Diving Hyperb Med
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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. ⋯ 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.
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Gas micronuclei are gas-filled voids in liquids from which bubbles can form at low gas supersaturation. If water is depleted of gas micronuclei, high gas supersaturation is required for bubble formation. This high gas supersaturation is required in part to overcome the Laplace pressure at the point of transition from dissolved gas to a bubble of perhaps nanometer-scale radius. ⋯ Surface nanobubbles typically have diameters less than 100 nanometers but have lifetimes that are orders of magnitude longer than would a bubble of similar dimensions. Surface nanobubbles do not grow into macroscopic bubbles when exposed to pressure waves sufficient to cause bubble formation from adventitious gas micronuclei elsewhere in the apparatus. This is surely not the last word in this new and active field of research into nanoscopic gas species; however, based on current evidence one must treat with skepticism speculation that unobserved surface nanobubbles are the gas micronuclei from which bubbles form in humans with low gas supersaturation and which underlie decompression sickness.
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Ultrasonic detection of venous gas emboli (VGE) in the precordial (PRE) region is commonly used in evaluation of decompression stress. While subclavian (SC) VGE detection can also be used to augment and improve the evaluation, no study has rigorously compared VGE grades from both sites as decompression stress indicators. ⋯ The association of bubble grades with DCS occurrence is stronger for SC than PRE when exposure severity is taken into account. The usefulness of SC VGE in decompression stress evaluation has been underestimated in the past.
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Diving rebreathers use "scrubber" canisters containing soda lime to remove carbon dioxide (CO2) from the expired gas. Soda lime has a finite ability to absorb CO2. We undertook an experiment to determine whether the manner of storage of a partly used scrubber affected subsequent CO2 absorption. ⋯ Rebreather divers should consider placing partially used soda lime scrubber canisters in vacuum-sealed plastic bags if storing them for longer periods than overnight. If a partially used scrubber canister is to be used again the next day then the storage modality is unlikely to influence scrubber efficacy.
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When a standard water-seal pleural drain unit (PDU) is used under hyperbaric conditions there are scenarios where excessive negative intrapleural pressure (IPP) and/or fluid reflux can be induced, risking significant morbidity. We developed and tested a pleural vacuum relief (PVR) device which automatically manages these risks, whilst allowing more rapid hyperbaric pressure change rates. ⋯ The PDU PVR device we have developed works well, minimising attendant workload and automatically avoiding the excessive negative IPPs that can otherwise occur. This device should only be used with suction.