Helium-oxygen Breathing Research Articles

Quantitative Study of Behavioral Disturbances in Rats Exposed to High Pressure.

When human divers or experimental animals are exposed to high pressure, they develop the High Pressure Neurological Syndrome (HPNS). Male Sprague-Dawley rats were exposed to high pressure in a conventional helium-oxygen breathing mixture to 80 bars. Pressure-induced behavioral motor disturbances including hyperlocomotor activity (HLA), tremor and myoclonia were monitored with a noninvasive piezoelectrical sensor device enabling a without discontinuity long-term analysis. New data were obtained on the development of the HPNS behavioral motor disturbances. Indeed, the present results suggest myoclonia would be more sensitive to constant high pressure exposure, while HLA and tremor would be more sensitive to increasing pressure. Moreover, myoclonia were found to occur significantly later in rats which developed epileptic seizures than in other. The present results constitute the quantitative basis of HPNS motor disturbances for future pharmacological pressure experiments.

Effect of helium-oxygen pressure on dopamine detected in vivo in the striatum of hamsters.

Free-moving hamsters chronically implanted in the striatum with carbon multifiber electrodes selective to dopamine were compressed in a helium-oxygen breathing mixture to 81 bars. Under these conditions, there was an increase in the electrochemical responses recorded from the carbon electrode by differential pulse voltammetry, which occurred during the compression and disappeared when the animals returned to the surface. This change was related to an increase in extracellular dopamine levels induced by the increase in pressure of the helium-oxygen mixture.

Density dependence of expiratory flow--a useful basis for lung function tests?

The aim of this investigation was to study the density dependence of forced expiratory flow and the ability of tests based on density dependence to disclose smoking-induced small airways dysfunction. The lung function of 212 systematically sampled men (mean age 40.3; range 30-48 years) was studied by recording flow-volume curves during air or helium-oxygen (HeOx) breathing and by the single breath N2-test. Density dependence was expressed as the percentage increase in flow from air to HeOx when 50 and when 25% of the vital capacity (VC) remained to be expelled (dMEF50 and dMEF25). The mean dMEF50 in 59 healthy non-smokers was 40% (range +7 to +72) and the mean dMEF25 24% (range -20 to +63). Density dependence apparently decreased with relative lung volume and also with increasing age. Despite the wide variation of density dependence in the reference group, dMEF50 was on average significantly reduced in smokers, and dMEF25 in ex-smokers and subjects with symptoms such as cough and/or sputum production, wheezing unrelated to common colds and dyspnea when walking on level ground. However, only 8% of the smokers exhibited 'abnormal' density dependence (dMEF25 less than (predicted value--2RSD] as compared to 11 and 33% for the forced expiratory volume in one second (FEV1) and dN2 (alveolar slope). If abnormal dN2 in the smoking group is taken to indicate smoking-induced small airway dysfunction, then the ability of dMEF50 and dMEF25 to disclose such dysfunction is limited.

Role of carotid chemoreceptors and pulmonary vagal afferents during helium-oxygen breathing in ponies.

Our purpose was to assess compensatory breathing responses to airway resistance unloading in ponies. We hypothesized that the carotid bodies and hilar nerve afferents, respectively, sense chemical and mechanical changes caused by unloading, hence carotid body-denervated (CBD) and hilar nerve-denervated ponies (HND) might demonstrate greater ventilatory responses when decreasing resistance. At rest and during treadmill exercise, resistance was transiently reduced approximately 40% in five normal, seven CBD, and five HND ponies by breathing gas of 79% He-21% O2 (He-O2). In all groups at rest, He-O2 breathing did not consistently change ventilation (VE), breathing frequency (f), tidal volume (VT), or arterial PCO2 (PaCO2) from room air-breathing levels. During treadmill exercise at 1.8 mph-5% grade in normal and HND ponies, He-O2 breathing did not change PaCO2 but at moderate (6 mph-5% grade), and heavy (8 mph-8% grade) work loads, absolute PaCO2 tended to decrease by 1 min of resistance unloading. delta PaCO2 calculated as room air minus He-O2 breathing levels at 1 min demonstrated significant changes in PaCO2 during exercise resistance unloading (P less than 0.05). No difference between normal and HND ponies was found in exercise delta PaCO2 responses (P greater than 0.10); however, in CBD ponies, the delta PaCO2 during unloading was greater at any given work load (P less than 0.05), suggesting finer regulation of PaCO2 in ponies with intact carotid bodies. During heavy exercise VE and f increased during He-O2 breathing in all three groups of ponies (P less than 0.05), although there were no significant differences between groups (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced lethality from ethanol or ethanol plus pentobarbital in mice exposed to 1 or 12 atmospheres absolute helium-oxygen.

The present experiments investigated the effects of 1 and 12 atmospheres absolute (ATA) helium-oxygen on potentially lethal doses of ethanol given alone or in combination with pentobarbital. Drug-naive, male C57BL/6J mice were injected IP with 5.4-6.5 g/kg ethanol, 4.5-6.9 g/kg ethanol plus 20 mg/kg pentobarbital, or 50-110 mg/kg pentobarbital plus 2.5 g/kg ethanol. Following injection, the mice were placed into chambers and exposed to environments of 1 ATA air, 1 ATA helium-oxygen, or 12 ATA helium-oxygen. Exposure to 1 or 12 ATA helium-oxygen significantly reduced the lethal effect (percent mortality at given doses and LD50) of ethanol given alone or with 20 mg/kg pentobarbital when compared to animals exposed to 1 ATA air. The pattern and degree of reduction in lethality for the 1 and 12 ATA helium-oxygen treatments were similar, suggesting that the antagonism resulted from increased helium or decreased nitrogen and not from increased atmospheric pressure. Exposure to these environments did not reduce lethality in mice given 2.5 g/kg ethanol in combination with relatively high doses (50-110 mg/kg) of pentobarbital. These findings suggest that helium-oxygen breathing mixtures may be useful in the treatment of some overdose patients.

Helium-Oxygen Breathing in Severe Chronic Obstructive Pulmonary Disease

The effect of breathing helium-oxygen (He-O2) mixtures was evaluated in 15 patients with severe chronic obstructive pulmonary disease (COPD). Gas exchange was assessed during quiet breathing at rest before and after 15 minutes of breathing 80 percent He-20 percent O2 mixtures in all patients. Functional residual capacity (FRC) determined during argon (Ar) washing studies fell significantly while breathing He-O2, but we did not find significant changes in minute ventilation, tidal volume, respiratory frequency, or inspiratory or expiratory timing. Eleven patients showed decreases in arterial PCO2 and CO2 excretion during resting breathing on He-O2. Expiratory flows were increased at a given lung volume during He-O2 breathing as expected. Apparently, mechanical work of breathing was decreased in patients with severe COPD while breathing He-O2, leading to a reduction in VCO2 and improvement in overall alveolar ventilation. These findings lend support to the therapeutic use of He-O2 under some conditions in patients with severe COPD.

Lung function of sheet metal workers exposed to fiber glass.

Out of 532 registered and contacted sheet metal workers, 251 responded, but only seven pairs were acceptable for the present study due to the following requirement: no history of smoking, pleural plaques or asbestos exposure. Seven of these workers were exposed daily to fiber glass, and seven were almost never exposed. In a second step nine additional exposed workers were included. Ordinary spirometry, lung volumes, closing volumes and the slope of the alveolar plateau, the maximum expiratory flow in air and after helium-oxygen breathing, and the elastic recoil pressures were measured. No evidence of small airway dysfunction or restrictive or obstructive ventilatory impairment was found, but the elastic recoil pressures of the exposed group were slightly increased. Fiber glass can conceivably cause a corresponding faint and probably harmless fibrous reaction in the lung parenchyma.

Metabolic and cardiorespiratory responses to He-O2 breathing during exercise.

ARTICLESMetabolic and cardiorespiratory responses to He-O2 breathing during exerciseA. G. Brice, and H. G. WelchA. G. Brice, and H. G. WelchPublished Online:01 Feb 1983https://doi.org/10.1152/jappl.1983.54.2.387MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByHeliox breathing equally influences respiratory mechanics and cycling performance in trained males and femalesSabrina S. Wilkie, Paolo B. Dominelli, Benjamin C. Sporer, Michael S. Koehle, and A. William Sheel1 February 2015 | Journal of Applied Physiology, Vol. 118, No. 3Physiological responses of a rodent to heliox reveal constancy of evaporative water loss under perturbing environmental conditionsChristine Elizabeth Cooper, and Philip Carew Withers15 October 2014 | American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, Vol. 307, No. 8Metabolic and Ventilatory Acclimatization to Cold Stress in House Sparrows ( Passer domesticus )Physiological and Biochemical Zoology, Vol. 78, No. 4Effect of heliox on lung dynamic hyperinflation, dyspnea, and exercise endurance capacity in COPD patientsPaolo Palange, Gabriele Valli, Paolo Onorati, Rosa Antonucci, Patrizia Paoletti, Alessia Rosato, Felice Manfredi, and Pietro Serra1 November 2004 | Journal of Applied Physiology, Vol. 97, No. 5Ventilatory response to exercise in aged runners breathing He-O2 or inspired CO2T. G. Babb, Darren S. DeLorey, and Brenda L. Wyrick1 February 2003 | Journal of Applied Physiology, Vol. 94, No. 2Hyperventilation with He–O2 breathing is not decreased by superimposed external resistanceRespiratory Physiology & Neurobiology, Vol. 133, No. 1-2Effects of Training With Heliox and Noninvasive Positive Pressure Ventilation on Exercise Ability in Patients With Severe COPDChest, Vol. 122, No. 2Effects of Helium/Oxygen and Temperature on Aerobic Metabolism in the Marsupial Sugar Glider, Petaurus brevicepsPhysiological and Biochemical Zoology, Vol. 74, No. 2Smaller lungs in women affect exercise hyperpneaSteven R. McClaran, Craig A. Harms, David F. Pegelow, and Jerome A. Dempsey1 June 1998 | Journal of Applied Physiology, Vol. 84, No. 6The Effects of Breathing He-O 2 Mixtures on Maximal Oxygen Consumption in Normoxic and Hypoxic Men30 September 2004 | The Journal of Physiology, Vol. 503, No. 1Ventilatory response to helium-oxygen breathing during exercise: effect of airway anesthesiaBharath S. Krishnan, Ron E. Clemens, Trevor A. Zintel, Martin J. Stockwell, and Charles G. Gallagher1 July 1997 | Journal of Applied Physiology, Vol. 83, No. 1The effect of He?O2 exposure on metabolic rate, thermoregulation and thermal conductance during normothermia and daily torporJournal of Comparative Physiology B, Vol. 166, No. 3Ventilatory Accommodation of Changing Oxygen Consumption in Dasyurid MarsupialsPhysiological Zoology, Vol. 67, No. 2The pattern of respiration with increasing metabolism in a small dasyurid marsupialRespiration Physiology, Vol. 93, No. 3Ventilatory accommodation of changing oxygen demand in sciurid rodentsJournal of Comparative Physiology B, Vol. 162, No. 8The Summit Metabolism of the Short-Tailed Shrew Blarina brevicauda: A High Summit Is Further Elevated by Cold AcclimationPhysiological Zoology, Vol. 60, No. 6 More from this issue > Volume 54Issue 2February 1983Pages 387-392 Copyright & PermissionsCopyright © 1983 the American Physiological Societyhttps://doi.org/10.1152/jappl.1983.54.2.387PubMed6833035History Published online 1 February 1983 Published in print 1 February 1983 Metrics

Assessment of Density Dependent Flow-Volume Parameters in Nonsmokers and Smokers: Measurement with Spirometry, Body Plethysmography and Respiratory Inductive Plethysmography

The purpose of this investigation was to assess the density-dependent flow-volume components of the forced vital capacity using simultaneous spirometry, respiratory inductive plethysmography, and body plethysmography in the detection of small airway disease. The forced vital capacity was measured during air, helium-oxygen and sulfur-hexafluoride breathing to provide a range of gas density influences. Combining flow measured at the mouth with volume referenced to change in alveolar gas volume as measured by body or respiratory inductive plethysmography during helium-oxygen breathing accentuated the differences between nonsmokers and smokers because of the variable degree of alveolar gas compression occurring over the second half of FVC. The volume of isoflow obtained when comparing the helium and oxygen mixture to air also effectively separated nonsmokers from smokers. The utilization of the high density gas mixture, sulfur hexafluoride-oxygen during the FVC maneuver did not provide useful diagnostic information. Therefore, density-dependent flow-volume information using helium as a test gas alone or compared to air with a variety of analyses is a good approach to detection of early lung disease in smokers.

Relationship between sites of airflow limitation and severity of chronic airflow obstruction.

We studied the relationship between sites of airflow limitation and severity of chronic obstructive pulmonary disease. Pre- and postbronchodilator physiologic testing was performed in 30 subjects with chronic airflow obstruction (CAO). Pulmonary function, including the increase in maximal expiratory flow at 50% of vital capacity after helium-oxygen breathing (delta VEmax50), was reduced before and after inhalation of 1.3 mu mg of metaproterenol. Significant correlations were present between values for delta VEmax50 and measurements of expiratory flow (p < 0.001). In subjects with severe CAO (one-second forced expiratory volume less than or equal to 1.2 L; percentage ratio of one-second forced expiratory volume to forced vital capacity < 50%), delta VEmax50 was always abnormally decreased. An inverse relationship was present between initial delta VEmax50 and changes in delta VEmax50 after inhalation of metaproterenol (p < 0.001). These results suggest that the site of airflow limitation becomes progressively more peripheral as CAO worsens, and that severe CAO is usually associated with peripheral sites of airflow limitation.

Sodium cromoglycate and ipratropium bromide in exercise-induced asthma.

In thirteen patients with extrinsic asthma the effects of placebo, sodium cromoglycate, ipratropium bromide, and ipratropium bromide plus sodium cromoglycate were studied in a random double-blind fashion to assess their inhibitory action in exercise-induced asthma (EIA). Exercise testing consisted of steady state running on an inclined treadmill for up to eight minutes. In eight of the 13 patients studied the baseline ratio of expiratory flow at 50% vital capacity (VC) breathing helium-oxygen (V50He) to V50air was over 1.20 and they were called responders; the remaining five patients were called non-responders. There was a significantly lower baseline maximum mid-expiratory flow rate (MMEF) in non-responders (P less than 0.02) as compared to responders but no difference in forced expiratory volume in one second (FEV1) or forced vital capacity (FVC). Sodium cromoglycate (P less than 0.02), ipratropium bromide (P less than 0.01), and ipratropium bromide plus spdium cromoglycate (P less than 0.01) all significantly inhibited the percentage fall in FEV1 after exercise in the responders. Ipratropium bromide had no preventive action on non-responders, unlike sodium cromoglycate (P less than 0.05) and ipratropium bromide plus sodium cromoglycate (P less than 0.02). It is postulated that mediator release is an important factor in development of EIA in most extrinsic asthmatics, whereas cholinergic mechanisms are relevant only in those patients in whom the main site of airflow obstruction is in the large central airways.

Effect of breathing helium-oxygen on static lung volumes and lung recoil in normal man.

Static lung volumes and static elastic recoil pressure (Pel) were measured in normal subjects breathing air and 80% helium plus 20% oxygen (He+O2). In 22 subjects, He+O2 produced small but significant increases in total lung capacity (TLC) (mean 0.11 liter, P less than 0.001) and residual volume (mean 0.10 liter, P less than 0.01) without change in vital capacity or functional residual capacity. The mechanisms for this change are obscure. In 10 subjects, breathing He+O2 had no significant effect on Pel (paired t-test) at any lung volume measured (50-80% TLC). In one subject, Pel at 70 and 80% TLC was significantly higher on air than on He+O2 (unpaired t-test, P less than 0.05). Because changes in lung volumes and lung recoil were small, we concluded that these effects do not negate the clinical utility of He+O2 flow-volume curves.

The lung following repair of congenital diaphragmatic hernia

To determine the effects of the pulmonary hypoplasia present at birth in infants with congenital diaphragmatic hernia upon subsequent development of the lung, 19 patients who had undergone surgical repair before the age of one year were studied at ages 6 to 18 years. Total lung capacity and vital capacity averaged 99% of predicted value. Diffusing capacity for carbon monoxide was normal. Forced expiratory volume in one second averaged 89% of predicted value and 80% of vital capacity. Total respiratory system conductance and maximum expiratory flow volume curves obtained during air and helium-oxygen breathing were normal. Xenon 133 radiospirometry performed in nine patients revealed equal distribution of lung volumes on the two sides. Ventilation to the hernia side was reduced in only two patients. Blood flow to the hernia side was reduced in all nine patients. Chest radiographs supported the physiologic observations. These findings are consistent with the persistence of a reduction in the number of branches or generations of pulmonary arteries and bronchi on the side of the hernia. Since a substantial part of the vascular resistance resides in peripheral vessels, this developmental abnormality influences the distribution of pulmonary blood flow, although it has little effect on tests reflecting airway resistance or the distribution of ventilation.

The Volume of Isoflow and Increase in Maximal Flow at 50 Percent of Forced Vital Capacity during Helium-Oxygen Breathing as Tests of Small Airway Dysfunction

The purpose of this report is to review the role of helium in the early detection of obstructive pulmonary disease. The underlying physiologic mechanisms of the volume of isoflow (the volume at which flow was the same with the subject breathing air and breathing a mixture of 80 percent helium and 20 percent oxygen) and increases in maximal flow at 50 percent of vital capacity (Vmax50) after breathing helium are reviewed. These tests are able to detect physiologic abnormalities in asymptomatic subjects when the results of other tests are normal; and following cessation of smoking, abnormal results may be reversible. The volume of isoflow is increased when maximal flow is reduced because of loss of elastic recoil or increase in upstream resistance. The increase in Vmax50 after breathing helium appears to be relatively specific for the caliber of the small airways, being uninfluenced by loss of elastic recoil; it can further help to localize the major site of obstruction to either small or large airways. At present, random screening for early unsuspected disease is not warranted, and these tests remain an investigative tool.

Helium depression of cholinergic sensitivity in the cat superior cervical ganglion tissue

The sensitivity of the superior cervical ganglion (SCG) tissue in the cat to activation by infusion of its normal cholinergic agonist acetylcholine (ACh +) has been compared for animal preparations breathing normal air and those breathing helium-oxygen ( 80% 20% ) at 1 atm. The ganglionic response to infusion of a 1.0 × 10 −3 m bolus of ACh + solution delivered intra-arterially to SCG tissue is approximately 15% less in HeO 2 breathing atmospheres than in N 2O 2. The response decay curves with increasing exposure time for the cat preparation in either breathing atmosphere are linear, and yield net decreases of 10–15% of control amplitudes over the course of 2 hr. The observed effect of 0.80 atm of He, relative to N 2, in partial desensitization of cholinergic response at the SCG, is discussed in terms of possible mechanisms of interaction of He with tissue receptor components.

Effects upon the EEG of psychometric performance during deep dives in helium—Oxygen atmosphere

A study of EEG modifications and psychometric performances was performed during two dives in hyperbaric chambers with a helium—oxygen breathing mixture (pO 2 maintained at 0.4 ATA). The depths attained were 500 m for the first experiment (Sagittaire II) and 610 m for the second (Physalie VI). Four subjects were studied. EEG modifications that could be considered as high pressure nervous syndrome began at 300 m. They were characterized by an increase of slow activity (particularly theta), depression of fast activity and transformation of the waking EEG into one resembling that of stage I sleep. The psychometric tests revealed a diminution of sensorimotor performance in all subjects (10–20%). Performance in intellectual tests varied according to subject and experiment, and did not fall more than 15% below normal values. An increase in theta activity was observed in the anterior regions while the subjects performed certain psychometric tests (number ordination; symbol recognition double word; digital dexterity). This increase, which could reach 700% of the values recorded during periods of rest preceding or following the tests, appeared at 350 m and deeper. These modifications could be due either to deficits in cerebral oxygenation, to perturbed cerebral blood flow, or to alterations in energetic or metabolic processes caused by hyperbaric conditions. These alterations appeared during repetitive tasks which necessitated constant effort and attention.

Maximal expiratory flow and lung volume changes associated with exercise-induced asthma in children and the effect of breathing a low-density gas mixture.

1. Lung volumes and maximum expiratory flow volume (MEFV) curves were measured before and after exercise and after a bronchodilator in eight asthmatic children. 2. Exercise produced significant changes in all volumes and flow rates measured, but the most sensitive measurement was of flow rate at an absolute volume in the terminal portion of the forced vital capacity. Of the more simply obtained measurements maximal flow at 50% of the exhaled vital capacity was the most sensitive, but reductions in forced expiratory volume at 1 s and peak flow rate were almost as marked. 3. The marked reductions in flow rates at low lung volumes after exercise were accompanied by large increases in residual volume and a reduction in the slope of the MEFV curve. These changes suggest functional closure of some lung units and an increase in the time-constant of emptying of other units. 4. The response of flow to breathing helium—oxygen (79:21, v/v) was assessed in the dilated state (before exercise or after bronchodilator) and the constricted state (after exercise) in five of the subjects. 5. An increase in density-dependence of flow rates at all lung volumes during constriction is evidence that, despite the reduction in flow rates, convective acceleration and turbulent flow constitute a greater proportion of the total upstream resistance after exercise than before exercise. The implication is that the cross-sectional area at equal pressure points (EPP) is smaller after exercise than before exercise. This could result from either bronchoconstriction with no change in the location of EPP, or from progression of the EPP further upstream to a region where loss of airways or reduction in their diameter has rendered the total cross-sectional area considerably smaller than under normal circumstances.

Helium speech unscramblers--A critical review of the state of the art

The development of saturation diving has enabled man to work in the sea at great depths and for long periods of time. This advance has resulted, in part, as a consequence of the substitution of helium for nitrogen in breathing gas mixtures. However, the utilization of HeO 2 breathing mixtures at high ambient pressures has caused problems in speech communication; in turn, electronic aids have been developed to improve diver communication. These helium speech unscramblers attempt to process variously the grossly unintelligible speech resulting from the effects of helium-oxygen breathing mixtures and ambient pressure, and to reconstruct such signals in order to provide adequate voice communication. This paper presents a discussion of the effects of HeO 2 /P on speech and then describes some of the techniques used to unscramble the distorted speech. Included among the techniques are: 1) frequency subtraction; 2) tape recorder playback; 3) vocoder approaches; 4) digital coding; and 5) convolution processing. In addition, a generalized evaluation of these approaches is included.

Respiratory gas exchange in exercise during helium-oxygen breathing.

Abstract : Six subjects were exercised on a treadmill while breathing air or 21% oxygen in helium through a low-resistance valve. Ventilation, O2 uptake, and CO2 output during He-O2 breathing were compared with values for air breathing at each workload. (Author)

Body temperature and metabolism in hyperbaric helium atmospheres.

ArticleBody temperature and metabolism in hyperbaric helium atmospheres.L W Raymond, W H Bell 2nd, K R Bondi, and C R LindbergL W Raymond, W H Bell 2nd, K R Bondi, and C R LindbergPublished Online:01 May 1968https://doi.org/10.1152/jappl.1968.24.5.678MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByModel of thermal comfort in the hyperbaric facilityPolish Maritime Research, Vol. 18, No. 1Mixed‐gas Saturation Diving1 January 2011Effect of high pressure on metabolic response to cold in ratsActa Physiologica Scandinavica, Vol. 135, No. 3Convective Heat Loss from a Horizontal Cylinder in Different Hyperbaric Environments1 December 2016 | Engineering in Medicine, Vol. 5, No. 3Man in the Ocean Environment: Physiological FactorsDiffusion in the gas phase: The effects of ambient pressure and gas compositionRespiration Physiology, Vol. 25, No. 3TREATMENT OF MULTIPLE SCLEROSIS WITH ANTI-LYMPHOCYTE GLOBULINThe Lancet, Vol. 305, No. 7910TEMPERATURE REGULATION IN HELIUM-OXYGEN ATMOSPHERESThe Lancet, Vol. 305, No. 7910The effect of helium-oxygen mixtures on body temperatureJournal of Pediatric Surgery, Vol. 9, No. 5Thermal Balance in Divers5 December 2011 | Proceedings of the Royal Society of Edinburgh. Section B. Biology, Vol. 73RESPIRATORY AND CARDIAC RESPONSES TO EXERCISE IN SUBJECTS BREATHING HELIUM–OXYGEN MIXTURES AT PRESSURES FROM SEA LEVEL TO 19.2 ATMOSPHERESARTERIAL BLOOD GASES, HEART RATE, AND GAS EXCHANGE DURING REST AND EXERCISE IN MEN SATURATED AT A SIMULATED SEAWATER DEPTH OF 1000 FEET More from this issue > Volume 24Issue 5May 1968Pages 678-84 https://doi.org/10.1152/jappl.1968.24.5.678PubMed5647646History Published online 1 May 1968 Published in print 1 May 1968 Metrics