Energy per ion pair measurements in pure helium and helium mixtures.
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Alpha Particles↗
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[Bone marrow reaction after injury of the eyes and skin by direct and reflected radiation of helium-xenon and helium-neon gas lasers].
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Animals↗
R.b.e. and o.e.r. of extended-Bragg-peak helium ions: survival and development of rat embryos.
Rats were exposed under aerobic or hypoxic conditions to 200-1200 rads of 60Co gamma-rays or extended-Bragg-peak helium ions on the eighth day of gestation. Uterine contents were examined on the twentieth day of gestation. At the 50 per cent embryonic survival level, helium ion r.b.e. was 1(.0) (aerobic) and 1(.2) (hypoxic). Maximum attainable gamma-ray and helium-ion o.e.r.s. were 2(.2) and 1(.7) respectively, indicating an oxygen-effect gain (o.e.g.) of 1(.2). At the 10 per cent survival level helium ion r.b.e. was 1(.1) (aerobic) and 1(.4) (hypoxic). Gamma-ray and helium-ion 0.e.r.s. were 2(.0) and 1(.5) respectively, indicating a helium ion o.e.g. of 1(.3). These data demonstrate that the small fraction of high-LET radiation present in this helium ion beam has a neglible effect on the aerobic r.b.e., but lowers the effective o.e.r. of the beam approximately 25 per cent relative to that of gamma-rays. Helium ions were significantly more effective than gamma-rays in killing embryos under hypoxic conditions, in producing congenital abnormalities under aerobic conditions, and in stunting foetal growth under both conditions.
Animals↗
Effect of helium and oxygen on airflow in a narrowed airway.
A mixture of 80% helium and 20% oxygen has physical properties that increase airflow and decrease resistance in the airway when used as a portion of inspired gas. This study was designed to demonstrate and quantify the effects of a helium-oxygen mixture in a normal airway and when airway resistance is increased. Thirty healthy volunteers were studied breathing room air and the helium-oxygen mixture through a normal airway and an airway that included a resistor. Pulmonary function tests, directed by a registered respiratory therapist, were performed on all subjects using a computerized spirometer. The functional vital capacity, one-second forced expiratory volume, half-second forced expiratory volume, and peak inspiratory flow rate were analyzed. There was a statistically significant increase in 1-second forced expiratory volume using a helium-oxygen mixture in a normal airway. All pulmonary function test scores statistically improved when volunteers inspired helium and oxygen through the restricted airway, demonstrating that helium and oxygen can increase airflow in the presence of an increased airway resistance. This substantiates a role for helium and oxygen in treating conditions associated with decreased airway size and increased airway resistance.
Adult↗
The output of four modern vaporizers in the presence of helium.
It has been previously demonstrated that the output of calibrated vaporizers is influenced by the concentration of nitrous oxide in the carrier gas. This study was performed to determine whether helium in the carrier gas affects the output of modern calibrated vaporizers. A factorial design was used to determine the influence of carrier-gas helium concentration, carrier-gas flow rate and vaporizer dial setting on the output of four vaporizers: Ohio Calibrated Enflurane, Ohio Calibrated Isoflurane, Ohmeda Isotec 4, and Dräger Vapor 19.1 Isoflurane. Three vaporizers of each model were tested. Output was converted to % of baseline so that different dial settings could be compared. For a given dial setting, baseline was defined as the output at a carrier-gas flow rate of 3 L.min-1 and helium concentration of zero. The data were analyzed using multiple linear regression. There was an effect of helium concentration on vaporizer output in all models. None of these changes was clinically important, since vaporizer output did not vary by more than +/- 10%, except at high flows and at high helium concentrations with the Ohmeda Isotec 4. It is concluded that these vaporizers can be used safely with helium.
Anesthesia, Inhalation↗
The effects of high pressure helium and nitrogen on the release of acetylcholine from the guinea-pig ileum.
1 The effects of high pressures of helium and of nitrogen on acetylcholine release were tested using the guinea-pig ileum as a model preparation. A superfusion system was designed in which this tissue could be maintained under physiological conditions in a high pressure chamber.2 Helium, at a pressure of 136 atm slightly increased the spontaneous output of acetylcholine but produced no significant changes at 68 atm (136 atm is close to the lethal pressure for small mammals).3 The acetylcholine release evoked by electrical stimulation or by 55 mM potassium was not altered by 136 atm of helium. Effects on tetrodotoxin-treated tissues were not consistent.4 Nitrogen, which in contrast to helium possesses general anaesthetic properties, caused considerable increases in spontaneous and in electrically evoked acetylcholine output at pressures which produce anaesthesia. These increases were not changed when helium was used to increase the total pressure to 136 atm, although this reverses the general anaesthetic actions of nitrogen in vivo.5 The increases in rate of acetylcholine release produced by nitrogen were observed in tetrodotoxintreated tissues and in tissues from reserpine-treated animals. In a calcium-free medium the increases were considerably smaller.6 The conclusions from these results are that while high pressures of helium caused little or no change in acetylcholine release rates, nitrogen produced large changes, which were not due to effects on axonal conduction. The effect of nitrogen is not apparently related to its general anaesthetic actions. Differences such as these in transmitter release would be likely to contribute to the differing physiological effects of these two gases.
Acetylcholine↗
The use of helium-oxygen spirometry in occupational lung disease.
One of the major problems in the study and management of occupational lung disease is to detect early impairment so that corrective measures can be taken before irreversible or more severe damage occurs. Unfortunately standard spirometric tests are not sensitive to functional impairment in small airways where the earliest abnormalities in many pulmonary diseases are thought to occur. A a result, several new tests have been devised in the last decade to study this so-called silent zone. Helium-oxygen spirometry, one such test, is safe, convenient, and can eaily be added to conventional air spirometry apparatus. Two studies using helium-oxygen and air spirometry done by the Appalachian Laboratory are presented. In the first, non-exposed controls were compared to flax workers with either low or high dust exposure. Both air and helium-oxygen flow volume curves showed decreased flow rates after a work-shift in the high exposure group but no change in controls. In the low-dust exposure group, only helium-oxygen spirometry detected decreased post-shift flow rates suggesting small airways disease. Coal miners were compared to controls in the second study. Subgroups of younger subjects, smokers, non-smokers, bronchitics, and non-bronchitics were also analyzed. In no case did helium-oxygen spirometry detect differences which were not present on routine air spirometry. It is concluded that further studies in this area are needed. At present, random screening with helium-oxygen spirometry for early occupational disease is not warranted, and this test remains an investigative tool.
Epidemiologic Methods↗
Effects of hyperbaric helium-oxygen on the antipyretic actions of aspirin and acetaminophen in rats.
The effects of two antipyretics, aspirin and acetaminophen, were studied under hyperbaric helium-oxygen conditions. Groups of yeast-fevered rats were given three different doses of each antipyretic in 1-ATA air and 31-ATA helium-oxygen. Neither agent was as effective an antipyretic in hyperbaric helium as it was in 1-ATA air. Responses to acetaminophen were reduced an average of 73%, and those to the two lower doses of aspirin by 56%; the highest dose of aspirin (135 mg/kg) caused a significant elevation of temperatures in the hyperbaric environment. A similar increase in temperatures was observed in rats treated with 135 mg/kg of aspirin and exposed to hot (30--31 degrees C) air at 1 ATA. It is concluded that the decreased efficacy of antipyretics in hyperbaric helium environments is caused by the high ambient temperatures maintained in helium (34--35 degrees C) to compensate for the greater thermal conductivity of helium compared to nitrogen, which may limit the heat-dissipating abilities of rats in the hyperbaric environment.
Acetaminophen↗
Helium-oxygen mixture in the treatment of postextubation stridor in pediatric trauma patients.
OBJECTIVE: To assess the effectiveness of a helium-oxygen mixture in reducing post-extubation stridor in children hospitalized for burns or trauma. DESIGN: Randomized, controlled crossover trial. SETTING: Harborview Medical Center's Burn and Trauma ICUs from March to September 1989. PATIENTS: Children less than 15 yr old who were electively extubated and had symptoms of postextubation stridor, but required less than or equal to 35% oxygen. INTERVENTION: Each treatment (helium-oxygen and oxygen-supplemented room air) was given in random order for 15 min after extubation. MEASUREMENTS: Respiratory distress was assessed by a physician blinded to treatment order using a standard stridor score and clinical judgment. RESULTS: There were 13 children with 15 extubations; seven (47%) of 15 patients required subsequent treatment with racemic epinephrine or reintubation. Stridor scores were lower with helium-oxygen than with oxygen-supplemented room air (2.8 vs. 3.7, p less than .005), and helium-oxygen was preferred in eight of nine trials in which one treatment was clearly favored by the physician. CONCLUSION: Because helium-oxygen therapy can reduce stridor scores and is clinically preferred by physicians caring for stridorous children, it may be a useful adjunctive therapy in pediatric trauma patients with postextubation stridor.
Adolescent↗
Hypobaric helium atmospheres for light and electron microscopy of mammalian cells.
The development of electron microscope environmental/hydration chambers (EMC's) for the examination of living biological specimens has necessitated a search for a suitable gaseous environment that is compatible with both electron imaging and cell survival. Helium has a lower electron scattering cross section than air. The effects of hydrated helium and hydrated air atmospheres in an EMC at pressures 50-200 Torr were examined with a JEM 200 transmission electron microscope operated at 200 kV and 22 degrees C. Results showed that whereas 200 Torr of air reduced beam transmission by more than 90% under these conditions, 200 Torr of moist helium only reduced beam transmission by 30%. The effects of sub-atmospheric or hypobaric helium atmospheres on human white blood cells attached to glass coverslips were investigated by phase-contrast light microscopy in a simulated EMC or light microscope environmental chamber (LMC) at ...37 degrees C. gross morphological changes were observed in cells held at pressures of 300 Torr of moist helium for exposure times of 15 min. At pressures below 300 Torr, morphological changes occurred more rapidly as the pressure was reduced. At the lowest pressures tested (60 and 80 Torr) 50% of the cell populations died within 6-7 min. The development of morphological changes produced by hypobaric stress followed a characteristic pattern. The filopodia, or microvilli attaching the cells to the substrate, became withdrawn, with only occasional retraction fibers remaining. Blends appeared around the cell surface and increased in size as hypobaric exposures progressed. Vacuoles, or cler spherical regions, appeared within the cytoplasm and the overall shape of the cells became circular. The cells became flatter during circularization, showing an apparent 2-2-5 X increase in size as they respread on the substrate...
Cytoplasm↗
Effect of helium on maximal expiratory flow in patients with asthma before and during induced bronchoconstriction.
The effect of breathing helium on maximal expiratory flow at 50 per cent of vital capacity (V50) was studied in 27 patients with asthma during remission and during induced bronchoconstriction. Nine patients gave a history of asthma induced by exercise; two had asthma due to timothy pollen allergy, and the remaining 16 had asthma due to exposure to western red cedar. Bronchoconstriction was induced by exercise in 10 patients, timothy pollen in 4 patients, methacholine in 4 patients, and red cedar in 16 patients. During remission, the increase in V50 with helium (deltaV50He) was greater than 20 per cent in 22 patients who were classified as responders; deltaV50He was less than 20 per cent in the remaining 5 patients, who were classified as nonresponders. There was a significant correlation between the severity of airway obstruction as measured by V50 and the response to helium, both during remission and during induced bronchoconstriction; however, there was no correlation between helium response and specific airway conductance. In general, patients who were responders during remission remained responders during induced bronchoconstriction, and nonresponders remained nonresponders, regardless of the method of challenge or the type of reaction (immediate verus late). There were a few exceptions in which a responder became a nonresponder during severe bronchoconstriction. The results of this study suggest that in most patients with asthma, the site of airway obstruction is likely to be in the large airways and, in most cases, remains constant in an individual asthmatic; however, an asthmatic who is a helium responder may become a nonresponder during severe bronchoconstriction.
Adult↗
Effects of helium and other inert gases on Echinosphaerium nucleofilium (protozoa, heliozoa).
The effects of helium, nitrogen, argon and krypton on Echinosphaerium nucleofilum (Heliozoa) have been studied at partial pressures of 10-130 atm. Additional experiments have been carried out with hydrostatic pressure alone. Helium causes shortening of the axopods over the whole range of pressures, and damage to the cell body at pressures of 60-90 atm, both with a maximum at 80 atm. These effects cannot be explained in terms of hydrostatic pressure alone; a 'pressure reversal' effect may be operating, causing the peak at 80 atm. Nitrogen also causes both cell damage and axopod shortening, the severity increasing with increasing pressure. Argon and krypton cause cell damage but no shortening. The order of potency for cell damage is krypton greater than argon greater than nitrogen greater than helium. It is suggested that there may be tuo sites of action, possibly the microtubules (for axopod shortening) and the cell membrane (for cell damage). In appropriate mixtures of helium and argon, both the cell damage usually caused by argon, and the axopod shortening usually caused by helium, are prevented. Possible mechanisms include the effects of hydrostatic pressure on gas solubility coefficients, reversal of the effects of the gases by the increase in total pressure, and competition for sites of action.
Argon↗
Helium-oxygen mixtures in intubated patients with status asthmaticus and respiratory acidosis.
Seven patients with status asthmaticus intubated for respiratory failure who had elevated airway pressures and persistent respiratory acidosis were successfully ventilated using a mixture of 60 percent helium and 40 percent oxygen. All patients experienced a rapid reduction in airway pressures, CO2 retention, and resolution of acidosis while breathing a helium-oxygen mixture. There were no untoward effects. Helium-oxygen mixtures improve ventilation by reducing the Reynolds number and reducing density dependent resistance. Helium's beneficial effects are due to its high kinematic viscosity, high binary diffusion coefficient for CO2, and high diffusivity. Helium-oxygen mixtures should be considered for use in mechanically ventilated asthmatics with respiratory acidosis who fail conventional therapy.
Acidosis, Respiratory↗
The volume of isoflow and increase in maximal flow at 50 percent of forced vital capacity during helium-oxygen breathing as tests of small airway dysfunction.
The purpose of this report is to review the role of helium in the early detection of obstructive pulmonary disease. The underlying physiologic mechanisms of the volume of isoflow (the volume at which flow was the same with the subject breathing air and breathing a mixture of 80 percent helium and 20 percent oxygen) and increases in maximal flow at 50 percent of vital capacity (Vmax50) after breathing helium are reviewed. These tests are able to detect physiologic abnormalities in asymptomatic subjects when the results of other tests are normal; and following cessation of smoking, abnormal results may be reversible. The volume of isoflow is increased when maximal flow is reduced because of loss of elastic recoil or increase in upstream resistance. The increase in Vmax50 after breathing helium appears to be relatively specific for the caliber of the small airways, being uninfluenced by loss of elastic recoil; it can further help to localize the major site of obstruction to either small or large airways. At present, random screening for early unsuspected disease is not warranted, and these tests remain an investigative tool.
Evaluation Studies as Topic↗
Measurement of helium elimination from man during decompression breathing air or oxygen.
Air breathing was compared with oxygen breathing during decompression from an 80-20% helium-oxygen dive to a depth equivalent to 120 fsw (4.6 ATA) in a dry chamber to see which was the most efficient gas for helium elimination. Helium elimination was measured in a closed circuit system for 90 min at the 40-fsw (2.2 ATA) stop. No significant difference was found in the efficiency of helium elimination breathing either air or oxygen in the five subjects tested.
Adult↗
The effect of the anoxic radiosensitizing agent TAN on induction of revertants by gamma-rays and helium ions in Salmonella tester strains.
The modification effect of the anoxic radiosensitizer TAN on the mutagenesis in various Salmonella tester strains after gamma-ray and helium ion irradiation was studied. The oxygen enhancement ratios (OER) for all 3 strains on the lethal assay after gamma-irradiation are approximately equal to 2. The induction of reversions in TA98 and TA100 does not modify under anoxia. The value of OER on the mutagenic assay in TA102 equals 1.6. The OER after helium ion irradiation on the lethal and mutagenic assays was less than after gamma-irradiation. The mutagenesis in 3 strains after irradiation under anoxia is enhanced by TAN. The value of the TAN modification effect after gamma-irradiation increases from 2.1 +/- 0.2 for TA102 to 5.2 +/- 0.4 for TA100. However, the TAN influence on mutagenesis in TA100 after helium ion irradiation decreases to 3.1 +/- 0.3. We conclude that peculiarities of mutagenesis in various tester strains under anoxia with TAN can be explained by considering the nature of premutational DNA damages.
Anaerobiosis↗
Helium microwave-induced plasma mass spectrometric detection for reversed-phase high-performance liquid chromatography.
Reversed-phase high-performance liquid chromatography (HPLC) is directly coupled to helium microwave-induced plasma mass spectrometry (He MIP-MS) for the element-selective detection of halogenated organic compounds. Absolute detection limits are approximately 50 pg Br for brominated compounds, 1 pg I for iodinated compounds, and 10 ng Cl for chlorinated compounds. The linear dynamic range for Br- and I-containing compounds is 3-4 orders of magnitude. However, the linear range for chlorinated species is severely limited by high background at m/z = 35. The relative standard deviation for repetitive injections is less than 10%. The helium microwave-induced plasma is operated at moderate powers (300-350 W) and with a total helium consumption of 6-8 L/min. The effect of organic solvents on the background mass spectrum is investigated.
Bromides↗
Mammalian cell survival response following irradiation with 4 MeV X rays or accelerated helium ions combined with hyperthermia.
The effects of hyperthermia on Chinese hamster ovary cell radioresponse were studied using either 4 MeV x rays or accelerated helium ions. Both pre-and postirradiation hyperthermic doses act to decrease the slope of the x-irradiation survival curve in a temperature-dependent manner, while the extrapolation number does not change appreciably. Pre-irradiation hyperthermic treatment has only a slightly greater dose-modifying effect than similar postirradiation hyperthermia. For cells irradiated with helium, pre-irradiation at 43 degrees C (1 hr.) changes the radiation survival curve slope and also the extrapolation number, implying that hyperthermia may act more readily to enhance lethal x-ray damage than lethal helium damage, while having a similar effect on the accumulation of sublethal damage for both of these radiations.
Animals↗