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Oxygen content in semi-closed rebreathing apparatuses for underwater use: Measurements and modeling
KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Environmental Physiology.ORCID iD: 0000-0001-7051-3256
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present series of unmanned hyperbaric tests were conducted in order to investigate the oxygen fraction variability in semi-closed underwater rebreathing apparatuses. The tested rebreathers were RB80 (Halcyon dive systems, High springs, FL, USA), IS-Mix (Interspiro AB, Stockholm, Sweden), CRABE (Aqua Lung, Carros Cedex, France), and Viper+ (Cobham plc, Davenport, IA, USA). The tests were conducted using a catalytically based propene combusting metabolic simulator. The metabolic simulator connected to a breathing simulator, both placed inside a hyperbaric pressure chamber, was first tested to demonstrate its usefulness to simulate human respiration in a hyperbaric situation. Following this the metabolic simulator was shown to be a useful tool in accident investigations as well as to assess the impact of different engineering designs and physiological variables on the oxygen content in the gas delivered to the diver by the rebreathing apparatuses. A multi-compartment model of the oxygen fractions was developed and compared to the previously published single-compartment models. The root mean squared error (RMSE) of the multi-compartment model was smaller than the RMSE for the single-compartment model, showing its usefulness to estimate the impact of different designs and physiological variables on the inspired oxygen fraction.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , x, 48 p.
Series
TRITA-STH : report, ISSN 1653-3836 ; 2015:6
Keyword [en]
Diving, rebreather, underwater breathing apparatus, unmanned testing, hyperbaric, metabolic simulator, scuba, semi-closed
National Category
Other Medical Engineering
Research subject
Medical Technology
Identifiers
URN: urn:nbn:se:kth:diva-172949ISBN: 978-917595-616-9 OAI: oai:DiVA.org:kth-172949DiVA: diva2:850861
Public defence
2015-09-25, D2, Lindstedtsvägen 5, KTH, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

QC 20150903

Available from: 2015-09-03 Created: 2015-09-02 Last updated: 2015-09-03Bibliographically approved
List of papers
1. Investigation of a demand-controlled rebreather in connection with a diving accident
Open this publication in new window or tab >>Investigation of a demand-controlled rebreather in connection with a diving accident
2011 (English)In: Undersea & Hyperbaric Medicine, ISSN 1066-2936, Vol. 38, no 1, 61-72 p.Article in journal (Refereed) Published
Abstract [en]

This paper describes the examination of a Halcyon RB80 semi-closed underwater breathing apparatus used in a diving accident in 2007. The apparatus was supplied with trimix (oxygen, nitrogen and helium) containing 31% oxygen. The duration of the dive was 105 minutes at 28 meters' average depth in fresh water, with a 19-minute oxygen decompression stop at 6 meters. Upon surfacing the diver experienced seizures and signs of severe neurological deficits. The apparatus was tested with regard to the oxygen fraction drop from the supply gas to the breathing loop - i.e., the oxygen fraction inhaled by the diver (FiO2) was investigated. The FiO2 was measured and found to be lower than the value stated on the manufacturer's web page at the time of the accident. This investigation suggests that during the dive, the actual FiO2% was 17.9-25.3%, which is considerably lower than the FiO2% used for decompression calculations (30%). The underestimation of FiO2 resulted in too short and/or too few decompression stops during ascent. The low FiO2 would also put a diver at risk of hypoxia at shallow depths. It is concluded that inadequate information on the performance of the rebreather was a major contributing factor to this accident.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-31589 (URN)000287180200008 ()21384764 (PubMedID)2-s2.0-79953035179 (Scopus ID)
Note
QC 20110325Available from: 2011-03-25 Created: 2011-03-21 Last updated: 2017-12-11Bibliographically approved
2. A Metabolic Simulator for Unmanned Testing of Breathing Apparatuses in Hyperbaric Conditions
Open this publication in new window or tab >>A Metabolic Simulator for Unmanned Testing of Breathing Apparatuses in Hyperbaric Conditions
Show others...
2014 (English)In: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 85, no 11, 1139-1144 p.Article in journal (Refereed) Published
Abstract [en]

Background: A major part of testing of rebreather apparatuses for underwater diving focuses on the oxygen dosage system. Methods: A metabolic simulator for testing breathing apparatuses was built and evaluated. Oxygen consumption was achieved through catalytic combustion of propene. With an admixture of carbon dioxide in the propene fuel, the system allowed the respiratory exchange ratio to be set freely within human variability and also made it possible to increase test pressures above the condensation pressure of propene. The system was tested by breathing ambient air in a pressure chamber with oxygen uptake (VO2) ranging from 1-4 L.min(-1), tidal volume (V-T) from 1-3 L, breathing frequency (f) of 20 and 25 breaths/min, and chamber pressures from 100 to 670 kPa. Results: The measured end-tidal oxygen concentration (FO2) was compared to calculated end-tidal FO2. The largest average difference in end-tidal FO2 during atmospheric pressure conditions was 0.63%-points with a 0.28%-point average difference during the whole test. During hyperbaric conditions with pressures ranging from 100 to 670 kPa, the largest average difference in FO2 was 1.68%-points seen during compression from 100 kPa to 400 kPa and the average difference in FO2 during the whole test was 0.29%-points. Conclusion: In combination with a breathing simulator simulating tidal breathing, the system can be used for dynamic continuous testing of breathing equipment with changes in V-T, f, VO2, and pressure.

Keyword
respiratory measurement, machine testing, oxygen consumption
National Category
Medical Engineering
Identifiers
urn:nbn:se:kth:diva-156103 (URN)10.3357/ASEM.4047.2014 (DOI)000343642500012 ()2-s2.0-84910068714 (Scopus ID)
Note

QC 20150109

Available from: 2015-01-09 Created: 2014-11-21 Last updated: 2017-12-05Bibliographically approved
3. Measurement and modeling of oxygen content in a demand mass ratio injection rebreather
Open this publication in new window or tab >>Measurement and modeling of oxygen content in a demand mass ratio injection rebreather
2015 (English)In: Undersea & Hyperbaric Medicine, ISSN 1066-2936, Vol. 42, no 6, 573-592 p.Article in journal (Refereed) Published
Abstract [en]

Mechanical semi-closed rebreathers do not need oxygen sensors for their functions, thereby reducing the complexity of the system. However, testing and modeling are necessary in order to determine operational limits as well as the decompression obligation and to avoid hyperoxia and hypoxia. Two models for predicting the oxygen fraction in a demand constant mass ratio injection (DCMRI) rebreather for underwater use were compiled and compared. The model validity was tested with an IS-MIX, Interspiro AB rebreather using a metabolic simulator connected to a breathing machine inside a water-filled pressure chamber. The testing schedule ranged from 0.5-liter (L) to 3-liter tidal volumes, breathing frequencies from five to 25 breaths/minute and oxygen consumptions from 0.5 L/minute to 4 L/minute. Tests were carried out at surface and pressure profiles ranging to 920 kPa(a) (81 meters of sea water, 266 feet of sea water). The root mean squared error (RMSE) of the single-compartment model was 2.4 percent-units of oxygen for the surface test with the 30% dosage setting but was otherwise below 1% unit. For the multicompartment model the RMSE was below 1% unit of oxygen for all tests. It is believed that these models will aid divers in operational settings and may constitute a helpful tool when developing semi-closed rebreathing apparatuses.

Place, publisher, year, edition, pages
Undersea and Hyperbaric Medical Society, 2015
National Category
Physiology
Identifiers
urn:nbn:se:kth:diva-172946 (URN)000368748500005 ()26742257 (PubMedID)2-s2.0-84954574239 (Scopus ID)
Note

Updated from Manuscript to Article. QC 20160118

Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2017-12-04Bibliographically approved
4. Modeling a demand constant volume ratio exhaust and a self-mixing constant oxygen injection semi-closed rebreather
Open this publication in new window or tab >>Modeling a demand constant volume ratio exhaust and a self-mixing constant oxygen injection semi-closed rebreather
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Unmanned tests of two types of gas dosage techniques for semi-closed underwater rebreathing apparatuses were carried out with a metabolic simulator in a water filled pressure chamber. Tests were conducted over a wide range of tidal volumes (0.5-3 L), respiratory frequencies (5-25 min-1), and oxygen consumptions (0.5-4 L/min), as well as with changing chamber pressures from 100 kPa to 920 kPa. Two models were set up, one single compartment model and one model assuming multiple serial compartments. Both models seem to have about the same level of accuracy at predicting the inspired oxygen levels at pressure, but the surface tests seem to favor the serial compartments model.

National Category
Other Medical Engineering
Identifiers
urn:nbn:se:kth:diva-172948 (URN)
Note

QS 2015

Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2015-09-03Bibliographically approved

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