Altitude Chamber Research Articles

Experimental study of small scale n-heptane pool fire with water bath in an altitude chamber

A series of experiments on n-heptane pool fires with water bath was conducted in an altitude chamber capable of reaching 26.4kPa to investigate the performance of small scale pool fires under hypobaric conditions. The fuel pools chosen ranged from 3cm to 8cm in diameter which are in the conduction dominated range. The mass loss and flame envelopes were recorded during the experiments. Specific heat transfer mechanisms are discussed in this paper. Fuels in pool fires boil eventually due to the heat transferred back from the pool to the fuel. Water bath equipment used in this paper was applied to prevent the boiling stage. Experimental findings reveal that the length of the quasi-steady stage varied inversely to the pressure and the pool diameter. Meanwhile, the averaged mass loss rate in the steady burning stage increased with the increasing pressures and pool sizes. The flame with water bath turned to be stable at lower pressure and the flame height also decreased as the pressure decreased.

Oxygen requirement to reverse altitude-induced hypoxemia with continuous flow and pulsed dose oxygen.

Hypoxemia secondary to reduced barometric pressure is a complication of ascent to altitude. We designed a study to compare the reversal of hypobaric hypoxemia at 14,000 ft with continuous flow oxygen from a cylinder and pulsed dose oxygen from a portable concentrator. There were 30 healthy volunteers who were randomized to one of three study groups, placed in an altitude chamber, and ascended to 14,000 ft. There were 10 subjects in each study group. Subjects breathed room air for 10 min to induce hypoxemia. Oxygen was then delivered via a nasal cannula from a cylinder at 1, 2, or 3 lpm of continuous flow for 10 min. The subjects again breathed room air at altitude for 10 min and were then placed on pulsed dose oxygen and titrated to obtain the continuous flow Spo2 equivalent. Spo2, Etco2, RR, HR, Hgb, and tissue oxygenation (Sto2) were continuously recorded. The 1-lpm group's Spo2 range was 89-99%. The 2-lpm group's Spo2 range was 95-98%, and the 3-lpm group's Spo2 range was 95-99%. The 2-lpm and 3-lpm flows were able to correct hypoxemia in every subject. The mean pulsed dose required to achieve an equivalent Spo2 ranged from 36.8 ml ± 18.9 ml in the 1-lpm arm, and 102.4 ml ± 53.8 in the 3-lpm arm. Portable oxygen concentrators using pulsed dose technology corrected hypoxemia in every subject. Oxygen concentrators may be an alternative to liquid oxygen or cylinders for use during aeromedical evacuation.

High Altitude Chamber Training for Military Flight Personnel – Altitude DCS Risk Assessment by Means of Echocardiographic Detection of Gas Bubbles

High Altitude Chamber Training for Military Flight Personnel – Altitude DCS Risk Assessment by Means of Echocardiographic Detection of Gas Bubbles

The burning behaviors of pool fire flames under low pressure

SummaryTo investigate the influence of low pressure on pool fire behaviors, liquid n‐heptane pool fires with the diameters of 6, 8, and 10 cm were tested in a low‐pressure altitude chamber. The tests were conducted under different static chamber pressures, ranging from 40 to 60 to 80 to 101 kPa. Fuel mass loss and high‐speed flame video were recorded during the whole burning process of each test. The mass burning intensity is determined by the convective and radiative heat feedback to the fuel, and analysis shows that the convective part is the major contributor to fuel evaporation. Video recordings show that flame height increases with the reduction of pressure, as supported by the dimensionless analysis. The flame puffing amplitude increases under low pressure, resulting in a portion of the flame being quenched. A special phenomenon was observed from the flame videos in that flame rotation emerged at the ending burning stage, which was attributed to the Coriolis force effect. Copyright © 2014 John Wiley & Sons, Ltd.

A Relationship between Flash Point and Boiling Point of the Flammable Liquids at Low Pressure

Flash point and boiling point are the important physical property of the flammable liquids, and are important parameters to evaluate their combustion behavior. In this study, as series of measurement of two mono compound fuels (N-decane and N-hexanol) and two mixture compound fuels (0# diesel and Jet A) at different pressure were carried out by using the flash point (open-closed cup) and boiling point measuring apparatus in an altitude chamber at different sub-atmospheric pressures at 35 KPa, 45 KPa, 55 KPa, 65 KPa, 75 KPa, 85 KPa, 95 KPa and 101 KPa were conducted. Based on the theoretical formula between the flash point (TF) and the boiling point (TB) and the atmosphere pressure, the relationship between TB and TF has been derived. The experiment results and the theoretical formula all show that the flash point is in linear relationship with the boiling point. The results can provide a more scientific insight into the production, storage, transport and use of fuel and the safety design in aircraft fuel tank.

White matter hyperintensities and hypobaric exposure.

Demonstrate that occupational exposure to nonhypoxic hypobaria is associated with subcortical white matter hyperintensities (WMHs) on fluid-attenuated inversion recovery magnetic resonance imaging (MRI). Eighty-three altitude chamber personnel (PHY), 105 U-2 pilots (U2P), and 148 age- controlled and health-matched doctorate degree controls (DOC) underwent high-resolution MRI. Subcortical WMH burden was quantified as count and volume of subcortical WMH lesions after transformation of images to the Talairach atlas-based stereotactic frame. Subcortical WMHs were more prevalent in PHY (volume p = 0.011/count p = 0.019) and U2P (volume p < 0.001/count p < 0.001) when compared to DOC, whereas PHY were not significantly different than U2P. This study provides strong evidence that nonhypoxic hypobaric exposure may induce subcortical WMHs in a young, healthy population lacking other risk factors for WMHs and adds this occupational exposure to other environmentally related potential causes of WMHs. Ann Neurol 2014;76:719-726.

Activity of Different Populations of Neurons of the Bulbar Respiratory Center of Rats in the Dynamics of Hypobaric Hypoxia

We examined the involvement of different groups of inspiratory and expiratory neurons, INs and ENs, respectively, of the bulbar respiratory center, RC, in the control of respiration under conditions of hypobaric hypoxia. Such conditions were created in a laboratory altitude chamber and corresponded to a “lift” up to 8000 m altitude. At the beginning of such a “lift,” at a pressure corresponding to an altitude of 4000–5000 m, a decrease in the pO2 in the inspired air to 98–85 mm Hg induced increases in the frequency of spiking of the examined neurons. Within a phase of extreme hypoxia, at an “altitude” of 7500 to 8000 m (pO2= 64–58 mm Hg), we observed considerable suppression of the activity of bulbar respiratory neurons. Impulse activity of INs and ENs within different stages of hypoxia demonstrated considerable specificity; INs were characterized by relatively higher resistivity with respect to the action of this factor. Among subgroups of these units, “early” and “full” INs were found to be more resistive with respect to the oxygen insufficiency. After “descent” of the animals and recovery of the normal atmospheric pressure, characteristics of spiking of most bulbar respiratory neurons gradually returned to the initial values.

Stimulated Saliva Aminotransaminase Alteration After Experiencing Acute Hypoxia Training

ObjectiveAcute hypobaric hypoxia is generally recognized to be the most serious single physiological hazard during flight at altitude. Simulation of acute hypoxia in an altitude chamber is used for the training of military aircrew. Acute hypobaric hypoxia affects critical organ systems in different manners. The purpose of this study was to investigate stimulated saliva glutamic pyruvic transaminase (GPT) and glutamic oxaloacetic transaminase (GOT) alteration after the hypobaric hypoxia process. MethodsA cross-sectional study was performed in 44 normal healthy military aircrew conducted at the hypobaric chamber of physiology at the University of Medical Sciences, Tehran, Iran. The GPT and GOT activities were assayed in stimulated whole saliva before and after the experience of hypobaric hypoxia by the International Federation of Clinical Chemistry method. Statistical analysis of the Student t-test was performed. ResultsThe mean stimulated saliva GPT activity was significantly higher after the experience of the hypobaric hypoxia process (2.83 ± 0.34 vs. 0.42 ± 0.029 U/L, respectively; P = .001). Saliva GOT activity was also increased after this process (3.32 ± 0.43 vs. 1.22 ± 0.18 U/L, respectively; P = .001). ConclusionResults suggest that subsequent to the experience of the hypobaric hypoxia process, there is a rise in the salivary activities of aminotransferases.

Intermittent hypoxia stimulates formation of binuclear neurons in brain cortex—A role of cell fusion in neuroprotection?

Oligodendrocyte fusion with neurons in the brain cortex is a part of normal ontogenesis and is a possible means of neuroregeneration. Following such fusion, the oligodendrocyte nucleus undergoes neuron-specific reprogramming, resulting in the formation of binuclear neurons, which doubles the functional capability of the neuron. In this study, we tested the hypothesis that the formation of binuclear neurons is involved in long-term adaptation of the brain to intermittent hypobaric hypoxia, which is known to be neuroprotective. Rats were adapted to hypoxia in an altitude chamber at a simulated altitude of 4000 m above sea level for 14 days (30 min increasing to 4 h, daily). One micrometer sections of the left motor cortex were analyzed by light microscopy. Phases of the fusion and reprogramming process were recorded, and the number of binuclear neurons was counted for all section areas containing pyramidal neurons of layers III-V. For the control group subjected to sham hypoxia, the density of binuclear neurons was 4.49 ± 0.32 mm(2). In the hypoxia-adapted group, this density increased to 5.71 ± 0.39 mm(2) (P < 0.04). In a subgroup of rats exposed to only one hypoxia session, the number of binuclear neurons did not differ from the number observed in the control group. We suggest that the increased content of binuclear neurons may serve as a structural basis for the neuroprotective effects of the adaptation to hypoxia.

The Value of Exercise Stress Testing for Renal-Cardiac Risk Assessment in Military Personnel: Exploring the Hidden Half!

For decades, the exercise stress test (EST) has been known as a well-established non-invasive diagnostic test in patients with suspected or known cardiovascular disease (CVD). However, EST is also used for several other purposes in the armed forces including fitness assessment and adjustment training in simulated non-conventional environments such as altitude chambers. While exercise stress test is a part of periodic health check-up in specific groups of the military forces such as aviators, divers, and commanders, its diagnostic value for cardiovascular disease (CVD) detection is unclear in asymptomatic healthy subjects with low and intermediate cardiovascular risk according to the current clinical practice guidelines. Furthermore, it is demonstrated that it has a modest sensitivity and specificity for the diagnosis of coronary artery disease (67-72% and 69-90% respectively) in symptomatic patients. Hence, the hidden half of the test including non-electrical variations such as hemodynamic changes would be taken into the account or results of other tests such as arterial evaluations would be combined to provide a diagnostic battery. Meanwhile, its performance is also related to the CVD pre-test probability and the prevalence of the disease in the target population. On the other hand, not only the heart, but also vessels and kidneys can be evaluated by EST. Current evidence demonstrates that the hemodynamic response to exercise and exercise-induced micro-albuminuria are associated with cardiac, renal, and arterial functional status. In addition, impaired hemodynamic response to exercise predicts the development of renal dysfunction in the future. In conclusion, EST would be particularly important in the early detection of cardiac, vascular, and renal diseases in military personnel; however, justification and arrangements for the testing must be individually assessed, and this process can be facilitated by decision analysis methods. Keywords: Exercise Test; Risk Assessment; Diabetes Mellitus

Serum Aminotransferase Alteration Following Altitude Chamber Experience in Military Aircrew

Background: Hypoxia is a serious threat in aviation. Aviators are trained in a type of hypobaric chamber (altitude chamber) in order to become familiar with the symptoms of hypoxia. This chamber simulates an altitude of 25,000 feet or more. Hypoxia could have an effect on various organs of the body, such as the liver. Objectives: The purpose of this study was to investigate alanine aminotransferase and aspartate aminotransferase alterations, as tissue damage markers, in aviators following altitude chamber experience. Patients and Methods: A cross-sectional study was carried out in 37 normal healthy male military aviators (age 22-43 years, height 165-192 cm and weight 63-105 kg) conducted in a hypobaric chamber. Total alanine aminotransferase and aspartate aminotransferase activities were assayed in their serum, before and after altitude chamber experience, by the international federation of clinical chemistry (IFCC) method. Statistical analysis of a paired Student’s t-test was performed. Results: The mean serum activities of aspartate aminotransferase (P = 0.001) and alanine aminotransferase (P = 0.014) were significantly increased following altitude chamber experience. Conclusions: Results suggest that subsequent to altitude chamber experience, there is a rise in the serum activities of aminotransferase.

Trichromatic and Dichromatic Relative Sensitivity to Green Light in a Mild Hypoxic Environment

Several studies have reported that individuals with normal color vision have a relative decrease in sensitivity to green light in hypoxic environments approximating altitudes above 4000 m. Because there is little available information describing the effects of mild hypoxic environments (less than 4000 m) in subjects with deficient color-vision, we examined the effect of mild hypoxia on the relative sensitivity to green light for color-normal and color-deficient subjects. Relative sensitivity to the green light was measured using the Medmont C-100 at ground and 3780 m in an altitude chamber. There were 30 subjects, 13 with normal color vision and 17 with a congenital red-green defect, who participated in the study. The relative sensitivity to the green light was determined from the average of four settings measured during the 4.5-h trial. Color-normals and anomalous trichromats showed a small decrease in the relative sensitivity to the green light at 3780 m compared to ground. In contrast to the trichromatic results, the relative sensitivity of the dichromats to the green light did not differ between 3780 m and ground. Our results show that a decrease in the relative sensitivity to green light can occur in hypoxic environments that are equivalent to altitudes greater than 3700 m in individuals with trichromatic but not dichromatic color vision. Although the change in sensitivity was significant, it was small and unlikely to have any operational impact.

THE EFFECTS OF ALTI-VIT ON EXERCISE PERFORMANCE AT ALTITUDE

This study examined the effects of ALTI-VIT supplementation on exercise performance and Acute Mountain Sickness (AMS) at altitude. Seven healthy males with no experience of exercise at altitude completed two...

Probability of Hypobaric Decompression Sickness Including Extreme Exposures

The fitting of probabilistic decompression sickness (DCS) models is more effective when data encompass a wide range of DCS incidence. We obtained such data from the Air Force Research Laboratory Altitude Decompression Sickness Research Database. The data are results from 29 tests comprising 708 human altitude chamber exposures (536 men and 172 women). There were 340 DCS outcomes with per-test DCS incidence ranging from 0 to 88%. The tests were characterized by direct ascent at a rate of 5000 ft x min(-1) (1524 m x min(-1)) to a range of altitudes (226 to 378 mmHg) for 4 h after prebreathe times of varying length and with varying degrees of physical activity while at altitude. Logistic regression was used to develop an expression for the probability of DCS [P(DCS)] using the Hill equation with decompression dose as the main predictor. Here, decompression dose is defined in terms of either the tissue ratio (TR) or a bubble growth index (BGI). Other predictors in the model were gender and peak exercise intensity at altitude. All three predictors (decompression dose, gender, and exercise intensity) were important contributions to the model for P(DCS). Higher TR or BGI, male gender, and higher exercise intensity at altitude all increased the modeled decompression dose. Using either TR or BGI to define decompression dose provided comparable results, suggesting that a simple TR is adequate for simple altitude exposures as an abstraction of the true decompression dose. The model is primarily heuristic and limits estimates of P(DCS) to only a 4-h exposure.

Flight Physiology Training Experiences and Perspectives: Survey of 117 Pilots

Human factors and awareness of flight physiology play a crucial role in flight safety. Even so, international legislation is vague relative to training requirements in hypoxia and altitude physiology. Based on a previously developed survey, an adapted questionnaire was formulated and released online for Portuguese pilots. Specific questions regarding the need for pilot attention monitoring systems were added to the original survey. There were 117 pilots, 2 of whom were women, who completed the survey. Most of the pilots had a light aviation license and flew in unpressurized cabins at a maximum ceiling of 10,000 ft (3048 m). The majority of the respondents never experienced hypoxic symptoms. In general, most of the individuals agreed with the importance of an introductory hypoxia course without altitude chamber training (ACT) for all pilot populations, and with a pilot monitoring system in order to increase flight safety. Generally, most of the pilots felt that hypoxia education and training for unpressurized aircraft is not extensive enough. However, almost all the respondents were willing to use a flight physiology monitoring system in order to improve flight safety.

A strategy for in-flight measurements of physiology of pilots of high-performance fighter aircraft

Some pilots flying modern high-performance fighter aircraft develop "hypoxia-like" incidents characterized by short periods of confusion and cognitive impairment. The problem is serious and recently led to the grounding of a fleet of aircraft. Extensive discussions of the incidents have taken place but some people believe that there is inadequate data to determine the cause. There is a tremendous disconnect between what is known about the function of the aircraft and the function of the pilot. This paper describes a plan for measuring the inspired and expired Po2 and Pco2 in the pilot's mask, the inspiratory flow rate, and pressure in the mask. A critically important requirement is that the interference with the function of the pilot is minimal. Although extensive physiological measurements were previously made on pilots in ground-based experiments such as rapid decompression in an altitude chamber and increased acceleration on a centrifuge, in-flight measurements of gas exchange have not been possible until now primarily because of the lack of suitable equipment. The present paper shows how the recent availability of small, rapidly responding oxygen and carbon dioxide analyzers make sophisticated in-flight measurements feasible. The added information has the potential of greatly improving our knowledge of pilot physiology, which could lead to an explanation for the incidents.

Experimental study of n-Heptane pool fire behavior in an altitude chamber

Constrained by the experimental conditions, field fire tests at high-altitude areas can only examine a limited number of low pressure environments. To explore more low pressure environments, an altitude chamber of size 3×2×2m has been built to simulate static low pressure environments in the range from 101kPa to 30kPa, as well as dynamic pressure environments depressurized from 101kPa to 30kPa at different descent rates. Then by aid of the altitude chamber, low-pressure fires under both static and dynamic pressures were tested. In the static fire tests, four static pressures, i.e. 101kPa, 75kPa, 64kPa and 40kPa were examined through automatically adjusting the pumping speed to maintain a fixed static pressure in the altitude chamber. In the dynamic fire tests, depressurization processes with three descent rates from 101kPa to 30kPa were examined in the altitude chamber through pumping gas and simultaneously replenishing air at the rates of 0, 15 and 20Nm3/h. The tested pool fire sizes were 6-cm-diameter and 10-cm-diameter round pans filled with a 2-cm-height layer of 99% pure liquid n-Heptane, and in the static tests cold water were laid beneath the fuel layer in order to cool the fuel. Multi-point axial flame temperature, radiative heat flux, mass burning rate, chamber pressure and hi-speed flame videos etc. were measured for each test. Some special phenomena were observed from the hi-speed flame videos for the liquid pool fires during the depressurization, e.g. the flame shifted from turbulent to laminar and its base turned blue as pressure drops, then at low enough pressure a polyhedral flame appeared and swirled in the pan. The flame temperature and radiative heat flux were analyzed in correlation with mass burning rate and pressure to reveal the pressure effect on fire behavior.

Effect of acute hypoxia on phenotype and plasticity of M1 and M2 macrophages

Federation Pathogenetic roles of hypoxia may be related with influences on immunity. The aim of study was to investigate the effect of hypoxia on the macrophage phenotype and plasticity in C57/BL mice, which have the pro‐inflammatory M1 macrophage phenotype, and in BALB/c mice, which have the anti‐inflammatory M2 one.MethodsHypoxia was produced in an altitude chamber. After hypoxia, macrophages were isolated from peritoneal lavage. NO production, inducible NO synthase content and cell shape were used as phenotype markers. To determine the phenotypic plasticity, we quantified the capability of macrophages for changing the phenotype to M1 and to M2.Results1) The response of macrophages to hypoxia has two successive phases, the immediate, anti‐inflammatory phase, and the delayed, pro‐inflammatory phase. These phases were more pronounced in Ñ57/BL6 M1 macrophages than in ÂÀLB/c M2 macrophages; 2) the effect of hypoxia on macrophage phenotypic plasticity depends on the genetically predetermined macrophage phenotype. Hypoxia increased the capability of macrophages for changing to the pro‐inflammatory M1 phenotype, while their capability for changing to the anti‐inflammatory M2 phenotype remained virtually unaffected.ConclusionEffects of hypoxia involve immune responses and depend on the genetically predetermined macrophage phenotype. This study was supported by the RFBR (12–04‐01191‐a)

Commercial suborbital space tourism-proposal on passenger's medical selection

Commercial human spaceflight has excellent economic and technical perspectives in the next decades. Passengers will be persons from a general population differing from culture, age, gender and health status. They all will have to withstand physical loads of spaceflight such as acceleration and deceleration forces, microgravity, vibration, noise and radiation. There is a necessity to mitigate all negative impacts on the passengers' health. Besides precautionary measures in construction and equipment, a diligent medical selection and pre-flight training is recommended. To ensure an easy and at the same time qualified selection procedure, it is necessary to define medical selection criteria and training methods. As experiences with suborbital spaceflight of private passengers are still few we recommend to implement in the beginning of this new era maximum safety standards. Having performed a satisfactory number of successful flights, some of the selection criteria and training sessions might be loosened or modified. This judicious approach is in the interest of the spaceflight participants as well as of the providing companies. As a guideline we propose a four step approach that allows a quick decision concerning the fitness of participants to fly as well as an intensive preparation of the passengers. For the first two steps positive experiences from medical screening and examination of professional pilots can be utilised. According to JAR-FCL 3 (Joint Aviation Requirements-Flight Crew Licensing, Chapter 3) a questionnaire with medical interview targeting the medical background of the respective person and including no-go criteria provides a first estimation for applicants and medical examiners whether there will be a chance to be accepted as a passenger. The second step of selection comprises the physical examination of the applicant adjusted to the professional pilot's examination procedure. As the physical challenges of the suborbital flight will exceed the impact of general aviation, the standardized diagnostic programme should be purposefully extended. The third part of the selection consists of an intensive training programme, preparing the passengers for the upcoming challenges. In detail this training should comprise lectures about aerospace physiology, countermeasures to g-forces and motion sickness, emergency practices (e.g. rapid decompression or hypoxia) and a centrifuge ride with g-forces adapted to the respective flight profile. An altitude chamber flight, hypoxia experience and participation in a Zero-G-Flight might also be included optionally. The fourth step of the evaluation is caused by a possible delay between medical examination and launch. In the interval, the health status might have changed and serious illnesses might have developed. So, a short re-evaluation should be performed 7–14 days before take-off. A brief check-out procedure for medical re-evaluation of passenger's health status is recommended. As launch of suborbital spaceflights will take place all over the world at so called “Spaceports”, the development of standards for medical examinations and the training programmes as well as a mutual acceptance of the participating medical test and training centres will be very helpful for development of this industry. Joint recommendations for the emergency equipment of commercial spaceships will also have to be developed.

THE EFFECT OF ADVANCE HYPOXIC TRAINING UPON TISSUE OXYGEN TENSION IN THE TUMOR DURING AQUTE HYPOXIA OF DIFFERENT TYPES

The tumors of rats who had not been acclimated to hypoxia subjected to acute hypoxic hypoxia (altitude chamber) as well as blood hypoxia (carbon monoxide) decreased tissue oxygen tension while histotoxic hypoxia (NaCN) on the contrary increased tissue oxygen tension. The tumor acclimated to hypoxia seems to select compensatory mechanisms mostly associated with increased tissue oxygen tension thus taking advantage of lower extent of tissue oxygen tension when subject to acute hypoxic hypoxia than in femoral muscle. All types of acute hypoxias caused a decrease of tissue oxygen tension in the malignancy.