Materials Suitable to Simulate Snow During Breathing Experiments for Avalanche Survival Research

Abstract

Terrain experiments for avalanche survival research require appropriate snow conditions, which may not be available year round. To prepare these experiments and test the protocol, it might be advantageous to test them in a laboratory with a snow model. The aim of the study was to find a material that can be used to simulate avalanche snow for studying gas exchange of a person covered with avalanche snow. Three loose porous materials (perlite, wood shavings and polystyrene) were tested in two forms—dry and moisturized. Each volunteer underwent six phases of the experiment in random order (three materials each dry or moisturized) during experimental breathing into the tested materials. Physiological parameters and fractions of oxygen and carbon dioxide in the airways were recorded continuously. All the materials selected as possible models of the avalanche snow negatively affected gas exchange during the breathing of the volunteers in a very similar extent. The time courses of the recorded parameters were very similar and were bordered from one side by the wet perlite and from the other side by the dry perlite. Therefore, other tested materials may be substituted with perlite with and appropriate water content. From all the tested materials, perlite is the best to simulate avalanche snow because of its homogeneity, reproducibility and easy manipulation.

Pulse Oximeter Performance during Rapid Desaturation

“…At the initiation of the stabilization phase, the subject was connected to the mouthpiece with a nose clip, breathing the ambient air; ventilation parameters with the gas analysis results were recorded. After five minutes, the customized tubing was attached to a cone-shaped container [26] filled with the tested material (snow or perlite) and the main part-the breathing phase-was initiated. Throughout the whole experiment, a clinical assessment of consciousness level of the volunteer was performed by a supervising physician: the physician asked the subject to calculate simple mathematical operations and show the result using their fingers which were not attached to the pulse oximeter probes.…”

“…Data from all breathing experiments (S, PD, PW) were analyzed together, as according to the already performed analyses [20,26], there are only minor differences in peripheral saturation trends and values among the experiments when subjects breathe into snow and its surrogate materials simulating avalanche snow. For the analysis, firstly, graphs for all five pulse oximeters measurements in all breathing experiments of all subjects were constructed.…”

“…However, the evaluation of these parameters-SpO 2 and EtCO 2 -in simulated avalanche experiments is burdensome [16][17][18]. The reliability of the end-tidal CO 2 monitoring during Sensors 2022, 22, 4236 2 of 13 simulated avalanche experiments, in which high level of gas rebreathing occurs, has already been assessed by Roubik and Filip [16].…”

“…However, the evaluation of these parameters-SpO 2 and EtCO 2 -in simulated avalanche experiments is burdensome [16][17][18]. The reliability of the end-tidal CO 2 monitoring during Sensors 2022, 22, 4236 2 of 13 simulated avalanche experiments, in which high level of gas rebreathing occurs, has already been assessed by Roubik and Filip [16]. They conducted a laboratory experiment using a snow model with a standard gas analyzer in Datex-Ohmeda S/5 (Datex-Ohmeda, Madison, WI, USA) anesthetic monitor and discovered that in as much as 71% of the time for which the volunteers were breathing into this model, the software of the monitor was displaying incorrect values of EtCO 2 , compared with the capnographic curve.…”

“…To date, an evaluation of the accuracy of pulse oximetry in simulated avalanche breathing trials, similar to the experiment with capnometry [16], has not been performed. Several studies addressed the correlation of SpO 2 with arterial blood oxygen saturation (SaO 2 ), the probe location, and the method-limiting factors (e.g., hypoxia, poor perfusion, dyshemoglobinemia, hypothermia, skin pigmentation, and hyperbilirubinemia) [1].…”