Helium ash exhaust studies with core fueling by a helium beam: L-mode divertor discharges with neutral-beam heating in the JT-60 tokamak.
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Journal Article↗
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[Comparative study of the optical properties of biological tissues in exposure to helium-neon and helium-cadmium laser radiation].
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Animals↗
Beneficial effects of helium:oxygen versus air:oxygen noninvasive pressure support in patients with decompensated chronic obstructive pulmonary disease.
OBJECTIVE: To test the hypothesis that, in decompensated chronic obstructive pulmonary disease (COPD), noninvasive pressure support ventilation using 70:30 helium:oxygen instead of 70:30 air:oxygen could reduce dyspnea and improve ventilatory variables, gas exchange, and hemodynamic tolerance. DESIGN: Prospective, randomized, crossover study. SETTING: Medical intensive care unit, university tertiary care center. PATIENTS: Nineteen patients with severe COPD (forced 1-sec expiratory volume of 0.83+/-0.3 l) hospitalized in the intensive care unit for noninvasive pressure support ventilation after initial stabilization with noninvasive pressure support for no more than 24 hrs after intensive care unit admission. INTERVENTIONS: Noninvasive pressure support ventilation was administered in the following randomized crossover design: a) 45 min with air:oxygen or helium:oxygen; b) no ventilation for 45 min; and c) 45 min with air:oxygen or helium:oxygen. MEASUREMENTS AND MAIN RESULTS: Air:oxygen and helium:oxygen decreased respiratory rate and increased tidal volume and minute ventilation. Helium:oxygen decreased inspiratory time. Both gases increased total respiratory cycle time and decreased the inspiratory/total time ratio, the reduction in the latter being significantly greater with helium:oxygen. Peak inspiratory flow rate increased more with helium:oxygen. PaO2 increased with both gases, whereas PaCO2 decreased more with helium:oxygen (values shown are mean+/-SD) (52+/-6 torr [6.9+/-0.8 kPa] vs. 55+/-8 torr [7.3+/-1.1 kPa] and 48+/-6 torr [6.4+/-0.8 kPa] vs. 54+/-7 torr [7.2+/-0.9 kPa] for air:oxygen and helium:oxygen, respectively; p<.05). When hypercapnia was severe (PaCO2 >56 torr [7.5 kPa]), PaCO2 decreased by > or =7.5 torr (1 kPa) in six of seven patients with helium:oxygen and in four of seven patients with air:oxygen (p<.01). Dyspnea score (Borg scale) decreased more with helium:oxygen than with air:oxygen (3.7+/-1.6 vs. 4.5+/-1.4 and 2.8+/-1.6 vs. 4.6+/-1.5 for air:oxygen and helium:oxygen, respectively; p<.05). Mean arterial blood pressure decreased with air:oxygen (76+/-12 vs. 82+/-14 mm Hg; p<.05) but remained unchanged with helium:oxygen. CONCLUSION: In decompensated COPD patients, noninvasive pressure support ventilation with helium:oxygen reduced dyspnea and PaCO2 more than air:oxygen, modified respiratory cycle times, and did not modify systemic blood pressure. These effects could prove beneficial in COPD patients with severe acute respiratory failure and might reduce the need for endotracheal intubation.
Adult↗
Helium-oxygen improves Clinical Asthma Scores in children with acute bronchiolitis.
OBJECTIVE: To determine the efficacy of a helium-oxygen mixture in children admitted to the pediatric intensive care unit with acute respiratory syncytial virus (RSV) bronchiolitis. DESIGN: Randomized, double-blind, controlled, crossover study and nonrandomized, prospective study. SETTING: A pediatric intensive care unit in a university hospital. PATIENTS: Nonintubated children with signs of acute lower respiratory tract infection and a positive rapid immunoassay for RSV admitted to the pediatric intensive care unit. INTERVENTIONS: Treatment with either helium-oxygen or air-oxygen was administered in random order for 20 mins. Nonrandomized patients received helium-oxygen as initial therapy. MEASUREMENTS AND MAIN RESULTS: Clinical Asthma Score, respiratory rate, heart rate, and pulse oximetry oxygen saturation values were recorded at baseline (before randomization) and at the end of each 20-min treatment period (helium-oxygen or air-oxygen). Nonrandomized patients were studied 20 mins into helium-oxygen delivery. Eighteen patients were studied, 13 of whom were randomized. Five children with severe bronchiolitis (Clinical Asthma Score of > or =6) were initially given helium-oxygen and scored at 20 mins. Mean Clinical Asthma Score was 3.04 (range 1 to 7.5) in the 13 randomized patients and 4.25 (range 1 to 9) in the 18 patients overall. Clinical Asthma Score decreased in the 13 randomized patients (mean 0.46, p < .05) and in the 18 patients overall (mean 1.23, p < .01) during helium-oxygen delivery. In randomized patients with Clinical Asthma Scores of <6 (n = 12), a positive correlation (rs = .72) was observed between the Clinical Asthma Score at baseline and the change in Clinical Asthma Score during helium-oxygen administration (p = .009). Respiratory rate and heart rate decreased during helium-oxygen treatment but were not statistically significant. No complications occurred during helium-oxygen delivery. CONCLUSIONS: Inhaled helium-oxygen improves the overall respiratory status of children with acute RSV lower respiratory tract infection. In patients with mild-to-moderate bronchiolitis (Clinical Asthma Scores of <6), the beneficial effects of helium-oxygen were most pronounced in children with the greatest degree of respiratory compromise.
Acute Disease↗
Influence of different gases used for laparoscopy (helium, carbon dioxide, room air, and xenon) on tumor volume, histomorphology, and leukocyte-tumor-endothelium interaction in intravital microscopy.
BACKGROUND: Previous studies indicate that helium pneumoperitoneum used for laparoscopic surgery suppresses whereas carbon dioxide pneumoperitoneum increases postoperative tumor growth. The pathomechanisms of decreased tumor growth by helium are unknown. This study was designed to examine the effect of the gases helium, carbon dioxide (CO(2)), and air, and xenon, which can be used to induce pneumoperitoneum in laparoscopy on tumor volume, histomorphology, and leukocyte-endothelium interaction measured by intravital microscopy in rats with implanted liver malignoma (Morris hepatoma 3924A). METHODS: In 46 rats, Morris hepatoma 3294A cells were implanted intrahepatically. After implantation, rats were randomized into two main groups. In the first main group, 10 animals were prepared for examination of leukocyte-endothelium interaction by intravital video microscopy and were randomized into two groups. Five days after implantation they underwent laparoscopy using either helium (n = 5) or CO(2) (n = 5). Ten days after implantation the rats underwent intravital video microscopy to assess leukocyte-endothelium interaction in the tumor and liver vessels. In the second main group 36 rats were prepared for examination of tumor volume arid histomorphology. They were randomized into five groups. Five days after implantation they underwent laparoscopy using helium (n = 7), carbon dioxide (n = 7), room air (n = 7), or xenon (n = 8). The control group (n = 7) received anesthesia only. Rats were killed 10 days after tumor implantation to assess tumor volume and histomorphology. RESULTS: Compared to the control group or groups that received CO(2), room air, or xenon for pneumoperitoneum, the establishment of helium pneumoperitoneum caused a significantly smaller tumor volume (Kruskal-Wallis test, p = 0.001; median tumor-volume: control group, 44 mm(3); helium 19 mm(3)). There was no significant difference in histomorphology between the groups. There was only a statistically significant difference in the development of central tumor necrosis in accordance to tumor volume (Mann-Whitney test, p = 0.03). In the tumor samples, roller counts were statistically significantly higher in the helium group compared to the CO(2) group (p = 0.04). For sticker counts, no statistically significant effects due to liver/tumor (p = 0.13) or treatment (p = 0.48) were observed. CONCLUSIONS: There was a significant decrease in tumor volume using helium pneumoperitoneum for laparoscopy compared to the other gases. Here, we demonstrate that suppression of tumor growth is not due to variation of histomorphology. It seems that helium pneumoperitoneum effects a higher leukocyte-endothelium interaction and thereby a higher immune activation. This could be one explanation for the statistically significantly smaller tumor volume after laparoscopy with helium compared to laparoscopy with CO(2).
Air↗
Rapid healing of gingival incisions by the helium-neon diode laser.
Fifty-eight extraction patients had one of two gingival flap incisions lased with a 1.4 mw helium-neon (670 nm) diode laser for 30 seconds (fluence = 0.34 J/cm2). Healing rates were evaluated clinically and photographically. Sixty-nine percent of the irradiated incisions healed faster than the control incisions. No significant difference in healing was noted when patients were compared by age, gender, race, and anatomic location of the incision. This study concludes that helium-neon diode lasers, at the previously mentioned energy level, increase the rate of gingival wound healing in 69 percent of patients, without any side effects. For the last 30 years, low-power lasers in dentistry have appeared to stimulate healing rates and increase the rate of repair of injured tissue. Helium-neon and similar lasers emit light in the red (600-700 nm) spectrums and produce energy densities (fluences) below 20 Joules/cm2. They have been studied in a variety of animal tissue culture and human evaluations to determine their ability to increase the rates of wound healing by biostimulation. Over the last three decades, researchers have found that ruby and gas helium-neon (low-power laser radiation) have a biostimulatory effect on living tissue. Studies show that under specific conditions, red spectrum laser light speeds the healing of wounds. Photons from the red light lasers, which include ruby lasers (694 nm), helium-neon gas lasers (632 nm), and helium-neon diode lasers (650-670 nm), appear to stimulate rapid epithelialization and fibroblast (collagen) proliferation in animal and human tissue cultures. Low-power lasers have been reported to reduce post-extraction pain and swelling and to increase rates of wound healing (including scar formation, phagocytosis) in cell culture, animal, and human clinical studies. The new, compact, and inexpensive (under $50) helium-neon diode lasers have produced similar effects. These FDA Class IIIa lasers have no hazards associated with them, although one should avoid direct exposure to the eye for a prolonged period of time. In the past, many biostimulation studies using red spectrum lasers produced confusing data and conflicting results. Some studies reported that the biostimulation effect did not occur in all cases of laser irradiation, while other research reported that it did. Results seem to depend on the delivery of appropriate energy fluence levels (between 1 and 20 J/cm2) and the type of laser (wavelength) used. Several of these studies never described the levels of laser energy used to promote the described biostimulatory results. This caused controversy when determining whether or not helium-neon lasers influence wound healing. Studies suggest that low-power laser exposure can significantly increase the healing rate during the first few days of the healing process; however, studies do not show appreciable net benefit as compared to controls toward the end of a two-week wound repair cycle. The increased healing effect appears to be centered around the early, most sensitive stages of the healing process. Several studies showed optimum tissue healing rates at helium-neon laser exposure levels between 1 J/cm2 and 20 J/cm2. Laser-enhanced biostimulation has been reported to produce metabolic changes within the cells. This results in faster cell division, rapid matrix production (increased collagen, myofibroblasts, etc.), and cell movement. There have been few controlled studies using adequate numbers of human subjects in identifying the beneficial effects of helium-neon laser biostimulation. Ethical concerns, bulky equipment, and problems with biased study designs have frustrated a practical evaluation of laser biostimulation for general dental practice. A recently published "preliminary" study involving 52 patients was designed to reduce these issues. The purpose of this study is to complement the above research and to evaluate whether helium-neon diode laser radiation at average fluences of 0.34 J/c
Adult↗
[The effect of inhaled nitric oxide and helium-oxygen mixture on the pulmonary function of asthmatics].
OBJECTIVE: To investigate the effect of inhaled nitric oxide (NO) combined with helium-oxygen mixture on the pulmonary function of asthmatics. METHODS: 18 asthmatic patients were included in this study. The patients were divided into two groups randomly. One group of patients inhaled 100 ppm NO combined with helium-oxygen mixture, the other group inhaled 40 ppm NO-containing helium-oxygen mixture. Pulmonary function was examined intermittently during the study process and compared with that of the patients treated with salbutamol. RESULTS: It is shown that inhalation of helium-oxygen mixture improved the forced vital capacity, forced expiratory volume during the first 1.0 second (FEV(1)), peak expiratory flow rate (PEFR) and maximal midexpiratory flow rate (MMEF) significantly as compared with inhalation of air. Although salbutamol inhalation improved FEV(1) and MMEF, the effect was weaker than helium-oxygen mixture inhalation. However the effect of helium-oxygen mixture lasted only one minute. Inhalation of 100 ppm NO with helium-oxygen mixture only slightly improved FEV(1) and PEFR as compared with inhalation of helium-oxygen mixture. 40 ppm NO with helium-oxygen mixture did not influence the pulmonary function in the asthmatic patient as compared with helium-oxygen mixture alone. CONCLUSION: It is suggested that inhalation of helium-oxygen mixture can improve the pulmonary function of asthmatic patients significantly. However, inhalation of NO exerts a weak bronchodilatory effect.
Administration, Inhalation↗
Helium-oxygen therapy for pediatric acute severe asthma requiring mechanical ventilation.
OBJECTIVE: To illustrate the use of helium-oxygen gas mixtures as therapy for pediatric patients with acute severe asthma requiring conventional mechanical ventilation. DESIGN: Retrospective review. SETTING: Tertiary care children's teaching hospital. PATIENTS: All mechanically ventilated patients with severe asthma admitted to the pediatric intensive care unit from August 1994 to October 2000. INTERVENTIONS: Within 24 hrs of intubation or admission, patients were stabilized on volume ventilation, bronchodilator therapy, corticosteroids, and antibiotics when indicated. Hypercapnia was permitted while maintaining arterial blood gas pH > or =7.25. A helium-oxygen gas mixture then was begun with helium flow set at 5-7 L/min, and oxygen flow was titrated to maintain desired oxygen saturation. Only sedated, chemically paralyzed patients with adequate pre-helium-oxygen and post-helium-oxygen measurements were statistically analyzed. MEASUREMENTS AND MAIN RESULTS: Twenty-eight mechanically ventilated patients with severe asthma placed on helium-oxygen gas mixtures were identified who met study entry criteria. Mean patient age was 8.8 yrs (range, 1.1-14.6). Before helium-oxygen therapy began, mean peak inspiratory pressure was 40.5 +/- 4.2 cm H(2)O, mean arterial blood gas pH was 7.26 +/- 0.05, and mean CO(2) partial pressure was 58.2 +/- 8.5 torr. After patients were placed on helium-oxygen therapy, there was a significant decrease in mean peak inspiratory pressure to 35.3 +/- 3.0 cm H(2)O. Mean pH increased significantly to 7.32 +/- 0.06, and mean partial pressure CO(2) decreased significantly to 50.5 +/- 7.4 torr. Initial mean inspired helium was 57 +/- 4% (range, 32-74). Mechanical ventilation days ranged from 1 to 23 days (mean, 5.0). Hospital stay ranged from 4 to 29 days (mean, 10.1), with an average pediatric intensive care unit stay of 6.9 days (range, 2-24). There were two incidences of pneumothorax. CONCLUSIONS: In the pediatric patient with severe asthma requiring conventional mechanical ventilation, helium-oxygen administration appears to be a safe therapy and may assist in lowering peak inspiratory pressure and improving blood gas pH and partial pressure CO(2).
Acute Disease↗
Helium-hyperoxia, exercise, and respiratory mechanics in chronic obstructive pulmonary disease.
RATIONALE: Hyperoxia and normoxic helium independently reduce dynamic hyperinflation and improve the exercise tolerance of patients with chronic obstructive pulmonary disease (COPD). Combining these gases could have an additive effect on dynamic hyperinflation and a greater impact on respiratory mechanics and exercise tolerance. OBJECTIVE: To investigate whether helium-hyperoxia improves the exercise tolerance and respiratory mechanics of patients with COPD. METHODS: Ten males with COPD (FEV(1) = 47 +/- 17%pred [mean +/- SD]) performed randomized constant-load cycling at 60% of maximal work rate breathing air, hyperoxia (40% O(2), 60% N(2)), normoxic helium (21% O(2), 79% He), or helium-hyperoxia (40% O(2), 60% He). MEASUREMENTS: Exercise time, inspiratory capacity (IC), work of breathing, and exertional symptoms were measured with each gas. RESULTS: Compared with air (9.4 +/- 5.2 min), exercise time was increased with hyperoxia (17.8 +/- 5.8 min) and normoxic helium (16.7 +/- 9.1 min) but the improvement with helium-hyperoxia (26.3 +/- 10.6 min) was greater than both these gases (p = 0.019 and p = 0.007, respectively). At an isotime during exercise, all three gases reduced dyspnea and both helium mixtures increased IC and tidal volume. Only helium-hyperoxia significantly reduced the resistive work of breathing (15.8 +/- 4.2 vs. 10.1 +/- 4.1 L . cm H(2)O(-1)) and the work to overcome intrinsic positive end-expiratory pressure (7.7 +/- 1.9 vs. 3.6 +/- 2.1 L . cm H(2)O(-1)). At symptom limitation, tidal volume remained augmented with both helium mixtures, but IC and the work of breathing were unchanged compared with air. CONCLUSION: Combining helium and hyperoxia delays dynamic hyperinflation and improves respiratory mechanics, which translates into added improvements in exercise tolerance for patients with COPD.
Aged↗
The effect of helium on ventilator performance: study of five ventilators and a bedside Pitot tube spirometer.
OBJECTIVE: To assess in vitro the performance of five mechanical ventilators-Siemens 300 and 900C (Siemens-Elma; Solna, Sweden), Puritan Bennett 7200 (Nellcor Puritan Bennett; Pleasanton, CA), Evita 4 (Dragerwerk; Lubeck, Germany), and Bear 1000 (Bear Medical Systems; Riverside CA)-and a bedside sidestream spirometer (Datex CS3 Respiratory Module; Datex-Ohmeda; Helsinki, Finland) during ventilation with helium-oxygen mixtures. DESIGN: In vitro study. SETTING: ICUs of two university-affiliated hospitals. METHODS AND MEASUREMENTS: Each ventilator was connected to 100% helium through compressed air inlets and then tested at three to six different tidal volume (VT) settings using various helium-oxygen concentrations (fraction of inspired oxygen [FIO(2)] of 0.2 to 1.0). FIO(2) and VT were measured with the Datex CS3 spirometer, and VT was validated with a water-displacement spirometer. MAIN RESULTS: The Puritan Bennett 7200 ventilator did not function with helium. With the other four ventilators, delivered FIO(2) was lower than the set FIO(2). For the Siemens 300 and 900C ventilators, this difference could be explained by the lack of 21% oxygen when helium was connected to the air supply port, while for the other two ventilators, a nonlinear relation was found. The VT of the Siemens 300 ventilator was independent of helium concentration, while for the other three ventilators, delivered VT was greater than the set VT and was dependent on helium concentration. During ventilation with 80% helium and 20% oxygen, VT increased to 125% of set VT for the Siemens 900C ventilator, and more than doubled for the Evita 4 and Bear 1000 ventilators. Under the same conditions, the Datex CS3 spirometer underestimated the delivered VT by about 33%. CONCLUSIONS: At present, no mechanical ventilator is calibrated for use with helium. This investigation offers correction factors for four ventilators for ventilation with helium.
Helium↗
Helium-neon laser irradiation stimulates migration and proliferation in melanocytes and induces repigmentation in segmental-type vitiligo.
Low-energy helium-neon lasers (632.8 nm) have been employed in a variety of clinical treatments including vitiligo management. Light-mediated reaction to low-energy laser irradiation is referred to as biostimulation rather than a thermal effect. This study sought to determine the theoretical basis and clinical evidence for the effectiveness of helium-neon lasers in treating vitiligo. Cultured keratinocytes and fibroblasts were irradiated with 0.5-1.5 J per cm2 helium-neon laser radiation. The effects of the helium-neon laser on melanocyte growth and proliferation were investigated. The results of this in vitro study revealed a significant increase in basic fibroblast growth factor release from both keratinocytes and fibroblasts and a significant increase in nerve growth factor release from keratinocytes. Medium from helium-neon laser irradiated keratinocytes stimulated [3H]thymidine uptake and proliferation of cultured melanocytes. Furthermore, melanocyte migration was enhanced either directly by helium-neon laser irradiation or indirectly by the medium derived from helium-neon laser treated keratinocytes. Thirty patients with segmental-type vitiligo on the head and/or neck were enrolled in this study. Helium-neon laser light was administered locally at 3.0 J per cm2 with point stimulation once or twice weekly. The percentage of repigmented area was used for clinical evaluation of effectiveness. After an average of 16 treatment sessions, initial repigmentation was noticed. Marked repigmentation (>50%) was observed in 60% of patients with successive treatments. Basic fibroblast growth factor is a putative melanocyte growth factor, whereas nerve growth factor is a paracrine factor for melanocyte survival in the skin. Both nerve growth factor and basic fibroblast growth factor stimulate melanocyte migration. It is reasonable to propose that helium-neon laser irradiation clearly stimulates melanocyte migration and proliferation and mitogen release for melanocyte growth and may also rescue damaged melanocytes, therefore providing a microenvironment for inducing repigmentation in vitiligo.
Adolescent↗
Impact of laparoscopy with carbon dioxide versus helium on local and systemic inflammation in an animal model of peritonitis.
Increased intraperitoneal pressure and insufflation of carbon dioxide during laparoscopy may cause sepsis by promoting systemic inflammation in patients with intra-abdominal inflammatory diseases. The influence of carbon dioxide and helium during laparoscopy on bacteremia, endotoxemia, the plasma concentration of tumor necrosis factor-alpha (TNF-alpha), TNF-alpha secretion ex vivo by peripheral blood mononuclear cells (PBMCs), and intraperitoneal abscess formation was investigated in an animal model. A standardized fecal inoculum was injected intraperitoneally, and rats underwent laparoscopy with either carbon dioxide (N = 20) or helium (N = 20) or no further manipulation (control group; N = 20). Bacteremia was significantly more common 1 hour after laparoscopy with CO2 than in animals receiving helium or the control group. Furthermore, helium use led to a significant decrease of bacteremia 1 week after intervention. Fecal inoculation caused significant leukocytopenia in all groups within 1 hour after intervention, with complete recovery only in the helium-treated group (p < 0.05). The TNF-alpha plasma concentration was significantly lower in the helium-treated group, and suppression of ex vivo production recovered only in the animals undergoing laparoscopy with helium (p < 0.05). The number of intraperitoneal abscesses was significantly lower after laparoscopy with helium (2+/-1.5) than after CO2 laparoscopy (6.3+/-5.1) or in the control group (5.2+/-4.8). Laparoscopy with CO2 increased systemic inflammation only slightly, while helium use was associated with a significant lower incidence of bacteremia and local and systemic inflammation compared with the control group.
Abscess↗
Effects of helium on high frequency jet ventilation in model of airway stenosis.
BACKGROUND: The addition of helium to the inspired gas may facilitate ventilation in the presence of clinically evident upper airway obstruction. However, there are no data on the effects of using a helium-oxygen mixture during high frequency jet ventilation (HFJV) in upper airway obstruction. METHODS: HFJV at a frequency of 150 min(-1) (driving pressure 2 bar, inspiratory time 30%) was applied to a trachea-lung model to simulate ventilation through varying degrees of fixed laryngotracheal stenosis (2.5-8.5 mm). HFJV was delivered from above, through and below the level of stenosis to simulate supraglottic, transglottic and infraglottic administration. Measurements of distal tracheal pressures were repeated for each route at steady state for each stenosis diameter using both 100% oxygen and helium-oxygen (50% oxygen, 50% helium). The output of the ventilator was measured during operation on oxygen and helium-oxygen. RESULTS: Peak, mean and end-expiratory pressures were greater during simulated supraglottic HFJV than during transglottic and infraglottic HFJV, and pressures increased markedly as the diameter of the stenosis decreased for all routes of ventilation (P<0.001). Generated pressures during HFJV using helium-oxygen and 100% oxygen were very similar overall, although reductions in pressures were observed during ventilation with helium-oxygen via the transglottic and transtracheal routes at stenosis diameters <4 mm (P<0.05). However, HFJV with the helium-oxygen mixture increased the delivered gas volumes by approximately 18%. CONCLUSIONS: Using 50% helium-oxygen during HFJV in the presence of airway stenosis allows an 18% increase in minute volume at generated airway pressures which are the same as or lower than those when using 100% oxygen.
Air Pressure↗
Effect of helium-oxygen (heliox) gas mixtures on the function of four pediatric ventilators.
OBJECTIVE: To evaluate the effects of helium on the function of four ventilators commonly used in pediatrics: the Bird VIP, Bird VIP Gold, Servo 300, and Servo 900C. DESIGN: Prospective setting. SETTING: Research laboratory at a university hospital. SUBJECTS: Helium was administered as an 80:20 mixture of helium-oxygen through the air inlet of the ventilator. Delivered fraction of inspired oxygen (Fio(2)) was compared with the Fio(2) set on the blender dial. Inspiratory displayed tidal volume was recorded as an indicator of what the ventilator "believed" it had delivered and was compared with the V(T) displayed during ventilation with 100% oxygen (control). Actual delivered V(T) was measured by a Neonatal Bicore connected to the side port of a "bag-in-box" spirometer, making measurements independent of inspired gas properties, and was compared with V(T) delivered during ventilation with 100% oxygen. INTERVENTIONS: Five gas mixtures were evaluated: Fio(2) = 0.2, 0.4, 0.6, 0.8, and 1.0 (balance helium). MEASUREMENTS AND MAIN RESULTS: Delivered Fio(2) was less than set Fio(2) on the Servo 900C and VIP ventilators. V(T) displayed was minimally altered by helium during volume-controlled ventilation but substantially decreased during pressure-controlled ventilation, particularly with the Bird ventilators. During volume-controlled ventilation, V(T) delivered was substantially increased by helium with the Bird and, to a lesser degree, the Servo 900C ventilators. In contrast, V(T) delivered decreased slightly in helium with the Servo 300. The same pattern, but with a decreased magnitude, was observed for V(T) delivered during pressure-controlled ventilation. CONCLUSIONS: The addition of helium has a significant effect on Fio(2) delivery, displayed inspiratory V(T), and actual delivered V(T) during both volume- and pressure-controlled ventilation in four ventilators commonly used in pediatric critical care. These effects are both ventilator specific and ventilation mode specific, mandating vigilance during helium ventilation in clinical practice.
Air Pressure↗
Perfusion-diffusion compartmental models describe cerebral helium kinetics at high and low cerebral blood flows in sheep.
This study evaluated the relative importance of perfusion and diffusion mechanisms in compartmental models of blood:tissue helium exchange in the brain. Helium has different physiochemical properties from previously studied gases, and is a common diluent gas in underwater diving where decompression schedules are based on theoretical models of inert gas kinetics. Helium kinetics across the cerebrum were determined during and after 15 min of helium inhalation, at separate low and high steady states of cerebral blood flow in seven sheep under isoflurane anaesthesia. Helium concentrations in arterial and sagittal sinus venous blood were determined using gas chromatographic analysis, and sagittal sinus blood flow was monitored continuously. Parameters and model selection criteria of various perfusion-limited or perfusion-diffusion compartmental models of the brain were estimated by simultaneous fitting of the models to the sagittal sinus helium concentrations for both blood flow states. Purely perfusion-limited models fitted the data poorly. Models that allowed a diffusion-limited exchange of helium between a perfusion-limited tissue compartment and an unperfused deep compartment provided better overall fit of the data and credible parameter estimates. Fit to the data was also improved by allowing countercurrent diffusion shunt of helium between arterial and venous blood. These results suggest a role of diffusion in blood:tissue helium equilibration in brain.
Animals↗
Sonographic comparison of intraarterial CO2 and helium microbubbles for detection of hepatocellular carcinoma: preliminary observations.
PURPOSE: To evaluate the usefulness of helium gas microbubbles in the detection of small hepatocellular carcinoma (HCC) lesions relative to that of CO2 microbubbles. MATERIALS AND METHODS: Ultrasonography (US) enhanced with both CO2 microbubbles and helium microbubbles was performed in 15 patients. CO2 microbubbles were injected into the proper hepatic artery under US observation. Next, helium microbubbles were injected. Duration and degree of enhancement with the two types of microbubbles were compared. Ten minutes after helium injection, the whole liver was examined with US to detect additional tumors. When new lesions were detected, biopsy was performed. RESULTS: Duration of enhancement with the helium microbubbles (mean, 37.2 minutes) was significantly longer than that with the CO2 microbubbles (mean, 3.6 minutes; P < .001). The degree of enhancement with helium was greater than that with CO2. Thirteen additional lesions were detected after injection of helium gas. All these lesions proved to be HCC at biopsy. CONCLUSION: The duration of enhancement is significantly longer with helium than with CO2 microbubbles. Therefore, helium microbubbles can be used for examination of the whole liver for detection of additional tumors.
Carbon Dioxide↗
Pharmaceutical container/closure integrity. III: Validation of the helium leak rate method for rigid pharmaceutical containers.
Validation of a helium leak rate method for pharmaceutical container/closure integrity quality assurance required the demonstration that this physical testing method was as good or better than microbial immersion challenge testing in detecting potential integrity failures. One lot of rubber-stoppered, broth-filled glass vials also containing defective vials with known leaks were subjected to both helium leak rate and microbial challenge testing. The defective vials were prepared by affixing glass micropipettes (0.1 to 10 microns) into the vial side walls. The validation lot included a 10% seeded defect rate of which about 50% contained leaks with a predicted probability of failing a microbial challenge (> 10%). Helium tracer was placed in the test units by charging them for 4 hours under a 40 psi helium pressure. The critical leak rate after charging was determined to be 10(-7) standard cc/second, and test units with measured leak rates greater than this value were considered helium leak rate failures. Microbial immersion challenge was conducted by exposing the test units in a bath inoculated with 10(9-10) viable E. coli and B. diminuta organisms for 24 hours followed by a 13 day (35 degrees C) incubation. Microbial failures were determined visually. The helium and microbial leak test methods were compared statistically using mean failure rates. The mean helium failure rate was 6.9%, whereas the mean microbial failure rate was 2.8%. The difference between helium and microbial failure rates was significantly greater than zero. Thus, helium leak rate testing was demonstrated to be a suitable pharmaceutical container/closure integrity method for microbial quality assurance of rigid containers.
Drug Packaging↗
Electron impact ionization of haloalkanes in helium nanodroplets.
Electron impact (EI) mass spectra of a selection of C1-C3 haloalkanes in helium nanodroplets have been recorded to determine if the helium solvent can significantly reduce molecular ion fragmentation. Haloalkanes were chosen for investigation because their EI mass spectra in the gas phase show extensive ion fragmentation. There is no evidence of any major softening effect in large helium droplets ( approximately 60 000 helium atoms), but some branching ratios are altered. In particular, channels requiring C-C bond fission or concerted processes leading to the ejection of hydrogen halide molecules are suppressed by helium solvation. Rapid cooling by the helium is not sufficient to account for all the differences between the helium droplet and gas phase mass spectra. It is also suggested that the formation of a solid "snowball" of helium around the molecular ion introduces a cage effect, which enhances those fragmentation channels that require minimal disruption to the helium cage for products to escape.
Journal Article↗