Atm Absolute Pressure Research Articles

Prenatal hyperbaric normoxia treatment improves healthspan and regulates chitin metabolic genes in Drosophila melanogaster.

Aging is a universal, irreversible process accompanied by physiological declines that culminate in death. Rapid progress in gerontology research has revealed that aging can be slowed through mild stress-induced hormesis. We previously reported that hyperbaric normoxia (HN, 2 atm absolute pressure with 10% O2) induces a cytoprotective response in vitro by regulating fibronectin. In the present study, we investigated the hormetic effects of prenatal HN exposure on Drosophila healthspan related to molecular defense mechanisms. HN exposure had no disruptive effect on developmental rate or adult body weight. However, lifespan was clearly enhanced, as was resistance to oxidative and heat stress. In addition, levels of reactive oxygen species were significantly decreased and motor performance was increased. HN stress has been shown to trigger molecular changes in the heat shock response and ROS scavenging system, including hsp70, catalase, glutathione synthase, and MnSOD. Furthermore, to determine the hormetic mechanism underlying these phenotypic and molecular changes, we performed a genome-wide profiling in HN-exposed and control flies. Genes encoding chitin metabolism were highly up-regulated, which could possibly serve to scavenge free radicals. These results identify prenatal HN exposure as a potential hormetic factor that may improve longevity and healthspan by enhancing defense mechanisms in Drosophila.

Early hyperbaric oxygen therapy improves outcome for radiation-induced hemorrhagic cystitis

Objectives To assess the clinical factors that affect the efficacy of hyperbaric oxygen (HBO 2) therapy in treating radiation-induced hemorrhagic cystitis. HBO 2 therapy is an effective treatment for radiation-induced hemorrhagic cystitis, with reported response rates ranging from 76% to 100%. Methods The data from patients with radiation-induced hemorrhagic cystitis treated at our institution between May 1988 and December 2001 were reviewed retrospectively. All patients received HBO 2 therapy at 2.36 atm absolute pressure, with 90 minutes of 100% oxygen breathing per treatment. The outcome was assessed after at least 12 months of follow-up. We evaluated patient demographics, types of pelvic malignancy and radiotherapy, total radiation dose, onset and severity of hematuria, and prior intravesical management. Clinical improvement was defined as the absence of, or reduction in, macroscopic hematuria. Results A total of 60 patients (55 men and 5 women), mean age 70 years, received an average of 33 HBO 2 treatments (range 9 to 63). Of the 60 patients, 48 (80%) had either total or partial resolution of hematuria. When treated within 6 months of hematuria onset, 96% (27 of 28) had complete or partial symptomatic resolution ( P = 0.003). All 11 patients with previous clot retention had clinical improvement if treated within 6 months of hematuria onset ( P = 0.007). Prior intravesical chemical instillation did not affect the clinical outcome. Patients who had undergone primary, adjuvant, or salvage external beam pelvic radiotherapy showed response rates of 81%, 83%, and 78%, respectively ( P = 0.950). Conclusions Our results show that delivery of HBO 2 therapy within 6 months of hematuria onset is associated with a greater therapeutic response rate. Treatment efficacy was independent of prior intravesical therapy and the timing of radiotherapy.

Treatment of Laryngeal Radionecrosis with Hyperbaric Oxygen Therapy: A Case Report

An 81-year-old male with early-stage laryngeal carcinoma had been treated with 60 Gy curative radiotherapy. He complained of a sore throat, foul odor in the mouth, progressive dyspnea, and fever 2 months after the completion of radiotherapy. Direct laryngoscopy revealed narrowing of the glottis with diffuse ulcerative necrotic tissue. Biopsies at multiple sites and pathology revealed intense coagulation necrosis with complete denudation of covering epithelium without any malignancy. Since laryngeal radionecrosis was suspected, the patient received hyperbaric oxygen (HBO) therapy 40 times for 1 hour of 100% O2 at 2 atm absolute pressure. His clinical symptoms gradually improved and repeated endolaryngeal biopsies were undertaken near the end of HBO therapy and again 6 months later. The patient's larynx healed completely with diffuse fibrosis and no malignant cells were found on pathology. Radionecrosis must be differentiated from cancer recurrence following curative radiotherapy for early laryngeal cancer. HBO therapy could be a useful treatment adjunct for laryngeal radionecrosis.

Sleep patterns during 30-m nitrox saturation dives and in a confined atmospheric environment.

Sleep patterns during saturation dives equivalent to a 30-m depth (pressurized condition) and habitation in a confined environment at 1 atm absolute pressure (non-pressurized condition) were studied to determine the effects of environmental pressure. Eight inexperienced divers experienced the pressurized condition of the saturation dives, and nine healthy subjects experienced the non-pressurized condition. Standard polysomnographs were recorded for 262 nights. For both conditions, reductions in total sleep time accompanied by lengthening in sleep latency and reduction in sleep efficiency were observed from the latter part of the experiments through to the recovery periods. These findings suggest that changes were related to psychological and physiological stresses caused by long stays in a confined environment and not by the environmental pressure.

Hyperbaric Oxygen Treatment Enhances Regeneration of the Rat Sciatic Nerve

The effect of hyperbaric oxygen (HBO) treatment on regeneration of the rat sciatic nerve was studied. The sciatic nerve was crushed with a pair of pliers and the animals were either left untreated or subjected to a series of 45-min exposures to 100% O2at 3.3 atm absolute pressure at 0, 4, and 8 h postoperatively and then every 8 h. Regeneration was evaluated using the pinch-reflex test at 3, 4, or 5 days following surgery and with neurofilament staining at 4 days. The regeneration distances at all time points were significantly longer in animals exposed to hyperbaric oxygen treatment independent of the evaluation procedure. A short initial period of the same HBO treatment schedule, with no more treatments after 25 h, appeared as effective as when treatments were maintained being given every 8 h until evaluation. We conclude that HBO treatment stimulates axonal outgrowth following a nerve crush lesion.

Increasing oxygen tension dilates fetal pulmonary circulation via endothelium-derived relaxing factor.

We examined the role of endothelium-derived relaxing factor (EDRF) in the increase in pulmonary blood flow caused by increasing oxygen tension in the lungs of the fetus. Fetal lambs at 133 days of gestation were instrumented for intrauterine measurement of pulmonary arterial, left atrial, and amniotic fluid pressure and pulmonary blood flow. Three days later oxygen tension in the pulmonary arterial blood of the fetus was doubled by having the ewe breathe 100% oxygen at 3 atm absolute pressure. In the control fetuses (n = 5), hyperbaric oxygenation increased pulmonary blood flow eightfold. Blocking EDRF production by infusing 45 mg of NG-monomethyl-L-arginine into the superior vena cava of the fetus over 5 min starting 30 min after the beginning of hyperbaric oxygen reversed the increase in pulmonary blood flow (n = 5). Blocking EDRF production by infusing NG-nitro-L-arginine at 1 mg/min for 60 min starting 30 min before hyperbaric oxygen blunted the initial increase in pulmonary blood flow and eliminated it by the end of the experiment (n = 5). As hyperbaric oxygen did not significantly alter pulmonary arterial or left atrial pressure, changes in pulmonary vascular conductance paralleled those in pulmonary blood flow. We conclude that the majority of the vasodilation of the fetal pulmonary circulation caused by increasing oxygen tension is mediated by EDRF. We speculate that EDRF is involved in maintaining low vascular tone at the relatively high oxygen tension of the postnatal lung.

Direct measurement of nitrous oxide MAC and neurologic monitoring in rats during anesthesia under hyperbaric conditions.

The minimum alveolar concentration (MAC) of nitrous oxide necessary to prevent purposeful movement in rats has not been directly measured; rather, it has been extrapolated because the required partial pressure exceeds 760 mm Hg, or 1 atm absolute pressure (ATA). Values reported have ranged from 1.36 to 2.20 ATA (136-220 vol%, or 1034-1672 mm Hg). By maintaining general anesthesia at 2.25 ATA (1710 mm Hg), we directly measured the nitrous oxide MAC in 17 Long-Evans rats during mechanical ventilation and monitoring of two-channel electroencephalogram, compressed spectral array and cortical evoked potentials, electrocardiograph, and respiratory and anesthetic gases by mass spectrometry. After a minimal stabilization period of 30 min during ventilation by 1.8 ATA nitrous oxide and 0.45 ATA oxygen, MAC measurements were begun. Each rat was given up to three noxious electrical stimulations of 50 V by 10-ms-duration pulses at 50/s for 45 s. The partial pressure of nitrous oxide was decreased by approximately 10% after each negative response. The MAC was taken as the nitrous oxide concentration midway between that at which there was no response and that at which the rat moved purposefully. The nitrous oxide MAC in Long-Evans rats was determined to be 1.55 +/- 0.16 ATA (mean +/- SD). Hyperbaric nitrous oxide decreased electroencephalogram wave frequency to a predominantly theta rhythm of increased amplitude. Cortical evoked potentials had decreased wave amplitudes and increased latencies with increasing partial pressures > 0.75 ATA.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of a low ionization potential dopant in a kinestatic charge detector: Experimental findings

The broadening of the line spread function (LSF) in the drift direction with increasing drift distance in the kinestatic charge detector is substantially reduced when small amounts (less than 1%) of trimethylamine [(CH3)3 N] are added to the x-ray detection medium (krypton or xenon). The LSF of a mixture of Kr and 0.01% trimethylamine (TMA) was measured as a function of distance at 15, 25, and 35 atm absolute pressure. The full width at half-maximum (FWHM) of the LSF was reduced from about 1.0 mm to less than 0.5 mm at a drift distance of 4.0 mm for the three pressures. The LSF's of mixtures of xenon and TMA at concentrations ranging from 0.0004% to 0.4% in one run and 0.06% to 4.0% in a second run were measured at a constant pressure of 20 atm. The FWHM of the LSF was reduced from 0.6 to 0.4 mm at 4.0 mm for the xenon measurements. The optimum concentration of TMA in Xe was found to be in the neighborhood of 0.1%. The use of TMA reduced the drift distance-dependent LSF broadening to the level expected from ionic diffusion, space charge repulsion, and electric field nonuniformity, and it may be possible to reduce the 0.4-mm FWHM plateau through the use of an improved Frisch grid design. Observation of negative charge carriers showed that electron attachment increases with increasing TMA concentration, although this could be caused by impurities in the TMA. The implications of these results are discussed in terms of extending the maximum drift distance attainable in a kinestatic charge detector.

Study of straw chamber lifetime with argon ethane

We present detailed laboratory measurements of the lifetime of a small test chamber, simulating the Mark III straw vertex chamber conditions. The tests were carried out with an argon-ethane 50 50 gas mixture at 3 atm absolute pressure and 3.9 kV applied to the wires. After the accumulation of ∼ 0.02 C/cm on a single straw, continuous discharges began. The addition of alcohol or water vapor to the gas mixture was found to extend the lifetime of the straws. Continuous flow of the gas mixture with water vapor through the straws prolonged the lifetime significantly. We present results on the effects of changing the gas mixture inside the straws at regular time intervals. Adding a small percentage of water vapor to the argon-ethane gas and flowing the gas mixture in the straws can improve the lifetime by more than an order of magnitude. An accumulated charge of 1.0 C/cm on a single straw has been obtained.

Design, construction, prototype tests and performance of a vertex chamber for the MAC detector

The design considerations, construction techniques, prototype tests and performance characteristics of a pressurized drift chamber used in the MAC detector at PEP are described. The chamber consists of 324 aluminized mylar tubes of 6.9 mm diameter with wall thickness of 100 μm. With appropriate shielding it operates successfully at 4.6 cm from the beam line. It was simple to construct and was configured to permit any malfunctioning tubes to be remotely disconnected without affecting operation. The chamber operated without problems for two years in the PEP environment with a gas mixture of 49.5% argon, 49.5% CO 2, 1% CH 4, at 4 atm absolute pressure. The mean spatial resolution averaged over all tubes was 45 μm. The time to distance relation for this gas mixture, along with the geometric positioning of individual wires relative to the central tracking chamber, was obtained with data from Bhabha scattering events. We also describe resolution studies performed with a prototype chamber in a SLAC test beam. A wide range of gases, gas pressures, and electronic parameters were explored. These studies proved that resolutions in the 10–50 μm range were possible. Our experience demonstrates that chambers of this type provide high precision tracking and are particularly suited for operation in regions with difficult physical access and/or high ambient radiation levels.

Steam corrosion of glass under polymer thin films

Polymer films averaging 600 Å in thickness were deposited on the outer surfaces of glass bottles to increase the lubricity and scratch resistance of the glass. The bottles were autoclaved in steam at 3 atm absolute pressure. Direct pull tests and in-depth XPS profiles were made to learn how adhesion and the polymer–glass interface changed with autoclaving time. It was found that sodium was depleted from the surface region under the polymer coating. The sodium depletion zone increased linearly with autoclaving time. Sodium was also leached from the uncoated surface, but after 30 min of leaching the sodium depletion depth remained essentially constant. The organic film continued to adhere well independently of autoclaving time.

The Doublet III Neutral Beam Source Cryopanel System

A cryogenic pumping system is designed to provide 1.4 × 106 l/sec. of hydrogen pumping speed for the Doublet III neutral beam ion source. The cryopump is made up of two elements; a cylindrical unit which uses a "Santeler" type of liquid nitrogen shield and a flat chevron shielded disk. Liquid helium and liquid nitrogen are circulated by forced flow. The liquid helium is circulated at 0.6 atm absolute pressure for cryopump operation at 3.8°K.

Stratospheric Aitken nuclei counter

An aircraft mounted system is described which permits the measurement of concentrations of Aitken nuclei in the stratosphere at altitudes up to 20 km. An automatic cycling cloud chamber, with a dark field optical system and photomultiplier detector, is used to analyze 2.5 samples/sec. A pressurization system is incorporated which standardizes ambient air samples to approximately 1 atm absolute pressure and 298 K temperature before analysis. Seven successful data flights have been accomplished in the period March–May 1974.

Pressure Effect on the Sensitivity of Quartz Bourdon Tube Gauges

The sensitivity change for a commercial fused quartz Bourdon tube precision pressure gauge, due to a change in absolute pressure level, has been analytically computed and experimentally confirmed. The computed differential pressure error is 2.5% of full scale at a 100 atm absolute pressure level. The experimental method compared the fused quartz Bourdon tube gauge digital output to the results obtained from a nitrogen gas pressure system which had a high pressure, well-type mercury manometer as the differential pressure reference.

Hyperbaric gas effects on critical flicker frequency in the rhesus monkey

Effects of exposures to hyperbaric pressures of nitrogen, oxygen, and argon on CFF were investigated using the rhesus monkey. Nitrogen and argon at pressures of up to 10 atm produced no change in CFF, but exposure to equivalent partial pressures of oxygen at 2 atm absolute pressure resulted in a dose-related depression of CFF. Concomitant measures of response rate on a VR schedule of reinforcement revealed dose-related depressions in the presence of hyperbaric nitrogen and argon but not in the presence of oxygen. The results were interpreted in terms of existing theories of the behavioral effects of hyperbaric exposure and were shown to imply that a reevaluation of these views may be necessary.

Effects of hyperbaric oxygen on growth and metastases of the C3HBA tumor in the mouse.

Mice with established C3HBA tumors were given oxygen at 3 atm absolute pressure (3 ATA) twice daily for 30 min during 6 days. After a further 2 days the tumors were removed and the animals were observed for 50 days. Control animals were given air at 3 ATA or one ATA pressure. Body weight was decreased in mice given hyperbaric oxygen but was rapidly regained after stopping treatment. There was no effect on tumor growth as determined by measurement of tumor volume and dry tumor weights. Hyperbaric oxygen had no effect on the incidence of lung metastases. The results suggest that the clinical use of hyperbaric oxygen is unlikely to increase the rate of cancer growth or the incidence of metastases.

Steady states of oxygen tension in human dermis

Mean oxygen tension in mid-dermis of human forearm skin was measured during the breathing of air, 100% oxygenat 1 and 4.5 atm absolute pressure, and mixtures of 10%, 40%, 60% and 80% oxygen in nitrogen. Hyperventilation increased the oxygen tension during the breathing of air, but decreased it during the breathing of oxygen. Adrenaline injected intradermally reduced the oxygen tension whereas the local application of thurfyl nicotinate increased it. Theoretical models to account for the mean levels of oxygen tension are presented. The best agreement with the measurements is obtained using a model where there is an arterio-venous difference in blood oxygen content of 0.6 vol %, and a difference of 50 mm Hg between mean capillary oxygen tension and that at some points between the capillaries. Skin blood flow Skin oxygen tension