Hyperbaric Conditions Research Articles

Effect of long-term exposure to hyperbaric conditions on lipid peroxidation and on erythrocyte structure and function

Effect of long-term exposure to hyperbaric conditions on lipid peroxidation and on erythrocyte structure and function

Evidence that tolerance to cultured thyroid allografts is an active immunological process. Protection of third-party grafts bearing new antigens when associated with tolerogenic antigens.

We studied the tolerance phenomenon that develops in long-term recipients of cultured thyroid allografts. Allogeneic mouse thyroids were cultured under hyperbaric oxygen or acidic conditions and then transplanted beneath the kidney capsule of C57BL/6 recipients. Donors differed from the recipients in minor antigens alone, major histocompatibility complex antigens alone, or both. At 35-77 weeks after the first cultured graft, recipients received two more cultured grafts under the capsule of the opposite kidney and were immunized with donor spleen cells (SC). At 5 weeks after the second transplantation, we observed that whereas second grafts carrying new antigens alone were rejected, second grafts carrying new antigens in association with antigens in the first graft were significantly protected. In another set of experiments, normal mice became tolerant to cultured allografts after 2 weeks in parabiosis with tolerant individuals. Tolerant mice showed reduced specific in vivo and in vitro cytotoxic T lymphocyte responses. However, the frequency of CTL precursors of tolerant mice was the same as in normal mice. The reduced in vitro CTL responses were restored to normal levels by the addition of a lymphokine rich medium. Also, we observed that the injection of specifically activated immune SC caused the rejection of cultured allografts in normal but not in tolerant recipients. We conclude that the tolerance that develops in recipients of cultured allografts is an active immunological process that affects the activation and effector function of CTL.

Whole lung lavage under hyperbaric conditions: 2. Monitoring tissue oxygenation.

Pulmonary Alveolar Proteinosis (PAP) is characterized by dyspnea and progressive detoriation of arterial oxygenation, caused by accumulation of lipid- and protein-rich insoluble material in the alveoli. Bronchoalveolar lavage is the basic principle of treatment and can be performed while ventilating one lung. However due to severe pulmonary insufficiency, ventilation of one lung lessens arterial PO2 to unacceptable levels. In order to prevent arterial and tissue hypoxemia we performed bronchoalveolar lavage under hyperbaric conditions as previously described1. During these lavage procedures hemodynamic and central circulatory oxygen parameters were continuously monitored2. Oxygenation of peripheral tissue was monitored by multiple assessments of skeletal muscle PO2 (quadriceps musculature) with a polarographic pO2 needle electrode3 and by transcutaneous pO2 measurements. The aim of this study was to study alterations in muscle oxygenation during and after bronchoalveolar lavage.

Carbon Monoxide Poisoning

Carbon monoxide is a common domestic and industrial poison which may be lethal. Survivors can develop permanent neuropsychiatric disability. The mechanisms of toxicity are poorly understood and the traditional criteria used to determine the severity of the poisoning have low predictability. Oxygen is the recommended antidote to carbon monoxide, but it appears that oxygen under hyperbaric conditions repeated either daily or as indicated by the patient's condition may be required to provide an effective dose. A reliable marker of the severity of carbon monoxide poisoning is urgently needed so that trials of alternative regimens can proceed.

Tolerance of low cerebral intracellular pH in rats during hyperbaric hypercapnia.

Brain acidosis from cerebral ischemia is characterized by average intracellular pH levels of approximately 5.8-6.2, which appear in turn to worsen cellular injury. We report that the brain is not injured when hypercapnia is used to reduce intracellular pH to about 6.2 during adequate oxygenation. A hyperbaric chamber is needed to achieve intracellular pH values so low because inspired CO2 tensions must be increased to approximately 1 atm. Using in vivo phosphorus-31 and proton nuclear magnetic resonance spectroscopy, we measured brain intracellular pH and lactate concentration of rats inside a nonmagnetic polycarbonate chamber at a barometric pressure of 1,500 mm Hg. Intubated rats were ventilated with a 50% O2/50% CO2 gas mixture for specific times. All six rats ventilated for 15 minutes with CO2 tensions of approximately 750 mm Hg woke up without neurological impairment, despite a decrease in intracellular pH to about 6.2. Higher CO2 tensions and longer exposures resulted in cardiovascular collapse and sudden death, followed by the postmortem appearance of brain lactate. Brain intracellular pH values near 6.2 can be induced briefly in vivo in ventilated rats without injury under hyperbaric hypercapnic conditions. If attempts are made to lower brain pH in vivo even further by increasing PCO2 beyond 750 mm Hg, mean arterial blood pressure and cerebral blood flow decrease to values incompatible with life.

Radiosensitization by 17 atmospheres pressure of air

As part of a study of the radiobiological effects of gas mixtures under ambient and hyperbaric conditions (Conere, 1989) we investigated the radiosensitivity of Chinese Hamster ovary (CHO) cells at 17 atmospheres pressure (1.7 × 106Pa) of air. We found that such hyperbaric air caused a significant increase in radiosensitivity.

Analysis of high‐frequency rotational angioplasty‐induced echo contrast

During high-frequency rotational angioplasty (HFRA), myocardial contrast enhancement (echo contrast) was observed by means of two-dimensional echocardiography. In order to evaluate the echo contrast produced by HFRA, an in vitro experimental model was built using a cylinder with the HFRA catheter scanned in a water bath. The cylinder was filled with blood, mineral water, and distilled water. With a 2.5-MHz transducer, echograms were recorded and analyzed by video intensitometer, and the maximum intensity IUmax and persistence time P were calculated. Rotation frequencies of 20,000-200,000 rpm with 2.0--mm burrs and times of 10 s were tested. In another model, hyperbaric conditions for the same media were produced. The influence of debris from arterioscleroic plaque and of hematocrit on echo contrast intensity were also analyzed. The effect of HFRA on hemolysis (LDH, free hemoglobin) within 10 s and temperature were also measured. The contrast effect was transient, depending on the rotation frequency. In blood, it appeared at 20,000 rpm (IUmax at 200,000 rpm: 237 IU), in mineral water at 40,000 rpm (IUmax 165 IU), and in distilled water at 80,000 rpm (IUmax 72 IU). Persistence time was measured up to about a half-minute. Echo contrast production was reduced at 0.5 bar and fully suppressed at 2.5 bar. Debris increased contrast intensity from about 219 IU to 225 IU (at 160,000 rpm). In blood IUmax decreased from 227 IU to 97 IU by lowering the hematocrit from 44.2% to 3.6%.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption in liver at the focus of an ultrasonic shock wave field

This experimental study is an extension of a previous investigation of finite amplitude ultrasound absorption at 1 MHz fundamental frequency in freshly excised rat liver at 37°C (Fry et al. 1989). The work reported here includes measurements of the absorption as a function of intensity under a variety of conditions (temperature, pressure, and tissue state). The maximum intensity employed in the investigation (700 W/cm −2) corresponds to a shock parameter of approximately 1.7 based on previous characterization of the acoustic field which established that shock ( σ = 1) occurred in the range 225 W/cm −2 to 275 W/cm −2 (Fry et al. 1989). Of the three temperatures chosen for the thermal study (30°C, 37°C, and 41°C), the only statistically significant differences ( p < 0.05) in absorption were between the 30°C and 41°C data in the intensity range just above σ = 1 (300–500 W/cm −2). The intensity-dependent absorption coefficient was also determined for excised liver under hyperbaric conditions and for liver in situ at 37°C. At a pressure of 350 psi, the absorption was generally less than at atmospheric pressure. In situ liver at 37°C had a lower absorption above 200 W/cm −2 than freshly excised liver, but the difference was only significant between 200 and 300 W/cm −2 and between 600 and 700 W/cm −2.

Radiosensitization with normobaric oxygen and carbogen

Although hypoxia is a cause of failure in clinical radiotherapy, the outcome of clinical trials with chemical radiosensitizers, such as misonidazole, has been disappointing [7,8]. Doselimiting toxicity restricts the drug dose per fraction, so that the intratumour concentrations achieved are far lower than those required for detecting a radiosensitizing effect [3]. Therefore, there is a need to identify hypoxic cell radiosensitizers which are non-toxic and effective in fractionated radiotherapy. Recent studies done with low radiation doses per fraction and clinically relevant fractionation regimes have shown, in a mouse mammary carcinoma, that normobaric 100% oxygen is an effective sensitizer [34]. Enhancement ratios (ER) * of 1.45 and 1.3 (at the TCDs0 level, i.e. the dose required to locally control 50% of tumours) were obtained for oxygen with 30 fraction given in an overall time of 6 weeks or 36 fractions in 12 days (Fig. 1). These relatively small enhancement ratios can be translated into a considerable practical gain e.g. by increasing the oxygen concentration from 21 to 100%, tumour control was increased from 0 to 80% (Fig. 1 panel c). A similar gain could be obtained in human tumours where hypoxia limits the response to treatment. Very recently, Gatenby et al. [12] have shown a remarkable and significant correlation between the degree of response to radiotherapy in metastases of the head and neck region and levels of oxygenation within these tumours. Previous studies done in a whole variety of rodent tumours, albeit with fewer fractions, also have shown significant increases in radiosensitivity for either oxygen or carbogen (a mixture of 95% 02 + 5% CO2) [10,15,18,21,32,33,37,40]. Table I and Fig. 2 summarize the ERs for oxygen and carbogen obtained by several investigators using fractionated treatments. Provided an adequate pre-irradiation breathing time (PIBT) is used, ERs in general lie between 1.3 and 1.6 for carbogen and between 1.3 and 1.45 for oxygen. The degree of sensitization achieved with normobaric gases in fractionated regimes is therefore much greater than that seen in almost all animal tumours and human tumour xenografts, with the radiosensitizer misonidazole [6,16,26,31]. Normobaric gases enhance radiosensitivity by increasing the partial pressure of oxygen (pO2) within tumours. The intracapillary saturation of haemoglobin with oxygen can be significantly enhanced in rat tumours by the administration of pure oxygen either under normoor hyperbaric conditions [28]. Improved tumour oxygenation results from increases in the amount of dissolved oxygen and by raising the systemic blood pressure [4,25]. Furthermore, carbogen enhances tumour blood flow and shifts the haemoglobin dissociation curve to the right, thus depressing the affinity of haemoglobin for oxygen [25]. Consequently, carbogen should be a more effective sensitizer than oxygen. Using a fluorescent immunologically labelled 2-nitroimidazole stain for detecting hypoxic cells, recently developed in our laboratory by Hodgkiss and collaborators [17], carbogen decreased the proportion of hypoxic cells in CaNT tumours to a greater extent than oxygen. Hypoxic fractions of 19.0 _ 1.6, 9.4 _+ 2.7 and 2.9 + 1.5% were determined for air, oxygen and carbogen, respectively [33]. These results are in agreement with the slightly higher ERs obtained with carbogen, in this same tumour model, using a local control and regrowth delay assay (Fig. 2, panel b and reference 33). However, the higher Ps0 values (i.e. the oxygen concentration at which 50% of the haemoglobin is saturated with oxygen) for rodent haemoglobin compared with that of humans [13]

Pulsed ultrasound and the hyperbarically exposed mouse fetus

To enhance the likelihood of cavitation, pregnant mice were subjected to hyperbaric conditions and quickly returned to atmospheric pressure. Following this treatment, they were exposed to spatial average, pulse average intensities of 100 W/cm2 (2.2-MHz, 20-microseconds pulses with a duty cycle of 1/1000 or a temporal average spatial average intensity of 0.1 W/cm2). Fetal weights, deaths and malformations were scored. No statistically significant effects were observed in the offspring.

Respiratory effects of cold-gas breathing in humans under hyperbaric environment

Changes in total lung resistance (R l) during inhalation of cold gas mixtures measured in 4 human volunteers during an experimental dive at 46 ATA. The subjects breathed helium-nitrogen-oxygen mixtures during the decompression schedule, and measurements were performed at 46, 36, 21, 12.5, 6 and 2 ATA (1 ATA = 100 kPa). R l was measured during eupneic ventilation when individuals inhaled either ambient gas at +30 to +33°C (control condition), or cooled gas at +7 to +18°C. R l values measured in control conditions increased with gas density. Thus, the changes in R l induced by cold gas breathing were expressed in percent of the corresponding control values. No cold-induced bronchospasm occurred at low ambient pressure, even at the lowest inspired temperature, +7°C. However, the airway response was present at pressure up to 21 ATA and then occurred at higher level of inspired gas temperature. The convective respiratory heat loss (Ċr), calculated at each pressure level and experimental condition, was linearly related to cold-induced changes in R l; the value of Ċr inducing 20% increase in R l was around 1.4 kcal·min −1. The bronchomotor response was related to the increase in respiratory heat loss induced by the high thermal capacity of the gas mixture used in hyperbaric environment. The present observations confirm previous data obtained under hyperbaric conditions (25 ATA) as well some experiments performed at sea level in normal individuals breathing very cold air.

Calcium‐associated cytoprotective effect of taurine on the calcium and oxygen paradoxes in isolated rat hepatocytes

Our study was designed to determine the calcium and oxygen paradoxes in isolated rat hepatocytes, and to evaluate the cytoprotective effects of taurine on hepatocytes during oxygenation, hypoxia, and on these paradoxes. The calcium and oxygen paradoxes were clearly revealed in isolated rat hepatocytes. As the formation of the superoxide radical was accelerated by the hyperbaric conditions and the calcium ions, drugs such as superoxide dismutase and a calcium channel blocking agent (verapamil), prevented these paradoxes. Taurine decreased the oxygenation-induced lipid peroxidation of hepatocytes, and prevented the hypoxia-induced hepatocyte death in a calcium-containing medium, but not in a calcium-free medium. Taurine also protected the hepatocytes from injuries associated with the calcium and oxygen paradoxes due to the inhibition of sudden calcium influx into the hepatocytes.

Effects of hyperbaric oxygen in cryobiologic wounds

Hyperbaric oxygen therapy (HBO) has been helpful in treating radiation burn lesions, osteomyelitis, gangrenous wounds, necrotic sites, and injuries caused by tissue hypoxia [5, 7]. For these reasons HBO could be a possible choice for a study to better define the role of hypoxia in the pathogenesis of cryobiologic wounds. Liquid oxygen, as employed in the HBO sessions described in this study, because of its ease of application can be used to show the importance of the same oxygen in the genesis and in the healing process of lesions [4, 7, 8]. For this purpose the effects of hyperbaric and normal oxygen conditions were tested on healing cryolesions experimentally induced in Winster rats. Test subjects were 20 Winster rats weighing between 200 and 220 g, housed individually in stainless steel cages and fed Purina rodent laboratory chow and tap water ad libitum. One thermocouple needle was used to measure in-depth temperature. The rats were divided into two groups of ten animals each. All were anesthetized with intraperitoneal injection of 0.5 ml ketamine. Skin epilation on two symmetrical areas of the dorsum ( 2 3 cm diameter) was done in all rats. Each area was treated with a double freeze-thaw cycle (the second immediately after the first) to 4 0 ~ using liquid nitrogen with the open spray technique (Frigitronic). The freezing time was 45 s and the thawing time was about 80 s. One group of rats was treated with HBO. The HBO session started immediately after the second thawing. HBO was accomplished by flushing a 45 pressure chamber with 100% oxygen up to 2.3 ATA. In this way HBO works on rats both locally and systemically. The treatment sessions were once a day for 45 min each, 5 days a week (pressurization and depressurization took

PROLONGED SURVIVAL OF MURINE THYROID ALLOGRAFTS AFTER 7 DAYS OF HYPERBARIC ORGAN CULTURE IN THE UW PRESERVATION SOLUTION AT HYPOTHERMIA

Organ culture of murine thyroid allografts in hyperbaric oxygen (95% O2 at 25 psi, 37 degrees C) for 48 hr, results in prolonged allograft survival. Endocrine tissues can be cultured at 37 degrees C--however, this method may not be applicable to vascularized organs at normothermia. The aim of this study was to apply hyperbaric oxygen culture (HOC) under organ preservation conditions (hypothermia, UW solution) that have been shown to be successful in clinical organ transplantation. B10BR/SGSNJ murine thyroid lobes were transplanted beneath the kidney capsule of C57BL/10J recipients. Thyroids were cultured in Eagle's MEM at 37 degrees C (controls) and at 5 degrees C, under hyperbaric conditions (95% O2:5% CO2, 25 psi). Alternatively, thyroids were cultured in UW solution (+/- allopurinol/GSH) at 5 degrees C, for up to 7 days. Graft survival was determined 21 days posttransplant by 125I uptake and by histology. In Eagle's MEM, HOC at 37 degrees C/48 hr and 5 degrees C/7 days, resulted in 93% and 20% allograft survivals, respectively. In UW solution (- allopurinol/glutathione [GSH]), HOC at 5 degrees C/7 days resulted in 83% allograft survival: immunoperoxidase staining showed a decrease of MHC class I alloantigen expression. Oxygen free radical scavenger (allopurinol/GSH) addition to the UW solution diminished this effect and suggested an oxygen free radical-mediated mechanism in immunoalteration. These results demonstrate that HOC for 7 days reduced the antigenicity and immunogenicity of murine thyroid grafts under conditions that simulate organ preservation. Hypothermic hyperbaric oxygen culture conditions require testing in a higher animal species and in vascularized grafts to determine if this method can be applied to whole-organ transplantation.

In vivo binding of carbon monoxide to cytochrome c oxidase in rat brain

The possibility of binding of CO to cytochrome c oxidase (cytochrome a,a3) in brain cortex has been examined in vivo by reflectance spectrophotometry. During ventilation with CO-containing gases, cytochrome a,a3 absorption at 605 nm increased in the parietal cortex of anesthetized rats during carboxyhemoglobin (HbCO) formation. HbCO levels, measured by changes in absorption at 569-586 nm in vivo, correlated positively with arterial HbCO by CO oximetry. Arterial blood pressure and calculated O2 content varied inversely with HbCO. During CO exposure, decreases in blood pressure, O2 content, and cytochrome a,a3 oxidation level could be reversed partly at constant HbCO by compression to 3 atmospheres absolute (ATA). After removing CO from inspired gas at 3 ATA, optical and physiological parameters recovered completely to control values except for minor persistent elevations of HbCO. Difference spectra from parallel experiments at constant HbCO revealed absorption minima at 588-592 nm and 600-605 nm as a result of hyperbaric exposure. Spectral analysis of these components was consistent with partial dissociation of a cytochrome a3-CO complex and cytochrome a reoxidation with increasing dissolved O2 in hyperbaric conditions.

Electroencephalographic and evoked potential monitoring in the hyperbaric environment

The purpose of this study was to investigate brain bioelectrical activity during hyperbaric oxygenation by continuous and simultaneous monitoring of electroencephalographic and bimodal (auditory, somatosensory) evoked potentials. Multivariable recordings (electroencephalogram, brainstem auditory evoked potentials, early somatosensory evoked potentials, heart rate, heart rate variability, and transcutaneous partial pressure of oxygen) were measured with a new technique in 12 healthy male volunteers 26 to 52 years old (mean +/- SD, 35.9 +/- 9.5 years). Recordings were obtained while the subjects breathed (1) air at normal atmospheric pressure, (2) 100% oxygen at normal atmospheric pressure, (3) air at 2 atm (10 meters sea water [msw]), and (4) 100% oxygen at 2 atm (10 msw). Spontaneous brain electrical activity, somatosensory evoked potentials, and heart rate variability were not significantly affected during hyperbaric oxygenation, whereas the heart rate showed a significant decrease (paired t test, P less than 0.05). Alterations in brainstem auditory evoked potentials were seen under hyperbaric conditions and did not reach statistical significance (increase of the I-V interpeak latency by paired t test; P less than 0.2). All subjects showed insignificant increases in dominant alpha frequency and decreases in delta frequency under hyperbaric situations.

Cold Tapping To Prolong Pipe Life

Utilisation du souturage a froid pour reparer des canalisations ou des pipelines en Mer du Nord ou pour developper de nouveaux champs marginaux en raccordant des conduites d'evacuation du petrole ou du gaz aux reseaux deja existants

Variations in the severity of retinopathy seen in newborn rats supplemented with oxygen under different conditions of hyperbarism

The purposes of this experimental study were to evaluate the effects of oxygen supplementation delivered under hyperbaric conditions on the retinas of newborn rats and to determine the minimum and maximum levels of hyperbarism capable of protecting the retinal vessels from the toxic effects of oxygen without determining lethal effects in this experimental model. A control group of newborn rats were maintained with their mother for the first 12 days of life under room-air conditions. A second group of animals were exposed to a hyperbaric environment (+81 kPa) under normoxic conditions for the first 7 days of life and subsequently returned to normobaric conditions for the next 5 days. Examination of the retinal flat mounts from this latter group of animals revealed essentially normal vascular networks with only a modest degree of vasoconstriction. Two other litters of ratlings, with their mothers, were given supplemental oxygen at an FiO2 of 80% under a compression pressure of +101.25 kPa. In this group of animals, death of both of the mother rats from pulmonary edema occurred on the first day of treatment, and, in spite of immediate mother substitution, the newborn rats succumbed to the same complication. Five other groups, each containing two litters of newborn rats with their mothers, were exposed to FiO2s of 80% at hyperbaric levels ranging from +20.25- to +81.0 kPa for the first 7 days of life. On the eighth day, the FiO2s were reduced to 21%. After 5 days of room-air recovery, the animals were killed.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of hyperthermia on the early- and late-appearing mouse foot reactions and on radiation carcinogenesis: Part II. Effect on radiation carcinogenesis (thermal enhancement and oxygen enhancement).

The effect of hyperthermia on radiation carcinogenesis was investigated in the C3Hf/Sed mouse foot. The foot was irradiated under hypoxic conditions, in air, or under hyperbaric oxygen conditions to evaluate the oxygen effect. Hyperthermia at 43.5 degrees C for 45 min was given by immersing the animal foot into a constant temperature water bath. A malignant tumor in the irradiated foot was first observed congruent to 250 days after irradiation. Tumors developed in the irradiated area until day 850. RCD50, or 50% radiation carcinogenesis dose was the endpoint and was calculated based on the tumor incidence 650 days after irradiation. RCD50 following radiation given alone under hypoxic conditions was 66.3 (60.0-73.2) Gy, and the oxygen enhancement ratio (hypoxic/hyperbaric oxygen) was 3.0 (2.5-3.5). Radiation carcinogenesis was enhanced by hyperthermia given with a 20 min treatment interval with no significant alteration in the oxygen effect. Thermal enhancement was greatest when hyperthermia was given 20 min prior to irradiation (2.5 [2.2-2.9] under hypoxia). No thermal enhancement was observed when two treatments were given with a treatment interval of 2 days. The median time to develop a malignant tumor decreased with increasing radiation dose. This median time was shorter following combined hyperthermia and irradiation (423 days) than following radiation alone (504 days). Histological studies revealed that more than 80% of tumors were soft tissue sarcomas, and the most common tumor was fibrosarcoma. Squamous cell carcinoma was found in 7% of all tumors.

Improvement of ethanol fermentation under hyperbaric conditions

Recently more and more interest is manifested in the utilization of high-pressure extraction using supercritical gases for the purification of products in biochemical processes. Some researchers have examined the possibility of circulating continuously a supercritical gas through the fermentor, under hyperbaric pressure, to recover the desired product while the fermentation is taking place. However, an earlier study has demonstrated that fermentation with baker's yeast was inhibited by a long exposure under hyperbaric pressure. This article is concerned with the improvement of ethanol production under hyperbaric pressure in view of the development of an integrated fermentation-extraction process where supercritical carbon dioxide would be used for the in situ recovery of ethanol. The selection of the best yeast strain and operation under cyclic pressures are considered.