Research of Effect of Hyperbaric Pressure on Dynamics and Efficiency of Complex Mental Processing

The paper presents the experimental plan, methodology and results of research of efficiency and dynamics of complex mental processing in 15 divers (diver demolition specialists) in simulated conditions of diving at the depth not exceeding 30 meters in hyperbaric chamber. Changes in efficiency (total time) and dynamics (speed, stability and accuracy) of mental processing were determined through 20 measurements (5 measurements per pressure entry ranging from 14 bars) with each examinee, and by means of the following chronometric cognitive tests: 1. test of perception of spatial location of light signal (CRD 311) 2. short-term operational memory test (CRD 324) 3. simple visual orientation test (CRD 21) 4. operational thinking connected with hand and foot coordination (CRD 413) 5. problem solving test (CRD 11) The research revealed significant changes in processing speed registered at the 2 b pressure (at the simulated 10-m depth) and processing stability at the 4 b pressure (30-m simulated depth) respectively, which affect the mental processing efficiency in general as it decreases abruptly at the 2 b hyperbaric pressure at the simulated 10-m depth, remains unchanged at the 20-m simulated depth and continues to decrease at the 30-m depth. 36 IAMPS Split, CROATIA 2000 81 INTRODUCTORY REMARKS The study of influence of increased pressure (simulated shallow air-diving) on changes of mental and psychomotoric efficiency of divers and seals is a part of original scientific research within macroproject "Development and Management of Human Resources in the Croatian Military", which has been in progress since 1992 as a part of research of defense strategy of the Republic of Croatia. During thematic workshop "Psychological Functioning Under Extreme Conditions", held during 36th IAMPS, in Split, Croatia, this paper was used to initiate discussion about the problem of influence of extreme conditions, often found in the militaries, on operative capabilities of soldiers, specially on their psychomotoric and mental efficiency. Nitrogen narcosis is a problem of constant concern for divers and diving physicians. It might seem that really everything has been already said about it, since this phenomenon has been extensively studied, and some extensive reviews are available (1-4). In the diving community it is usually considered that the effects of nitrogen narcosis on performance under the water could be detected at 40 meters and deeper, further impairment occurring with the increase of depth. Behnke and co-workers described performance impairment at 20 meters characterized by euphoria, retardation of the higher mental processes, and impairment of muscular coordination, and at 30 meters as well, characterized by feeling of stimulation, excitement, and euphoria (5). Bennett and co-workers found "...the minimal partial pressure of nitrogen likely to produce an effective deterioration of performance was 3.2 atm (323 kPa), or that in air at 30 m..."(6). Having in mind possible nitrogen narcosis at even shallower depths, Bennett later stated: "No doubt, there are very sensitive tests which, under the right conditions, will show evidence of quantitative narcosis, but it would seem that such evidence is but of academic interest." (1). Since divers, novice and experienced, report from time to time minor psychomotoric problems while air diving in shallow waters, we tested possible nitrogen narcosis effects at 10m, 20m, and 30 m (2.0, 3.0, and 4.0 bars, respectively). Since most of the similar studies are based on multiple retesting, i.e. on multiple measurement of the same functions the same subjects, in designing such studies special attention should be paid to selection of adequate tests and standardization of experimental conditions, as well as to methodology and analysis of individual differences. There are only few psychological tests applicable for multiple retesting on the same subjects, since the object of measurement changes during the experiment. Many psychological tests that measure capabilities, if used for multiple retesting, become tests of knowledge, thus interindividual and intraindividual variabilities of the results of the measurement diminish. THE FOCUS OF THIS RESEARCH The main problem of this research is mental processing efficiency under pressures from 2.0 to 4.0 bars, i.e. understanding changes of total efficiency and dynamical characteristics of mental processing under these circumstances. This makes the frame for the following questions: changes of total mental efficiency, changes of efficiency of different forms of mental processing, and variations of characteristics of dynamics of mental processing, expressed as indicators of speed, stability, and accuracy of mental processing. Specific objective of this study imposed further problems dealing with the methodology of processing of the obtained data and analysis of the results. Therefore, the paper also deals with the problem of elimination of marked interindividual differences on the level and dynamical characteristics of subjects as well as elimination of effects of exercise in multiple retesting. METHODS Subjects 15 healthy male divers, average age of 28.3ą4.6 years, with 5.7ą4.8 years of diving experience, after signing informed consent, participated in the study, previously approved by the appropriate ethical committee. 36 IAMPS Split, CROATIA 2000 82 Apparatus The experiment was conducted in hyperbaric chamber Draeger-Galeazzi. Figure 1. Hyperbaric chamber Performance was tested using battery of computerized tests Complex Reactionmeter Drenovac (CRD-series). Before the experiment, the subjects were trained using CRD-series two hours per day and after three days obtained five results in a row without tendency of improvement. This was considered to be a "stable" result, i.e. "entry level". Amongst hundreds of tests that could be given on CRD-series, only five representative tests (11, 21, 311, 324, and 413) were selected for the study (first digits represent CRD-series instrument number). Figure 2. Set up of CRD-series instruments inside the chamber. The sequence of the tests given was from simple to more complicated, i.e. 311, 324, 21, 11, and 413. The goal was to complete any given test as quickly as possible, and with as few errors. Correct hit in every test would automatically results in a new task. We measured total solving time (TT), i.e. total result of mental processing on any given test, minimal single task solving time (TMIN), i.e. maximal speed of mental processing, total "ballast" (TB), i.e. sum of differences between various single task solving times and TMIN, representing "stability" of mental processing, and finally total number of errors (TE), i.e. credibility and accuracy of processing. These parameters could be understood as descriptors of psychomotoric manipulations of certain type or level. Test 311 was used to measure the ability of visual discrimination of signal localization. This test consists of 60 single tasks. Light-emitting diodes (LEDs) illuminate in random order, and the correct answer is given by pressing the button below the corresponding LED. Test 324 was used to measure the ability of actualizing short-term memory. It also consists of 60 single tasks. LEDs illuminate in random order and correct answer is given by pressing the button defined by certain sequence known to the subjects before testing. This position might be left, right or just below the LED. In this experiment the sequence was "leftright-right-below", and the subjects were obliged to actualize this memorized sequence. 36 IAMPS Split, CROATIA 2000 83 Test 21 was used to measure the ability of simple convergent visual orientation. In each of 35 single tasks two LEDs illuminate simultaneously the first either in the left or in the right column, the second either in the upper or in the lower row. The correct answer is given by pressing the button at the intersection of the two LEDs. Test 11 was used to measure the ability of convergent thinking, i.e. general ability to perform in problematic situations. This function is provoked by constructing and solving simple mathematical tasks. Out of 35, 18 tasks were addition, 17 subtraction. In each of the tasks two LEDs emit at the same time. One of 12 LEDs positioned in the central part of the instrument indicates which numbers in the upper row and lateral columns should be used to construct mathematical problem. The second LED is one of the two in upper corners, and indicates which operation to use. The correct answer is given by pressing the corresponding button, i.e the result of mathematical operation, in the lower part of the instrument. Test 413 was used to test the ability of operative thinking or complex psychomotoric coordination (eye-hand). Field "A" of the instrument was used, consisting of four LEDs (upper two for hands, lower two for legs), as well as buttons and pedals. Each of 35 given tasks was a specific command. A combination of two or three LEDs would illuminate at the same time, requiring various combination of hands and legs to be pressed simultaneously for the correct answer. Figure 3. Hyperbaric chamber and set up of CRD-series instruments inside the chamber (schematic). Procedure The experiment was conducted in a multiplace hyperbaric chamber (figure 1) by repetitive measuring of the same indicators of mental and psychomotoric functions at 1.0, 2.0, 3.0, and 4.0 bars, respectively, during five consecutive days. The subjects were fully familiarized with the experimental environment during their earlier chamber exposures. During the experiment they were not provided with any feedback about the results of the tests. The testing was commenced five minutes after reaching the pressure. In a group of 8 randomly chosen subjects the testing would begin at the atmospheric pressure, followed by testing at 2.0, 3.0, and 4.0 bars, respectively. Every other day this order was inverted. In the second group consisting of 7 subjects, the subjects were first tested at 4.0 bars, than to 3.0, 2.0, and finally at the atmospheric pressure. Every other day this order was inverted in this group, too. In statistical analysis ANOVA and MANOVA procedures, Median-test, and Kruskal-Wallis test were used. P-values less than 5% were considered significant. 36 IAMPS Split, CROATIA 2000 84 PROCESSING AND ANALYSIS OF RESULTS Processing of the obtained data was done in three steps. In the first step preliminary analysis of interindividual differences of levels and functional characteristics of mental processing was done, as well as the analysis of changes of these parameters as a function of the experiment. Since significant interindividual differences and significant changes of efficiency and dynamical characteristics of mental processing as a function of duration of the experiment (days) were found, the second step included sorting and transposition of the obtained data, i.e. transposition into standard z-values and sorting into relative rankings. Transformation of the original values into standard z-values was done for every subject individually, and transposition of the original values into relative rankings was done for every subject according to the cycles of the measurement (4 measurements for every “dive”). The effects of these transformations is presented in figures 4 and 5. Figure 4. Elimination of interindividual differences Great interindividual differences were noticed in all 5 tests. By transposition into standard z-values, the differences were leveled to “0” (zero). ±1.96*Std. Err. ±1.00*Std. Err. Mean TT CRD 11