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↗
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↗
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↗
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↗
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↗
Repair of sublethal and potentially lethal radiation damage by rat embryos exposed to gamma rays or helium lons.
Embryonic survival was examined in rats exposed to a 24-hour split-dose regimen of gamma rays or extended-Bragg-peak (EBP) helium ions on the fifth and sixth days of gestation. The data indicate that EBP helium ions, which are known to have a single-dose relative biological effectiveness (RBE) of 1.0, exhibit a split-dose RBE of 1.5 with respect to embryo killing. Using an experimental rat embryo system, delayed implantation, it was also noted that the embryocidal damage induced by EBP helium ions contains a smaller potentially lethal component than that induced by gamma rays.
Animals↗
Salicylate hypothermia in rats exposed to hyperbaric air and helium.
Rectal temperatures of salicylate-treated and untreated rats were observed in 21-23 degrees C air at 1, 3, 6, and 8 ATA, in 21-23 degrees C helium at 1 and 6 ATA, and in 1 ATA thermal neutral air (28 degrees C). Significant dose-related temperature decreases occurred in 21-23 degrees C 1 ATA air with 180 and 300 mg/kg of salicylate; 60 mg/kg had no effect. However, in thermal neutral air, 300 mg/kg significantly elevated temperatures. Hyperbaric air and helium had temperature-lowering effects which were correlated with thermal properties of these environments, and in them the hypothermic effects of salicylate were similar to those in 1 ATA air, the total temperature decreases being the sum of the salicylate hypothermia and that caused by the hyperbaric air or helium. These additive temperature effects are unlike previously reported results in which the temperature lowering effects of 5 degrees C cold exposure and salicylate together were greater than the sum of the two individual effects.
Animals↗
Physiological responses of men working in 25.5 degrees C water, breathing air or helium tri-mix.
Fourteen scuba divers in swim trunks did ergometer work while breathing air at 3 m in 25.5 degrees C water. They were stressed by work and cold. Exercise produced increases in heart rate, minute ventilation (VE), oxygen consumption (VO2), and catecholamine excretion. Cold lowered rectal temperature (Tre) despite exercise, and contributed to the increase in VO2 and catecholamine excretion. Immersion, cutaneous vasoconstriction, work, and scuba breathing contributed to a brisk diuresis, probably by centralizing blood volume and thus stimulating central vascular volume receptors. Similar exercise in 25.5 degrees C water, breathing helium tri-mix (gas density less than air), produced higher VE but lower VO2 when compared to air breathing. Tri-mix scuba breathing resulted in a smaller diuresis, perhaps because its lower density leads to lesser atrial distension during work. The fall in Tre during work in 25.5 degrees C water was identical whether air or helium tri-mix was respired, since helium does not accentuate respiratory convective heat transfer.
Adult↗
A simplified method for measuring helium closing volume.
A simple method for delivering a constant volume of helium for the measurement of airway closing volume is described. Using a standard fiveway valve and PVC plastic irrigation pipe, a device was constructed which permits the delivery of a uniform volume of helium and avoids the troublesome valve change during inspiration. Results obtained when using this device were comparable to those with the use of conventional bag to contain the helium.
Helium↗
[Formation of indium-111 in alpha and helium-3 bombardment of natural cadmium (author's transl)].
Formation cross sections and thick-target yields were studied in detail for alpha reactions and helium-3 reactions of natural cadmium in the energy range 10-40 MeV in order to determine the optimum condition for the production of medical use 11In. The helium-3 reactions were found to give higher 111In yield; namely, at the optimum helium-3 particle energy of 40 MeV and with the cadmium foil of 280 mg/cm2 thickness the amount of 11In produced was 270 muCi/muA . h. A cooling-time of 54 hours was required for the best radiochemical purity. The extraction of HBr-isopropyl ether followed by the anion exchange method was found to be the best chemical method for the carrier-free indium-111 separation.
Alpha Particles↗
[Effectiveness of a helium-oxygen gas mixture in transverse accelerations].
Healthy male test subjects, aged 20 to 45, were exposed to acceleration of +6 Gx for 1200 sec and of +10 Gx for 60 sec. Three gradients of the centrifuge acceleration were used in the latter case. In every experimental run the test subjects were exposed to accelerations while breathing air or a helium-oxygen atmosphere. The positive effect of the helium-oxygen atmosphere was seen in an increase of the respiration intensity and in an elevation of pulmonary ventilation and gas exchange. This may be associated with a decline of the aerodynamic resistance to breathing. The positive effect of the helium-oxygen atmosphere was more pronounced during accelerations of +4 to 8 Gx and depended on the total exposure time.
Acceleration↗