Useful Consciousness Research Articles

Hypoxia and Time of Useful Consciousness in Hypobaric Chamber at 25,000 feet in Aircrew at dr. Saryanto Health Institute of Aeronautics and Space

Introduction: Hypoxia is a condition characterized by insufficient oxygen supply to tissues which causes body tissues to fail to get adequate oxygen supply. Hypobaric hypoxia is generally recognized as the most serious physiological hazard during high-altitude flight. This puts active crew members at risk for hypoxia and so they rely on effective performance time (EPT) or time useful consciousness (TUC) to take appropriate corrective and protective actions when hypoxia occurs. This study aimed to describe TUC scores and hypoxia symptoms experienced by active flight crew at dr. Saryanto Health Institute of Aeronautics and Space in 2021. Methods: A descriptive research design using medical record data from 99 flight crew with simple random sampling. The variables in this study consisted of hypoxia symptoms and TUC scores. This study uses univariate analysis to see the frequency distribution of the variables of hypoxia symptoms and TUC score. Results: The results showed that 18.2% experienced cognitive symptoms, 4% experienced psychomotor symptoms, 16.2% experienced visual symptoms, 3% experienced psychological symptoms, 54.5% experienced non-spesific symptoms, and 37.4% did not feel any symptoms. Most of the flight crew (68.7%) had sufficient EPT/TUC scores (3-4 minutes). Conclusion: Active flight crews feel symptoms of hypoxia and have sufficient TUC scores.

FLIGHT HOURS AND BMI AGAINST TUC IN HYPOBARIC CHAMBER ALTITUDE 25.000 FEET

Background: Time of Useful Consciousness (TUC) is the time interval a person can survive carrying out flight duties due to a decrease in oxygen pressure and the point at which there is a decrease in the level of consciousness. The TUC time interval is influenced by various factors including Body Mass Index (BMI) and flying hours which affect the increase in the duration of the body's exposure to hypoxic conditions in pilots. Purpose: This research was conducted to determine the relationship between total flight hours and BMI on TUC. Method: This research employed observational analytic research with a cross-sectional method. Sampling was taken by simple random sampling technique. The sample for this research included active flight crew members from Lakespra dr. Saryanto 202 who met the inclusion criteria. Result: There were 53 research subjects, with the results showing that 48 subjects (90.6%) had a TUC <4 minutes, and 5 subjects had a TUC >4 minutes. There were 47 subjects (88.7%) with total flight hours >1000 hours and 6 subjects (11.3%) with total flight hours <1000 hours. In BMI, 37 subjects (69.8%) had an overweight BMI, and 16 subjects (30.2%) had a normal BMI. Conclusion: After examining 53 subjects, it was found that there was no relationship between total flight hours and TUC (p-value = 1.000) or BMI and TUC( p-value = 0.307) in the hypobaric chamber at an altitude of 25.000 feet.

Oxygen Saturation Curve Analysis in 2298 Hypoxia Awareness Training Tests of Military Aircrew Members in a Hypobaric Chamber.

We aim to provide reference values for military aircrews participating in hypoxia awareness training (HAT). We describe several parameters with potential biomedical interest based on selected segments and slopes of the changes in oxygen saturation (SatO2) during a standard HAT. A retrospective analysis of 2298 records of the SatO2 curve was performed, including 1526 military men aged 30.48 ± 6.47 years during HAT in a hypobaric chamber. HAT consisted of pre-oxygenation at 100% and an ascent to 7620 m, followed by O2 disconnection starting the phase of descent of SatO2 until reaching the time of useful consciousness (TUC), and finally reconnection to 100% O2 in the recovery phase. Using an ad hoc computational procedure, the time taken to reach several defined critical values was computed. These key parameters were the time until desaturation of 97% and 90% (hypoxia) after oxygen mask disconnection (D97/D90) and reconnection (R97/R90) phases, the time of desaturation (TUC-D97) and hypoxia (TUC-D90) during disconnection, the total time in desaturation (L97) or hypoxia (L90), and the slopes of SatO2 drop (SDSAT97 and SDSAT90) and recovery (SRSAT97). The mean of the quartiles according to TUC were compared by ANOVA. The correlations between the different parameters were studied using Pearson's test and the effect size was estimated with ω2. Potentially useful parameters for the HAT study were those with statistical significance (p < 0.05) and a large effect size. D97, D90, R97, and R90 showed significant differences with small effect sizes, while TUC-D97, TUC-D90, L97, L90, and SDSAT97 showed significant differences and large effect sizes. SDSAT97 correlated with TUC (R = 0.79), TUC-D97 (R = 0.81), and TUC-D90 (R = 0.81). In conclusion, several parameters of the SatO2 curve are useful for the study and monitoring of HAT. The SDSAT97 measured during the test can estimate the TUC and thus contribute to taking measures to characterize and protect the aircrew members.

The Relationship Between Anaerobic Performance Test and Time of Useful Consciousness Determined in Low-Altitude Chamber (25.000 Feet) with Heart Rate Variability

Understanding the relationship between anaerobic performance and time of useful consciousness (TUC) is important for individuals engaged in activities at high altitudes such as climbers, pilots, or astronauts. The aim of this research is to investigate the relationship between anaerobic capacity and TUC determined in a low-altitude chamber (LAC), in terms of performance and heart rate variability (HRV), in healthy males. Thirty male participants were included in the study as volunteers (mean age: 23.2±0.8 years; height: 180.6±6.0 cm; weight: 77.0±8.2 kg). In the scope of the research, participants were exposed to oxygen in a LAC at an atmospheric level of 25.000 feet after body measurements were taken on the first day, and TUC was determined. Anaerobic capacities of the participants were determined the following day using the Wingate Anaerobic test (WAnT). HRV was recorded before, during, and after both tests. According to the findings of our research, the parameter changes of Mean-RR, SDNN, and frequency domain parameters HFnu were significant for both WAnT and LAC in terms of TUC in the pre-test, during the test, and post-test periods. RMSSD change was significant for LAC, while LFnu change was significant for WAnT. In intra-group comparisons, there was a significant difference between pre-test and during the test for WAnT, but no significant difference between during the test and post-test. For LAC, there was a significant difference between pre-test and during the test, as well as between during the test and post-test. In terms of the relationship between anaerobic capacity and time to achieve TUC, TUC showed a non-significant negative correlation with relative peak power (r=-0.03; p=0.86), and non-significant positive correlations with total peak power (r=0.19; p=0.31) and total mean power (r=0.23; p=0.23). The most striking result of this research is the lack of significant relationship between TUC duration and anaerobic performance of the participants. Additionally, in terms of TUC, recovery was significant after TUC in LAC, while no recovery was observed after WAnT. According to the results of this research, anaerobic exercises are not a priority in terms of performance and HRV change to increase TUC. Anaerobic performance may not be the primary criterion for personnel selection for high altitude missions.

'Towards a Warmer World: What climate change will mean for New Zealand’s future' and 'Time of Useful Consciousness: Acting urgently on climate change'

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An Igor Pro 8.01 Procedure to Analyze Pulse Oximetry during Acute Hypoxia Test in Aircrews.

The recognition of hypoxia symptoms is a critical part of physiological training in military aviation. Acute exposure protocols have been designed in hypobaric chambers to train aircrews to recognize hypoxia and quickly take corrective actions. The goal of the acute hypoxia test is to know the time of useful consciousness and the minimal arterial oxygen saturation tolerated. Currently, there is no computer system specifically designed to analyze the physiological variables obtained during the test. This paper reports the development and analytical capabilities of a computational tool specially designed for these purposes. The procedure was designed using the Igor Pro 8.01 language, which processes oxygen saturation and heart rate signals. To accomplish this, three functional boards are displayed. The first allows the loading and processing of the data. The second generates graphs that allow for a rapid visual examination to determine the validity of individual records and calculate slopes on selected segments of the recorded signal. Finally, the third can apply filters to generate data groups for analysis. In addition, this tool makes it possible to propose new study variables that are derived from the raw signals and can be applied simultaneously to large data sets. The program can generate graphs accompanied by basic statistical parameters and heat maps that facilitate data visualization. Moreover, there is a possibility of adding other signals during the test, such as the oxygenation level in vital organs, electrocardiogram, or electroencephalogram, which illustrates the test's excellent potential for application in aerospace medicine and for helping us develop a better understanding of complex physiological phenomena.

The Effects of Body Composition, Physical Fitness on Time of Useful Consciousness in Hypobaric Hypoxia.

Several previous studies have reported that hypoxia accidents of fighter pilots are rarer than gravity-induced loss of consciousness and spatial disorientation; however, the risk is greater. Therefore, this study aimed to investigate the relationship between physical fitness and body composition on time of useful consciousness (TUC) in hypobaric hypoxia. Body composition and physical fitness testing on human participants were performed; subsequently, they were exposed to hypobaric hypoxia at a simulated altitude of 25,000 ft. Cognitive testing of the participants was accomplished by having them perform arithmetic task tables until they stopped writing for a period exceeding 5 seconds, at which point, they were placed on 100% oxygen. TUC was measured from the time the participants removed their oxygen masks to the time when the oxygen masks were placed back on them. Pearson's correlation was used to determine the relationship between TUC and other variables, and multiple regression was performed to determine the independent variables that best explain the TUC. TUC was positively correlated with the maximum oxygen uptake, stroke volume, arteriovenous oxygen difference, and endurance (sit-up and push-up). The maximum heart rate on the ground, high altitude, body fat mass, and percent body fat were negatively correlated with TUC. A regression analysis showed that 84.5% of the TUC can be explained by body composition and physical fitness. Our results revealed that increased cardiorespiratory fitness and decreased body fat mass could significantly impact the TUC. Therefore, for Air Force pilots who are frequently at high altitudes and at risk for exposure to hypoxia, aerobic exercise is significant to hypoxia tolerance.

Retro-fitment of an oxygen system in a transport aircraft of Indian Air Force: Decompression chamber trials to assess system functionality

The aeromedical concerns of sudden onset hypoxia and rapid decompression are an omnipresent threat to flight safety when flying over 10,000 ft. The concept of Time of Useful Consciousness (TUC) provides the aircrew a window to correct his predicament. The issues of hypoxia are mitigated in transport aircraft with cabin pressurization. However, the requirement of an oxygen system in these aircraft is considered essential in an emergency in case of cabin failure of cabin pressurization or rapid decompression, despite adequate TUC, as it provides immediate succor from anxiety, and subtle performance decrements, especially in VIP carriage or casevac roles. With this background, a requirement for retro-fitment of a functional oxygen system of a small transport ac of Indo-German origin into a pressurized medium-lift cargo aircraft of British Origin was envisaged. Toward this, ground-based simulator trials were conducted on the oxygen system to assess its functionality before undertaking flight trials in the aircraft. The assessment consisted of the ground trial of the test oxygen system in the Explosive Decompression Chamber with three experiment protocols. The experimentation involved exposure to a simulated altitude of 15,000 ft for 25 min and rapid decompression from 7000 to 15,000 ft. Physiological parameters, endurance, and flow of oxygen in the system were evaluated. The trial results indicated that the physiological parameters (heart rate, respiratory rate, oxygen saturation [SpO2], and end-tidal carbon dioxide [EtCO2]) were within normal limits during the entire duration of exposure to 15,000 ft and decompression from 7000 ft to 15,000 ft. In addition, the physiological parameters were also within normal limits during exposure to 1 min of simulated hyperventilation. Neither any subjective or objective symptoms of hypoxia were observed nor any appreciation of increased breathing resistance reported by the subjects. The endurance of the system in terms of delivering continuous oxygen flow at 15,000 ft was assessed to be 73 min. From the trials, it was inferred that the oxygen system in a single crew configuration could be used satisfactorily up to the operational ceiling altitude specified for the subject aircraft.

Hypoxic Hypoxia and Brain Function in Military Aviation: Basic Physiology and Applied Perspectives.

Acute hypobaric hypoxia (HH) is a major physiological threat during high-altitude flight and operations. In military aviation, although hypoxia-related fatalities are rare, incidences are common and are likely underreported. Hypoxia is a reduction in oxygen availability, which can impair brain function and performance of operational and safety-critical tasks. HH occurs at high altitude, due to the reduction in atmospheric oxygen pressure. This physiological state is also partially simulated in normobaric environments for training and research, by reducing the fraction of inspired oxygen to achieve comparable tissue oxygen saturation [normobaric hypoxia (NH)]. Hypoxia can occur in susceptible individuals below 10,000 ft (3,048 m) in unpressurised aircrafts and at higher altitudes in pressurised environments when life support systems malfunction or due to improper equipment use. Between 10,000 ft and 15,000 ft (4,572 m), brain function is mildly impaired and hypoxic symptoms are common, although both are often difficult to accurately quantify, which may partly be due to the effects of hypocapnia. Above 15,000 ft, brain function exponentially deteriorates with increasing altitude until loss of consciousness. The period of effective and safe performance of operational tasks following exposure to hypoxia is termed the time-of-useful-consciousness (TUC). Recovery of brain function following hypoxia may also lag beyond arterial reoxygenation and could be exacerbated by repeated hypoxic exposures or hyperoxic recovery. This review provides an overview of the basic physiology and implications of hypoxia for military aviation and discusses the utility of hypoxia recognition training.

The utility and safety of hypoxia experiences for rebreather divers.

Aircrew training often includes an hypoxic experience aimed at improving symptom recognition and self-rescue in a subsequent hypoxic event. Similar training has been advocated for rebreather divers. We investigated the effect of a prior hypoxic experience on actual and perceived cognitive function during subsequent hypoxia and measured the physiological responses to severe progressive hypoxia. Twenty-five subjects underwent two hypoxic hypoxia experiences (trials one and two) approximately five weeks apart. Subjects breathed 5.5% oxygen whilst performing a playing card recognition test. The primary endpoint was the time taken to make three consecutive errors in the card recognition test (time of useful consciousness, TUC). Secondary endpoints were the total number of errors made, accuracy of error recollection and physiological variables. Mean (SD) TUC was 166 seconds (37) and 169 s (35), and subjects made 8.9 (2.4) and 7.8 (2.0) errors in trials one and two respectively. Error recall was identical between trials with participants failing to recall 6 (3) and 6 (2) errors made in trials one and two respectively. Across both trials mean nadir arterial blood and cerebral oxygen saturations were 52% and 49% respectively. The mean (SD) increase in heart rate was 42 (16) beats·min⁻¹. An hypoxic experience did not improve cognitive performance or subject insight into performance in a second exposure five weeks later. Hypoxia imposes a significant physiological stress which may be hazardous in unscreened, non-medically supervised subjects. Hypoxia experience training is not recommended for rebreather divers at this time.

The Effects Of Body Composition, Physical Fness On Time Of Useful Consciousness In Hypobaric Hypoxia

PURPOSE: The purpose of this study was to investigate the effect of body composition and physical fitness of Air Force pilots on hypoxic tolerance (Time of Useful Consciousness, TUC) under hypoxic hypoxic conditions. METHODS: At the sea level, we measured the body composition and physical fitness of 99 adults who were not exposed to hypoxic environment. In the hypoxia chamber, which can simulate high altitudes, we set the altitude to 25,000 feet and measured the TUC and the maximum heart rate (HRmax(H)). Pearson's Correlation was used to determine the relationship between TUC and other variables, and multiple regression was performed to determine the independent variables that best explain the TUC. RESULTS: TUC is positively correlated with maximum oxygen uptake (VO2max), Stroke Volume (SV), arteriovenous oxygen difference (a-vO2 diff) and endurance (Sit-up, Push-up). The maximum heart rate on the ground (HRmax(S)), HRmax(H), body fat mass, and percent body fat were negatively correlated with TUC. A regression analysis showed that 84.5% of the TUC can be explained by body composition and physical fitness. CONCLUSION: Our results revealed that increased cardiorespiratory fitness and decreased fat could significantly impact TUC. Therefore, for Air Force pilots who are always at high altitudes and at risk for exposure to hypoxia, aerobic exercise is essential.

Relationship of fatigue, physical fitness and cardiovascular endurance to the hypoxic response of military pilots in Indonesia

Even with pressurized aircraft cabins, hypoxic conditions present a continual threat for pilots. The purpose of this study was to determine the risk factors associated with hypoxia for Indonesian military pilots. This cross-sectional study consecutively recruited 120 military pilots who carried out education and aerophysiology exercises during June 2017 at Saryanto Institute for Medical and Health Aviation and Aerospace, Jakarta, Indonesia. The subjects exercised in a hypobaric chamber simulating an altitude of 25,000 ft (7600 m), and their response to hypoxia were characterized by time of useful consciousness (TUC). Multivariate logistic regression was used to analyze relationships between TUC with a cutoff of <4 min and parameters of fatigue, physical fitness, cardiovascular endurance (VO2max), and characteristics of the pilots. Fatigue, physical fitness, and VO2max max did not show a statistically significant relationship with TUC (p > 0.05). Total flight hours and smoking habits were found to be the main factors affecting TUC. The subjects with more than 1000 flight hours were at 2.6 times higher risk to have TUC <4 min (odds ratio 2.65; 95% confidence interval 1.21–5.78; p = 0.014). Compared with the non-smokers, the smokers showed a 63% lower risk of TUC <4 min (odds ratio 0.37; 95% confidence interval 0.14–0.95; p = 0.039). In summary, fatigue, physical fitness, and cardiovascular endurance were not associated with a hypoxic response characterized by TUC <4 min, but total flight hours ≥1000 increased the risk of TUC <4 min and being a smoker reduced the risk.

Hypoxia and Cognitive Performance

The study investigated short-term eff ects of hypoxia on higher cognitive functions. Stroop test (classic and Reverse Stroop task) was chosen as the assessment tool. The sample consisted of 29 paratroopers (males, mean age 33.97). They were subjected to hypoxia at a simulated altitude of 7500 meters during altitude training in a hypobaric chamber. Time of Useful Consciousness (TUC) for every subject was recorded. Each subject performed the Stroop test prior to entering the hypobaric chamber and about 30 minutes after hypoxia exposure. Although reaction times were signifi cantly faster during posttest, the interference susceptibility in Reverse Stroop task increased (t(28) = 2.16, p < 0.05, Cohen’s d = 0.41). While controlling for baseline performance, the increase of susceptibility positively correlated with TUC (r(25) = 0.37). The results are of academic and practical importance. Results suggest that short, non-life-threatening hypoxia could aff ect higher cognitive functions even after exposure. The magnitude of this eff ect is associated with the time of oxygen shortage even among persons whose individual TUC was not exceeded. cognitive functions, hypobaric chamber, hypoxia, pilots, Stroop test

Physiological consequences of rapid or prolonged aircraft decompression: evaluation using a human respiratory model.

Aircraft passengers and crew may be subjected to rapid or prolonged decompression to high cabin altitude when an aircraft develops a hole in the fuselage. The accepted measure of neurological damage due to the hypobaric hypoxia produced is the subjective 'time of useful consciousness' (TUC) measure, which is appropriate for pilots and crew who perform their given tasks, however, TUC is measured under conditions different than the decompression scenarios that passengers undergo in today's aircraft. Ernsting proposed that prolonged exposure to alveolar O2 pressures less than 30 mmHg (P30) causes neurological damage. The current study proposes that a critical value of arterial O2 saturation of 70% (S70) can be used in place of P30 and that this physiological measure is more suited for determination of hypobaric hypoxia in passengers. The study shows the equivalence of model-predicted P30 and S70 values in the Ernsting-decompression scenarios. The model is also used to predict values of these physiological measures in actual aircraft-decompression scenarios. The model can be used by others to quantitatively predict the degree of hypobaric hypoxia for virtually any kind of decompression scenario, including those where supplemental O2 is used. Use of this tool avoids the prohibitive costs of human-subject testing for new aircraft and the potential danger inherent in such tests.

Oxygen and Acceleration

Significant numbers of high performance fighter aircraft continue to be lost due to acceleration (Gz)-induced loss of consciousness. This is due to the rapid onset of high sustained Gz which results in the sudden loss of blood flow to the brain. Present research efforts to extend Gz tolerance are directed toward the maintenance of cerebral blood flow, i.e. straining maneuvers, anti-G suits, tilt seats. The purpose of this paper is to review the present situation and discuss the potential benefit of breathing 100% oxygen at high pressure. Basic science evidence and experience with hyperbaric oxygen in the clinical setting suggest that if the oxygen concentration in the brain tissue is increased, prior to the onset of Gz, additional time of useful consciousness may be realized. The advanced tactical fighter, now in the design stage, will have a sustained Gz capability of 12-14 Gz. This is above human tolerance at the present time and provides an impetus for future acceleration research. Continued aircraft loss due to Gz loss of consciousness will remain an operational problem in aerospace pathology in the 1990s and beyond.

Hypoxia tolerance of rats after adaptation to hypercapnia.

Thirty rats were tested for time of useful consciousness (TUC) by recording the time they could cling to a steeply sloping surface after decompression to a barometric pressure corresponding to 30,000 ft altitude (226 torr). After testing, the rats were returned to ground level conditions for 1 month. They were then exposed continuously for 3-4 days to an environment containing a partial pressure of 90 torr CO2 and tested for TUC again immediately after removal from the high CO2. TUC decreased from 17.6 min to 4.8 min (p<.01) after adaptation to hypercapnia. These data support present theories concerning the role of CO2 in the regulation of respiration.

Effects of Alcohol on Hypoxia

In an effort to determine the effects of alcohol upon the time of useful consciousness of a subject when he is suddenly subjected to hypoxic conditions, ten normal subjects were taken to an atmosphere simulating 25,000 feet (288 mm Hg) in an altitude chamber. After their oxygen masks were removed, they performed various tasks requiring mental and physical coordination until definite hypoxic symptoms were manifested. Later, these same subjects were submitted to identical conditions after the administration of 0.5 cc of 100-proof whiskey per pound of body weight. Blood alcohol levels were determined upon the completion of experiment. A comparison of results demonstrated a 38% reduction in the time of useful consciousness under such hypoxic conditions. In the age of pressurized aircraft subject to rapid decompression, this 38% reduction may easily spell the difference between life and death.