No abstract

The pressure reactivity index (PRx) is a parameter for the assessment of cerebrovascular autoregulation, but its calculation is affected by artifacts in the source biosignals—intracranial pressure (ICP) and arterial blood pressure. We sought to describe the most common short-duration artifacts and their effect on the PRx. A retrospective analysis of 935 h of multimodal monitoring data was conducted, and five types of artifacts, characterized by their shape, duration, and amplitude, were identified: rectangular, fast impulse, isoline drift, saw tooth, and constant ICP value. Subsequently, all types of artifacts were mathematically modeled and inserted into undisturbed segments of biosignals. Fast impulse, the most common artifact, did not alter the PRx index significantly when inserted into one or both signals. Artifacts present in one signal exceeded the threshold PRx in less than 5% of samples, except for isoline drift. Compared to that, the shortest rectangular artifact inserted into both signals changed PRx to a value above the set threshold in 55.4% of cases. Our analysis shows that the effect of individual artifacts on the PRx index is variable, depending on their occurrence in one or both signals, duration, and shape. This different effect suggests that potentially not all artifacts need to be removed.

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.

The reliability of pulse oximetry is crucial, especially in cases of rapid changes in body oxygenation. In order to evaluate the performance of pulse oximeters during rapidly developing short periods of concurrent hypoxemia and hypercapnia, 13 healthy volunteers underwent 3 breathing phases during outdoor experiments (39 phases in total), monitored simultaneously by five different pulse oximeters. A significant incongruity in values displayed by the tested pulse oximeters was observed, even when the accuracy declared by the manufacturers were considered. In 28.2% of breathing phases, the five used devices did not show any congruent values. The longest uninterrupted congruent period formed 74.4% of total recorded time. Moreover, the congruent periods were rarely observed during the critical desaturation phase of the experiment. The time difference between the moments when the first and the last pulse oximeter showed the typical study endpoint values of SpO2 85% and 75% was 32.1 ± 23.6 s and 24.7 ± 19.3 s, respectively. These results suggest that SpO2 might not be a reliable parameter as a study endpoint, or more importantly as a safety limit in outdoor experiments. In the design of future studies, more parameters and continuous clinical assessment should be included.