control and Prevention’s website notes the use of race correction and a race-specific reference value in step four of "normal" spirometry.[10]
Motivations
The use of reference values and discrete categorizations of sources of variability has been motivated by ideas of anthropometry and vital capacity. Studies have looked specifically at the relationship between anthropometric variables and lung function parameters.[11]
Implications
The use of reference values has thus far not accounted for the social labelling of race and ethnicity. Often, determinations are subjective or silently ascribed by a practitioner. Another concern of using reference values is misdiagnosis.[12] This was an important factor in the management and control of compensation for miners in Britain in the interwar period. In this politically loaded context, in which new X-ray technology could not be fully trusted, the spirometer represented secure evidence of respiratory disease in numerical terms that could be used in the complex compensation network.[13]
Evaluation of vital capacity has influenced other sectors of life other than medicine as well, including evaluation of life insurance applicants and diagnosis of tuberculosis.[5]
Regarding gender, some population studies have indicated no difference based on gender.[11] Notably, spirometers have been used to evaluate vital capacity in India since 1929, recording a statistically significant difference between males (21.8 mL/cm) and females (18 mL/cm).[14] Additionally, by 1990, around half of pulmonary training programs in both the United States and Canada adjusted for race and ethnicity.[15]
The spirometer popularized notions of 'race corrections' and 'ethnic adjustments,' which suggested that black individuals have weaker lungs than white individuals. For example, Thomas Jefferson noted physical distinctions between different races such as a 'difference in the structure of the pulmonary apparatus,' which made black individuals 'more tolerant of heat and less so of cold, than the whites.'[16] Jefferson's theories encouraged speculation on the natural conditioning of blacks for agricultural labor on southern plantations in the U.S.[17] Samuel Cartwright, a slavery apologist and plantation owner, used the spirometer to make the claim that black people consumed less oxygen than white people[18] in addition to racial 'peculiarities' he laid out in the New Orleans Medical and Surgical Journal that described racial differences in the respiratory system and the implication of them on labor.[19]
South African studies also used the spirometer to address racial and class differences. Eustace H. Cluver conducted vital capacity measurement research at the University of Witwatersrand[20] and found that poor white people had physical unfitness but that it was attributable to environmental issues rather than genetics. Using these studies, Cluver argued to the South African Association for the Advancement of Science during World War Two that improving both nutrition and physical training programs could help produce wealth and win the war by increasing the working capacity of individuals across all races as their labor was necessary to achieve these ends.[21] Racism and the spirometer intersected again in these studies when further research was conducted on the effects of physical training on poor white recruits; vital capacity studies showed that 'the poor-white is biologically sound and can be turned into a valuable citizen'[22] but no comment was made on the outcome of black South Africans.
Beyond the United States and South Africa, the spirometer was used in racial studies in India in the 1920s. Researchers found that the vital capacity of Indians was smaller than that of Westerners.[23]
Altering interpretations
Many have questioned whether the current standards are sufficient and accurate.[24][25] As a multiethnic society develops, racial and ethnic origin as a factor becomes more and more problematic to utilize.[26] Ideas connecting ethnicity to lack of nutrition and birthplace in a poor country become invalid as people immigrate to or may be born in richer nations.[26]
This type of spirometer gives a more accurate measurement for the components of lung volumes as compared to other conventional spirometers. A person is enclosed in a small space when the measurement is taken.
Pneumotachometer
This spirometer measures the flow rate of gases by detecting pressure differences across fine mesh. One advantage of this spirometer is that the subject can breathe fresh air during the experiment.[27]
Fully electronic spirometer
Electronic spirometers have been developed that compute airflow rates in a channel without the need for fine meshes or moving parts. They operate by measuring the speed of the airflow with techniques such as ultrasonic transducers, or by measuring pressure difference in the channel. These spirometers have greater accuracy by eliminating the momentum and resistance errors associated with moving parts such as windmills or flow valves for flow measurement. They also allow improved hygiene by allowing fully disposable air flow channels.
This device is useful for measuring how well a person's lungs expel air.
Windmill-type spirometer
This type of spirometer is used especially for measuring forced vital capacity without using water; it has broad measurements ranging from 1000 ml to 7000 ml. It is more portable and lighter than traditional water-tank type spirometers. This spirometer should be held horizontally while taking measurements because of the presence of a rotating disc.
↑ Hankinson, John L.; Odencrantz, John R.; Fedan, Kathleen B. (1 January 1999). "Spirometric Reference Values from a Sample of the General U.S. Population". American Journal of Respiratory and Critical Care Medicine. 159 (1): 179–187. doi:10.1164/ajrccm.159.1.9712108. PMID9872837. S2CID16197063.
↑ Jouasset, D (1960). "Normalisation des épreuves fonctionnelles respiratoires dans les pays de la Communauté Européenne du Charbon et de l'Acier". Poumon Coeur. 16: 1145–1159.
↑ Cara, M; Hentz, P (1971). "Aidemémoire of spirographic practice for examining ventilatory function, 2nd edn". Industrial Health and Medicine Series. 11: 1–130.
↑ Ghio A. J., Crapo R. O., Elliott C. G. (1990). "Reference Equations Used to Predict Pulmonary Functions". Chest. 97 (2): 400–403. doi:10.1378/chest.97.2.400. PMID2298065.{{cite journal}}: CS1 maint: multiple names: authors list (link)
↑ Thomas Jefferson, "Notes on the State of Virginia", in Race and the Enlightenment: A Reader, ed. Emmanuel Eze (Malden, Mass., and London: Blackwell Publishing, 1997), 98.
↑ Braun, Lundy. Breathing race into the machine: the surprising career of the spirometer from plantation to genetics. Minneapolis: U of Minnesota Press, 2014, p. 28.
↑ Braun, Lundy. Breathing race into the machine: the surprising career of the spirometer from plantation to genetics. Minneapolis: U of Minnesota Press, 2014, p. 29.
↑ Cartwright, Samuel A. (May 1851). "Report on the diseases and physical peculiarities of the Negro race". New Orleans Medical and Surgical Journal. 7: 691–715. OCLC57141108.
↑ Braun, Lundy. Breathing race into the machine: the surprising career of the spirometer from plantation to genetics. Minneapolis: U of Minnesota Press, 2014, p. 126.
↑ "Vital Discovery on Poor White Problem". Johannesburg Sunday Times. 31 May 1941.
Lundy Braun, Breathing Race into the Machine: The Surprising Career of the Spirometer from Plantation to Genetics. Minneapolis, MN: University of Minnesota Press, 2014.
Diffusing capacity of the lung (DL) measures the transfer of gas from air in the lung, to the red blood cells in lung blood vessels. It is part of a comprehensive series of pulmonary function tests to determine the overall ability of the lung to transport gas into and out of the blood. DL, especially DLCO, is reduced in certain diseases of the lung and heart. DLCO measurement has been standardized according to a position paper by a task force of the European Respiratory and American Thoracic Societies.
Lung volumes and lung capacities refer to the volume of air in the lungs at different phases of the respiratory cycle.
Exhalation is the flow of the breath out of an organism. In animals, it is the movement of air from the lungs out of the airways, to the external environment during breathing. This happens due to elastic properties of the lungs, as well as the internal intercostal muscles which lower the rib cage and decrease thoracic volume. As the thoracic diaphragm relaxes during exhalation it causes the tissue it has depressed to rise superiorly and put pressure on the lungs to expel the air. During forced exhalation, as when blowing out a candle, expiratory muscles including the abdominal muscles and internal intercostal muscles generate abdominal and thoracic pressure, which forces air out of the lungs.
Spirometry is the most common of the pulmonary function tests (PFTs). It measures lung function, specifically the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. Spirometry is helpful in assessing breathing patterns that identify conditions such as asthma, pulmonary fibrosis, cystic fibrosis, and COPD. It is also helpful as part of a system of health surveillance, in which breathing patterns are measured over time.
A plethysmograph is an instrument for measuring changes in volume within an organ or whole body. The word is derived from the Greek "plethysmos", and "graphein".
Capnography is the monitoring of the concentration or partial pressure of carbon dioxide (CO 2) in the respiratory gases. Its main development has been as a monitoring tool for use during anesthesia and intensive care. It is usually presented as a graph of CO 2 (measured in kilopascals, "kPa" or millimeters of mercury, "mmHg") plotted against time, or, less commonly, but more usefully, expired volume (known as volumetric capnography). The plot may also show the inspired CO 2, which is of interest when rebreathing systems are being used. When the measurement is taken at the end of a breath (exhaling), it is called "end tidal" CO 2 (PETCO2).
The peak expiratory flow (PEF), also called peak expiratory flow rate (PEFR), is a person's maximum speed of expiration, as measured with a peak flow meter, a small, hand-held device used to monitor a person's ability to breathe out air. It measures the airflow through the bronchi and thus the degree of obstruction in the airways. Peak expiratory flow is typically measured in units of liters per minute (L/min).
Vital capacity (VC) is the maximum amount of air a person can expel from the lungs after a maximum inhalation. It is equal to the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume. It is approximately equal to Forced Vital Capacity (FVC).
DLCO or TLCO is the extent to which oxygen passes from the air sacs of the lungs into the blood. Commonly, it refers to the test used to determine this parameter. It was introduced in 1909.
An incentive spirometer is a handheld medical device used to help patients improve the functioning of their lungs. By training patients to take slow and deep breaths, this simplified spirometer facilitates lung expansion and strengthening. Patients inhale through a mouthpiece, which causes a piston inside the device to rise. This visual feedback helps them monitor their inspiratory effort. Incentive spirometers are commonly used after surgery or other illnesses to prevent pulmonary complications.
Obstructive lung disease is a category of respiratory disease characterized by airway obstruction. Many obstructive diseases of the lung result from narrowing (obstruction) of the smaller bronchi and larger bronchioles, often because of excessive contraction of the smooth muscle itself. It is generally characterized by inflamed and easily collapsible airways, obstruction to airflow, problems exhaling, and frequent medical clinic visits and hospitalizations. Types of obstructive lung disease include; asthma, bronchiectasis, bronchitis and chronic obstructive pulmonary disease (COPD). Although COPD shares similar characteristics with all other obstructive lung diseases, such as the signs of coughing and wheezing, they are distinct conditions in terms of disease onset, frequency of symptoms, and reversibility of airway obstruction. Cystic fibrosis is also sometimes included in obstructive pulmonary disease.
Restrictive lung diseases are a category of extrapulmonary, pleural, or parenchymal respiratory diseases that restrict lung expansion, resulting in a decreased lung volume, an increased work of breathing, and inadequate ventilation and/or oxygenation. Pulmonary function test demonstrates a decrease in the forced vital capacity.
Pulmonary function testing (PFT) is a complete evaluation of the respiratory system including patient history, physical examinations, and tests of pulmonary function. The primary purpose of pulmonary function testing is to identify the severity of pulmonary impairment. Pulmonary function testing has diagnostic and therapeutic roles and helps clinicians answer some general questions about patients with lung disease. PFTs are normally performed by a pulmonary function technician, respiratory therapist, respiratory physiologist, physiotherapist, pulmonologist, or general practitioner.
The FEV1/FVC ratio, also called Tiffeneau-Pinelli index, is a calculated ratio used in the diagnosis of obstructive and restrictive lung disease. It represents the proportion of a person's vital capacity that they are able to expire in the first second of forced expiration (FEV1) to the full, forced vital capacity (FVC). The result of this ratio is expressed as FEV1%.
Structured Light Plethysmography (SLP) technology is a noninvasive method for collecting accurate representations of chest and abdominal wall movement. A checkerboard pattern of light is projected from a light projector onto the chest of an individual. Movements of the grid are viewed by two digital cameras, digitalised, and processed to form a 3D model and can be interrogated to assess lung function. The system has been tested on over 70 adults. SLP is simple to use, accurate and cost effective, is self-calibrating and does not require the use of plastic consumables, reducing cost, risk of cross infection and the device's carbon footprint. In conjunction with the Cambridge Veterinary School, proof of concept studies have indicated that the device is sensitive enough to noninvasively pick up respiratory movements in domestic animals.
Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. Systemic manifestations are known. COPD and asthma may coexist and converge in some individuals. The main symptoms of COPD include shortness of breath and a cough, which may or may not produce mucus. COPD progressively worsens, with everyday activities such as walking or dressing becoming difficult. While COPD is incurable, it is preventable and treatable.
The post bronchodilator test, also commonly referred to as a reversibility test, is a test that utilizes spirometry to assess possible reversibility of bronchoconstriction in diseases such as asthma.
A respiratory pressure meter measures the maximum inspiratory and expiratory pressures that a patient can generate at either the mouth (MIP and MEP) or inspiratory pressure a patient can generate through their nose via a sniff manoeuvre (SNIP). These measurements require patient cooperation and are known as volitional tests of respiratory muscle strength. Handheld devices displaying the measurement achieved in cmH2O and the pressure trace created, allow quick patient testing away from the traditional pulmonary laboratory and are useful for ward based, out patient, and preoperative assessment as well as for use by pulmonologists and physiotherapists.
Race adjustment, also known as race-correction, is the calculating of a result which takes into account race. It is commonly used in medical algorithms in several specialties, including cardiology, nephrology, urology, obstetrics, endocrinology, oncology and respiratory medicine. Examples include the eGFR to assess kidney function, the STONE score for the prediction of kidney stones, the FRAX tool, to evaluate the 10-year probability of bone fracture risk, and lung function tests, to identify the severity of lung disease.
Lundy Braun is professor of pathology and laboratory medicine, and Africana studies at Brown University, United States, who researches history of racial health disparities. She wrote Breathing Race Into the Machine: The Surprising Career of the Spirometer From Plantation to Genetics (2014), which looks at the history of correcting for race in spirometers, and for which she received the Ludwik Fleck Prize in 2018.
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