Helium-oxygen Mixture Research Articles

HELIUM-OXYGEN MIXTURES DO NOT IMPROVE PULMONARY FUNCTION IN CHILDREN WITH ASTHMA 1820

Helium-oxygen mixtures (heliox) have been used in patients with bronchial asthma with variable results. To better understand the effects of heliox on respiratory function we studied 36 children with moderate to severe chronic asthma who were not acutely ill. Ages ranged from 6 to 17 years (mean 11.6) and 10 to 15 years (mean 11.8) for 27 males and 9 females, respectively. Spirometry (PK Morgan Spiroflow) was performed before and after breathing two heliox mixtures (80:20 and 60:40) for 7.5 minutes each. The order of heliox mixture administration was randomized and the washout period between tests was 15 minutes. The data were expressed as mean% predicted (Polgar) ± SEM and means of groups were compared using ANOVA (Sigma Stat).Table

Inhaled helium-oxygen revisited: Effect of inhaled helium-oxygen during the treatment of status asthmaticus in children

Objectives: To assess the effects of breathing a low-density gas mixture on dyspnea and the pulsus paradoxus in children with status asthmaticus. Design: In an urban academic tertiary referral center, 18 patients, aged 16 months to 16 years, who were being treated for status asthmaticus with continuously inhaled β-agonist and intravenously administered methylprednisolone and had a pulsus paradoxus of greater than 15 mm Hg received either an 80%:20% helium-oxygen gas mixture (HELIOX patients) or room air (control patients) at 10 L/min by nonrebreathing face mask in a double-blind, randomized, controlled trial. In all patients, baseline data, including pulsus paradoxus (determined by sphygmomanometer or arterial catheter blood pressure readings), respiratory rate, heart rate, investigator-scored dyspnea index, and oxygen saturation, were compared with values obtained 15 minutes during and after intervention. In a subset of patients, peak flows before and after breathing HELIOX or room air were measured. When clinically indicated, arterial blood gases were obtained. Results: The pulsus paradoxus (in millimeters of mercury) fell significantly from an initial mean value of 23.3 ± 6.8 to 10.6 ± 2.8 with HELIOX breathing ( p <0.001) and increased again to 18.5 ± 7.3 after cessation of HELIOX. Peak flow increased 69.4% ± 12.8% during HELIOX breathing ( p <0.05). The dyspnea index decreased from an initial mean value of 5.7 ± 1.3 to 1.9 ± 1.7 with HELIOX breathing ( p <0.0002) and increased again to 4.0 ± 0.5 after cessation of HELIOX breathing. In control patients, there was no significant difference in pulsus paradoxus or dyspnea index at any time during the study period. Mechanical ventilation was averted in three patients in whom dyspnea lessened dramatically during breathing of HELIOX. Conclusion: During acute status asthmaticus, inhaled HELIOX significantly lowered the pulsus paradoxus, increased peak flow, and lessened the dyspnea index. Moreover, HELIOX spared three patients a planned intubation and caused no apparent side effects. Thus HELIOX reduces the work of breathing and may forestall respiratory failure in children with status asthmaticus, thus preventing the need for mechanical ventilation. (J Pediatr 1997;130:217-24)

Small airways dysfunction in patients with AIDS and Pneumocystis carinii pneumonia.

Abnormalities of small airways function may have clinical relevance in AIDS patients with Pneumocystis carinii pneumonia (PCP) since obstructive dysfunction at alveolar levels may impede delivery of aerosolized medication. This study was designed to determine if small airways dysfunction is present in AIDS patients with PCP despite normal standard spirometric results. Ten AIDS patients with documented PCP and no other identifiable pulmonary infection without respiratory failure and with a normal FEV1/FVC ratio were evaluated. Small airways function was assessed by the FEF75 and the change in maximum expiratory flow while breathing a helium-oxygen mixture compared to room air (delta Vmax50%) with and without bronchodilator administration. Testing was done before and after completion of intravenous therapy for PCP. Despite absence of cough or wheezing at the time of evaluation and a normal FEV1/FVC ratio, significant obstructive dysfunction of the small airways was demonstrated in 6 of 10 patients, which improved with bronchodilators. Three weeks of intravenous therapy for PCP had no effect on these abnormalities. The degree of small airways dysfunction was greater than could be explained by smoking history alone. Small airways dysfunction, which can be improved with bronchodilator administration, may be present in AIDS patients with PCP despite normal spirometry and absence of cough or wheezing. Screening for small airways dysfunction may identify patients who might benefit from bronchodilator administration prior to inhalation of aerosolized medications.

Evaluation of static work load in a helium-oxygen saturation dive at 31 ATA.

The purpose of the present study is to evaluate the static work load as a model work in Submersible Decompression Chamber (SDC) during a deep sea saturation dive with helium-oxygen gas mixture. Heart rate (HR) and electromyogram (EMG) power spectrum changes were studied during a 7-minute static work, half-rising posture or flexed knee posture in four healthy male subjects. During the static work, EMG of the rectus femoris was recorded with surface electrodes, and changes in the EMG power spectrum were presented in the ratio of a high-frequency to low-frequency band (H/L ratio) after the Fourier transform analysis. The HR decreased at 31 ATA and increased remarkably after the decompression to 1 ATA. HR at post-decompression was higher than pre-compression. The lowering phenomena of EMG presented by H/L ratios during the static work were similarly observed in all three conditions. But the changes of the high and low frequency components were different in the post-decompression condition from the pre-compression and 31 ATA conditions. HR as a parameter of static work load might underestimate the work load at the hyperbaric environment due to hyperbaric bradycardia and overestimate it after decompression by "decompression tachycardia." The EMG lowering phenomenon observed after decompression might not be caused by the same mechanism as seen in the pre-compression and hyperbaric environments. Extreme care must be taken to evaluate the static work load not only at hyperbaric helium-oxygen environments but after decompression from a deep saturation dive.

Evidence for inert gas narcosis mechanisms in the occurrence of psychotic-like episodes at pressure environment.

Psychotic-like episodes in divers exposed to high pressure have been attributed to either the high-pressure neurological syndrome, confinement in pressure chamber, the subject's personality, or the addition of nitrogen or hydrogen to the basic helium-oxygen breathing mixture used for deep diving. Alternatively, it is suggested that these disorders are in fact paroxysmal narcotic symptoms that result from the sum of the individual narcotic potencies of each inert gas in the breathing mixture. This hypothesis is tested against a variety of lipid solubility theories of narcosis. The results clearly support the hypothesis and provide new information about the cellular interactions between inert gases at raised pressure and pressure itself.

Mechanisms compensating for altered resistance to respiration during muscular exercise in man

Alterations in respiratory parameters following the substitution of a helium-oxygen (He−O2) or sulfur hexafluoride-oxygen (SF6−O2) mixture for air were analyzed during the first 10 respiratory cycles in human volunteers exposed to either of these mixtures for 3 min at rest and during forced respiration. Both at rest and during moderate physical exercise neither the volume of pulrnonary ventilation nor the partial carbon dioxide pressure differed significantly in the subjects breathing air, He−O2, or SF6−O2. When the He−O2 mixture was substituted for air, the forces developed by the inspiratory muscles, the work of breathing, the activity of the parasternal intercostal muscles, and the central inspiratory activity were all reduced, whereas substitution of the SF6−O2 mixture for air led to significant increases in these four parameters. It is concluded that compensatory responses of the respiratory system to altered density of the gaseous medium develop on the basis of the afferent impulse traffic from mechanoreceptors of the lungs and respiratory muscles and also on account of segmental reflexes and intrinsic properties of the muscle fibers themselves.

Use of a helium-oxygen mixture in the treatment of postextubation stridor in pediatric patients with burns.

A mixture of helium and oxygen is less dense than room air. This property allows the gas to flow with less turbulence past airway narrowings, thereby decreasing airway resistance and increasing the volume of gas exchange. Previous studies demonstrated that airway obstruction that is manifested by stridor was present in 92% of patients requiring reintubation. Eight pediatric patients with burns in whom postextubation stridor or retractions unresponsive to racemic epinephrine developed, were treated with "heliox" (helium and oxygen) for 28 +/- 5 hours with an initial helium concentration between 50% and 70%. Of the eight patients treated with heliox, only two experienced respiratory distress and required reintubation. Both patients had stridor for a longer time before the initiation of heliox therapy compared with those patients who did not require reintubation. After initiation of heliox therapy, patients experienced a significant decrease in respiratory distress scores (6.8 +/- 0.7 vs 2.0 +/- 0.7). Heliox was able to relieve persistent stridor and thereby aid in the prevention of respiratory distress and reintubation.

Low-level hyperbaric exposure antagonizes locomotor effects of ethanol and n-propanol but not morphine in C57BL mice.

Low-level hyperbaric exposure antagonizes a broad range of behavioral effects of ethanol in a direct, reversible, and competitive manner. This study investigates the selectivity of the antagonism across other drugs. C57BL/6 mice were injected with saline, ethanol, n-propanol, or morphine sulfate, and then were exposed to 1 atmosphere absolute (ATA) air, 1 ATA helium-oxygen gas mixture (heliox), or 12 ATA heliox. Locomotor activity was measured from 10 to 40 min following injection. N-propanol produced a dose-dependent depression of locomotor activity from 1.0 g/kg. Morphine produced a dose-dependent stimulation of locomotor activity at doses of 3.75-12.0 mg/kg. Exposure to 12 ATA heliox significantly antagonized the locomotor depressant effects of 1.0 g/kg n-propanol and 2.5 g/kg ethanol, without significantly affecting blood concentrations of these drugs measured at 40 min postinjection. Exposure to 12 ATA heliox did not significantly antagonize the locomotor-stimulating effects of the two morphine doses tested (3.75 and 7.5 mg/kg). These findings suggest that exposure to 12 ATA heliox antagonizes the behavioral effects of intoxicant-anesthetic drugs like ethanol and n-propanol, which are believed to act via perturbation or allosteric modulation of functional proteins, but does not antagonize the effects of drugs like morphine, which act via more direct mechanisms. This demonstration of selective antagonism adds important support for the hypothesis that low-level hyperbaric exposure is a direct mechanistic ethanol antagonist, with characteristics similar to a competitive pharmacological antagonist.

Repeatability of Maximal Aerobic Performance in Belding's Ground Squirrels, Spermophilus beldingi

Summary 1. The repeatability of a trait is a critical factor in determining how that trait is affected by natural selection. We examined the repeatability of a key physiological trait, maximum oxygen consumption ( O 2max ), in a wild population of Belding’s Ground Squirrels, Spermophilus beldingi. O 2max is an integrated measure of organismal metabolic performance. It can be intuitively related to fitness because it sets an upper limit to sustainable power output during ecolog ically important activites such as locomotion and thermoregulatory heat production. 2. We used respirometry to determine O 2max during exercise and thermogenesis. Exercise O 2max was elicited in an enclosed running wheel. Thermogenic O 2max was obtained with acute cold exposure in a helium-oxygen gas mixture. 3. Repeatability of both exercise and thermogenic O 2max was high over 2 h intervals but declined over longer test periods (6-18 days and 1-2 years). In general, repeatability was higher for exercise O 2max than for thermogenic O 2max . 4. We found no repeatability for animals tested initially as juveniles and then 1 or 2 years later as adults; evidently there is sufficient plasticity in O 2max to decouple aerobic performance between these life stages. A small number of adults tested in successive years showed significant repeatability of exercise O 2max but no repeatability of thermogenic O 2max .

Helium/Oxygen Breathing Improved Hypoxemia After Cardiac Surgery

Helium/Oxygen Breathing Improved Hypoxemia After Cardiac Surgery

Evidence for inert gas narcosis mechanisms in the occurrence of psychotic-like episodes at pressure environment.

Psychotic-like episodes in divers exposed to high pressure have been attributed to either the high-pressure neurological syndrome, confinement in pressure chamber, the subject's personality, or the addition of nitrogen or hydrogen to the basic helium-oxygen breathing mixture used for deep diving. Alternatively, it is suggested that these disorders are in fact paroxysmal narcotic symptoms that result from the sum of the individual narcotic potencies of each inert gas in the breathing mixture. This hypothesis is tested against a variety of lipid solubility theories of narcosis. The results clearly support the hypothesis and provide new information about the cellular interactions between inert gases at raised pressure and pressure itself.

Heliox Therapy in Acute Severe Asthma

To assess how patients with respiratory acidosis from acute severe asthma respond to helium-oxygen (heliox) mixtures. Consecutive case series. Urban community teaching hospital. Over a 2-year period, 12 asthmatics (mean age, 33.8 +/- 11.3 years) presented to the emergency department with acute respiratory acidosis (pH < 7.35 and PaCO2 > or = 45 mm Hg). All 12 patients were treated with heliox (60 to 70% helium/30 to 40% oxygen). Five patients received heliox through a ventilator and seven received heliox via face mask. Arterial blood gases (ABGs) were drawn immediately before and at a mean of 49.2 +/- 25.2 min after beginning heliox therapy. No therapeutic interventions were made between ABGs. For the entire group, the mean PaCO2 decreased from 57.9 to 47.5 mm Hg (p < 0.005) and the arterial pH increased from 7.23 to 7.32 (p < 0.001). In an attempt to find characteristics that might predict the response to heliox, a clinically significant response to heliox was defined as a drop in PaCO2 (to normal or by > or = 15%) coupled with a rise in pH by > or = 0.05. Using this definition, there were eight responders (67%) and four nonresponders (33%). The responders had a shorter duration of symptoms (17.8 vs 78.0 h, p < 0.05) and a lower preheliox pH (7.20 vs 7.30, p < 0.05). All of the responders presented within 24 h of symptom onset. Three of the four nonresponders reported prolonged (> or = 96 h) duration of symptoms, and two eventually required intubation. Heliox can rapidly improve ventilation in patients presenting to an emergency department with acute severe asthma with respiratory acidosis and a short duration of symptoms.

Effects of high pressures of various gas mixtures on rat striatal dopamine detected in vivo by voltammetry

This work was performed to study the effect of pressure of various gas breathing mixtures on dopaminergic activity in the striatum by in vivo differential pulse voltammetry using carbon multifiber electrodes chronically implanted in 23 freely moving rats. Compression (0.5 bar/min) in a helium-oxygen mixture induced an increase in striatal extracellular dopamine (DA) beginning at 10-20 bars and reaching 32% above precompression levels when arriving at 90 bars (n = 9). To demonstrate that this increase is dopaminergic, nine rats with right nigrostriatal pathway 6-hydroxydopamine lesions were compressed in the same conditions. In this case, the increase in DA did not occur in the right caudate nucleus but was recorded in the intact left caudate nucleus. To study the effects on DA increase of narcotic gases, which are known to reduce some high-pressure nervous syndrome symptoms, eight and six rats were compressed in helium-nitrogen-oxygen and hydrogen-helium-oxygen mixtures, respectively. They produced similar changes in striatal DA level in the same pressure range (23 and 20% increase, respectively, at the end of the compression). Consequently, the increase in striatal DA seems independent of the nature of the breathing mixture and seems related to the increase of pressure. The origin of this increase could be a pressure effect at the pre- or postsynaptic level.

Theoretical validation of the respiratory benefits of helium-oxygen mixtures

A theoretical analysis of convective gas transport validates the clinically demonstrated advantage of using helium-oxygen mixtures in treating patients with respiratory problems. Previous studies have attributed that advantage to the ability of helium-oxygen to stay laminar at higher velocities than nitrogen-oxygen. The present work shows that helium-oxygen does not need to be laminar to provide higher flow rates and that its benefits persist under turbulent conditions. The analysis is applied to steady flow through the lungs and through a circular airway obstruction. A simplified model of the lungs gives pressure-flow relations that show a significant increase in oxygen flow rate when nitrogen is substituted by helium. A similar improvement is found for flow through an obstruction. For a given pressure difference across the lungs or across an obstruction, the turbulent flow rate of oxygen increases by approximately 50% when nitrogen is replaced by helium in a mixture containing 20% oxygen.

Low‐Level Hyperbaric Antagonism of Ethanol's Anticonvulsant Property in C57BL/6J Mice

This study investigated the ability of hyperbaric exposure to antagonize ethanol's anticonvulsant effect on isoniazid (INH)-induced seizures. Drug-naive, male C57BL/6 mice were injected intraperitoneally with saline, 1.5, 2.0, or 2.5 g/kg ethanol followed immediately by an intramuscular injection of 300 mg/kg of INH. The mice were then exposed to either 1 atmosphere absolute (1 ATA) air, 1 ATA helium-oxygen gas mixture (heliox), or 12 ATA heliox at temperatures that offset the hypothermic effects of helium. Ethanol increased the latency to onset of myoclonus in a dose-dependent manner. Exposure to 12 ATA heliox antagonized ethanol's anticonvulsant effect at 2.0 and 2.5 g/kg, but not at 1.5 g/kg. Ethanol also increased the latency to onset of clonus in a dose-dependent manner beginning at 2.0 g/kg. Exposure to 12 ATA heliox antagonized this anticonvulsant effect. When exposed to 12 ATA heliox, the blood ethanol concentrations at time to onset of myoclonus were significantly higher in mice treated with 2.5 g/kg of ethanol as compared with blood ethanol concentrations of mice exposed to 1 ATA air. These findings extend the acute behavioral effects of ethanol known to be antagonized by hyperbaric exposure and support the hypothesis that low-level hyperbaric exposure blocks or reverses the initial action(s) of ethanol leading to its acute behavioral effects.

Demonstration of dilatation of peripheral airways

To investigate the ability of various lung-function tests to demonstrate dilatation of peripheral airways, ten asthmatics inhaled increasing doses of a beta 2-agonist by two different and controlled techniques. Low inspiratory flow with a long post-inspiratory pause favoured peripheral deposition, and a high inspiratory flow with a short post-inspiratory pause favoured central deposition of drug in the airways. Ordinary spirometry, maximum expiratory flow rates after breathing air as well as a helium-oxygen mixture, a single breath N2-test and resistance of the respiratory system were obtained before and after each of five terbutaline doses with both inhalation techniques. By using a double-dummy technique, the study could be performed double blinded. Effects were compared at doses giving equal effects on PEF, assumed to represent equal deposition of bronchodilator and effects on central airways. At such 'iso delta PEF doses', particularly FVC and the slope of phase III of the N2-test improved more following the slow inhalation technique. It is concluded that changes in those tests reflect dilatation in peripheral airways in asthmatics.

ヘリウム，アルゴン吸入による中耳圧変化

Middle ear pressure is thought to be an important factor in the pathogenesis of otitis media. It is well known that body position, type of breathing, and kind of inhaled gas influence middle ear pressure. There is an increase in middle ear pressure when general anesthesia is induced with a gas such as nitrous oxide. In this study, an attempt was made to answer the question as to whether the inhalation of non-anesthetic inert gas can increase middle ear pressure.Eight ears were selected: 4 atelectatic ears and 4 infantile ears. Helium-oxygen mixture gas (He 79%, O2 21%) or argon-oxygen mixture gas (Ar 79%, O2 21%) was administered via face mask for 120 minutes, and middle ear pressure was measured with tympanometry just before and during gas inhalation. The middle ear pressure changes during gas inhalation were compared with those during air respiration.The results were as follows;1. Middle ear pressure was increased by the inhalation of argon-oxygen mixture gas. However, no specific pressure change was noted in the middle ear during inhalation of helium-oxygen mixture gas.2. The difference in pressure in the middle ear during helium-oxygen inhalation and argon-oxygen inhalation might be due to the different solubility coeffients of the two inert gases.

Speaking and whistling with non-air gases

Whistling by humans after a deep breath of helium was observed to sound normal, with subsequent speech on the remainder of the breadth sounding strange. Inadvertent correction movements may have occurred, but effort was made not to shift any structures as the gas composition was changed. Large pressure changes do not make it difficult to speak but do somewhat change the sound composition. Human deep divers usually breathe a helium-oxygen mixture, which considerably changes the sound. However, a whistle language would not be ideal for divers. The effects of heavy gas at atmospheric pressure were also studied. An attempt was made to speak after a breath of SF/sub 6/, and the frequency was found to be lowered, the resonance being modified. However, the frequency of whistling did not change. Experiments were also tried with the very heavy gas perfluoropropane, with similar results. The voice took on a low pitch, while whistling was not changed. >

Pressure-induced disorders in neurotransmission and spontaneous behavior in rats: An animal model of psychosis

Disorders in neurotransmission and spontaneous behavior in rats exposed to a high pressure helium-oxygen mixture that shows interesting parallels with the dopaminergic hypothesis of schizophrenia at both the biochemical and the therapeutic responding levels are reviewed. Furthermore, as human subjects exposed to a very high pressure have shown psychotic episodes, we conclude that the pressure-induced disorders in neurotransmission and spontaneous behavior in rats could constitute a valid animal model of schizophreniform psychosis and a useful tool for both the investigation of the biological mechanisms underlying schizophrenia and the development of new antipsychotic drugs.

Helium-Oxygen Mixture in Respiratory Distress Syndrome

Service of Neonatal Reanimation, Pellegrin Hospital, and Physiology Laboratory, University of Bordeaux, Bordeaux, France