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

The influence of regional alveolar oxygen and carbon dioxide tensions on the distribution of lung blood flow and gas exchange was studied in unanaesthetised sheep. Right apical lobe (RAL) hypoxia, induced by administering nitrogen or nitrogen/oxygen mixtures to the lobe, stimulated a prompt, graded and well sustained reduction in lobar blood flow. Maximum hypoxia was accompanied by an approximate 65% reduction in perfusion, a significant fall in RAL carbon dioxide tension and output, a reversal of lobar oxygen flux and an average 13 Torr fall in arterial oxygen tension. The reduction in perfusion and gas exchange persisted in the face of elevated systemic oxygen tensions produced by giving pure oxygen instead of air to the remainder of the lung (RL). Mild RAL hypercapnia potentiated the hypoxia-induced change in perfusion and gas exchange. During lobar hypoxia RL blood flow and gas exchange increased to maintain total pulmonary gas exchange at an essentially constant level. RAL hyperoxia did not significantly alter the distribution of perfusion or gas exchange.
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PMID:Regional alveolar gas composition and lung function in sheep. 49 47

Using the technique of artificial ponto-medullary perfusion, the steady state ventilation during hyperoxia was measured in 15 anaesthetized cats as a function of the central PaCO2 (PaCO2) and peripheral PaCO2 (PapCO2). To a first approximation the ventilatory response was linearly related to both the central and peripheral arterial carbon dioxide pressures, viz. VE=SC . PacCO2 + Sp . PapCO2 - K where Sc and Sp represent the overall central and peripheral sensitivity to carbon dioxide. The mean ratio Sp/Sc was 0.48 (range 0.21 to 1.08). In carotid sinus denervated cats Sp was zero, while the values of Sc in these cats were in the range of Sc of cats with intact carotid sinus nerves. It is concluded that the peripse to CO2 under steady-state conditions. Chemodenervation experiments revealed that the carotid bodies play an essential role in this contribution.
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PMID:Relative contribution of central and peripheral chemoreceptors to the ventilatory response to CO2 during hyperoxia. 49 56

The reactivity of subpleural strips of lung parenchyma reflects primarily the tone of the smooth muscle in the peripheral airways. Lung strips taken from ten dogs relaxed when the oxygen level in the gas bubbling through the bath was reduced from 95% to 18%. Subsequent hypocapnia (carbon dioxide reduced from 5% to 0%) induced contraction of all strips. These changes were reversed when the oxygen or carbon dioxide tensions were restored to control levels. Addition of either indomethacin or meclofenamate, two chemically dissimilar inhibitors of prostaglandin synthetase, reduced the resting tone in each of six strips and prevented the hyperoxic constriction which was observed in paired, control strips (oxygen increased from 18% to 95%). Blockers of histamine and catecholamines had no effect. The reactivity of the distal airways to changes in gas tension provides a mechanism by which ventilation and perfusion can be matched. The action of indomethacin and meclofenamate indicates that a prostaglandin-like substance may be involved in the maintenance of distal airway tone and in the constriction produced by hyperoxia. The addition of prostaglandin F2 alpha or E1, after meclofenamate, in a further nine pairs of strips did not restore the hyperoxic constriction. This suggests that prostaglandins may mediate, rather than merely facilitate, the response.
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PMID:Distal airway responses to changes in oxygen and carbon dioxide tensions. 52 47

Cidal activities of 24-h exposures to 100% O2 and 95% O2 + 5% CO2 were assayed at 1 and 3 ATA. Studied were 21 yeasts isolated from humans: Candida albicans (8 strains), C. tropicalis (3 strains), C. krusei (3 strains), C. parapsilosis (2 strains), C. guilliermondii (2 strains), and one strain each of C. pseudotropicalis, C. stellatoidea, and Torulopsis sp. Generally, these were extremely sensitive to hyperbaric oxygen, although species and strain differences were observed. Indices of kill from 80-100 (total kill) characterized 17 of the 21 yeasts (81%). Hyperoxia (O2 +/- CO2 at 1 ATA) was not lethal. Deprivation of CO2 as a consequence of hyperbaric exposure to 100% O2 enhanced cidal activity for only 2 of 21 yeasts, whereas hyperbaric exposure to the mixture enhanced activity against four yeasts. Cidal activities were not significantly different for the remaining 15 yeasts. This response to deprivation of CO2 is different from that of bacteria, and manifests fundamental differences between procaryotic and eucaryotic cells.
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PMID:Quantitative cidal activity of hyperbaric oxygen for opportunistic yeast pathogens. 56 66

In anaesthetized rabbits the influence of vagal cold-block on the ventilatory response to lowered arterial oxygen pressure was investigated. With intact carotid chemoreflexes, lowered PaO2 caused hyperventilation, which was progressively intensified with the degree of hypoxia, regardless of whether the alveolar PCO2 was uncontrolled or kept constant at the hyperoxic control. The V-PaO2 response was to a greater extent due to an increase of respiratory rate than to one of tidal volume. During hyperoxia, vagal cold-block caused a distinct increase in ventilation provided the alveolar PCO2 was not allowed to decrease. During moderate hypoxia, vagal block caused only a slight increase in ventilation, when PACO2 was not controlled, but a distinct decrease in ventilation, when PACO2 was maintained at the hyperoxic level. Without carotid chemoreflexes, lowered PaO2 did not change ventilation at any level, provided the vagus nerves were left intact. This was due to a substantial increase in respiratory rate counteracting a corresponding decrease in tidal volume. Then vagal block led to a ventilatory depression depending on the degree of hypoxia, which was due to a simultaneous decline in respiratory rate and tidal volume. It is concluded that during hypocapnic hypoxia the vagal stretch reflex primarily inhibits the carotid chemoreflex drive of ventilation. During normocapnic hypoxia, however, the mode of interaction between the peripheral and the central chemical drive has to be considered, which without vagal feed-back is occlusive. This occlusion appears to be counteracted by a vagal mechanism sensitive to CO2 in the airways--and possibly also to a lack of O2--, mainly shortening respiratory cycle duration.
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PMID:The role of the vagus nerves in the ventilatory response to lowered PaO2 with intact and eliminated carotid chemoreflexes. 57 48

1. Periods of breath-holding are interrupted by episodes of continuous breathing in the aquatic turtle Pelomedusa subrufa, whereas single breaths and short periods of breath-holding alternate in the terrestrial tortoise Testudo pardalis. This implies that partial pressures of O2 and CO2 in expired air are stable in Testudo in contrast to cyclic fluctuations in Pelomedusa. 2. In spite of this, air convection requirements (VA/VO2, ml BTPS/ml STPD) are not significantly different for the two species (25.4 in Testudo, 27.3 in Pelomedusa), and differences in weight-specific ventilation between the mean body weight. 3. The end-tidal PCO2 in Pelomedusa (mean 15.2 mmHg) is lower than in Testudo (mean 24.7 mmHg), which reflects aquatic CO2 elimination in Pelomedusa. 4. In Testudo, the time course of ventilation correlates with the time course of increase of end-tidal PCO2 during CO2 breathing, but no simple relationship is evident between ventilation and blood PCO2 in Pelomedusa. 5. In both species tidal volume as well as respiratory frequency increase approximately in proportion to the end-tidal PCO2, although the response to 6% CO2 breathing could be less than expected from extrapolation of the responses to 2 and 4% CO2. Both species also increase ventilation during hypoxia, but hyperoxia depresses ventilation.
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PMID:Ventilation in an aquatic and a terrestrial chelonian reptile. 62 95

Blood flow to subunits of the lung was studied in the duck by use of radioactive microspheres. In spontaneously breathing, unanesthetized animals (series I) neopulmo was slightly better perfused than the average lung and along the paleopulmonic parabronchi, blood flow was found to decrease in the direction of ventilatory gas flow and thus of decreasing PO2 and increasing PCO2 in lung gas. The effects of respiratory gases on regional lung perfusion were investigated in unidirectionally ventilated animals (series II) in which gas mixtures offered to both lungs could be controlled independently. Local hypoxia resulted in reduction of local blood flow, whereas effects from hyperoxia or CO2 could not be substantiated. Reversal of the direction of unidirectional ventilatory flow (series III), and thus reversal of the profiles of respired gas concentrations along the parabronchi, suggest that the inhomogeneity in blood flow observed in spontaneously breathing animals of series I can only in part be explained as an acute adjustment to the local hypoxia. Calculations show that this inhomogeneity of blood flow constitutes an only minor impairment of the overall gas exchange efficacy of the parabronchial lung.
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PMID:Blood flow distribution in the duck lung and its control by respiratory gases. 62 69

Resting respiratory parameters and respiratory responses to acute changes in end-tidal O2 and CO2 pressure (PETO2 and PETCO2) were investigated in Peru in 23 newborn and 4 older infants at 3.850 m and in 13 newborns at 800 m. The study was done with the subjects asleep in a thermoneutral environment. The transient increase in ventilation in both high- and low-altitude newborns was followed by a decrease in response to acute hypoxia. During hyperoxia the two groups showed a slight but not clearly significant decrease in ventilation, whereas older high-altitude infants showed a sustained decrease. All subjects showed a prompt and clear response to CO2 inhalation during hyperoxia. We conclude that ventilatory peripheral chemoreflex is not fully developed in newborns regardless of altitude. The weak link in the reflex arc may reside in the afferent component because CO2 response was not impaired. Since hypoxic response became persistent in older infants its blunting in adult high-altitude natives is not a legacy of newborns.
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PMID:Regulation of breathing in newborns at high altitude. 64 68

The measurement of pressure in the mouth 0.1 sec after the initiation of an occluded inspiratory effort (P0.1) has been proposed as an index of activity of medullary inspiratory neurons. If changes in FRC can be interpreted as important changes in the length-tension curve of the diaphragm or the total respiratory musculature, then changes in FRC from one occlusion pressure measurement to another can complicate such an interpretation of the P0.1 measurement. Forty-five subjects divided into three different groups were seated in a variable volume body plethysmograph. They had their FRC, P0.1, VT and VE measured while breathing air, 100% oxygen, 11% oxygen balance nitrogen, and 4% carbon dioxide in 20% oxygen balance nigrogen. All 45 showed a decrease in FRC during hyperoxia (-12%); 40 of 43 showed increases in FRC during hypoxia (14%); 42 of 43 showed an increased FRC during hypercapnia (15%). Changes in VE were small as were changes in P0.1 values. These latter changes generally followed the same pattern of changes as FRC though the magnitude of the changes showed more variability. We were unable to demonstrate a significant correlation between changes in FRC and changes in P0.1 under the conditions of our experiments.
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PMID:The effect of hyperoxia, hypoxia and hypercapnia on FRC and occlusion pressure in human subjects. 69 49

1. The effect on respiration of a single dose of propranolol has been studied in normal subjects. 2. The degree of beta-adrenoreceptor blockade was assessed in terms of the impaired heart-rate response to progressive exercise and the plasma propranolol concentration. 3. No effect of propranolol was demonstrated on either the ventilatory response to rebreathing CO2 in hyperoxia, or the response to progressive isocapnic hypoxia. Simple indices of maximal expiratory flow (FEV 1.0% and PEFR) were also unchanged. 4. The absence of any effect of propranolol on the chemical control of breathing in man is discussed in relation to the conflicting literature.
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PMID:Propranolol and the ventilatory response to hypoxia and hypercapnia in normal man. 72 3


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