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PubMed2000

The impact of laparoscopic biopsy of pancreatic lymph nodes with helium and carbon dioxide on port site and liver metastasis in BOP-induced pancreatic cancer in hamster.

The influence of pancreatic biopsy during laparoscopy with carbon dioxide (CO2) and helium on the incidence of port site and liver metastasis in pancreatic carcinoma is still unknown. Ductal adenocarcinoma of the pancreas was induced in Syrian hamsters (n = 30) by injection of N-nitrosobis-2-oxopropylamin (BOP, 10 mg/kg body weight/week) for 12 weeks. In week 13, hamsters were randomized in 3 groups (n = 10): While in group 1 (gr. 1) a laparotomy and biopsy of pancreatic lymph nodes was performed, gr. 2 and gr. 3 underwent a laparoscopic biopsy either with CO2 or helium. Therefore, one trocar was located in the left (biopsy) and the right abdominal wall (camera). In the 18th week all animals were sacrificed and the incidence of abdominal wall, port site and liver metastases was histologically determined. While there were abdominal wall metastases after laparotomy in 10% (n = 1), we observed trocar metastases in the CO2 group in 20% (n = 2). However, there were no trocar metastases in the helium group. The incidence of liver metastasis did not differ between the laparotomy and the helium group (20% vs 30%), but was increased in the CO2 group (60%). Laparoscopic biopsy of pancreatic lymph nodes with CO2 increased the incidence of port site and liver metastases in pancreatic cancer. The helium group was equal to the laparotomy group in this respect. Thus, staging laparoscopy with helium might become an alternative to explorative laparotomy in pancreatic cancer.

Animals↗
PubMed1994

Gas embolism: helium is more lethal than carbon dioxide.

The search for alternatives to carbon dioxide (CO2) for insufflation during laparoscopy has included the consideration of helium. Helium is attractive because it is noncombustible and has no pharmacologic effects. Unfortunately, it is also relatively insoluble in blood, which potentially could exacerbate a venous gas embolism. We performed rapid intravenous injections of CO2 and helium into 4 dogs in amounts ranging from 5 to 10 ml of gas per kilogram body weight. Recovery after CO2 injection always occurred within 1 min. In 4 of 6 instances, the helium injection was fatal. Our results confirm that helium is more lethal than CO2 when injected intravenously. This implies that the use of helium for insufflation during laparoscopy might place patients at greater risk for adverse effects should venous gas embolism occur.

Animals↗
PubMed1995

Effects of pneumoperitoneum with helium on hemodynamics and oxygen transport: a comparison with carbon dioxide.

Pneumoperitoneum with CO2 is associated with adverse effects, such as hypercarbia, arrhythmias, and circulatory depression, which may limit its use in patients with underlying disease. Some of these effects may be caused by CO2 absorption resulting in acid-base disturbances. Laparoscopic insufflation with helium may be a good alternative for CO2, since it is chemically inert. Because there are few data on the use of helium for laparoscopy, we studied hemodynamics and gas exchange during insufflation with CO2 or helium in 8 pigs at 10, 15, and 20 mm Hg intraabdominal pressure. Heart rate did not change significantly with both gases. Arterial blood pressure increased with CO2 (p < 0.05) but not with helium. Cardiac output, mixed venous oxygen saturation, and oxygen consumption did not decrease, whereas central venous filling pressures increased during insufflation with either gas. Insufflation with CO2 resulted in mild increases in arterial, central venous, and end-expiratory CO2. The results suggest that pneumoperitoneum with helium will not be associated with profound circulatory depression or oxygen transport abnormalities. In addition, the use of helium is not associated with acid-base disturbances, although central venous filling pressures are similarly increased as with the use of CO2 pneumoperitoneum.

Acid-Base Imbalance↗
PubMed1999

Administration of either non-NMDA receptor agonists or NMDA receptor antagonists into the substantia nigra or the globus pallidus reduces the psychostimulant effect of high helium pressure on locomotor activity in rats.

Helium pressure of >2 MPa is a well known factor underlying pressure-dependent central neuroexcitatory disorders that include locomotor and motor activity (LMA) and myoclonia. We investigated the effects of bilateral injection in either the substantia nigra (SN) or the globus pallidus (GP) of the AMPA receptor agonist (+/-)AMPA, the kainate receptor agonist kainic acid, the NMDA receptor agonist (+/-)-cis-piperidine-2,3-dicarboxylic acid (PDA), and the NMDA receptor antagonist (+/-)-2-amino-7-phosphono-heptanoic acid (AP-7) in the occurrence of helium pressure-induced LMA and myoclonia. Administration of AMPA, kainate, or AP-7 in either the SN or the GP significantly reduced high helium pressure-induced LMA, whereas the NMDA receptor agonist showed no significant effect. Injection in the SN of the non-NMDA receptor agonist AMPA and the NMDA receptor agonist PDA increased the development of high helium pressure-induced myoclonia, whereas injection of the NMDA receptor antagonist AP-7 into the SN or the GP decreased it. This confirms that NMDA transmission in the SN and the GP would play a major role in the development of helium pressure-induced LMA; manipulation of AMPA and kainate systems may have therapeutic potential. The opposite effects of AMPA on LMA and myoclonia also confirm the neural substrates involved in the motor disorder produced by helium pressure differ substantially between LMA and myoclonia.

2-Amino-5-phosphonovalerate↗
PubMed1985

Use of an acoustic helium analyzer and microprocessor for rapid measurement of absolute lung volume during mechanical ventilation.

A technique developed to measure functional residual capacity during mechanical ventilation uses an acoustic helium analyzer and microprocessor to perform open-circuit helium washout. The acoustic helium analyzer has acceptable linearity up to a helium concentration of 50% and is stable. The microprocessor combines output from the acoustic analyzer and a ventilator with an expiratory flow signal, to compute lung volume rapidly during mechanical ventilation. In a sample of ten patients with various lung problems, open-circuit helium washout gave results similar to those of a closed-circuit helium-dilution technique during assist control or intermittent mandatory ventilation modes, with or without positive end-expiratory pressure. This open-circuit system has an advantage over other techniques because it is small and portable and can measure lung volume quickly without complicated maneuvers.

Acoustics↗
PubMed1998

Helium versus oxygen for tracheal gas insufflation during mechanical ventilation.

OBJECTIVE: To evaluate and compare the effect of tracheal gas insufflation using two gases with different physical properties, helium and oxygen, as an adjunct to conventional mechanical ventilation in patients with respiratory failure. DESIGN: Prospective, intervention study. SETTING: General intensive care unit in a tertiary university medical center. PATIENTS: Seven sedated and paralyzed patients with respiratory failure of various etiologies. All patients were ventilated in the volume-control mode (tidal volume 5 to 7 mL/kg). Inclusion criteria were PaCO2 of > or =50 torr (> or =6.7 kPa), together with peak inspiratory pressure of > or =35 cm H2O and respiratory rate of > or =14 breaths/min. INTERVENTIONS: All patients were intubated with an endotracheal tube that had an additional lumen opening at its distal end, through which tracheal gas insufflation was administered. The tracheal gas insufflation was applied continuously throughout the respiratory cycle at three flow rates (2, 4, and 6 L/min) with two gases, oxygen and helium, while the ventilatory settings were maintained constant. MEASUREMENTS AND MAIN RESULTS: In addition to airway pressures and arterial blood gases, the relative efficacy of tracheal gas insufflation with each gas was estimated using a "coefficient of efficiency" (which we defined as the change in PaCO2/peak inspiratory pressure) compared with baseline measurements. Tracheal gas insufflation with both gases decreased PaCO2 significantly (p < .05) at all flow rates. This effect was accompanied by an increase in airway pressure with both gases (oxygen and helium). However, at flow rates of 6 L/min, tracheal gas insufflation with helium resulted in lower peak inspiratory pressure than with oxygen. Tracheal gas insufflation with helium was more effective (as estimated by the coefficient of efficiency) than with oxygen at all flow rates (p < .05). CONCLUSION: In volume-controlled, mechanically ventilated patients with respiratory failure, tracheal gas insufflation with helium might be suggested as an alternative to oxygen.

Acute Disease↗
PubMed1979

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↗
PubMed1988

Comparison of helium-ion radiation therapy and split-course megavoltage irradiation for unresectable adenocarcinoma of the pancreas. Final report of a Northern California Oncology Group randomized prospective clinical trial.

Forty-nine patients with locally advanced carcinoma of the pancreas were treated in a randomized, prospective study comparing definitive helium ion radiation therapy with conventional split-course megavoltage photon irradiation. Patients in each treatment arm underwent exploratory staging laparotomy followed by concurrent radiation therapy and 5-fluorouracil chemotherapy. Patients treated with photons received 6,000 cGy over a period of 10 weeks; patients treated with helium irradiation received a 6,000-7,000-cGy-equivalent dose over a period of 8-9 weeks. There was no significant difference in overall survival between patients in the two treatment arms (P = .29). Patients treated with helium ions had a slightly longer median survival (7.8 months) than the photon-treated patients (6.5 months). Local control rates were slightly higher in the helium-treated patients (10% vs 5%). Complications included one chemotherapy-related death. Four of the five helium-treated patients who survived longer than 18 months died of local failure without distant metastases. These results suggest that more aggressive local therapy could result in improved survival in helium-treated patients.

Adenocarcinoma↗
PubMed1988

Bronchomotor response to cold air or helium-oxygen at normal and high ambient pressures.

Effects of inhalation of cold air or helium-oxygen mixture on lung resistance (RL) were studied in anesthetized and tracheotomized rabbits under normal ambient pressure and in human volunteers under normo- and hyperbaric conditions. In artificially ventilated rabbits, an increase in RL occurred when the tracheal temperature fell to 10 degrees C. This effect was more than double with helium breathing compared to air, despite a lower respiratory heat loss by convection (Hc) with helium. In 3 normal humans, inhalation of cold air (mouth temperature = 8 degrees C) at sea level had no effect on RL value. However, with a helium-nitrogen-oxygen mixture, a weak but significant increase in RL due to cold gas breathing was measured in 1 subject at 2 ATA and in 2 individuals at 3.5 ATA. The density of inhaled gas mixture (air or He-N2-O2) was near the same in the three circumstances (1, 2, and 3.5 ATA) but Hc value increased with helium. At 8 ATA a 30-55% increase in RL occurred in the 3 divers during inhalation of cold gas (Hc was multiplied by 6 compared to air at sea level) and at 25 ATA the cold-induced bronchospasm ranged between 38 and 95% (Hc multiplied by 27). Thus, in rabbits and humans helium breathing enhanced the cold-induced increase in RL at normal or elevated ambient pressure, and this effect was interpreted as resulting from different mechanisms in the two circumstances.

Adult↗
PubMedDate not supplied

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↗
PubMed1978

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↗
PubMed1995

Helium insufflation in laparoscopic surgery.

Carbon dioxide is the most commonly used gas for abdominal insufflation in laparoscopy today. Due to the solubility of carbon dioxide large volumes are absorbed into the circulation causing a high PCO2 and a low pH (respiratory acidosis). Carbon dioxide is also stored in several sites in the body and is released at the conclusion of the procedure prolonging the respiratory acidosis when the patient is least able to cope with this additional burden. Cardiac effects of CO2 consist of a lowering of the arrhythmia threshold, increased blood pressure, pulse and cardiac output. At a sustained high level this can lead to cardiac depression and death. These effects are particularly prone to occur in cardiac and respiratory cripples. Other gases that have been used include air, oxygen, nitrous oxide and nitrogen. Their use has been discontinued because of the danger of embolism. Air, oxygen and nitrous oxide are also not safe to use in the presence of electrosurgical instruments thereby limiting their usefulness even further. Helium has been proposed as a very promising alternative to CO2. In the laboratory and in a clinical trial, helium has not produced the respiratory acidosis associated with CO2 insufflation. This is further evidence that the acidosis is not primarily due to elevation of the diaphragm and consequent increased dead space, but to the large amount of CO2 that is absorbed directly from the peritoneal cavity. Helium would seem to be the gas of choice at this time as it comes close to fitting the criteria for an ideal insufflating gas. Helium is clear and colorless, allowing unimpeded vision to the operator. It is non toxic, not flammable or explosive and can be safely used with electrocautery and laser. Helium is easy to handle and not very soluble which decreases the amount absorbed from the peritoneal cavity and consequently the amount used. That which is absorbed is quickly cleared by the lungs. Helium is metabolically inactive (in contrast to CO2) and does not interfere with normal metabolic processes. In view of this promising initial work, further studies are indicated.

Abdomen↗
PubMed2000

Pulsed helium introduction into a quadrupole ion trap for reduced collisional quenching during infrared multiphoton dissociation of electrosprayed ions

Previous infrared multiphoton dissociation (IRMPD) experiments utilizing a quadrupole ion trap mass spectrometer yielded limited photodissociation efficiencies. Helium buffer gas continuously infused into the analyzer region at pressures of typically 1 x 10(-3) Torr to improve ion trap performance can collisionally quench photoexcited ions during the IRMPD process. Photodissociation experiments have indicated that uncorrected pressures below 2 x 10(-5) Torr are necessary to avoid collisional deactivation of photoexcited ions. This paper describes IRMPD in the quadrupole ion trap at reduced pressures utilizing a dual-pulsed introduction of helium buffer gas incorporated into the ion trap scan function. The pulsed introduction of helium buffer gas before ion injection allows the efficient trapping of ions injected from an electrospray source and the removal of helium before laser irradiation. A second pulse of helium directly before ion detection improves the intensity of the ion signal. The use of this dual-pulsed inlet of helium for improved IRMPD is demonstrated with the carbohydrate antibiotics neomycin and erythromycin. Copyright 2000 John Wiley & Sons, Ltd.

Journal Article↗
PubMed2004

Microsolvation of phthalocyanines in superfluid helium droplets.

Experimental and theoretical investigations of the spectroscopy of molecules in superfluid helium droplets provide evidence for the key role of the first helium layer surrounding the dopant molecule in determining the molecule's spectroscopic features. Recent investigations of emission spectra of phthalocyanine in helium droplets revealed a doubling of all transitions. Herein, we present the emission spectra of Mg-phthalocyanine and of phthalocyanine-argon clusters in helium droplets, which confirm the splitting as a general effect of the helium environment. A scheme of levels is deduced from the emission spectra and attributed to quantized states of the first helium layer surrounding the dopant molecule.

Journal Article↗
PubMed2001

Constraints on hydrothermal processes and water exchange in Lake Vostok from helium isotopes.

Lake Vostok, the largest subglacial lake in Antarctica, is covered by the East Antarctic ice sheet, which varies in thickness between 3,750 and 4,100 m (ref. 1). At a depth of 3,539 m in the drill hole at Vostok station, sharp changes in stable isotopes and the gas content of the ice delineate the boundary between glacier ice and ice accreted through re-freezing of lake water. Unlike most gases, helium can be incorporated into the crystal structure of ice during freezing, making helium isotopes in the accreted ice a valuable source of information on lake environment. Here we present helium isotope measurements from the deep section of the Vostok ice core that encompasses the boundary between the glacier ice and accreted ice, showing that the accreted ice is enriched by a helium source with a radiogenic isotope signature typical of an old continental province. This result rules out any significant hydrothermal energy input into the lake from high-enthalpy mantle processes, which would be expected to produce a much higher 3He/4He ratio. Based on the average helium flux for continental areas, the helium budget of the lake leads to a renewal time of the lake of the order of 5,000 years.

Journal Article↗
PubMed2006

Quantum solvation dynamics of HCN in a helium-4 droplet.

Ultracold nanodroplets of helium-4, containing several thousands of He atoms, offer considerable promise as microscopic cryogenic chambers. Potential applications include the creation of tailor-made chemical or biomolecular complexes and studies of superfluidity in nanoscale systems. Recent experiments have succeeded in interrogating droplets of quantum solvent which consist of as few as 1-20 helium-4 atoms and which contain a single solute molecule. This allows the transition from a floppy, but essentially molecular, complex to a dissolved molecule to be followed and, surprisingly, the transition is found to occur quite rapidly, in some cases for as few as N = 7-20 solvent atoms. For example, in experiments on helium-4 droplets seeded with CO molecules [Tang and McKellar, J. Chem. Phys. 119, 754 (2003)], two series of transitions are observed which correlate with the a-type (Delta K = 0) and b-type (Delta K = +/-1) lines of the binary complex, CO-He (K is the quantum number associated with the projection of the total angular momentum onto the vector connecting the atom and the molecular center of mass). The a-type series, which evolves from the end-over-end rotational motion of the CO-He binary complex, saturates to the nanodroplet limit for as few as 10-15 helium-4 atoms, i.e., the effective moment of inertia of the molecule converges to its asymptotic (solvated) value quite rapidly. In contrast, the b-type series, which evolves from the free-molecule rotational mode, disappears altogether for N approximately 7 atoms. Similar behavior is observed in recent computational studies of HCN(4He)N droplets [Paolini et al., J. Chem. Phys. 123, 114306 (2005)]. In this article the quantum solvation of HCN in small helium-4 droplets is studied using a new fixed-node diffusion Monte Carlo (DMC) procedure. In this approach a Born-Oppenheimer-type separation of radial and angular motions is introduced as a means of computing nodal surfaces of the many-body wave functions which are required in the fixed-node DMC method. Excited rotational energies are calculated for HCN(4He)N droplets with N = 1-20: the adiabatic node approach also allows concrete physical mechanisms to be proposed for the predicted disappearance of the b-type series as well as the rapid convergence of the a-type series to the nanodroplet limit with increasing N. The behavior of the a-type series is traced directly to the mechanics of angular momentum coupling-and decoupling-between identical bosons and the molecular rotor. For very small values of N there exists significant angular momentum coupling between the molecule and the helium atoms: at N approximately 10 solvation appears to be complete as evidenced by significant decoupling of the molecule and solvent angular momenta. The vanishing of the b-type series is predicted to be a result of increasing He-He repulsion as the number of solvent atoms increases.

Journal Article↗
PubMed1998

Superfluidity within a small helium-4 cluster: the microscopic andronikashvili experiment

The infrared spectrum of single oxygen carbon sulfide (OCS) molecules was measured inside large superfluid pure helium-4 droplets and nonsuperfluid pure helium-3 droplets, both consisting of about 10(4) atoms. In the helium-4 droplets, sharp rotational lines were observed, whereas in helium-3 only a broad peak was found. This difference is interpreted as evidence that the narrow rotational lines, which imply free rotations, are a microscopic manifestation of superfluidity. Upon addition of 60 helium-4 atoms to the pure helium-3 droplets, the same sharp rotational lines were found; it appears that 60 is the minimum number needed for superfluidity.

Journal Article↗
PubMed2003

Helium-oxygen reduces work of breathing in mechanically ventilated patients with chronic obstructive pulmonary disease.

OBJECTIVE: To evaluate whether helium-oxygen mixture reduces inspiratory work of breathing (WOB) in sedated, paralyzed, and mechanically ventilated patients with acute exacerbation of chronic obstructive pulmonary disease (COPD). DESIGN AND SETTING: Open, prospective, randomized, crossover study in the medical intensive care unit in a university hospital. PATIENTS AND PARTICIPANTS: 23 patients admitted for acute exacerbation of COPD and mechanically ventilated. MEASUREMENTS: Total WOB (WOBt), elastic WOB (WOBel), resistive WOB (WOBres), and WOB due to PEEPi (WOBPeepi) were measured. Static intrinsic positive end expiratory pressure (PEEPi), static compliance (Crs), inspiratory resistance (Rins), inspiratory (tinsp) and expiratory time constant (texp) were also measured. These variables were compared between air-oxygen and helium-oxygen mixtures. RESULTS: WOBt significantly decreased with helium-oxygen (2.34+/-1.04 to 1.85+/-1.01 J/l, p<0.001). This reduction was significant for WOBel (1.02+/-0.61 J/l to 0.87+/-0.47, p<0.01), WOBPeepi (0.77+/-0.38 J/l to 0.54+/-0.38, p<0.001), and WOBres (0.55+/-0.19 J/l to 0.44+/-0.24, p<0.05). PEEPi, Rins, tinsp and texp significantly decreased. Crs was unchanged. CONCLUSIONS: Helium-oxygen mixture decreases WOB in mechanically ventilated COPD patients. Helium-oxygen mixture could be useful to reduce the burden of ventilation.

Aged↗