Silvanius Mårten, Mitchell Simon J, Pollock Neal W, Frånberg Oskar, Gennser Mikael, Lindén Jerry, Mesley Peter, Gant Nicholas
Swedish Armed Forces Diving and Naval Medicine Centre, Karlskrona, Sweden.
Blekinge Institute of Technology, Karlskrona, Sweden.
Diving Hyperb Med. 2019 Mar 31;49(1):48-56. doi: 10.28920/dhm49.1.48-56.
Diving rebreathers use canisters containing soda lime to remove carbon dioxide (CO2) from expired gas. Soda lime has a finite ability to absorb CO₂. Temperature sticks monitor the exothermic reaction between CO₂ and soda lime to predict remaining absorptive capacity. The accuracy of these predictions was investigated in two rebreathers that utilise temperature sticks.
Inspiration and rEvo rebreathers filled with new soda lime were immersed in water at 19°C and operated on mechanical circuits whose ventilation and CO₂-addition parameters simulated dives involving either moderate exercise (6 MET) throughout (mod-ex), or 90 minutes of 6 MET exercise followed by 2 MET exercise (low-ex) until breakthrough (inspired PCO₂ [PiCO₂] = 1 kPa). Simulated dives were conducted at surface pressure (sea-level) (low-ex: Inspiration, n = 5; rEvo, n = 5; mod-ex: Inspiration, n = 7, rEvo, n = 5) and at 3-6 metres' sea water (msw) depth (mod-ex protocol only: Inspiration, n = 8; rEvo, n = 5).
Operated at surface pressure, both rebreathers warned appropriately in four of five low-ex tests but failed to do so in the 12 mod-ex tests. At 3-6 msw depth, warnings preceded breakthrough in 11 of 13 mod-ex tests. The rEvo warned conservatively in all five tests (approximately 60 minutes prior). Inspiration warnings immediately preceded breakthrough in six of eight tests, but were marginally late in one test and 13 minutes late in another.
When operated at even shallow depth, temperature sticks provided timely warning of significant CO₂ breakthrough in the scenarios examined. They are much less accurate during simulated exercise at surface pressure.
潜水循环呼吸器使用装有苏打石灰的滤毒罐从呼出气体中去除二氧化碳（CO₂）。苏打石灰吸收CO₂的能力有限。温度棒监测CO₂与苏打石灰之间的放热反应以预测剩余吸收能力。在两台使用温度棒的循环呼吸器中研究了这些预测的准确性。
将装满新苏打石灰的Inspiration和rEvo循环呼吸器浸入19°C的水中，并在机械回路中运行，其通风和CO₂添加参数模拟潜水，全程包括适度运动（6代谢当量）（中度运动组），或90分钟的6代谢当量运动，然后是2代谢当量运动（轻度运动组），直至出现突破（吸入二氧化碳分压[PiCO₂]=1千帕）。模拟潜水在水面压力（海平面）下进行（轻度运动组：Inspiration，n = 5；rEvo，n = 5；中度运动组：Inspiration，n = 7，rEvo，n = 5），以及在3 - 6米海水（msw）深度下进行（仅中度运动组方案：Inspiration，n = 8；rEvo，n = 5）。
在水面压力下运行时，两台循环呼吸器在五项轻度运动测试中的四项中都给出了适当警告，但在12项中度运动测试中未能做到。在3 - 6 msw深度下，13项中度运动测试中的11项在突破前发出了警告。rEvo在所有五项测试中都发出了保守警告（大约提前60分钟）。Inspiration在八项测试中的六项中在突破前立即发出警告，但在一项测试中略微延迟，在另一项测试中延迟了13分钟。
在所研究的场景中，即使在很浅的深度运行时，温度棒也能及时发出重大CO₂突破的警告。在水面压力下的模拟运动期间，它们的准确性要低得多。
