Moderate muscle cooling induced by single and intermittent/prolonged cold-water immersions differently affects muscle contractile function in young males

Background: We investigated the impact of moderate muscle cooling induced by single and intermittent/prolonged cold-water immersions (CWI) on muscle force and contractility in unfatigued state and during the development of fatigue resulting from electrically induced contractions.Methods: Twelve young males participated in this study consisting of two phases [single phase (SP) followed by intermittent/prolonged phase (IPP)], with both phases including two conditions (i.e., four trials in total) performed randomly: control passive sitting (CON) and cold-water immersions (10°C). SP-CWI included one 45 min-bath (from 15 to 60 min). IPP-CWI included three baths (45 min-bath from 15 to 60 min, and 15 min-baths from 165 to 180 min and from 255 to 270 min), with participants sitting at room temperature the rest of the time until 300 min. Blood pressure and intramuscular (Tmu) temperature were assessed, and neuromuscular testing was performed at baseline and 60 min after baseline during SP, and at baseline, 60, 90, 150 and 300 min after baseline during IPP. A fatiguing protocol (100 electrical stimulations) was performed after the last neuromuscular testing of each trial.Results: In unfatigued state, SP-CWI and IPP-CWI reduced electrically induced torque at 100 Hz (P100) but not at 20 Hz (P20), and increased P20/P100 ratio. The changes from baseline for P100 and P20/P100 ratio were lower in IPP-CWI than SP-CWI. Both cold-water immersion conditions slowed down muscle contraction and relaxation, and reduced maximal isokinetic contraction torque, but the changes from baseline were lower after IPP-CWI than SP-CWI. cold-water immersions did not impair maximal voluntary isometric contraction. During the fatiguing protocol, torque fatigue index and the changes in muscle contractile properties were larger after IPP-CWI than SP-CWI, but were in the same range as after CON conditions. The differences of muscle contractile function between SP-CWI and IPP-CWI were accompanied by a lower reduction of superficial Tmu and a smaller increase in systolic blood pressure after IPP-CWI than SP-CWI.Conclusion: IPP-CWI induces a less pronounced fast-to-slow contractile transition compared to SP-CWI, and this may result from the reduced vasoconstriction response and enhanced blood perfusion of the superficial muscle vessels, which could ultimately limit the reduction of superficial Tmu

Innate and adaptive responses to acute cold stress in humans

From beginning of mankind, humans have been confronted to extreme temperature fluctuations and yet they have managed to survive. Several individual factors, such as age, sex, body composition, exercise, acute and chronic diet, genotype, fitness level, and health may modify the body’s responses to cold (Launay, Savourey, 2009; Lupien et al., 2009). It is well known that exposure to an acute cold stress increases the levels of catecholamine (Shansky, Lipps, 2013; Morsella et al., 2009) and other stress hormones (Palmieri-Smith et al., 2007; LaVoy et al., 2011; Shansky, Lipps, 2013); impairs vigilance, overall mood (Lieberman et al., 2009), motor and cognitive performance (Roedinger et al., 2005; Drinkwater, 2008; Duncko et al., 2009; Lieberman et al., 2009; Brazaitis et al., 2010; Racinais, Oksa, 2010; Brazaitis et al., 2012); increases spinal reflex excitability (Dewhurst et al., 2005; Owen et al., 2005); and suppresses (LaVoy et al., 2011; Schwabe et al., 2012) or stimulates (Brenner et al., 1999; Tikuisis et al., 1999; Deng et al., 2003; Joëls et al., 2006) the immune system. These are physiological characteristics that are of critical importance for the survival, health, and well-being of humans who are exposed to occupational and/or recreational extreme-cold conditions. In our first experiment we address the question of why some people have a greater chance of surviving and/or better resistance to cold related-injuries in prolonged exposure to acute cold environments than do others, despite similar physical characteristics. From our earlier experiments, we recognized that originally the humans with similar physical characteristics can response to cold differently: those whose rectal temperature (Tre) decreased to the set point of 35.5 oC before the end of the 170-min cooling time (fast cooling (FC)) and those who’s Tre did not decrease to the set point of 35.5 oC before the end of the 170-min cooling time (slow cooling (SC)). We reasoned (1 hypothesis) that during single 14 °C CWI the FC group would therefore perceive greater cold stress, which would be reflected in larger increases in the cold strain index (CSI) and would have greater effects than SC on stress markers (cortisol, corticosterone, epinephrine (EPI) and norepinephrine (NE) concentrations), and in markers of immune function (neutrophils, leucocytes, lymphocytes, monocytes, interleukin 6 (IL-6) and tumour necrosis factor- (TNF-) concentrations). We also expected that major cold stress induced by FC would have greater effects than SC on motor (spinal reflexes, supraspinal reflexes and voluntary and electrically induced skeletal muscle contraction force) and cognitive (unpredictable task switching (executive function), the forward digit-span task (short term memory), and the forced-choice recognition memory test (short term spatial recognition) performance. Also no one has explored the effects of heat stress (39.5 oC increase in Tre) on motor and cognitive performance, immune variables, and the HPA-axis and autonomic nervous system in young men who react differently (SC vs FC) in physiological mechanism response to cold stress. Here we hypothesized (2 hypothesis) that the reduced ability to perceive cold stress might be related to a deficiency in the response to heat stress. Heat stress contrasts with cold stress because heat stress does not require the body to produce heat through shivering and non-shivering mechanisms to maintain Tc (body insulation mechanisms). Instead, during heat stress, the excess heat must be removed effectively and heat production reduced. If the resistance mechanisms to cold and heat are antagonistic (van Marken Lichtenbelt et al., 2009), then one might expect that the SC group would perceive greater heat stress, as indicated by the physiological stress index (PSI), than the FC group and that heat stress would have greater effects on stress indicators, such as cortisol, EPI, and NE levels, and immunity in the SC group. We also expected that greater induced heat stress would have greater effects in the SC group than in the FC group on motor (skeletal muscle, spinal reflexes, supraspinal reflexes, and voluntary contraction force) and cognitive performance. Alternatively, we hypothesized that resistance to cold and resistance to heat are controlled by different and independent mechanisms, which do not suppress one another. If so, we would expect to find no difference in the response to hyperthermia between the FC and SC groups. Whole-body adaptation to cold in humans can be expressed differently, as indicated by the development of the metabolic, hypothermic or insulative type of acclimation (induced experimentally) or acclimatization (induced naturally) (Hammel, 1962; Young et al., 1986; Bittel, 1992; Vybiral et al., 2000; Taylor, 2006; Launay, Savourey, 2009; Makinen, 2009). The existence of insulative-hypothermic (Scholander et al., 1958; Young et al., 1986; Launay, Savourey, 2009; Makinen, 2009) or metabolic-insulative (Bittel, 1992; Makinen, 2009) subtypes is sometimes evident as well. More than four decades ago, S. Skreslet, F. Aarefjord (1968) suggested that the different types of cold acclimation (CA) do not represent mutually exclusive physiological states; rather, they are different successive stages of the development of complete cold adaptation. We hypothesized (3 hypothesis), that the day-to-day time course of physiological responses during CA (17 controlled head-out water immersions at a temperature of 14 C over 20 days) is expressed as a transitional shift from shivering thermogenesis (ST) to non-shivering thermogenesis (NST), from the development of metabolic to hypothermic to insulative pattern of acclimation and from peripheral-to-central to central temperature input thermoregulation. We also expect that chronic cold stress will yield a greater activation of the specific, rather than the innate, immune system (Dhabhar et al., 1995, 2009; Leon, Helwig, 2010). Moreover, a greater amount of white adipose tissue (as indicated by body mass index (BMI) and subcutaneous fat thickness) in the subjects after acclimation will show a lesser (i.e., more blunted) increase in NST (van Marken Lichtenbelt et al., 2009; Ouellet et al., 2012) after CA. The aim of the research The aim of the research was to determine innate and adaptive response to cold stress on physiological and psychological characteristics in humans. Research objectives: 1. To investigate the effect of acute cold stress (intermittent 14 oC CWI) on physiological and psychological characteristics and their possible complex-interaction in two cold tolerance groups FC vs SC. 2. To compare the physiological and psychological responses to heat stress (immersed to the waistline to 43–44 oC water bath), between people who exhibited fast or slow cooling responses to 14 oC CWI. 3. To determine whether 17 head-out acute CWI over 20 days is sufficient to develop CA by remodelling proportional changes in the development of metabolic versus hypothermic versus insulative patterns of physiological response. Originality, novelty and practical significance of the research This is the first experiment that indicate a difference in responses of motor and cognitive performance, markers of stress, and immune system between physically similar subjects who innately exhibited two different (innate) response strategies to single acute cold stress (i.e., 14 °C CWI). Also no one has explored the effects of heat stress (i.e., 43–44 oC HWI), on those two groups (FC vs SC). In general we have found, that humans have similar chances of risk to get heat exhaustion, heat stroke and to be overheated in hot environment, despite of their different reaction to cold stress. In most studies, the researchers explore only the pre- and post-effects of CA. Because of this it is possible to find many research publications with contradictory results. In our third experiment, we used a day-to-day evaluation of three generally accepted physiological markers (i.e., Tsk, Tre and MHP) throughout whole-body CA. This allowed us to explore a day-to-day transitional change of three general patterns of the CA, which we believe was studied here for the first time. Better understanding how humans innately and adaptively reacting to the acute cold stress is of critical importance for the survival, health and well-being of humans who are exposed to occupational (military, industry, clinic and sports) or recreational (swimming, skiing, diving) extreme temperature conditions. Also it should help updating, occupational health care and safety guidance for work, sporting and recreational events in hot and cold conditions. The information may also be utilized for developing monitoring systems predicting accidental hypothermia and hyperthermia hazards. We hope that our findings will help to make a deeper understanding about the human innate and adaptive thermoregulation and will serve as the foundation for new discoveries. Conclusions: 1. First experiment reports that humans according to the innate reaction to acute cold stimulus could be divided in to two groups (fast-cooling and slow-cooling) despite their similar physical characteristics. The response of the fast-cooling group to cooling vs the slow-cooling group response was more likely an insulative–hypothermic response and that the slow-cooling vs the fast-cooling group displayed a metabolic-insulative response. Despite the larger cold strain index in the fast-cooling group the changes in stress markers did not differ between groups. The most important finding is that subjects with a lower cold strain index showed stimulation of some markers of innate immunity and suppression of markers of specific immunity. However, contrary to our expectation, motor and cognitive performance response to cold stress did not differed between the fast-cooling and slow-cooling groups. 2. Second experiment reports that despite the greater cold strain index after acute cold exposure in subjects in the fast-cooling than in the slow-cooling group, the changes in stress markers after passive body heating to a rectal temperature of 39.5 °C did not differed between the fast-cooling and slow-cooling groups. Heat stress did not changed markers of innate and specific immunity. An interesting finding was that heat stress did not affected motor and cognitive function in either group, although central fatigue during 1-min maximal voluntary contraction increased after heat stress in both groups, but did not differ between groups. 3. As expected, the data obtained in third experiment, suggest that the subjects exhibited a thermoregulatory shift from peripheral-to-central input thermoregulation, as well as from shivering to non-shivering thermogenesis. Contrary to our expectation, in the first six, acclimation to cold sessions, a hypothermic type of acclimation was found; further acclimation to cold sessions (from seventh acclimation to cold session to sixteenth) led to a transitional shift to a hypothermic–insulative type of acclimation. Interestingly, during the seventeenth acclimation to cold session when the subjects were immersed in water for the same time as that used in the first session, the acclimation to cold led to a hypothermic type of acclimation. Finally, the presence of a metabolic type of thermogenesis was evident only under thermo neutral conditions. Despite the fact that cold strain index was increased significantly after acclimation, cold-water immersion decreased the concentration of cold-stress markers, reduced the activity of the innate immune system, suppressed specific immunity to a lesser degree and yielded less discomfort and cold sensation

Computer system attack classification

The computer system security modeling needs a numerical attack severity evaluation. Some hypothetical attack severity values are usually used. With the aim to make modeling more accurate and to expand the model abilities it is necessary to relate numerical values used in modeling with real attacks and their classes. In this article most popular attack classifications have been analyzed and the computer system attack classification covering 14 aspects of the attack and suitable for future research is suggested. The method of the attack severity numerical evaluation applying the computer system attack classification using a 5 level attack severity numerical evaluation, based on the attack objective, is suggested. 111. 1, bibl. 14 (in Lithuanian; summary in English6 Russian and Lithuanian)

Computer Networks

The Computer Networks laboratory works and methodical guidelines are designed to help students to acquire knowledge about computer network technologies, network equipment, network design principles, configuration and troubleshooting tasks. Twelve laboratory works are presented in the book. Each laboratory work consists of theoretical material that introduces the object of investigation, laboratory work assignments and methodical guidelines. At the end of each laboratory work the references and review questions and problems are presented. This book is intended for students studying Computer Engineering and Information Systems Engineering courses, also for students studying the subject of computer networks. This publication has been produced with the financial assistance of Europe Social Fund and VGTU (Project No VP1-2.2-ŠMM-07-K-01-047). The book is a part of the project “The Essential Renewal of Undergraduates Study Programs of VGTU Electronics Faculty”

Tinklo žvalgos aptikimo sistemos modeliavimas

The network scan detection provides information about the attempts of attackers to determine servers and to prevent potential trials to compromise them. In the work the model for simulation of the network scanning and its detection using the stochastic activity network and their simulation tool Mobius is proposed. The model allows operative evaluation of the influence of simulated computer system parameters on the scan detection efficiency and proper configuration of the intrusion detection system. The results of the horizontal scan simulation are presented. The IDS parameters having the highest influence on the intrusion detection performance for a specific case have been determined. Ill. 3, ref. 5 (in English; summaries in English, Russian and Lithuanian).Lietuviška santrauka. Žvalgos aptikimas suteikia informacijos apie atakuojančiųjų bandymus nustatyti paslaugas teikiančias tarnybines stotis ir užkirsti kelią potencialiems bandymams jas sukompromituoti. Straipsnyje pasiūlytas modelis tinklo žvalgai ir jos atpažinimui modeliuoti, panaudojant stochastinius veiklos tinklus ir jų modeliavimo įrankį Mobius. Modelis leidžia operatyviai įvertinti modeliuojamos kompiuterių sistemos parametrų įtaką žvalgos aptikimo efektyvumui ir teisingai sukonfigūruoti atakų atpažinimo sistemą. Pateikti horizontaliosios žvalgos modeliavimo rezultatai. Nustatyti IDS parametrai, turintys daugiausia įtakos atakų aptikimo efektyvumą konkrečiu atveju. Il. 3, bibl.5 (anglų kalba; santraukos anglų, rusų ir lietuvių k.)

Packet inter-arrival time distribution in academic computer network

The article presents the statistical analysis results of network packet inter-arrival time distribution in academic computer network. Most popular transport protocols TCP and UDP are addressed in the research. Data was gathered using NetFlow protocol. Network traffic was divided into sections according its direction and usage trends, then packet inter-arrival time distributions were found. Kolmogorov-Smirnov test was used to evaluate goodness - of-fit of packet inter-arrival time distributions and it was determined, that Pareto Second Kind distribution fits the majority of the experimental distributions

Exposure to acute noxious heat evokes a cardiorespiratory shock response in humans

Background: Noxious acute cold stimuli cause cold shock via the sympathetic nervous system. However, no studies have investigated respiratory “heat shock” in response to noxious acute heat stimuli (≥ 42 °C). Methods: In the present study, we examined whether short-duration whole-body immersion (for 5 min) in noxious hot water (45 °C) is a sufficient stimulus to induce a respiratory acute shock response. Results and conclusion: Our results indicate that short-duration whole-body immersion in noxious 45 °C water produces a significantly greater body temperature, heart rate, and perceptual and respiratory strain than immersion in innocuous warm 37 °C water (p < .05). The initial first minute of hot water immersion (HWI) at 45 °C (vs. immersion at 37 °C) caused a cardiorespiratory shock response, which manifested as acute hyperventilation, and increased ventilatory tidal volume, respiratory exchange ratio, and heart rate (p < .05). Adjustment to this initial respiratory heat shock response within the first minute of immersion was observed as compared with remaining HWI time (1–5 min). Intriguingly, the time-course kinetics of breathing frequency, oxygen uptake, and carbon dioxide washout did not differ between whole-body immersion at 37 °C and immersion at 45 °C, but were higher than in control thermoneutral conditions of an empty bath (p < .05). This may be because of events initiated not only by the water temperature but also by the change in the hydrostatic pressure acting upon the body when immersed in the water bath

The role of age on neuromuscular performance decay induced by a maximal intensity sprint session in a group of competitive endurance athletes

Age -related changes in the neuromuscular system functions may affect profoundly high -level athletes ' performance across their career s. The present study aimed to analyse the fatiguing effect of a maximal intensity sprint session (MISS) on competitive athletes of diffe rent age s. Thirty - one competitive endurance athletes completed a knee extensors and flexors ' maximal -voluntary- isometric -contraction (MVC) test before and after a maximal -intensity -sprint -session (MISS) consisting of 4x15s Wingate -tests. The data have been stratified considering three age categories (18 -28, n=11, 29- 38; n=10; 39 -43, n=10). Overall, both quadricep and hamstring muscles early and late rate of torque development (RTD) dropped significantly more than the maximal voluntary torque (MVT) (p<.05). Age had a significant effect on early RTD , with older athletes exhibiting greater RTD (p<.05). A significant effect of age also emerged for the changes in surface sEMG variables, in which the frequency spectrum variables dropped significantly more than the sEMG amplitude (RMS) (p<.05). The dynamics of changes in neuromuscular performance markers after a MISS suggested that getting older competitive athletes may potentially experience a greater loss in early explosive strength compared to maxim al or late exp losive strength

Age-Related Difference in Cognitive Performance under Severe Whole-Body Hyperthermia Parallels Cortisol and Physical Strain Responses

Background and Objectives: To date, understanding age-related changes in cognitive processes during heat exposure still needs to be better-understood. Thus, the main aim of the current study was to evaluate the effects of whole-body hyperthermia (WBH), i.e., a ≈ 2.5 °C increase in rectal temperature (Tre) from overnight-fast baseline value, on cognitive functioning in old and young men and to explore factors, such as stress and thermophysiological strain, that could influence such changes. Materials and Methods: Ten young (19–21 years of age) and nine old (61–80 years of age) healthy men underwent an experimental trial with passive lower-body heating in hot water immersion (HWI) at 43 °C (HWI–43 °C) until Tre reached 39 °C in old adults and 39.5 °C in young adults. Cognitive performance and cortisol concentration were assessed before and after HWI, and the physiological strain index (PSI) was assessed during HWI–43 °C. Results: PSI was lower and cortisol concentration was greater after HWI–43 °C in the old group compared with the young group (p Conclusions: A ≈ 2.5 °C increase in rectal temperature can improve executive function in old adults, and this increase parallels the increased cortisol concentration and the lower thermophysiological strain under severe WBH conditions

Survivability modelling of Lithuanian government information system

This paper presents a new approach which allows us to find the system compromise probabilities and applying them to simulate computer system survivability. Also, four computer system survivability simulation models were composed and according to requirements for recovery time and accessibility of Lithuanian government information systems computer system survivability simulations were performed. Simulation models were composed using Stochastic Activity Network (SAN) formalism. Presented model allows evaluating system survivability based on threat type, incident severity and the amount of implemented security mechanisms. The model is flexible, expandable and can be adapted to other computer systems