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Query: UMLS:C0242706 (hyperoxia)
 5,219 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Effects of three curvilinear inspiratory resistances (R1, R2, R3) on the cardiorespiratory responses of seven well-trained men during incremental cycling tests to exhaustion were studied by comparison to the low resistance R0 (at 1 l/s, R0 = 0.2; R3 = 6.5 cmH2O-s/l). Submaximal VO2 and the gas exchange anaerobic threshold (AT) were not affected by increasing resistance. Although maximal work rates were not significantly changed, highly significant reductions were observed for VE (R0 = 166.3; R3 = 99.7 l/min BTPS), VO2 max (R0 = 4,26; R3 = 3.74 l/min), HR (R0 = 185; R3 = 176 beats/min), and endurance (R0 = 17.3; R3 = 15.5 min) suggesting that aerobic work tolerance was dependent on ventilatory capacity. In additional tests removal of R3 at exhaustion abruptly increased VE and VO2, and permitted work to continue. Ventilation and work tolerance were therefore limited by R3 before the legs fatigued. Breathing 35% O2 against R3 produced significant, although small, increases in AT, VO2 max, peak HR, and endurance while decreasing the hyperventilatory response to work above AT. Thus, aerobic work tolerance reduced with high inspiratory resistance was partly restored by moderate hyperoxia, apparently because the ventilatory limit was delayed.
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PMID:Combined effects of breathing resistance and hyperoxia on aerobic work tolerance. 83 65

Cardiorespiratory responses of four men to submaximal and maximal cycling exercise were observed during 17 days at 18.6 ATA. Inspired gas at pressure consisted of hyperoxic (PO2 = 232 mmHg) and normoxic (PO2 = 159 mmHg) helium mixtures with relative gas densities of 3.8 and 2.8, respectively. The average of pre- and postdive VO2max (1 ATA air), which were not significantly different, was 3.10 liters - min-1. During 5 min of submaximal exercise at 50% of VO2max, no significant difference in work rate, VO2, VCO2, VE, respiratory rate, heart rate (HR), stroke volume, blood pressures, or rectal temperature was noted at 18.6 ATA compared to 1 ATA with either gas mixture. Submaximal HR tended to decrease by 5 to 10 beats - min-1 at pressure, and in hyperoxia the VO2/HR ratio was significantly higher. Maximal exercise was performed to exhaustion at work rates requiring about 120% of VO2max. Significant increased in VO2max of 0.10 liter - min-1 (3%) and in endurance time of 2 min (48%) were found during hyperoxic gas breathing, whereas normoxic values at 18.6 ATA were similar to those at 1 ATA. Significant reductions in maximal HR of 8 beats - min-1 (4%) were observed with both gas mixtures at pressure, and VE was significantly decreased by 36 liters - min-1 (26%) in hyperoxia and 29 liters - min-1 (21%) in normoxia. No change was found in the calculated cardiac output. Maximal voluntary ventilation, which was measured only for the hyperoxic gas, fell significantly by 80 liters - min-1 (40%). Results indicate that aerobic power and endurance performance were affected by oxygen pressure. Normoxic work capacity, however, was not decreased at 18.6 ATA, despite marked reductions in HR and VE.
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PMID:Hana kai ii: a 17-day dry saturation dive at 18.6 ATA. V. Maximal oxygen uptake. 91 Mar 18

The purpose of the study was to examine the influence of oxygen-breathing on maximal oxygen uptake (VO2max) and submaximal endurance performance. Six young women and five men rode a cycle-ergometer while breathing compressed air (normoxia, NOX) or a 55% O2 in N2 mixture (hyperoxia, HOX). The VO2max increased significantly by 12% (P less than 0.01) with HOX in the women but not in the men (+4%; nonsignificant). Maximal heart rate was also increased with HOX in the women but not in the men. Endurance time during work to exhaustion at 80% of normoxic VO2max was 41% longer in HOX than in NOX (P less than 0.025) with no significant difference between the men and the women. The variation among individuals was large. The oxygen uptake and respiratory quotient were not different in the two endurance tests, but pulmonary ventilation (VE) and blood lactate concentration were lower in HOX than in NOX, especially during the latter part of the task. Plasma base deficit (BDpl) increased initially by 3.5 mmol.l-1 during HOX and then stabilized. In NOX, a continuous increase was seen and the change was more than twice as large. Relative to BDpl, VE was higher in HOX than in NOX indicating a more efficient ventilatory compensation of the metabolic acidosis. The reduced ventilatory demand and lower metabolic acidosis in HOX in combination with lower relative exercise intensity may have contributed to the longer time to exhaustion. However, the pattern of individual variation suggested that other mechanisms were also involved.
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PMID:Increased working capacity with hyperoxia in humans. 139 41

Daily exposures of rabbits to the HBO (2 ata, 1 hr) enhanced activity of glutathione-peroxidase for all 28 days of exposure. Other parameters of the antioxidative defence and the contractile function remained unchanged. The 2.5-ata oxygenation sharply reduced the activity of antioxidative enzymes, the antioxidative activity of lipids, and the tissue resistance against the induced peroxide oxidation of lipids. The heart contractile function was obviously worsened. Sites of necrosis appeared in the myocardium tissue. Increase in oxygenation seems to lead to changes of adaptation of the antioxidative system, but the exhaustion of the latter's power reserves potentiates the toxic effect of hyperoxia.
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PMID:[Contractile function and antioxidative system of the myocardium of the intact rabbit during hyperbaric oxygenation]. 301 94

Six subjects pedaled a stationary cycle ergometer to exhaustion on three separate occasions while breathing gas mixtures of 17, 21, or 60% O2 in N2. Each subject rode for 3 min at work rates of 60, 90, 105 W, followed by 15-W increases every 3 min until exhaustion. Inspired and expired gas fractions, ventilation (V), heart rate, and blood lactate were measured. O2 uptake (VO2) and CO2 output (VCO2) were calculated for the last minute of each work rate; blood samples were drawn during the last 5 s. "Break points" for lactate, V, VCO2, V/VO2, and expired oxygen fraction (FEO2) were mathematically determined. VO2 was not significantly different at any work rate among the three different conditions. Nor did maximal VO2 differ significantly among the three treatments (P greater than 0.05). Lactate concentrations were significantly lower during hyperoxia and significantly higher during hypoxia compared with normoxia. Lactate values at exhaustion were not significantly different among the three treatments. Four subjects were able to work for a longer period of time during hyperoxic breathing. The variations in lactate accumulation as reported in this study cannot be explained on the basis of differences in VO2. The results of this research lend support to the hypothesis that differences in the performance of subjects breathing altered fractions of inspired oxygen may be caused by differences in lactate (or H+) accumulation.
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PMID:Lactate accumulation during incremental exercise with varied inspired oxygen fractions. 662 44

Six subjects rode a bicycle ergometer on three occasions breathing 17, 21, or 60% oxygen. In addition to rest and recovery periods, each subject worked for 10 min at 55% of maximal oxygen uptake (VO2 max) and then to exhaustion at approximately 90% VO2 max. Performance time, inspired and expired gas fractions, ventilation, and arterialized venous oxygen tension (PO2), carbon dioxide tension (PCO2), lactate, and pH were measured. VO2, carbon dioxide output, [H+]a, and [HCO3-]a were calculated. Performance times were longer in hyperoxia than in normoxia or hypoxia. However, VO2 was not different at exhaustion in normoxia compared with hypoxia or hyperoxia. During exercise, hypoxia was associated with increased lactate levels and decreased [H+]a, PCO2, and [HCO3-]a. The opposite trends were generally associated with hyperoxia. At exhaustion, [H+]a was not different under any inspired oxygen fraction. These results support the contention that oxygen is not limiting for exercise of this intensity and duration. The results also suggest that [H+] is a possible limiting factor and that the effect of oxygen on performance is perhaps related to control of [H+].
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PMID:Oxygen uptake, acid-base status, and performance with varied inspired oxygen fractions. 677 81

Pulmonary and intracardiac hemodynamic findings are reported. They were obtained by means of catheterization of right cardiac departments and the pulmonary artery with thermodilution in 57 patients with chronic nonspecific pulmonary diseases (CNPD), under conditions of resting, rationed bicycle-ergometric exercise, hypo- and hyperoxia, and nitroglycerin administration. Changes in pulmonary and intracardiac hemodynamics which reflect the ongoing exhaustion of compensatory mechanisms in the external respiration apparatus, the pulmonary vascular system and the heart, are shown to precede the formation of right ventricular hypertrophy in obstructive CNPD A classification of secondary pulmonary hypertension, based on clinical and instrumental signs, is offered.
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PMID:[Pulmonary hypertension in chronic nonspecific lung diseases]. 716 25

Hyperoxic gas mixtures improve exercise tolerance in humans. It is not clear whether this improvement is due to 1) a decreased anaerobiosis in the working cell, 2) a decreased cost of breathing resulting from the relative hypoventilation in hyperoxia, 3) the reduction of a possible metabolic depressant-N2, or a combination of these. This study made use of He/O2 breathing mixtures to gather data relative to #2 and #3, primarily. Ten subjects ran to exhaustion on a treadmill breathing one of four mixtures-20 O2/80 N2, 20 O2/80 He, 80 O2/20 N2, 80 O2/20 He. Running time to exhaustion, minute ventilation, respiratory frequency, tidal volume, and heart rate were measured. Performance increased significantly on hyperoxic mixtures (P < .001) and He/O2 mixtures (P < .001). Although the peak ventilatory volumes were higher on He/O2 mixtures, the ventilatory mass moved was significantly less (P < .001) on those mixtures conceivably resulting in a decreased cost of breathing. These data did not reject any of the hypotheses but offered the greatest support for hypothesis #2.
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PMID:Effects of varying concentrations of N2/O2 and He/O2 on exercise tolerance in man. 745 18

This study evaluated the dynamic response of VO2 in 6 healthy men at the onset and end of submaximal step changes in work rate during a pseudorandom binary sequence (PRBS) exercise test and during ramp incremental exercise to exhaustion while breathing three different gas mixtures. The fractional concentrations of inspired O2 were 0.14, 0.21, and 0.70 for the hypoxic, normoxic, and hyperoxic tests, respectively. Both maximal VO2 and work rate was significantly reduced in hypoxic tests compared to normoxic and hyperoxic tests. Maximal work rate was greater in hyperoxia than in normoxia. Work rate at ventilatory threshold was lower in hypoxia than in normoxia and hyperoxia but above the upper limit of exercise for the submaximal tests. Hypoxia significantly slowed the response of VO2 both at the onset and end of exercise compared to normoxia and hyperoxia. Hypoxia also modified the response to PRBS exercise, and again there was no difference between normoxia and hyperoxia. These data support the concept that VO2 kinetics can be slowed from the normoxic response by a hypoxic gas mixture.
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PMID:Kinetics of oxygen uptake for submaximal exercise in hyperoxia, normoxia, and hypoxia. 764 Jun 46

These experiments examined the effect of hypoxia and hyperoxia on ventilation, lactate concentration and electromyographic activity during an incremental exercise test in order to determine if coincident chances in ventilation and electromyographic activity occur during an incremental exercise test, despite an enhancement or reduction of peripheral chemoreceptor activity. In addition, these experiments were completed to determine if electromyographic activity and ventilation are enhanced or reduced in response to the inspiration of oxygen-depleted and oxygen-enriched air, respectively. Seven subjects performed three incremental exercise tests, until volitional exhaustion was achieved, while inspiring air with a fractional concentration of oxygen of either 66%, 21% or 17%. In addition, another single subject completed two tests while inspiring air with a fractional concentration of either 17% or 21%. During the tests, ventilation, mixed expired oxygen and carbon dioxide, arterialized venous blood and the electromyographic activity from the vastus lateralis were sampled. From these values ventilation, electromyographic and lactate thresholds were detected during normoxia, hypoxia and hyperoxia. The results showed that although ventilation and lactate concentration were significantly less during hyperoxia as compared to normoxia or hypoxia, the carbon dioxide production values were not significantly different between the normoxic, hypoxic and hyperoxic conditions. For a particular condition, the time, carbon dioxide production and oxygen consumption values that corresponded to the ventilation and electromyographic thresholds were not significantly different, but the values corresponding to the lactate threshold were significantly less than those for the electromyographic and ventilation thresholds. Comparisons between the three conditions showed that the time, carbon dioxide production and oxygen consumption values corresponding to each of these thresholds were not significantly difficult.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The ventilation, lactate and electromyographic thresholds during incremental exercise tests in normoxia, hypoxia and hyperoxia. 780 64


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