Continuous Oxygen Flow Research Articles

Vanadium Chloroperoxidase as a Catalyst for Hydrogen Peroxide Disproportionation to Singlet Oxygen in Mildly Acidic Aqueous Environment

AbstractChemiluminescence studies show that the enzyme vanadium chloroperoxidase from the fungus Curvularia inaequalis is a highly efficient catalyst for the production of singlet oxygen from hydrogen peroxide in a mildly acidic aqueous environment, with a maximum turnover frequency of 100 s−1 with respect to H2O2 consumption. The enzyme studied here can be regarded as a supplementary catalyst to inorganic molybdate, which operates in basic aqueous media. The enzyme system is 103 – 104 times faster than the molybdate system when compared at their optimal pH. The enzyme is very stable against singlet oxygen, in contrast to heme‐containing peroxidases which, due to inactivation by singlet oxygen, only produce a short burst, presumably by oxidation of the labile cofactor. The vanadium chloroperoxidase was compared with vanadium bromoperoxidase from the seaweed Ascophyllum nodosum and was found to be even more stable; it is stable towards a continuous flow of singlet oxygen for at least 1 hour and also it is not inactivated by 500 mM H2O2. An important difference with vanadium bromoperoxidase is that the vanadium chloroperoxidase is able to effectively use chloride as a cocatalyst (20 s−1) instead of bromide. This offers an important advantage from an application point of view; using chloride, no side products are observed when the chemical trap anthracene‐9,10‐bis(ethanesulphonate) is fully converted by singlet oxygen into its corresponding endoperoxide. By contrast, when bromide is used, 20% side product is formed. During the conversion the enzyme remains fully stable for 25,000 turnovers.

Effektivität von Sauerstoff-Demand-Systemen bei Patienten mit chronisch obstruktiver Atemwegserkrankung

To maintain mobility in patients with chronic hypoxemia who are under long-term oxygen therapy, portable oxygen systems are available. They have the disadvantage of a short range. To prolong the range and to reduce the cost of oxygen treatment, demand oxygen delivery systems (DODS) are used. Aim of the study was to compare three DODS (DOC-2000 [D], TransTracheal Inc.; Oxytron [O], Weinmann; Pulsair [P], DeVilbiss, Sunrise Medical) with continuous oxygen delivery. 17 patients (age 67.82 +/- 9.46 years; FEV1 1.23 +/- 0.69 l; PaO2 48.8 +/- 6.7 mm Hg) were studied. The continuous flow oxygen (CONT) and the DODS were applied to the patients for 30 minutes each in random sequence with an airflow of 2 l/min. After 15 and 30 minutes arterial blood gas analysis was done. Oxygen saturation was recorded continuously by pulseoximetry. After 15 minutes no significant differences in PaO2 were found between CONT and DODS. After 30 minutes no significant difference in PaO2 was found in CONT as compared to P. Significant lower PaO2 values were found for O and D as compared to CONT (p < 0.01). With P the range of a portable oxygen source was increased by 161.5 percent, with O by 172 percent, with D the range was increased by only 17.2 percent. Prolongation of range of a portable oxygen source can be achieved by means of DODS without a decrease of PaO2 and thus without loss of quality of the oxygen treatment. However, there are differences in efficacy between the DODS.

Effect of oxygen on emulsion polymerisation kinetics: a study by reaction calorimetry

The influence of oxygen on the kinetics of chemically initiated seeded emulsion homopolymerisation of styrene and the seeded emulsion copolymerisation of styrene/butyl acrylate was investigated by reaction calorimetry. A decrease of the inhibition period and an increase of the polymerisation rate have been observed when the system is purged with nitrogen. It has also been seen that oxygen has a great influence on the polymerisation kinetics. producing not only inhibition, but also decreasing the reaction rate. An increase of the dependence of the average number of radicals per particle with the initiator concentration with respect to theoretical predictions was observed in the presence of oxygen. The overall experimental results show that, after an inhibition period, there is a continuous flow of oxygen from the gas phase, which causes the retardation of the polymerisation rate.

Flame-spreading Process over Thin Aluminum Sheets in Oxygen-enriched Environments

An experimental study of flame-spreading process over thin aluminum (99 % Al and 1 % Mn( sheets was investigated in oxygen-enriched environments. The objective of this study was to determine the dependency of flame-spreading rate over aluminum sheets as a function of initial chamber pressure, sample thickness, oxygen purity, oxygen flow condition, and sample orientation. The reaction mechanism of aluminum in oxygen was also studied by examining the recovered partially-burned sample using a scanning electron microscope (SEM( coupled with an energy dispersive spectrometer (EDS(. The flame-spreading rate over aluminum sheets was measured by an array of fast-response lead-selenide (Pb-Se( IR photodetectors. The initial chamber pressure was varied from 0.1 to 6.3MPa. Two grades of oxygen gas were used with purities of 99.996 % and 99.75 %. In terms of the effect of pressure on the flame-spreading rate, as the initial chamber pressure was increased, the flame-spreading rate was found to increase to a maximum, decrease to a minimum, and then increase again. Based upon the comparison of flame-spreading rates in horizontal, upward, and downward orientation, the flame-spreading process over aluminum sheets was found to be dominated by the solid-phase heat conduction mechanism. The continuous oxygen flow showed a strong influence on the flame-spreading behavior, and it was demonstrated that the flame can be blown off when the counter-current flow velocity exceeds a critical value. The flame-spreading rates under high-purity (∼ 99.996 %( oxygen environments were found to be significantly greater than those in commercial grade (∼ 99.75%( oxygen. In addition, the oxygen content in the while ceramic-type nodules formed on the burned edge of the recovered partially-burned sample is much higher than that on the unbumed surface. These imply that there exist heterogeneous reactions between aluminum and either oxygen or gaseous aluminum sub-oxides on the burning surface.

Partial oxidation of methane to synthesis gas over rhodium catalysts

The partial oxidation of methane to synthesis gas has been studied using the temporal-analysis-of-product (TAP) set-up on different Rh catalysts. Rh sponge diluted with either SiC or α-Al 2O 3, and 0.3 wt% Rh/α-Al 2O 3 were investigated using pulses and continuous flow of methane and oxygen. The effect of introducing a support in the catalyst system was given special concern. Blank experiments on the α-Al 2O 3 support showed no activity for the partial oxidation of methane in the 673–1123 K range. Oxygen multipulse experiments on the 0.3 wt% Rh/α-Al 2O 3 and on the pure support showed that α-Al 2O 3 is not inert concerning adsorption, desorption and storage of oxygen. Totally oxidized catalysts show low activity because of few sites for methane dissociation. Mainly, total oxidation products CO 2 and H 2O are formed. The formation of these products partially reduces the catalyst whereupon with time-on-stream a steep discontinuity is observed in the methane and oxygen conversion as reduced metal sites largely increase the rate of methane dissociation. The discontinuity is followed by a continuous change in the product distribution from CO 2 and H 2O towards CO and H 2. The time-on-stream, before an active catalyst was obtained, increased with increasing amount of oxygen in the feed. The time before obtaining an active catalyst also depended on the catalyst system and changed in the following way: Rh sponge mixed with SiC<Rh sponge mixed with α-Al 2O 3<Rh/α-Al 2O 3. The latter indicates a spillover effect of oxygen from the support to the metal which also affects the steady-state methane conversion and syngas selectivity. The CO, CO 2 and H 2O pulse responses shifted to shorter times with increasing amount of oxygen in the feed, while H 2 showed the opposite effect. This indicates a faster formation of the products containing oxygen but sorption effects may not be excluded. Removal of surface oxygen by methane pulsing led to oxygen migration from the Rh bulk resupplying the surface. When the catalyst is at steady state, CO and H 2 are formed as primary products on a Rh sponge mixed with SiC. Experiments on Rh sponge mixed with α-Al 2O 3 or a Rh/α-Al 2O 3 showed the same product sequence and unless sorption effects disguise the real primary product formation the sequence is not altered by the support. It is believed that the formation of primary products depends on the amount of oxygen available on the surface.

Oxygen enrichment of entrained room air during Venturi jet ventilation of children undergoing bronchoscopy.

Intermittent oxygen jet ventilation at an inspiratory:expiratory ratio of 1:3 was used to ventilate 15 children undergoing rigid Storz bronchoscopy for removal of inhaled foreign body. Oxygenation of the patient was continuously monitored by pulse oximetry. In all children SpO2 was above 95% when the bronchoscope was above the carina. When the bronchoscope was introduced into one of the bronchi, SpO2 decreased to 70-85% in five children. Delivery of a continuous flow of oxygen via a T-piece attached to the side-arm of the bronchoscope increased the SpO2 > 95% in the five children. Oxygen jet ventilation during bronchoscopy is based on the Venturi principle; the oxygen jet will entrain room air from the side arm of the bronchoscope which functions as an entrainment orifice. This will decrease the FIO2. The FIO2 can be increased by flowing oxygen continuously via the T-piece attached to the side arm of the bronchoscope.

The Efficacy of Nebulized Budesonide in Dexamethasone-treated Outpatients With Croup

To determine the added clinical benefit of nebulized budesonide in children with mild to moderate croup treated with 0.6 mg/kg oral dexamethasone. Randomized, double-blind, placebo-controlled trial. Emergency department of a tertiary-care pediatric hospital with 47,000 visits per year. Children 3 months to 5 years of age with a syndrome consisting of hoarseness, inspiratory stridor, and barking cough and a croup score of 3 or greater after at least 15 minutes of mist therapy. Patients were excluded from the study if they had diagnoses of epiglottitis, chronic upper or lower airway disease (not including asthma), or severe croup or had received corticosteroids within the preceding 2 weeks. All patients received 0.6 mg/kg oral dexamethasone and were randomly assigned to receive 4 mL (2 mg) of budesonide solution (n=25) or 4 mL of 0.9% saline solution (n=25) by updraft nebulizer with a continuous flow of oxygen at 5 to 6 L/min. The primary outcome measure was the proportion of patients in each group who had clinically important changes (two points) in the croup score during the 4 hours after treatment. Eighty-four percent (n=21) of the patients who received budesonide had clinically important responses, compared with 56% (n=14) in the placebo group. The number of patients who would need to be treated with nebulized budesonide for one patient to have a clinically important response is four patients. Despite receiving simultaneous oral dexamethasone, pediatric outpatients with mild to moderate croup have added, clinically important improvement in respiratory symptoms after treatment with budesonide.

Modifications hémodynamiques induites par le test d'apnée chez le patient en état de mort cérébrale

Objective In France, an apnoea test is compulsory to confirm brain death. This test results in a major hypercarbia and respiratory acidosis. This study aimed to assess haemodynamic changes elicited by the apnoea test. Study design Prospective clinical study. Patients Fifteen patients with brain death. Methods Before the apnoea test, the lungs were ventilated with pure oxygen for 20 minutes. Thereafter, the test was conducted with continuous oxygen flow through the endotracheal tube, and SpO 2 monitoring. Blood gases and haemodynamic parameters, including systemic arterial pressure, pulmonary artery pressure, pulmonary artery occlusion pressure, cardiac index and right ventricular function parameters were assessed before, during and 20 minutes after the apnoea test. Mean values at the various times were compared. Results Hypercarbia and acidosis induced a major pulmonary hypertension and an increase in cardiac output, associated with a decrease in systemic vascular resistances. Despite pulmonary hypertension and acidosis, right ventricular function was maintained. All haemodynamic modifications were reversed by reventilation. Conclusion Apnoea test induces a reversible pulmonary hypertension

Is Tracheal Gas Insufflation an Alternative to Extrapulmonary Gas Exchangers in Severe ARDS?

Tracheal gas insufflation (TGI) of pure oxygen combined with mechanical ventilation decreases dead space and increases CO2 clearance. In the present study, TGI was used in six patients with ARDS who met extracorporeal membrane oxygenation criteria and who were severely hypoxemic and hypercapnic despite optimal pressure-controlled ventilation. This open clinical study aimed to investigate the effects of 4 L/min continuous flow of oxygen given via an intratracheal catheter. PaCO2 decreased from 108 +/- 32 to 84 +/- 26 mm Hg (p < 0.05), and no significant change in PaO2 (68 +/- 18 vs 96 +/- 43, p = 0.06). There was no change in airway pressures and hemodynamic variables. A slight increase in end-expiratory and end-inspiratory volumes with TGI possibly occurred, as seen on tracings from respiratory inductive plethysmography (Respitrace). We conclude that TGI improves tolerance of limited pressure ventilation by removing CO2, but it may induce changes in lung volumes that are not detected by ventilator measurements.

A Hazard of an Anesthesia Delivery System in a Developing Country

A Hazard of an Anesthesia Delivery System in a Developing Country

Comparison of Six Oxygen Delivery Systems for COPD Patients at Rest and during Exercise

Five different oxygen-conserving devices were tested in each of ten oxygen-dependent patients with COPD who had met the NOTT criteria for continuous oxygen use. They were tested on room air, their prescribed continuous oxygen flow and then on each of the five devices. The devices which delivered a bolus of oxygen during early inspiration or increased oxygen delivery as the respiratory rate increased did better than those devices which delivered oxygen at a normal flow rate during inspiration or a fixed portion of inspiration. In at least one of the subjects each device was associated with desaturation to less than 80 percent during a 12-min walk. It is concluded that oxygen-conserving devices vary in their ability to maintain SaO2 levels during exercise. It is recommended that a home oxygen evaluation include measurement of an exercise SaO2 utilizing the prescribed oxygen delivery system.

Transtracheal Oxygen, Nasal CPAP and Nasal Oxygen in Five Patients with Obstructive Sleep Apnea

The effect of transtracheal oxygen administration by means of a 9-French (2.7 mm) percutaneous catheter was assessed in five patients with severe obstructive sleep apnea. We hypothesized that the delivery of oxygen below the site of airway obstruction should reduce the arterial oxygen desaturation during apneas and hypopneas, thereby increasing respiratory stability. Standard sleep and respiratory measurements were recorded in these subjects with all-night polysomnography on nonconsecutive nights during four experimental conditions: room air (BL), nasal continuous positive airway pressure (CPAP), nasal O2 (NC O2), and transtracheal O2 (TT O2). In three of these subjects, room air was infused (TT RA) at flow rates comparable to TT O2. Compared with baseline room air measurements, TT O2 not only significantly increased the SaO2 nadir from 70.4 percent to 89.7 percent (p less than 0.01), but it also reduced the frequency of sleep apnea/hypopnea from 64.6 to 26.2/h sleep (p less than 0.01). NC O2 ameliorated desaturation during apnea/hypopnea (mean SaO2 nadir, 86.2 percent; p less than .01) but did not significantly alter frequency (59.0/h sleep). Nasal CPAP was the most effective means of reducing sleep apnea/hypopnea (13.8/h sleep) but did not abolish desaturations when apneas occurred (mean SaO2 nadir, 80.0 percent). Compared with oxygen, transtracheal infusion of room air appeared to be somewhat effective; however, the small number of studies with TT RA precluded statistical analysis. We believe that TT O2 is superior to NC O2 for some patients with obstructive sleep apnea because continuous oxygen flow below the site of airway obstruction more reliably prevents alveolar hypoxia and respiration is stabilized. Infusion of air or oxygen through the tracheal catheter flow may also increase mean airway pressure and reduce obstructive apnea similar to nasal CPAP. We conclude that TT O2 may be an effective alternative mode of therapy for some patients with severe sleep apnea/hypopnea when nasal CPAP is not tolerated or when combined oxygen and nasal CPAP are required.

Oxygenation and Ventilation during Cardiopulmonary Resuscitation Utilizing Continuous Oxygen Delivery via a Modified Pharyngeal-Tracheal Lumened Airway

Use of continuous transtracheal oxygen delivery systems combined with rhythmic chest compressions can provide excellent oxygenation and ventilation during cardiopulmonary resuscitation. However, occasional displacement of the transtracheal catheter results in life-threatening pneumomediastinal complications. We investigated using the pharyngeal lumen of a pharyngeal-tracheal lumened airway (PtL) as an alternative delivery system for continuous oxygen flow in 21 large mongrel dogs. Excellent ventilation was possible in anesthetized, apneic, and paralyzed dogs in normal sinus rhythm from the "bellows" effect of chest compressions. The hypercapnia and respiratory acidemia resulting from 5 min of complete apnea in ten dogs during normal sinus rhythm was readily corrected (p less than 0.01). In an additional 11 dogs, external chest compressions were performed and oxygen was delivered continuously via the PtL during 20 min of ventricular fibrillation. During this period of cardiac arrest, pH declined (7.38 +/- 0.01 vs 7.19 +/- 0.02; p less than 0.01), but PaCO2 (35 +/- 1 vs 38 +/- 3 mm Hg) and PaO2 (67 +/- 2 vs 68 +/- 3 mm Hg) were not significantly different from prearrest values. Successful resuscitation was achieved in 8 of 11 (73 percent) animals, which is similar to the results in historical controls with endotracheal intubation. No pneumomediastinal complications were seen with use of the PtL. We conclude that using the pharyngeal lumen of the PtL for continuous delivery of oxygen combined with external chest compressions can provide a safe and effective mode of oxygenation and ventilation during cardiac arrest.

A combustion method for the simultaneous determination of 3H, 14C, and 35S in triply labeled organic samples by liquid scintillation counting

The organic samples triply labeled with 3H, 14C, and 35S were combusted in a flow-type combustion flask under a continuous oxygen flow. The oxygen gas containing the combustion products, which were mainly 3H 2O, 14CO 2, and 35SO 2, was introduced into successive 0.5 m H 2O 2 and Oxisorb (2-methoxyethylamine). The 35SO 2 and 3H 2O that had been partially adsorbed onto the inner wall of the combustion flask were recovered by rinsing the wall with an H 2O 2 solution. 3H and 35S were quantitatively recovered from the H 2O 2 solutions. 14C was not found in the H 2O 2 solutions and was recovered from Oxisorb quantitatively. The amounts of 3H, 35S, and 14C were determined by measuring the radioactivity of the H 2O 2 solutions and of Oxisorb with a liquid scintillation counter. Thus the separate determination of 14C and 35S in a sample was achieved. Through this combustion method, the materials including fresh animal tissues up to ca. 300 mg were conveniently combusted with quantitative recovery of 3H, 14C, and 35S.

Preliminary Findings in the Treatment of Obstructive Sleep Apnea with Transtracheal Oxygen

The effects of continuous low flow oxygen via transtracheal oxygen delivery (TTOD) were assessed in four patients with obstructive sleep apnea (OSA) and daytime hypersomnolence who were unable to tolerate continuous positive nasal airway pressure (CPAP). The overall quality of sleep, sleep fragmentation, pattern of respiration, and nocturnal oxygen saturations were evaluated with the patients receiving 2 to 3 L/min of oxygen by TTOD, and the results were compared to polysomnograms with and without nasal cannula oxygen. The mean respiratory disturbance index (apneas plus hypopneas/hour of sleep) was improved by TTOD compared to no therapy or nasal cannula oxygen, and improvement in sleep disturbance was associated with improvement in overall nocturnal oxygen saturation. The mean apnea duration was not increased by TTOD and the duration of the longest apneic spells was decreased by 33 to 85% with this therapy. These improvements in respiratory status were accompanied by symptomatic improvement in daytime sleepiness, and there were no significant side effects. These findings suggest that TTOD may be a safe and effective alternative treatment of OSA for some patients who are unable to tolerate nasal CPAP therapy.

Clinical Efficacy and Cost Benefit of Pulse Flow Oxygen in Hospitalized Patients

Pulse flow oxygen administered during early inspiration is a promising approach to oxygen conservation. Previous short-term studies show equivalent arterial PO2, 55 to 60 percent oxygen savings, and no reduction of nasal humidity when compared with continuous flow nasal cannula oxygen. This study compares the clinical efficacy of pulse flow and continuous flow oxygen in 100 patients recently hospitalized for diseases requiring O2 therapy. In an unblinded crossover design, pulse and continuous O2 were administered alternately during four 51/2-hour periods. Oxygen saturation was monitored continuously during the 23-hour study. Mean SaO2 on pulse flow (95.6 +/- 2.7 percent) was clinically the same as continuous flow (95.3 +/- 2.6 percent). Mean SaO2 on pulse flow during the 30 minutes before or after each crossover (95.5 +/- 3.3 percent) was similar to continuous flow during the 30 minutes near crossover (95.3 +/- 3.1 percent). It is concluded that the two delivery systems produce similar levels of SaO2 over the course of a day and night. Analysis of potential cost savings achieved by use of the device for a 350-bed hospital suggests a savings of about $50,000 yearly when accompanied by termination of oxygen humidification.

Continuous low-flow supracarinal and subcarinal oxygen insufflation in addition to intermittent positive-pressure ventilation does not improve gas exchange

Recent studies in animals have demonstrated that continuous insufflation of oxygen near the tracheal carina results in ventilation and carbon dioxide removal that is proportional to the flow rate. The purpose of this study was to determine whether the addition of supracarinal and subcarinal low-flow oxygen insufflation to conventional intermittent positive-pressure ventilation (IPPV) of critically ill and anesthetized patients results in increased ventilation and improved oxygenation. In eight studies a supracarinal catheter (3.7 mm ON was placed 1 to 2 cm above the carina, and in another eight studies two subcarinal catheters (1.7 mm ON were placed 2 cm below the tracheal carina under direct vision with a fiberoptic bronchoscope. Both supracarinal and subcarinal catheters were passed within the lumen of an 8 mm ID endotracheal tube. In both groups, conventional IPPV consisted of a tidal volume of 10–12 mL/kg, respiratory rate of 8 to 10 breaths/min, O cm H 2O positive end-expiratory pressure (PEEP), and F 1O 2 of 1.0. In both groups, continuous oxygen insufflation flow rates were 0.05, 0.10, and 0.20 L/ kg/min. It was found that compared with control conditions (no insufflation), oxygen insufflation at all flow rates in both supracarinal and subcarinal insufflation groups did not cause any significant change in either oxygenation or ventilation. There was a significant increase in proximal peak airway pressure with each incremental increase in continuous oxygen flow rate. Conversely, there was a significant decrease in mean arterial pressure and cardiac output with each incremental increase in continuous oxygen flow rate. It is concluded that use of continuous low-flow insufflation of oxygen with simple administration systems (catheters within the lumen of endotracheal tube) in addition to conventional IPPV is contraindicated at the present time. Further studies using different insufflation systems may prove to be worthwhile.

Cricothyroid membrane puncture

A method for pediatric airway support was evaluated for the situation when mask ventilation or intubation is impossible. Mongrel dogs were sedated, intubated, and allowed to breathe room air for 30 min. Baseline variables were recorded, and the airway obstructed. After 2 to 3 min of hypoxia, arterial blood gas and hemodynamic data were again recorded. A percutaneous cricothyroid membrane puncture (PCMP) was then performed with a 12-ga iv catheter. Studies were carried out both in the presence and absence of spontaneous ventilatory efforts. With spontaneous ventilation, continuous low flow (1.0 L/min) oxygen insufflation provided oxygenation for 30 min and reversed increases in mean arterial pressure, pulmonary artery pressure (PAP), and systemic and pulmonary vascular resistance that had been produced by the obstruction. Respiratory acidosis occurred but was well tolerated. With paralyzed animals, whose ventilation was supported by a self-inflating bag with 10.0 L/min of oxygen, all hemodynamic variables except PAP returned to normal, oxygenation was excellent, and PaCO2 values were maintained at steady, but elevated levels. Complications included bilateral tension pneumothorax in one animal. This experimental study supports anecdotal experiences where PCMP has been used and has proven lifesaving when standard resuscitative measures to establish a clear airway have failed.

Effects of hyperbaric, normobaric and hypobaric oxygen supplementation on retinal vessels in newborn rats: a preliminary study

An experimental study was conducted on eight litters of newborn rats to evaluate the effects of supplemental oxygen administration on the retinal vasculature. The animals and their mothers were kept inside a pressure chamber and treated for the first 5 days of life. On the sixth day, they were removed and kept for five more days under room air and normobaric conditions. Three litters received continuous flow oxygen at 80% at a compression pressure of +81 kPa, one litter oxygen at 80% at a pressure of -39.5 kPa atms and three other litters received oxygen at 80% under normobaric conditions. The eighth litter was treated with room air oxygen at a compression pressure of +81 kPa. A severe retinopathy with marked retinal neovascularization was seen only in the newborn animals of the litters that received oxygen supplementation under normobaric or hypobaric conditions. Retinal vessels showed no pathological changes in the litters treated with hyperbaric normoxia or hyperoxia. It is possible to hypothesize that the prolonged period of oxygen supplementation failed to produce harmful effects on the retinal vasculature because the moderate hyperbarism caused mild retinal and choroidal vasoconstriction thus preventing excessive oxygen transport to the inner retina from the choroid during hyperoxia without inducing structural damage to the retinal tissue.

Effectiveness of a New Oxygen Demand Valve in Chronic Hypoxemia

The purpose of this study was to compare the efficacy of nasal oxygen delivery by an inspiratory demand valve, which delivers oxygen only during the inspiratory phase, to standard continuous flow oxygen. The inspiratory demand valve attaches to an oxygen source and delivers oxygen after the sensor detects negative pressure through a standard nasal cannula. Seventeen male patients with chronic hypoxemia secondary to COPD were studied under resting conditions. Nine patients with hypoxemia at rest or with exercise were studied using an exercise protocol. Oxygen was delivered at a flow rate which improved the oxygen saturation by 4 percent. Oxygen saturation was measured continuously by an ear oximeter. The results indicate that oxygen saturation was not significantly different for either method of oxygen delivery at rest or during exercise. The time oxygen was delivered was significantly reduced during demand valve use, being 55 percent less at rest and 52 percent less during exercise when compared to continuous oxygen. Further study would be helpful to determine whether the device would reliably deliver oxygen during continuous use and whether it could be adapted to portable systems.