Automated Breathing Metabolic Simulator (ABMS)

Purpose of an Automated Breathing Metabolic Simulator

The goal of any Automated Breathing Metabolic Simulator (ABMS) is to “accurately simulate both the breathing and the metabolic functions of a human being for testing of closed-circuit breathing apparatus” (Kyriazi, 1986).

To simulate human respiration and metabolism, an ABMS needs to control:

·       carbon dioxide production

·       oxygen consumption

·       inhalation/exhalation pressures

·       carbon dioxide percentage

·       temperatures

·       respiratory frequencies while monitoring oxygen percentage

History of Breathing Metabolic Simulators

Respiratory researchers have long desired an accurate method of simulating the breathing and metabolic processes of a human in a lab setting. Simulators have become a vital resource for research institutes, regulatory centers, testing houses, and manufacturers due to their ability to produce data that can accurately resemble a human’s breathing without the risk of direct human exposure to the tested device. Prior to the early 1980’s, accurately simulating human breathing in a controlled and repetitive manner was not possible due to the lack of technological development and human knowledge on the respiratory system.

In the past, human understanding of the respiratory system was simply limited and at times misdirected. During the Renaissance intellectuals understood the form of the lungs but did not understand what their function was. Around the 17^th century a rudimentary understanding of the function on the lungs had began to take place under William Harvey, in his lectures on the while of Anatomy (1653) he claimed that “Life and respiration are complementary” (The History of the Lungs). In the late 19^th century Eduard Friedrich Wilhelm Pflüger settled the debate that metabolism took place in the peripheral tissues rather than having the lung consume oxygen outright. During and after the Second World War understanding of the pulmonary gas exchange began to develop at a faster rate in large part due to the introduction of blood gas electrodes in the 1960s (West, 2011). Once understanding of human respiratory system was better understood the Breathing Metabolic Simulators (BMS) were able to be developed in a rudimentary manner. The basic design was restricted by the technology of the time, this led to inaccurate procedures being developed due to inaccurate testing equipment.

The first BMS was developed by U.S. Bureau of Mines funding and research, it was installed in 1973. The U.S. Bureau of Mines continued funding the development of BMS’s until 1985. These efforts led to the design that is currently used at NIOSH-NPPTL and the U.S. Navy (Sinkule, 2013).

Current manufactures of BMS’s include: CSE, Dräger (Kyriazi, 2011) , and Ocenco (Kyriazi 2011).

The first BMS was designed under the following guidelines:

o The simulations produced by the ABMS were to be as physiologically appropriate as possible.

o The construction was to employ low cost methods using standard, commercially available items wherever possible.

o Operation was to be simple and easily learned. Complex computer programs were to be avoided.

o The ABMS was to be capable of manual as well as automatic operation. All data inputs into the computer were to be paralleled with analog outputs suitable for general purpose laboratory recorders (Development Of An Automated Breathing Metabolic Simulator, 1984).

However, as understanding of human respiration developed and respiratory standard requirements advanced, manufacturers of BMS’s are now steering towards the development and refinement of ABMS’s. The advancement of technology will allow for ABMS’s to simulate the human respiratory metabolic process to a greater degree of accuracy. These developments will lead to the creation of better quality respiratory protection products.

History of Automated Metabolic Breathing Simulators

A Breathing Metabolic Simulator (BMS) is a manual version of an Automated Breathing Metabolic Simulator (ABMS). The first BMS’s were designed around a manual pump that the technician would use to simulate human breathing. The ABMS is designed to work in the same form as an BMS, but with electronic components which offered more accurate control over the system. The first ABMS contained three modules designed to be able to function independently from each other or work as a unit. The three modules were a Breathing Simulator Module (BSM), a Gas Analysis Module and a Supervisory Controller (Wischhoefer, L.L., & Reimers, 1984).

The First attempts at making a breathing simulator resulted in the use of bellows. The problem with the use of bellows was their large-scale inaccuracy of human breathing along with this inability to reproduce breathing in a repetitive fashion. This form was replaced with a rigid piston design. The rigid piston solved the problem of replicability and proved that controlled breathing patterns were possible. This is due to the rigid piston having a known displacement and the ability to create wave forms from a mathematical or empirical source.

Oxygen consumption has been simulated through various methods over the time of BMS development. Older methods of oxygen consumption includes catalytic conversion which was expensive and involved the introduction of hydrogen, this method was limited in its use. The preferred method used to remove a mixture of the breathing media, analyze the sample for the oxygen content, and then adjust the flow to contain the correct number of liters required for the correct oxygen consumption rate. The algorithm would then subtract the oxygen content from 100% and the remainder would then be assumed to be nitrogen, the sample would then be returned into the breathing loop via a separate measurement. At times CO₂ would be a small percentage of the mix that is withdrawn to accomplish oxygen consumption. This gas would then be analyzed separately and considered within the algorithm. This percentages would then have to be reintroduced into the breathing loop.

BMS’s use to use rotameters in the 1970s and 1980s to simulate oxygen consumption. Rotameters were crude instruments for what their intended use was intended for. The rotameters were used to try to replicate the changing percentage of gases in the mixture being withdrawn to accomplish oxygen consumption. When the gasses were withdrawn, nitrogen would then be reintroduced into the mix. This method proved to be inaccurate due to the process demanding immediate calculations for human operators to manually alter gas flow rates. In the new ABMS’s, the job of rotameters has been given to mass flow controllers. Now, mass flow controllers, in conjunction with high speed gas analyzers, provide continuous updates and inputs into the algorithm to calculate oxygen consumption through a range a gas mixtures.  

Past BMS designs utilized paper charts as a means to record data for the users. This resulted in requiring days of analyzing to have data in a usable format. Modern ABMS’s work digitally allowing for manipulation of the data through the software that is preinstalled. This change allows for the users to be able to have added functionality and better control over the operations of the ABMS.

Prior to automation, operators of the BMS’s would manually implement each stage of the testing and analysis processes, often utilizing multiple machines. Automation has helped to eliminate operator errors, allowing for more precise and repeatable data collection, and enabled faster design iteration on the part of respiratory protective device manufacturers.

Current manufacturers of ABMS’s include: Ocenco (Kyriazi, 2011) and ATOR LABS

Relevant ISO Number

The industry standard for Respiratory Protective Device (RPD) manufacturing is shifting towards becoming ISO 16900 series. This series provides scientific procedures and guidelines on how the RPDs needs to perform. ISO 16900 is a relatively new standard which places new restrictions on RPDs. This is relevant to ABMS development due to it being the testing device that ensures that the RPDs that are going through the various testing houses pass the new standards. In order for ISO 16900 to be implemented, it requires an ABMS that is capable of accurately reading the more stringent requirements. Ultimately, ABMS manufacturers will be required to advance to the new demand or submit the market to those who are capable.

At present time, 2018, the U.S. testing houses have not conformed with the ISO 16900 standards. Specifically, the ABMSs that are currently being used were produced in the 1980s. A study has shown that should NIOSH – NPPTL were to conform to the ISO 16900 standards, it would result in a one-time cost of $13.1 million.  While the initial cost may be high, having NIOSH – NPPTL comply with the ISO 16900 standard would lead to better quality end product for all companies that apply through the government entity (Miller).

ISO 17420 is also being developed for new testing standards for RPDs. The new standard looks at special applications for fire, escape, and special application other than fire services and escape. The last section includes the guidelines for CBRN respiratory protection devices.

There are criticisms within the standardization community related to the implementation of the ISO 17420 standard . Specifically, complaints on how mild improvements in the testing standards will force qualified RPDs under past standards into having to requalify under the new standard. It is projected that this will lead to massive economic advantages placed on the companies which pass the new ISO 17420 first, and with limited ability to progress in the lines of a testing house in an expedited manner those companies will likely stay in the lead with limited competition. Ultimately, the ISO 17420 is expected to drive the prices of RPDs up due to the cost of new testing (Spasciani, 2012).

References

Wischhoefer, L.L., & Reimers, S.D.(1984). Development of an automated breathing metabolic simulator (ABMS). Open File report. United States.

Kyriazi, N. (1986). Development of an automated breathing and metabolic simulator. Pittsburgh, PA: U.S. Dept. of the Interior, Bureau of Mines.

Doc. No. DEVELOPMENT OF AN AUTOMATED BREATHING METABOLIC SIMULATOR (ABMS)-25-85 at 1-50 (1984).

Sinkule, E. J. (2013). AUTOMATED BREATHING AND METABOLIC SIMULATOR (ABMS) EVALUATION OF N95 RESPIRATOR USE WITH SURGICAL MASKS (Unpublished doctoral dissertation). University of Pittsburgh.

(n.d.). Retrieved from https://www.draeger.com/en-us_us/Home

(n.d.). Retrieved from http://www.ocenco.com/index.html

Kyriazi, N. (2011). Performance Comparison of Breathing and Metabolic Simulators. Journal of the International Society for Respiratory Protection, 1-25.

Spasciani, Alberto. (2012). A critical approach to ISO 17420 (All that glitters is not gold). The International Society for Respiratory Protection.

Miller, C. (n.d.). Determining the Feasibility of Using ISO Voluntary Consensus Standards for Verification of Respiratory Protective Devices. Retrieved from https://yokohama.isrp.com/docman/presentations-yokohama/189-pof036p/file

The History of the Lungs. (n.d.). Retrieved from https://web.stanford.edu/class/history13/earlysciencelab/body/lu bvngspages/lung.html

West, J. B. (2011, July). History of respiratory gas exchange. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/23733651

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