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      Work of Breathing into Snow in the Presence versus Absence of an Artificial Air Pocket Affects Hypoxia and Hypercapnia of a Victim Covered with Avalanche Snow: A Randomized Double Blind Crossover Study

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          Abstract

          Presence of an air pocket and its size play an important role in survival of victims buried in the avalanche snow. Even small air pockets facilitate breathing. We hypothesize that the size of the air pocket significantly affects the airflow resistance and work of breathing. The aims of the study are (1) to investigate the effect of the presence of an air pocket on gas exchange and work of breathing in subjects breathing into the simulated avalanche snow and (2) to test whether it is possible to breathe with no air pocket. The prospective interventional double-blinded study involved 12 male volunteers, from which 10 completed the whole protocol. Each volunteer underwent two phases of the experiment in a random order: phase “AP”—breathing into the snow with a one-liter air pocket, and phase “NP”—breathing into the snow with no air pocket. Physiological parameters, fractions of oxygen and carbon dioxide in the airways and work of breathing expressed as pressure-time product were recorded continuously. The main finding of the study is that it is possible to breath in the avalanche snow even with no air pocket (0 L volume), but breathing under this condition is associated with significantly increased work of breathing. The significant differences were initially observed for end-tidal values of the respiratory gases (EtO 2 and EtCO 2) and peripheral oxygen saturation (SpO 2) between AP and NP phases, whereas significant differences in inspiratory fractions occurred much later (for F IO 2) or never (for F ICO 2). The limiting factor in no air pocket conditions is excessive increase in work of breathing that induces increase in metabolism accompanied by higher oxygen consumption and carbon dioxide production. The presence of even a small air pocket reduces significantly the work of breathing.

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          Comparison of avalanche survival patterns in Canada and Switzerland.

          Current recommendations for rescue and resuscitation of people buried in avalanches are based on Swiss avalanche survival data. We analyzed Canadian survival patterns and compared them with those from Switzerland.
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            Field management of avalanche victims.

            The median annual mortality from snow avalanches registered in Europe and North America 1981-1998 was 146 (range 82-226); trend stable in Alpine countries (r=-0.29; P=0.24), increasing in North America (r=0.68; P=0.002). Swiss data over the same period document 1886 avalanche victims, with an overall mortality rate of 52.4% in completely-buried, versus 4.2% in partially-, or non-buried, persons. Survival probability in completely-buried victims in open areas (n=638) plummets from 91% 18 min after burial to 34% at 35 min, then remains fairly constant until a second drop after 90 min. Likewise, survival probability for completely-buried victims in buildings or on roads (n=97) decreases rapidly following burial initially, but as from 35 min it is significantly higher than that for victims in open areas, with a maximum difference in respective survival probability (31% versus 7%) from 130 to 190 min (P 35 min combating hypothermia becomes of paramount importance. Thus, gentle extrication, ECG and core temperature monitoring and body insulation are mandatory; unresponsive victims should be intubated and pulseless victims with core temperature <32 degrees C (89.6 degrees F) (prerequisites being an air pocket and free airways) transported with continuous cardiopulmonary resuscitation to a specialist hospital for extracorporeal re-warming.
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              Respiratory muscle oxygen consumption estimated by the diaphragm pressure-time index.

              The O2 consumption of the respiratory muscles (VO2resp), work of breathing, and the time integral of the transdiaphragmatic pressure (TTdi) were measured in four normal subjects breathing against inspiratory resistance. A total of 39 runs were performed at mean tidal transdiaphragmatic pressures (Pdi) ranging from 15 to 53 cmH2O, respiratory frequencies from 3.5 to 22 breaths/min, and inspiratory time durations (TI) from 32 to 76% of the total breath duration. Each run was maintained from 8 to 17 min and the above parameters were kept constant by the subject via visual feedback of Pdi and TI with an oscilloscope. Most of the runs (36 of 39) were performed at TTdi values below those known to produce respiratory muscle fatigue. We found a strong linear correlation between the VO2resp and the TTdi (r = 0.74, P less than 0.001) and a weaker correlation between VO2resp and W (r = 0.31, P less than 0.05). These data suggest that TTdi is a good estimator of VO2resp over a wide range of respiratory patterns during inspiratory resistance breathing. The high variability seen in respiratory muscle efficiency during resistive breathing may be due to W not being a good indicator of the energy consumed by the respiratory muscles.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                14 December 2015
                2015
                : 10
                : 12
                : e0144332
                Affiliations
                [1 ]Department of Biomedical Technology, Faculty of Biomedical Engineering, Czech Technical University in Prague, Prague, Czech Republic
                [2 ]Department of Physics, Faculty of Electrical Engineering, Czech Technical University in Prague, Prague, Czech Republic
                [3 ]Department of Physiology and Biochemistry, Faculty of Physical Education and Sport, Charles University, Prague, Czech Republic
                Erasmus Medical Centre, NETHERLANDS
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: KR KS LS. Performed the experiments: KR KS LS. Analyzed the data: KR KS LS. Contributed reagents/materials/analysis tools: KR KS LS. Wrote the paper: KR KS LS. Obtaining permission from the Institutional Review Board: KS.

                Article
                PONE-D-15-26166
                10.1371/journal.pone.0144332
                4682855
                26666523
                1f292c2f-85c2-4e61-8ee9-0fda66033a41
                © 2015 Roubík et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

                History
                : 3 September 2015
                : 17 November 2015
                Page count
                Figures: 8, Tables: 1, Pages: 16
                Funding
                The experiment conducted as a part of this study was supported by research grant SVV 2015–260236 of Charles University, Faculty of Physical Education and Sport, and by a research grant SGS14/216/OHK4/3T/17 of Czech Technical University in Prague. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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