Helium-oxygen Breathing Research Articles

Вreathing in helium-oxygen gas mixtures as a means of emergency restoration of the working capacity of specialists of hazardous occupations

OBJECTIVES: To evaluate the effectiveness of using helium-oxygen breathing mixtures for emergency restoration of the working capacity of specialists of hazardous occupations.MATERIALS AND METHODS: 18 male military personnel (age 25–40 years), divided into the main group and the comparison group (9 people each). All servicemen showed signs of decreased efficiency. In the main group, a procedure of 40-minute breathing with a heated gas mixture with an Oxygen content of 25% vol., Helium content of 75% vol. was prescribed. The comparison group underwent standard 40-minute Oxygen therapy.RESULTS: Using of helium-oxygen gas media demostrated much more effective means of emergency restoration of the work capacity of specialists than oxygen therapy. This was evidenced by the better dynamics of physical performance indicators and the level of physiological reserves in the main group.CONCLUSIONS & DISCUSSION: Helium-oxygen therapy can be considered as an effective and safe method of restoring working capacity, applicable in the «field» conditions.

Altering blood flow does not reveal differences between nitrogen and helium kinetics in brain or in skeletal miracle in sheep.

In underwater diving, decompression schedules are based on compartmental models of nitrogen and helium tissue kinetics. However, these models are not based on direct measurements of nitrogen and helium kinetics. In isoflurane-anesthetized sheep, nitrogen and helium kinetics in the hind limb (n = 5) and brain (n = 5) were determined during helium-oxygen breathing and after return to nitrogen-oxygen breathing. Nitrogen and helium concentrations in arterial, femoral vein, and sagittal sinus blood samples were determined using headspace gas chromatography, and venous blood flows were monitored continuously using ultrasonic Doppler. The experiment was repeated at different states of hind limb blood flow and cerebral blood flow. Using arterial blood gas concentrations and blood flows as input, parameters and model selection criteria of various compartmental models of hind limb and brain were estimated by fitting to the observed venous gas concentrations. In both the hind limb and brain, nitrogen and helium kinetics were best fit by models with multiexponential kinetics. In the brain, there were no differences in nitrogen and helium kinetics. Hind limb models fit separately to the two gases indicated that nitrogen kinetics were slightly faster than helium, but models with the same kinetics for both gases fit the data well. In the hind limb and brain, the blood:tissue exchange of nitrogen is similar to that of helium. On the basis of these results, it is inappropriate to assign substantially different time constants for nitrogen and helium in all compartments in decompression algorithms.

Inhalation pressure distributions for medical gas mixtures calculated in an infant airway morphology model

A numerical pressure loss model previously used for adult human airways has been modified to simulate the inhalation pressure distribution in a healthy 9-month-old infant lung morphology model. Pressure distributions are calculated for air as well as helium and xenon mixtures with oxygen to investigate the effects of gas density and viscosity variations for this age group. The results indicate that there are significant pressure losses in infant extrathoracic airways due to inertial effects leading to much higher pressures to drive nominal flows in the infant airway model than for an adult airway model. For example, the pressure drop through the nasopharynx model of the infant is much greater than that for the nasopharynx model of the adult; that is, for the adult-versus-child the pressure differences are 0.08 cm H2O versus 0.4 cm H2O, 0.16 cm H2O versus 1.9 cm H2O and 0.4 cm H2O versus 7.7 cm H2O, breathing helium–oxygen (78/22%), nitrogen–oxygen (78/22%) and xenon–oxygen (60/40%), respectively. Within the healthy lung, viscous losses are of the same order for the three gas mixtures, so the differences in pressure distribution are relatively small.

Using Helium-Oxygen to Improve Regional Deposition of Inhaled Particles: Mechanical Principles

Helium-oxygen has been used for decades as a respiratory therapy conjointly with aerosols. It has also been shown under some conditions to be a means to provide more peripheral, deeper, particle deposition for inhalation therapies. Furthermore, we can also consider deposition along parallel paths that are quite different, especially in a heterogeneous pathological lung. It is in this context that it is hypothesized that helium-oxygen can improve regional deposition, leading to more homogeneous deposition by increasing deposition in ventilation-deficient lung regions. Analytical models of inertial impaction, sedimentation, and diffusion are examined to illustrate the importance of gas property values on deposition distribution through both fluid mechanics- and particle mechanics-based mechanisms. Also considered are in vitro results from a bench model for a heterogeneously obstructed lung. In vivo results from three-dimensional (3D) imaging techniques provide visual examples of changes in particle deposition patterns in asthmatics that are further analyzed using computational fluid dynamics (CFD). Based on analytical modeling, it is shown that deeper particle deposition is expected when breathing helium-oxygen, as compared with breathing air. A bench model has shown that more homogeneous ventilation distribution is possible breathing helium-oxygen in the presence of heterogeneous obstructions representative of central airway obstructions. 3D imaging of asthmatics has confirmed that aerosol delivery with a helium-oxygen carrier gas results in deeper and more homogeneous deposition distributions. CFD results are consistent with the in vivo imaging and suggest that the mechanics of gas particle interaction are the source of the differences seen in deposition patterns. However, intersubject variability in response to breathing helium-oxygen is expected, and an example of a nonresponder is shown where regional deposition is not significantly changed.

Effects of ambient pressure on pulmonary nitric oxide

Airway nitric oxide (NO) has been proposed to play a role in the development of high-altitude pulmonary edema. We undertook a study of the effects of acute changes of ambient pressure on exhaled and alveolar NO in the range 0.5-4 atmospheres absolute (ATA, 379-3,040 mmHg) in eight healthy subjects breathing normoxic nitrogen-oxygen mixtures. On the basis of previous work with inhalation of low-density helium-oxygen gas, we expected facilitated backdiffusion and lowered exhaled NO at 0.5 ATA and the opposite at 4 ATA. Instead, the exhaled NO partial pressure (Pe(NO)) did not differ between pressures and averaged 1.21 ± 0.16 (SE) mPa across pressures. As a consequence, exhaled NO fractions varied inversely with pressure. Alveolar estimates of the NO partial pressure differed between pressures and averaged 88 (P = 0.04) and 176 (P = 0.009) percent of control (1 ATA) at 0.5 and 4 ATA, respectively. The airway contribution to exhaled NO was reduced to 79% of control (P = 0.009) at 4 ATA. Our finding of the same Pe(NO) at 0.5 and 1 ATA is at variance with previous findings of a reduced Pe(NO) with inhalation of low-density gas at normal pressure, and this discrepancy may be due to the much longer durations of low-density gas breathing in the present study compared with previous studies with helium-oxygen breathing. The present data are compatible with the notion of an enhanced convective backtransport of NO, compensating for attenuated backdiffusion of NO with increasing pressure. An alternative interpretation is a pressure-induced suppression of NO formation in the airways.

Helium in the adult critical care setting

Helium is a low-density inert gas whose physical properties are very different from those of nitrogen and oxygen. Such properties could be clinically useful in the adult critical care setting, especially in patients with upper to more distal airway obstruction requiring moderate to intermediate levels of FiO2. However, despite decades of utilization and reporting, it is still difficult to give any firm clinical recommendation in this setting. Numerous case reports are available in the context of upper airway obstruction of different origins, but there is a lack of controlled studies for this indication. One study reported a helium-induced beneficial effect on surrogates of work of breathing after extubation in non-COPD patients, possibly in relation to laryngeal consequences of tracheal intubation. Physiological benefits of helium-oxygen breathing have been demonstrated in the context of acute severe asthma, but there is a lack of large controlled studies demonstrating an effect on pertinent clinical endpoints, except for a study reported only as an abstract, which mentioned a reduction in the intubation rate in helium-treated patients. Finally, there are a number of physiological studies in the context of COLD-COPD patients demonstrating a beneficial effect, mainly by a reduction in the resistive inspiratory work of breathing but also by a reduction in hyperinflation. Reduction of hypercapnia was mainly observed in spontaneously breathing and noninvasively ventilated helium-treated patients but not in intubated patients during controlled ventilation, suggesting that the decrease in PaCO2 was mainly in relation to a diminution in CO2 production, related to the diminution in work of breathing and not an improved alveolar ventilation. Moreover, there is little evidence that helium-oxygen could improve parameters of heterogeneity in such patients. Two RCTs were unable to demonstrate a reduction in the intubation rate in such setting, but they were likely underpowered. An adequately powered international multicentric study is ongoing and will help to determinate the exact place of the helium-oxygen mixture in the future. The place of the mixture during the weaning period will deserve further evaluation.

The ventilation distribution of helium–oxygen mixtures and the role of inertial losses in the presence of heterogeneous airway obstructions

The regional distribution of inhaled gas within the lung is affected in part by normal variations in airway geometry or by obstructions resulting from disease. In the present work, the effects of heterogeneous airway obstructions on the distribution of air and helium–oxygen were examined using an in vitro model, the two compartments of a dual adult test lung. Breathing helium–oxygen resulted in a consistently more uniform distribution, with the gas volume delivered to a severely obstructed compartment increased by almost 80%. An engineering approach to pipe flow was used to analyze the test lung and was extrapolated to a human lung model to show that the in vitro experimental parameters are relevant to the observed in vivo conditions. The engineering analysis also showed that helium–oxygen can decrease the relative weight of the flow resistance due to obstructions if they are inertial in nature (i.e., density dependent) due to either turbulence or laminar convective losses.

Helium-oxygen reduces the production of carbon dioxide during weaning from mechanical ventilation

BackgroundProlonged weaning from mechanical ventilation has a major impact on ICU bed occupancy and patient outcome, and has significant cost implications.There is evidence in patients around the period of extubation that helium-oxygen leads to a reduction in the work of breathing. Therefore breathing helium-oxygen during weaning may be a useful adjunct to facilitate weaning. We hypothesised that breathing helium-oxygen would reduce carbon dioxide production during the weaning phase of mechanical ventilation.Materials/patients and methodsWe performed a prospective randomised controlled single blinded cross-over trial on 19 adult intensive care patients without significant airways disease who fulfilled criteria for weaning with CPAP. Patients were randomised to helium-oxygen and air-oxygen delivered during a 2 hour period of CPAP ventilation. Carbon dioxide production (VCO2) was measured using a near patient main stream infrared carbon dioxide sensor and fixed orifice pneumotachograph.ResultsCompared to air-oxygen, helium-oxygen significantly decreased VCO2 production at the end of the 2 hour period of CPAP ventilation; there was a mean difference in CO2 production of 48.9 ml/min (95% CI 18.7-79.2 p = 0.003) between the groups. There were no significant differences in other respiratory and haemodynamic parameters.ConclusionThis study shows that breathing a helium-oxygen mixture during weaning reduces carbon dioxide production. This physiological study supports the need for a clinical trial of helium-oxygen mixture during the weaning phase of mechanical ventilation with duration of weaning as the primary outcome.Trial registrationISRCTN56470948

Prognostic Factors of Spinal Cord Decompression Sickness in Recreational Diving: Retrospective and Multicentric Analysis of 279 Cases

This study aims to determine the potential risk factors associated with the development of severe diving-related spinal cord decompression sickness (DCS). Two hundred and seventy nine injured recreational divers (42 ± 12 years; 53 women) presenting symptoms of spinal cord DCS were retrospectively included from seven hyperbaric centers in France and Belgium. Diving information, symptom latency after surfacing, time interval between symptom onset and hyperbaric treatment were studied. The initial severity of spinal cord DCS was rated with the Boussuges severity score, and the presence of sequelae was evaluated at 1 month. Initial recompression treatment at 2.8 ATA with 100% oxygen breathing or deeper recompression up to 4 or 6 ATA with nitrogen or helium-oxygen breathing mixture were also recorded. Twenty six percent of DCS had incomplete resolution after 1 month. Multivariate analysis revealed several independent factors associated with a bad recovery: age ≥ 42 [OR 1.04 (1-1.07)], depth ≥ 39 m [OR 1.04 (1-1.07)], bladder dysfunction [OR 3.8 (1.3-11.15)], persistence or worsening of clinical symptoms before recompression [OR 2.07 (1.23-3.48)], and a Boussuges severity score >7 [OR 1.16 (1.03-1.31)]. However, the time to recompression and the choice of initial hyperbaric procedure did not significantly influence recovery after statistical adjustment. Clinical symptoms of spinal cord DCS and their initial course before admission to the hyperbaric center should be considered as major prognostic factors in recovery. A new severity score is proposed to optimize the initial clinical evaluation for spinal cord DCS.

Serum Heat Shock Protein after Simulated Deep Diving in Navy Divers

Deep sea diving might cause a tremendous physical or psychological stress to the divers. The present study aims to evaluate the stress response to a simulated wet dive in Navy divers. Nineteen Navy divers took part in this study when they were undergoing annual deep dive training. Ten divers were exposed to 190 feet of sea water (fsw) breathing compressed air on day 1 and to 250 fsw breathing helium-oxygen (Heliox) gas mixture on day 3. Another 9 divers were exposed to 220 fsw on day 1 and 285 fsw on day 3 breathing Heliox gas mixture. The bottom time ranged from 5 to 8 min, and then the standard U.S. Navy air and Heliox decompression tables were followed for surfacing. Predive levels of serum heat shock protein 72 (sHsp72) were 9.95 +/- 0.56 ng/ml, which were significantly higher than those in the control group (8.01 +/- 0.77 ng/ml). After simulating Heliox dive, the sHsp72 increased to 10.43 +/- 0.56 ng/ml, but this was not statistically significant. Our results demonstrated that the serum level of Hsp72 is higher in the Navy divers who underwent regular intensive exercise. However, it remains unknown whether this increase of stress protein is associated with the diving stress or exercise preconditioning in the Navy divers.

Risk factors and treatment outcome in scuba divers with spinal cord decompression sickness

Purpose This study was designed to determine the recompression strategy and the potential risk factors associated with the development of severe diving-related spinal cord decompression sickness (DCS). Material and Methods Sixty-three injured recreational divers (52 men and 11 women; 46 ± 12 years) presenting with symptoms of spinal involvement were retrospectively included. Diving information, symptom latency after dive completion, and time interval between symptom onset and hyperbaric treatment were studied. The severity of spinal cord DCS was rated numerically for both the acute event and 1-month later. Initial recompression treatment at 2.8 atmosphere absolute (ATA) with 100% oxygen breathing or deeper recompression at 4 atmosphere absolute with nitrogen-oxygen or helium-oxygen breathing mixture was also noted. Results Twenty-one divers (33%) had incomplete resolution after 1 month. The clinical severity at presentation was the only independent predictor of poor outcome (odd ratio, 2.68; P < .033). Time to treatment did not influence the recovery with a similar median delay (3 hours) between the divers with or without long-term sequelae. Choice of recompression procedure was not also a determinant factor for treatment outcome. Conclusion The initial clinical course before treatment is a major prognostic factor of spinal cord DCS. Delay to recompression less than 3 hours and use of deep treatment tables did not improve outcome in DCS divers.

Helium–oxygen: A versatile therapy to “lighten the load” of chronic obstructive pulmonary disease (COPD)

Breathing helium–oxygen mixtures has a number of favorable physiological effects that could be beneficial in the treatment of both stable and unstable patients with chronic obstructive pulmonary disease (COPD). Helium–oxygen breathing reduces airway resistance, duty cycle, end-expiratory lung volume and intrinsic positive end-expiratory pressure, all leading to a reduction in the work of breathing in patients with airflow limitation. Important hemodynamic effects directly related to the reduction in the work of breathing also occur through enhanced lung–heart interaction. In the unstable patient, these physiological effects may decrease the need for intubation, reduce extubation failure and improve patient outcome. In the stable patient, similar effects lead to reduced dyspnea and improved exercise capacity, potentially enhancing the outcomes of exercise rehabilitation. To date, studies frequently include small sample sizes and less than rigorous methodology, so conclusive evidence regarding the effectiveness of breathing helium–oxygen mixtures for improving health outcomes in patients with COPD remains limited.

Heliox in the treatment of chronic obstructive pulmonary disease

Objective: To determine if breathing helium oxygen mixtures in addition to conventional therapy in non-intubated adult chronic obstructive airways disease (COPD) patients reduces the arterial partial pressure of carbon dioxide...

Microdialysis study of striatal dopaminergic dysfunctions induced by 3 MPa of nitrogen– and helium–oxygen breathing mixtures in freely moving rats

Previous studies have demonstrated opposite effects of high-pressure helium and nitrogen on extracellular dopamine (DA) levels, which may reflect disturbances on the synthesis, release or metabolic mechanisms. Intrastriatal microdialysis was used to measure the precursor (tyrosine), DA and its metabolites (DOPAC, HVA) levels under nitrogen- or helium- at pressure up to 3 MPa. Under 3 MPa of helium–oxygen breathing mixtures, the extracellular concentration of tyrosine is decreased while the extracellular concentration of DA is increased. On the contrary, nitrogen–oxygen breathing mixture at the same pressure increased extracellular tyrosine concentration and decreased DA release. Under both conditions, an increment of the DOPAC and HVA levels could be noted. Our results suggest that changes in DA release and metabolism during high-pressure helium exposure reflect the effect of the pressure per se, whereas the intrinsic effects of narcotic gases, although sensitive to pressure, would be revealed by hyperbaric nitrogen exposure.

Opposing effects of narcotic gases and pressure on the striatal dopamine release in rats

Nitrogen–oxygen breathing mixtures, for pressures higher than 0.5 MPa, decrease the release of dopamine in the rat striatum, due to the narcotic potency of nitrogen. In contrast, high pressures of helium–oxygen breathing mixtures of more than 1–2 MPa induce an increase of the striatal dopamine release and an enhancement of motor activity, referred to as the high pressure nervous syndrome (HPNS), and attributed to the effect of pressure per se. It has been demonstrated that the effect of pressure could be antagonized by narcotic gas in a ternary mixture, but most of the narcotic gas studies measuring DA release were executed below the threshold for pressure effect. To examine the effect of narcotic gases at pressure on the rat striatal dopamine release, we have used two gases, with different narcotic potency, at sublethargic pressure, nitrogen at 3 MPa and argon at 2 MPa. In addition, to dissociate the effect of the pressure, we have used nitrous oxide at 0.1 MPa to induce narcosis at very low pressure, and helium at 8 MPa to study the effect of pressure per se. In all the narcotic conditions we have recorded a decrease of the striatal dopamine release. In contrast, helium pressure induced an increase of DA release. For the pressures used, the results suggest that the decrease of dopamine release was independent of such an effect of the pressure. However, for the same narcotic gas, the measurements of the extracellular DA performed in the striatum seem to reflect an opposing effect of pressure, since the decrease in DA release is lower with increasing pressure.

Pallidal administrations of gabazine and 5-AVA affect pressure-induced behavioral disorders in rats

The aim of this work was to study the role of pallidal GABAa and GABAb neurotransmission in the behavioral disorders induced by pressure. The effects of GABAb antagonist 5-aminovalleric acid (5-AVA) or GABAa antagonist gabazine administrations in the globus pallidus (GP) on locomotor and motor hyperactivity (LMA) and myoclonia expressions in the model of the rat submitted to 8 MPa of helium–oxygen breathing mixture were analyzed. The administration of GABAa antagonist gabazine enhances the occurrence of the epileptic seizures, slightly increases LMA but decreases myoclonia. In contrast, the administration of GABAb antagonist 5-AVA decreases both LMA and myoclonia during the compression and the beginning of the holding time at 8 MPa. These data indicate that some behavioral disorders induced by pressure are in relation with GABAergic neurotransmission and establish clearly that GABAa and GABAb receptor mediations have distinct functions in the GP of the rat.

Determinants of the difference between expired and core temperatures: effect of a breath-hold.

After a 30-s breath-hold (BH), expired temperature (TE) does not reach core temperature. One explanation is that the gas in the airways is not in thermal equilibrium with the airway walls. This possibility was eliminated by comparing TE in six subjects breathing either helium-oxygen or air after a BH. Another possibility is that the airway walls and surrounding tissues have sufficient thermal inertia to slow down thermal equilibrium during BH. This was checked by measuring oral and upper esophageal temperatures after cooling or heating the airways. It took more than 2 min for these temperatures to recover their steady-state value. Six subjects were requested to perform a long apnea after hyperventilating for 1 min and then taking a single breath of 100% oxygen. TE was still lower than core temperature after a 1-min BH, and there was no difference after a 2-min BH. The difference between expired and core temperatures during BH thus appears to be due to the thermal inertia of the airways and their surrounding tissues.

Oxygenation in status asthmaticus improves during ventilation with helium-oxygen.

To determine the effect of breathing helium-oxygen (HELIOX) mixtures on pulmonary gas exchange during severe asthma. A retrospective case-match control design was used to compare the changes in alveolar to arterial gradient [(A-a)gradient] in the first 2 hrs of mechanical ventilation (MV) for status asthmaticus (SA) in patients who received HELIOX with those who did not. Patients were matched for diagnosis of asthma, ventilatory failure, ventilator mode and settings, and equivalent pharmacologic therapy. The adult and pediatric intensive care units of a tertiary-care hospital. Adult and pediatric patients undergoing MV for SA. Use of HELIOX or standard nitrogen-oxygen mixtures during MV. A total of 11 patients receiving HELIOX in the first 2 hrs of MV for SA were compared with 11 case-matched controls who did not. At baseline, the HELIOX and control groups had similar (A-a)gradients (216+/-92 torr and 226+/-82 torr, respectively). The (A-a)gradient decreased significantly to 85+/-44 torr after initiation of ventilation with HELIOX (p < .0003), whereas it did not change significantly in the control group in a similar time frame and during identical treatment without HELIOX. The reduction in (A-a)gradient in the HELIOX group facilitated a reduction in F(IO)2 from 0.8+/-0.2 initially to 0.4+/-0.1 at the time of the second blood gas determination, thus permitting greater concentrations of helium to be administered. MV with HELIOX improves (A-a)gradient in patients with SA. Although this improvement adds little to routine therapy with supplemental oxygen, it does permit reduction in concentration of inspired oxygen to levels that maximize helium concentration and thus permit full benefits of HELIOX on lung mechanics to be realized in even the most severely ill asthmatics.

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.

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.