Hyperbaric Conditions Research Articles

Tumor oxygenation under normobaric and hyperbaric hyperoxia. Impact of various inspiratory CO2 concentrations.

Tumor hypoxia is an important factor limiting the efficiency of sparsely ionizing ra-diation and O2-dependent chemotherapy. Since the tumor pO2 is the result of a dynamic steady state between oxygen supply and O2 consumption of the tumor tissue, hypoxia could be reduced either by increasing the O2-supply or by reducing the O2 demand of the tumor cells. The O2 supply can be improved for instance by (i) increasing the arterial oxy-gen partial pressure, (ii) improving (and homogenizing) the tumor perfusion, or (iii) en-hancing the O2 release from blood into the tissue by right-shifting the HbO2 dissociation curve. Theoretically, it should also be possible to improve tumor oxygenation by a rela-tively small decrease in O2 consumption rate of the tumor cells. However, at present in-creasing the arterial pO2 by breathing hyperoxic gas mixtures seems to be the most effective method to improve tumor oxygenation and, thus, to enhance the efficiency of standard radio- and chemotherapy in experimental malignancies [1,7,10,11,15,24] as well as in human tumors [3,9,12,14,22,29,30]. However, since in some tumor entities oxygena-tion is inadequate and anisotropic [27], normobaric hyperoxia is often not sufficient to completely eradicate tumor hypoxia [6,16,18,26]. In these cases only breathing of hyper-oxic gases under hyperbaric conditions may be sufficient to lead to therapeutic results. On the other hand, studies on experimental tumors in animals as well as clinical trials in pa-tients showed non-uniform results concerning the therapeutic benefit of inspiratory hyper-oxia ranging from clear improvement of radiosensitivity [3,4,20,30] to no effect on therapeutic outcome [3,4]. Finally, enhancement of tumor growth by hyperbaric oxygenation has been discussed [13,23].

Eustachian tube function and middle ear barotrauma associated with extremes in atmospheric pressure.

Eustachian tube (ET) function was studied by means of sonotubometry and tubotympano-aerodynamography (TTAG) prior to and following exposure to hypobaric or hyperbaric conditions. Forty normal adults were subjected to hypobaric pressure. Fifty adults who underwent hyperbaric oxygen (HBO) therapy also were studied. Following hypobaric exposure, 14 of 80 ears (17.5%) exhibited middle ear barotrauma. Following hyperbaric exposure, 34 of 100 ears (34%) exhibited middle ear barotrauma. Dysfunction of the ET, characterized by altered active and passive opening capacity, was more prevalent following exposure to extremes in atmospheric pressure compared to baseline. The ET function, which was impaired after the first HBO treatment, improved gradually over the next 2 hours. Overall, however, ET function was worse after the seventh treatment. The patients who developed barotrauma exhibited worse ET function prior to hypobaric or hyperbaric exposure. Thus, abnormal ET function can be used to predict middle ear barotrauma prior to exposure to hypobaric or hyperbaric atmospheric pressure.

Effect of High Hydrostatic Pressure and Additives on the Dynamics of Water: a Raman Spectroscopy Study

In this work we study the dynamics of pure water and alkaline halogenide solutions under hydrostatic pressure (0.1–650 MPa) by means of Raman spectroscopy. This technique allows us to follow modifications in intramolecular and hydrogen bonds present in water at atmospheric pressure and ambient temperature. Studying pure water, we recorded the particular behaviour of this liquid in the pressure range 0.1–650 MPa and evidenced a singular point near 200 MPa. Below 200 MPa an increase in pressure as in temperature leads to a weakening of the hydrogen bonds, whereas above 200 MPa, pressure strengthens these intermolecular bonds. Upon adding salts such as chlorides and bromides of sodium and potassium at atmospheric pressure, water loses its organized structure and the hydration shells of ions are the pertinent dynamical entities giving specific signatures in the isotropic part of the Raman spectra. The modifications of water structure due to salt addition are enhanced in hyperbaric conditions. Moreover, water organization at atmospheric pressure as at 300 MPa is strongly dependent on salt concentration.

Effect of High Hydrostatic Pressure and Additiveson the Dynamics of Water: a Raman SpectroscopyStudy

In this work we study the dynamics of pure water and alkaline halogenide solutions under hydrostatic pressure (0.1–650 MPa) by means of Raman spectroscopy. This technique allows us to follow modifications in intramolecular and hydrogen bonds present in water at atmospheric pressure and ambient temperature. Studying pure water, we recorded the particular behaviour of this liquid in the pressure range 0.1–650 MPa and evidenced a singular point near 200 MPa. Below 200 MPa an increase in pressure as in temperature leads to a weakening of the hydrogen bonds, whereas above 200 MPa, pressure strengthens these intermolecular bonds. Upon adding salts such as chlorides and bromides of sodium and potassium at atmospheric pressure, water loses its organized structure and the hydration shells of ions are the pertinent dynamical entities giving specific signatures in the isotropic part of the Raman spectra. The modifications of water structure due to salt addition are enhanced in hyperbaric conditions. Moreover, water organization at atmospheric pressure as at 300 MPa is strongly dependent on salt concentration.

31P-NMR analysis of lethal and sublethal lesions produced by KCl-intoxication in the zebra mussel,Dreissena polymorpha

Noninvasive phosphorus-31 nuclear magnetic resonance spectroscopy (31P-NMR) was utilized to investigate the mechanism of potassium chloride (KCl) toxicity in zebra mussels. 31P-NMR spectra showed several bioenergetically important high energy phosphates, including ATP, ADP, phosphoarginine, and inorganic phosphate. Exposure of mussels to 8.6 mM KCl caused changes in these metabolites and proved lethal to the mussels when exposed over a 24 h period. This result matched that of the molluscicide Bayluscide. Here, losses in phosphoarginine and ATP were accompanied by a rise in inorganic phosphate and a shift toward intracellular acidosis. KCl levels below 8.6 mM caused marked changes in mussel high energy phosphates and pH1. However, these changes were reversible once mussels were returned to fresh standard reference water (SRW). In contrast, mussels exposed to 8.6 mM KCl under hyperbaric conditions (20 mg/L O2) survived during the 24 h KCl exposure and showed normal ATP peaks and pH1. The latter mussels, however, died when O2 supplementation was removed and mussels were transferred to SRW. Exposure to hypoxic conditions (<1.5 mg/LO2) resulted in loss of ATP and reduction in pH1 similar to that produced to exposure to 8.6 mM KCl. The effect of KCl on ciliary beating within the zebra mussel gills was also examined. Ciliary beating stopped in all mussels receiving treatment with KCl including those jointly exposed to 8.6 mM KCl and elevated O2 (20 mg/L). However, ciliary beating resumed in mussels exposed to KCl concentrations less than 4.3 mM when the mussels were transferred to clean SRW. Ciliary beating was not affected by exposure to hypoxic conditions or to elevated O2 alone. These data suggest: (1) cessation of ciliary beat is a specific response to potassium intoxication but is insufficient to cause mussel death; (2) two levels of potassium-induced injury were observed and were dependent upon the concentration of potassium to which mussels were exposed. Exposure to KCl below, 4.3 mM resulted in reversible alterations of gill physiology while exposure to concentrations above 4.3 mM resulted in permanent lesions from which recovery was not possible. © 1996 Wiley-Liss, Inc.

96/04377 Experimental measuring of coal exlosibility for its use at hyperbaric conditions

96/04377 Experimental measuring of coal exlosibility for its use at hyperbaric conditions

Effect of gas density variations on respiratory input impedance in humans

The forced oscillation technique is a widely-used non-invasive method of characterizing the dynamic behaviour of the respiratory system. We used the forced oscillation technique to investigate respiratory mechanics in healthy subjects during simulated dives in dry hyperbaric chambers. We observed frequency dependence of input impedance, which was mainly density-dependent. To explain this result, we propose a model of the respiratory system, based on flow redistribution in a two-pathway circuit. This model, using the electrical analogue, is composed of two Resistance-Self Inductance-Capacitance (R-I-C) pathways set up in parallel. It allowed us to explain the dynamic behaviour of respiratory impedance under hyperbaric conditions in healthy subjects. Changes in respiratory impedance according to frequency vary with the relative importance of the inequalities of the two time constants RC and I/R between the two pathways. With low values of density, RC inequality predominates, whereas I/R inequality tends to predominate with high values of density.

Dynamics of ion currents in the membrane of the isolated mollusc neuron under high pressure.

The action of helium (up to 101 abs. atm.) under high pressure on ionic currents through the cellular membrane was studied in experiments on isolated neurons of a gastropod. A method of intracellular dialysis which is new for physiological investigations under hyperbaric conditions was used. A substantial decrease in the inward (sodium) current with increased pressure was found. Its amplitude was decreased by 10-15% at 25 abs. atm. and by 64% at 101 abs. atm. as compared with the control. At the same time, a shift in the currentvoltage characteristics along the abscissa was not observed. Significant changes in the outward (potassium) current were not appreciable. The inhibition of the sodium current observed in these experiments with increased pressure is associated with a possible change in the structure of the cell membrane under the influence of pressure; this leads in its turn to shifts in the functioning of the membrane components participating in the generation of the nerve impulse.

Effects of hypoxia and hypercapnia on contact lens-induced corneal acidosis.

It has been assumed that contact lens wear (CLW) may induce stromal acidosis, which is a result of corneal hypoxia and the accumulation of CO2 (hypercapnia) at the tear-lens interface. However, it has not been directly shown whether hypoxia and hypercapnia are the only causes of CL-Induced corneal acidification. In this study, we provide preliminary data about the relative contributions of hypercapnia and hypoxia to CL-induced stromal acidification by monitoring pH while the cornea was exposed to a hyperbaric oxygen atmosphere. This paradigm minimized if not eliminated the pH effects of lens-induced hypoxia on all but one subject without altering the pH effect of hypercapnia. Seven subjects were fitted with hydrogel lenses; 5 with low O2 transmissibility (Dk/LO2 = 14.0 x 10(-9) (cm/s) (ml O2/[ml x mm Hg)]), and 2 with medium O2 transmissibility (Dk/LO2 = 17.2 x 10(-9) (cm/s) (ml O2/[ml x mm Hg])) lenses. After lens insertion, modified goggles were fitted to control the corneal environment by exposing 1 eye to 20%O2 and 80%N2 (air), and the contralateral eye to 80%O2 and 20%N2 (hyperbaric O2). Corneal thickness (CT) was measured before CL insertion and over 120 min of wear. We assumed that corneal hypoxia was present if CT increased during the test period. Stromal pH was measured using a slitlamp fluorophotometer before lens insertion and at 20-min intervals for a total of 80 min. After 80 min of wearing the low Dk/L lens under hyperbaric exposure, 4 of 5 subjects showed reduced pH (mean delta pH = 0.23 +/- 0.05) and no increase in CT, suggesting that only hypercapnia was contributing to acidosis. For the same lens, but with exposure to air, 4 of 5 subjects showed a larger drop in pH (mean delta pH = 0.62 +/- 0.48) compared to hyperbaric exposure and an increase in CT, indicating that both hypoxia and hypercapnia reduced pH. Subjects wearing the medium Dk/L lens showed a small but equal drop in pH under both air and hyperbaric conditions without changes in CT, suggesting that only hypercapnia was contributing to acidosis. These preliminary results suggest that both mechanisms contribute to the pH shift accompanying CLW and that the contribution of hypercapnia is approximately 30%. Finally, the effects of hypercapnia and hypoxia are dependent on individual metabolic requirements and the transmissibility of the lens to O2 and CO2.

Histological Evaluation of Phthalocyanine Mediated Photodynamic Occlusion of Corneal Neovascularization Enhanced by Hyperbaric Oxygenation

We evaluated the effective irradiation parameters for photodynamic thrombosis of experimental corneal neovascularization enhanced by simultaneous hyperbaric oxygenation. Neovascularization was provoked in both eyes of each of 35 albino rabbit corneas using the intracorneal suture technique. The lasered animals were divided in 3 groups. Group 1 (10 rabbits) was treated under hyperbaric conditions (28 atm for 25 min.); group 2 (5 rabbits) was treated breathing pure oxygen delivered by a face mask; group 3 (10 rabbits) was treated breathing room air. The fourth group (10 rabbits) was used for control. Animals were anaesthetized, and irradiation of new corneal vessels was carried out 30 minutes after the injection of 5 mg/kg chloroaluminum sulfonated phthalocyanine. A 670 nm diode laser with a power 4 mW and a spot diameter 350 mm was used. Exposure times necessary for vascular occlusion were registered. Histological examination was carried out at the end of the follow-up time. Exposure times were significantly lower in groups 1 and 2 as compared to group 3 (1.75 +/- 0.15 min., 3.1 +/- 0.4 min., and 4.75 +/- 0.15 min. respectively). Total light dose averaged 490 J/cm,2 870 J/cm,2 and 1330 J/cm,2 respectively. Histological examination revealed thrombus formation in the targeted vessels of all three investigated groups. Combination of PDT with hyperbaric oxygenation results in an acceleration of the photodynamic process and provides for a possibility of significant reduction of photodynamic dose.

The effect of antibiotics on bacteria under hyperbaric conditions.

The sensitivity of selected bacteria to a range of antibiotics was tested under hyperbaric conditions used in saturation diving. The effect of hyperbaric helium and oxygen (heliox) on antibiotic stability and on induction of beta-lactamase was also determined. Increased resistance to penicillin (up to 23%) was shown by Staphylococcus aureus and to gentamicin (up to 46%) and rifampicin (up to 18%) by Escherichia coli and Salmonella typhimurium at 36 and 71 bar pressure. Exposure to 71 bar heliox did not affect antibiotic activity but increased the production of beta-lactamase in inducible S. aureus and Bacillus subtilis and production of beta-galactosidase in inducible E. coli. Increased resistance to antibiotics in saturation diving conditions can be attributed in some cases to the influence of hyperbaric pressure on induction mechanisms in bacteria. The experimental system devised for this work is suitable for more detailed examination of the influence of hyperbaric stress on antibiotic resistance and of its effect on induction mechanisms in general.

Kinetic Mechanism Studies of the Soluble Hydrogenase from Alcaligenes eutrophus H16

Purified soluble hydrogenase (H2:NAD+ oxidoreductase, EC 1.12.1.2) from Alcaligenes eutrophus was activated to high specific activities by flushing the enzyme consecutively with N2 and H2 and then adding substoichiometric quantities of NADH. H2-dependent NAD+ reduction activities ≥ 110 μmol NADH formed/min/mg protein at pH 8.0 and 30°C were obtained which were stable for several hours at 4°C. Kinetic studies were conducted anaerobically using activated enzyme for the purpose of evaluating the potential of using hydrogenase to enhance decompression of mammals breathing H2/O2 mixtures under hyperbaric conditions (i.e., at ambient pressures greater than 1 atm). Using nonlinear curve fitting of the kinetic data, it was found that H2 and NAD+ bind hydrogenase via a ping pong bi bi mechanism with Km values (±SE) of 11 ± 0.9 and 138 ± 11 μM, respectively, at 30°C and pH 8.0. Sodium ions were found to reversibly inhibit hydrogenase via a dead-end type of inhibition in which two catalytic forms of the enzyme bind Na+ with dissociation constants calculated to be 8.3 ± 1.2 and 49.8 ± 11.5 mM. In the absence of NaCl, maximum NAD+ reduction activity was measured at pH 8.3 at 30 and 37°C. In the presence of 50 mM NaCl, inhibition was observed primarily at alkaline pH, and at assay pH values ≤ 7.0, little or no difference was observed in activity in the presence or absence of 50 mM NaCl at a given temperature. Least squares analyses of the kinetic data indicated that substrate inhibition by H2 occurs at high substrate concentrations (Ki = 1.46 ± 0.64 mM), which would become a significant influence on enzyme catalytic activity at hyperbaric levels of H2.

Serum-free organ culture of suckling rat jejunum: Effect of regulatory hormones

To facilitate the study of regulators of differentiation and proliferation of small intestinal epithelium in the suckling rat we have developed a serum-free organ culture system and used it to examine epithelial responsiveness to various regulatory hormones. These hormones included the insulin-like growth factors (IGFs) whose action can be blocked by binding proteins in serum. Jejunal explants from 5-day-old suckling rats maintained better brush border enzyme activity and better histology when cultured under hyperbaric conditions for 24 h in serum-free Dulbecco's modified Eagle's medium/F12 medium than in RPMI 1640 plus 10% fetal bovine serum. Tissue responsiveness to various regulatory hormones was then tested in the serum-free medium. Insulin had no significant effect on morphology, proliferation rate, or enzyme activity in 5-day explants after 24 h in culture. However, insulin did increase lactase activity and induce the early appearance of sucrase in 10- and 12-day explants after 48 h in culture. Dexamethasone increased specific activities of alkaline phosphatase (30%, P < 0.001) and lactase (15%, P < 0.001), and reduced shedding of alkaline phosphatase into the medium (P < 0.001), in explants of 5-day-old rats cultured over 24 h. Dexamethasone combined with insulin had no obvious effect on the rate of protein or DNA synthesis but did increase villus height (P = 0.04) and crypt depth (P = 0.001) and acted synergistically to further increase lactase activity above levels obtained by either alone. IGF-I and IGF-II, des-(1-3)IGF-I, fibroblast growth factor (FGF), and growth hormone (GH) had no effect on morphology or biochemical activity of explants after 24 or 48 h culture.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of hyperbaric conditions on vibrotactile thresholds

The effects of low-frequency, water-borne vibration upon swimmers and divers are virtually unknown. It has been reported that divers can ‘‘feel’’ underwater sounds on various parts of their bodies. The current experiments were conducted as an initial investigation of these reports to determine if barometric pressure and breathing mixture has an effect on vibrotactile thresholds measured in air. Vibrotactile thresholds at the thenar eminence were determined on four divers during a ‘‘saturation dive’’ (8 days) in a dry hyperbaric chamber. Measurements were made prior to the dive (pre-test) in a normobaric environment (sea level) at 132 ft of seawater (fsw), at 198 fsw, at 300 fsw, and following the dive at sea level (post-test). The gas mixture in which the divers lived was varied according to standard procedures to prevent adverse body reactions during compression and decompression. Vibrotactile thresholds were measured by standard procedures at 1, 10, 100, and 250 Hz. Results indicate that neither air pressure nor breathing mixture had any effect on vibrotactile thresholds within any of the four mechanoreceptor channels that innervate normal skin. The results are internally consistent within this experiment and also when compared to threshold standards accumulated over thirty years. [Work supported by Geo-Centers, Inc. under Navy Contract.]

Nonmagnetic hyperbaric chamber for in vivo NMR spectroscopy studies of small animals

A description is given of the design, construction, and initial use of a polycarbonate resin hyperbaric chamber for in vivo NMR spectroscopy studies of anesthetized, ventilated rats in a horizontal bore 4.7 Tesla magnet. The chamber and its associated equipment, initially used for hyperbaric studies of rats in states of extreme hypercapnia, are also well suited for conventional hyperbaric studies, such as those related to hyperbaric oxygen therapy, oxygen toxicity, and diving. Basic technical challenges that required innovations involved: a) preservation of magnetic field homogeneity; b) avoidance of a metallic chamber body that would overload gradient and RF coils; c) physiological monitoring; and, d) remote control and stabilization of electromagnetic and physiologic factors (especially ventilatory stability) during pressure changes. A small paramagnetic bulk magnetic susceptibility shift from chamber-associated hyperbaric oxygen was observed when chamber oxygen tensions were only one atmosphere. High-quality NMR imaging and spectroscopy were demonstrated during hyperbaric conditions.

Experimental study of the absorption dynamics of harmful admixtures in hermetic chambers under normal and hyperbaric conditions

Experimental study of the absorption dynamics of harmful admixtures in hermetic chambers under normal and hyperbaric conditions

Pedicle Musculocutaneous Flap Transplantation

In pedicle musculocutaneous flaps, a local circulatory insufficiency with a total or subtotal ischemia may occur and jeopardize the result of the reconstructive surgery. Transcutaneous oxygen pressure (PtcO2) monitoring has been shown to reflect tissue perfusion and has been advocated to predict the final outcome of ischemic flaps. Unfortunately, under normal atmospheric conditions, this test is not sufficiently discriminative. We evaluate the effect of hyperbaric oxygen conditions on the efficiency of this test. Fifteen patients with pedicle musculocutaneous flap were evaluated by clinical examination and transcutaneous oxygen tension measurements. The final outcome was healing in 7 and failure in 8. In order to determine the predictive value of transcutaneous oxygen tension, measurements were done immediately after the surgical procedure. In ambient air, neither the absolute value of transcutaneous oxygen tension (2.6 +/- 3.6 versus 11.7 +/- 12.6 torr; N.S.) nor the difference or the ratio between the transcutaneous oxygen tension of the flap and the subclavicular reference shows any significant difference according to the outcome (failure or success). The same is true in normobaric oxygen. In hyperbaric oxygen, however, there is a significant difference in transcutaneous oxygen tension between the two groups (12 +/- 12 versus 378 +/- 385 torr; p < 0.01). A transcutaneous oxygen tension higher than 50 torr in hyperbaric oxygen (2.5 atm abs) is the best cutoff value to discriminate success from failure.

Hyperbaric welding by the FCAW process

Summary The present work is part of a research project aiming at full implementation of robots for underwater welding at great depths (beyond 600 m). This study discusses preliminary results from basic investigations on the weld metal microstructures and toughness of the flux‐cored C‐Mn‐1% Ni wire used for welding under hyperbaric conditions. Under the conditions studied, the chemical composition of the weld metal was not much affected by differences in the working depth. The limited variations in weld metal oxygen content (approximately 620 to 720 ppm) led to small but significant changes in the volume fraction of the various microconstituents and in the transition temperature for a Charpy impact energy of 41 J. The prior austenite grain size, on the other hand, was not apparently affected.

Relationship between inspired and expired gas temperatures in a hyperbaric environment

When breathing room air at sea level the expired gas temperature (T e) increases in proportion to the inspired one (T i). Previous studies conducted under hyperbaric conditions have assumed that the T e vs T i relationship was the same when humans breathed room air at atmospheric pressure or helium-oxygen mixture under hyperbaric conditions. We hypothesized that the use of dilutant gases, as helium (He) or hydrogen (H 2), having low density but high specific heat compared to nitrogen, could change the T e vs T i regression. The present study was conducted on 3 professional divers participating in the COMEX Hydra IX experiment. Three conditions were studied: A, (23.5 ATA, HeH 2O 2 mixture); B, (21 ATA, H 2O 2 mixture); and C, (21 ATA, HeO 2 mixture). In each condition six different inspired temperatures were tested, while minute ventilation, T i and T e values were measured simultaneously. In all cases a linear relationship was found between T e and T i, but the slopes of the regression lines obtained in conditions A and B (gas mixture containing H 2) were significantly lower than in condition C (HeO 2 mixture). Computation of the convective respiratory heat loss (Ċr) revealed that, when the subjects breathed the coldest gas mixtures (+ 10°C), Ċr value was 1.6 times higher in condition B than in C. These data are consistent with theoretical considerations and they demonstrate that a single equation cannot be used to predict the T e vs T i relationship in all environmental circumstances.

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)