SEARCH · PubMed Health

Results for “Atmosphere Exposure Chambers”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources

PubMed1994

Test for pressure control capacity of the Eustachian tube.

Because of Eustachian tube controls middle ear pressure to maintain the best hearing level, we tested the equilibration capacity of the Eustachian tube by measuring hearing levels in a soundproof pressure chamber. The number of swallows to recover normal hearing after the chamber pressure reached -200 mm H2O (an index of equilibration capacity for the static pressure differences across the eardrum) was less than 9 in normal subjects. The worst level of hearing and the time required to recover normal hearing from the beginning of alteration in the chamber pressure to -700 mm H2O (indexes of equilibration capacity for dynamic pressure differences across the eardrum) were 0-17 dB and within 120s in normal subjects. It was difficult to determine definitive normal ranges of the equilibrium capacity of the Eustachian tube when positive pressure was applied.

Adult↗

PubMedDate not supplied

[Changes in the maximum permissible supersaturation coefficient in altitude decompression].

This paper presents experimental data obtained during 383 altitude chambers tests in which 70 subjects participated. The purpose of the tests was to verify experimentally the safety of altitude decompression regimens that simulated transition from the orbital station atmosphere at a normal barometric pressure to the space suit oxygen atmosphere at a lowered pressure. The results help better understand correlations between the maximal allowable super-saturation coefficient and total postdecompression pressure.

Adult↗

PubMedDate not supplied

Acute adaptation of mice to hypoxic hypoxia.

Tolerance to hypoxia in vivo and in vitro was significantly increased by acute and repetitive exposure of mice to autoprogressive hypoxia. The average tolerance times of the successive 2nd, 3rd, 4th and 5th runs of exposure were, respectively, 2, 4, 6 and 8 times as long as that of the first exposure. The survival times under hypobaric chamber and cyanide toxification in the 4th exposure were, respectively, 10 (and even as much as 86) and 4 times those in control mice without exposure to hypoxia. Mandibular respiration and spinal reflex in vitro in hypoxia-resistant animals lasted 5-6 times as long as in control animals not previously exposed to hypoxia. Animals that received brain homogenate from hypoxia-resistant mice remained alive in a hypobaric chamber 2 times as long as those that received homogenate from controls and those that received saline. These results indicate that a kind of quickly developing adaptation with increased tolerance is achieved by acute and repetitive exposure of mice to progressive autohypoxia and some plastic or adaptive changes occur in the brain of hypoxia-resistant animals, including the production of some kind of water-soluble antihypoxic factors.

Adaptation, Physiological↗

PubMed2003

R-R interval variability with lower body positive pressure assessed by wavelet packet transform.

Lower body positive pressure (LBPP) is used for simulation of microgravity due to central fluid shift. In the present study, we evaluate R-R interval variability, which is sometimes considered as an index of human cardiovascular autonomic nerve status. 10 healthy male subjects were set in a chamber with standing position. Chamber pressure was raised 10 mmHg each for every 3 minutes, up to +40 mmHg. Wavelet packet transform (WPT) followed by Hilbert transform was employed to analyze time-dependent changes in low frequency component (LF) and high frequency component (HF) of R-R interval variability. Calf circumference lowered according to chamber pressure. ABP was maintained throughout measurements. R-R interval was significantly higher at +30 and +40 mmHg compared to that of control. Standing LBPP causes higher HF and lower L/H probably due to central fluid shift, and WPT followed by Hilbert transform shows time-dependent changes in R-R interval variability.

Atmosphere Exposure Chambers↗

PubMedDate not supplied

[Possibility of the development of decompression sickness during testing of G suits].

This paper presents the results of 1179 altitude chamber tests of special suits performed by 193 subjects. The probability of altitude decompression disease observed during 29 experiments (2.5%) in 26 test subjects (13.4%) is calculated. The safety of decompression tables is evaluated as applied to the pressure 14-43 kPa after oxygen breathing for 0.25-2 hrs at sea level or for 1-6 hrs at 40 kPa.

Accidents↗

PubMed1994

Pressure test in normal subjects.

The application of pressure to the middle ear changes the normal inner ear pressure in animal experiments. In this study we tested the effect of exposure to under- or overpressure on hearing in a total of 78 normal ears (40 subjects) in a soundproof pressure chamber. [After exposure to underpressure, a 10 dB or more gain in 3 ears and loss in 2 ears for at least one of the test frequencies was observed in 38 ears. After exposure to overpressure, a 10 dB or more gain in 5 ears and loss in 1 ear for at least one of the test frequencies was observed in 40 ears.] The characteristics of transferred inner ear pressure during a series of exposures to underpressure seemed to be similar to those during exposures to overpressure.

Acoustic Impedance Tests↗

PubMedDate not supplied

[Immunologic response of divers working in the conditions of increased microbial contamination of water under pressure up to 5.1 MPa].

The complex investigation of immune and nonspecific reactivity of 30 aquanauts was carried out during five experimental saturation divings up to 350-500 m accompanied by an increase of microbic contamination in water of the hyperbaric chamber. Peculiarities of humoral immune response and phagocyte functions were found to depend on the inflammatory disease of aquanauts. It is concluded that the situational transitory immune deficiency development under the influence of hyperbaric factors is possible and changes in the microbe spectrum are real.

Atmosphere Exposure Chambers↗

PubMed1994

Effect of atmospheric pressure on hearing in normal subjects.

Hearing is assumed to be altered during or immediately after a change in atmospheric pressure, although this has not been tested experimentally. We used a soundproof pressure chamber to examine the effect of alterations in atmospheric pressure on hearing in 26 normal healthy subjects. The subjects were placed in the soundproof pressure chamber in a supine position and instructed to actively equilibrate middle ear pressure or to abstain from doing so. When the pressure was changed to +/- 500 mmH2O at 33 mmH2O/s the results were as follows: When subjects did not equilibrate middle ear pressure, air conduction at low frequency tones increased more than bone conduction. The degree of deterioration in hearing was greater when the chamber pressure was increased (descent) than where pressure was decreased (ascent). When the subjects equilibrated middle ear pressure, little change in the levels of air or bone conduction was observed. Most of the deterioration in bone conduction was considered to reflect functional loss due to increased stiffness and damping of the sound transmission mechanism.

Adult↗

PubMed1994

Pressure test for the diagnosis of Menière's disease.

In the last 15 years, a pressure chamber able to generate negative air pressure has been used to treat patients with Menière's disease. In this study we sought to clarify whether the underpressure chamber can be used to diagnose Menière's disease. We studied 45 ears from patients with neurotological diseases. The subjects were placed supine in a soundproof pressure chamber. The pressure was first decreased to -500 mmH2O, and after 5 min to -700 mmH2O. The pressure was kept at this level for another 5 min and then increased to 0 mmH2O. This procedure was done three times in succession. While the chamber pressure was below 0 mmH2O, the subjects were instructed to abstain from actively equilibrating middle ear pressure. When the chamber pressure was raised to 0 mmH2O, they were instructed to equilibrate middle ear pressure, and if necessary Politzerization or catheterization of the Eustachian tube was done. As a result, hearing was improved after this procedure only in patients with Menière's disease (50%) and/or cochlear Menière's disease (32%) in which endolymphatic hydrops was suspected.

Acoustic Impedance Tests↗

PubMed1996

Saturation diving as a submarine rescue tool.

The U.S. Navy Submarine Rescue Diving and Recompression System (SRDRS) uses saturation diving to provide human intervention at the hatch of a disabled submarine. The system incorporates the basic elements of traditional saturation diving platforms to provide life support to divers at the worksite as well as in a decompression chamber in between work assignments. The demands of the submarine rescue mission require that the system provide quick response to an emergency virtually anywhere in the world. To answer these demands, SRDRS uses a mixture of state-of-the-art diving technologies and traditional approaches to life support in a quickly mobilized, easily transportable diving system capable of operating in extremely harsh environments.

Air Conditioning↗

PubMed1977

[Maximum exercise testing during hypobaria and normoxia (author's transl)].

The effects of high altitude (3000 m, low-pressure chamber) on maximum exercise and maximum oxygen uptake were studied in four normal subjects. In order to separate the effects of hypobaria and of hypoxia, exercise testing was performed under normoxic, hypobaric conditions and compared with the results under normoxic, normobaric conditions. There was no significant difference in performance, nor in the effects of exercise on the measured cardiovascular parameters.

Adult↗

PubMed1978

Explosive decompression of subjects up to a 20,000-m altitude using a two-pressure flying suit.

The RSAF two-pressure flying suit system to protect the pilot at high altitude has been tested from different medical safety aspects. To secure adequate alveolar oxygen pressure, the suit admits up to 70 mm Hg (9.3 kPa) positive pressure breathing by counter-pressure against the thorax and by a 3.2 times higher pressure in the anti-G suit. After 1 h of oxygen breathing, subjects were exposed to explosive decompression from an altitude of 9,000 m to 17,500 or 20,000 m in 0.5 s in a hypobaric chamber. No symptoms of decompression sickness or of alveolar rupture with gas embolism to the central nervous system were seen. Pulmonary X-rays after the test did not reveal any signs of lung rupture with extrapulmonary gas leakage. With the precordial Doppler ultrasound technique, intracardial gas bubbles (silent bubbles) could be detected only in one subject after explosive decompression to a 20,000-m altitude in the 10 experiments.

Adult↗

PubMed1981

A system for pharmacological studies in small animals at high pressure.

A four-liter pressure chamber was constructed for pharmacological experiments in rats; it consisted of the following: 1) a system for repeated, accurate injection; 2) an alternative single-dose injection system; 3) a system for direct blood sampling to the outside. The injection and sampling systems were tested for possible drug adsorption at 71 ATA. The accuracy of drug concentration measurements in samples collected through the sampling system at pressure was found to be satisfactory.

Animals↗

PubMed1978

[Behavior of impedance of the middle ear during rapid changes in barometric pressure].

The first results on the dynamic behaviour of middle ear impedenzometric variations starting from an altitude of 3,000 mt and descending constantly by about 1,500 mt/min to sea level, are reported. The research was carried out in a hypobaric chamber, under simulated flight conditions, using the equipment of the Aeronautics and Space Medicine Studies and Research Centre of the Air Force. Evaluation of the results obtained in subjects trained for rapid descents and in others not so trained suggests that the technique used is a useful aid in the diagnosis of the tubal conditions of subjects who are to be subjected to rapid ascents and descents.

Acoustic Impedance Tests↗

PubMed1995

Simulated descent v dexamethasone in treatment of acute mountain sickness: a randomised trial.

OBJECTIVE: Evaluation and comparison of the therapeutic efficacy of a portable hyperbaric chamber and dexamethasone in the treatment of acute mountain sickness. DESIGN: Randomised trial during the summer mountaineering season. SETTING: High altitude research laboratory in the Capanna Regina Margherita at 4559m above sea level (Alps Valais). SUBJECTS: 31 climbers with symptoms of acute mountain sickness randomly assigned to different treatments. INTERVENTIONS: One hour of treatment in the hyperbaric chamber at a pressure of 193 mbar or oral administration of 8 mg dexamethasone initially, followed by 4 mg after 6 hours. MAIN OUTCOME MEASURES: Symptoms of acute mountain sickness (Lake Louise score, clinical score, and AMS-C score) before one and about 11 hours after beginning the different methods of treatment. Permitted intake of mild analgesics before treatment and in the follow up period. RESULTS: After one hour of treatment compression with 193 mbar caused a significantly greater relief of symptoms of acute mountain sickness than dexamethasone (Lake Louise score: mean (SD) -4.6 (1.9) v -2.5 (1.8); clinical score: -4.0 (1.2) v -1.5 (1.4); AMS-C score: -1.24 (0.51) v -0.54 (0.59)). In contrast after about 11 hours subjects treated with dexamethasone suffered from significantly less severe acute mountain sickness than subjects treated with the hyperbaric chamber (-7.0 (3.6) v -1.6 (3.0); -4.1 (1.9) v -1.0 (1.5); -1.78 (0.73) v -0.75 (0.82) respectively). Intake of analgesics was similar in both groups. CONCLUSION: Both methods were efficient in treatment of acute mountain sickness. One hour of compression with 193 mbar in the hyperbaric chamber, corresponding to a descent of 2250 m, led to short term improvement but had no long term beneficial effect. On the other hand, treatment with dexamethasone in an oral dose of 8 mg initially followed by 4 mg every 6 hours resulted in a longer term clinical improvement. For optimal efficacy the two methods should be combined if descent or evacuation is not possible.

Acute Disease↗

PubMedDate not supplied

[Evaluation of energy metabolism and physical work capacity of divers for determining the optimal oxygen level during breathing gas mixture under pressure up to 5.1 MPa].

A complex evaluation of energy metabolism, oxygen-transport function of blood and physical work capacity of aquanauts has been performed during three imitation divings at depths of 400, 450 and 500 m in heliox as a breathing medium. These experiments have shown that optimal levels of partial oxygen pressure in artificial chamber environment are 30-33 kPa at 4.1 MPa, 32-35 kPa at 4.6 MPa and 33-34 kPa at 5.1 MPa. It is established that 24-days exposure of aquanautes to 4.6 MPa and 10-days exposure to 5.1 MPa yield no unfavourable changes of the examined organism functions. The activated lipid exchange in combination with stable carbohydrate catabolism, the elevated levels of oxygen consumption and its partial pressure in blood and transient fluctuations of erythropoiesis activity are interpreted as compensatory responses of diverse organisms under the influence of hyperbaric factors.

Administration, Inhalation↗

PubMed1996

Acute mountain sickness: increased severity during simulated altitude compared with normobaric hypoxia.

Acute mountain sickness (AMS) strikes those in the mountains who go too high too fast. Although AMS has been long assumed to be due solely to the hypoxia of high altitude, recent evidence suggests that hypobaria may also make a significant contribution to the pathophysiology of AMS. We studied nine healthy men exposed to simulated altitude, normobaric hypoxia, and normoxic hypobaria in an environmental chamber for 9 h on separate occasions. To simulate altitude, the barometric pressure was lowered to 432 +/- 2 (SE) mmHg (simulated terrestrial altitude 4,564 m). Normobaric hypoxia resulted from adding nitrogen to the chamber (maintained near normobaric conditions) to match the inspired PO2 of the altitude exposure. By lowering the barometric pressure and adding oxygen, we achieved normoxic hypobaria with the same inspired PO2 as in our laboratory at normal pressure. AMS symptom scores (average scores from 6 and 9 h of exposure) were higher during simulated altitude (3.7 +/- 0.8) compared with either normobaric hypoxia (2.0 +/- 0.8; P < 0.01) or normoxic hypobaria (0.4 +/- 0.2; P < 0.01). In conclusion, simulated altitude induces AMS to a greater extent than does either normobaric hypoxia or normoxic hypobaria, although normobaric hypoxia induced some AMS.

Acute Disease↗

PubMed2006

Predicting hypoxia in cystic fibrosis patients during exposure to high altitudes.

BACKGROUND: For patients with cystic fibrosis (CF)-related partial respiratory insufficiency and reduced arterial oxygen tension at ground level, the mild hypobaric environment on commercial jet aircraft poses the risk of severe hypoxemia. Thus, physicians should be able to estimate the extent of in-flight hypoxia. OBJECTIVES: To derive tools for estimating the expected drop in arterial oxygen partial pressure (paO(2)) and oxygen saturation (saO(2)) in young adult CF patients with mild to moderate airway obstruction during exposure to the hypobaric conditions aboard commercial aircraft and to test the predictive power of a hypobaric chamber simulation. METHODS: Blood gases of 12 CF patients were measured at ground level, at two altitudes in a hypobaric chamber (2000 and 3000 m) and during two 3.5-h flights at cabin altitudes of 1855 m and 1700 m. The altitude dependence of paO(2) and saO(2) in the chamber and during the flights was calculated and results were used to derive estimation equations for in-flight values. RESULTS: In the chamber, saO(2) decreased by 0.33% per 100 m vertical ascent, and this rate increased significantly at altitudes >2000 m. Predicted saO(2) differed from in-flight value by <5%, and agreement between in-flight saO(2) decrease rate and chamber data was good. paO(2) decreased at a rate of 0.99 mm Hg/100 m in the chamber and by 1.33 mm Hg/100 m during flights. None of the subjects showed any clinical symptoms during the flights and the chamber simulation. CONCLUSION: During our worst-case scenario, i.e. the hypobaric chamber simulation at 3000 m, 90% of patients tolerated paO(2) values below the commonly recommended threshold of 50 mm Hg, probably due to adaptation to chronic hypoxemia and lung function impairment. We propose the following equations for an estimation of the expected extent of in-flight hypoxemia in CF patients with mild to moderate airway obstruction and a flight duration of up to 3.5 h: -paO2[Alt]=paO2[ground] -1.33 x Alt[mm Hg], and -saO2[Alt]=saO2[ground] -0.33 x Alt [%], with Alt=altitude in 100 m. In addition to the overall clinical situation of a patient, these equations will serve as a practical supportive tool for the assessment of the fitness to fly in the primary care setting.

Adult↗