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PubMed1983

Reversal of arterial-to-expired CO2 partial pressure differences during rebreathing in goats.

Whether CO2 partial pressure (PCO2) in expired gas may exceed that in arterial blood has been controversial. We measured arterial PCO2 (Paco2) and end-tidal PCO2 (PETco2) in four awake goats during air breathing and during hyperoxic CO2 rebreathing in various conditions of acid-base balance. During air breathing, Paco2 was slightly higher than PETco2; i.e., the mean (+/- SE) difference, Paco2 - PETco2, was positive by + 2.36 +/- 0.53 Torr (P less than 0.001). In contrast, during CO2 rebreathing with the same techniques of measurement, this difference was always negative (mean +/- SE = -11.63 +/- 0.22 Torr, P less than 0.001), and it widened as Paco2 increased with rebreathing. Magnitude of the negative difference during rebreathing was too great to be accounted for by incorrect assumptions or measurement error, even if reasonable contributions from all known sources of error were concurrently invoked. We conclude that during hyperoxic CO2 rebreathing in goats, PETco2 exceeds Paco2.

Animals↗

PubMed1993

Long-lasting effect of prolonged hypoxemia after birth on the immediate ventilatory response to changes in arterial partial pressure of oxygen in young lambs.

The effect of prolonged hypoxemia (H) after birth on the evolution of the ventilatory response to changes in arterial partial pressure of O2 was determined in unanesthetized, awake lambs. H was induced for 12 d after birth in seven lambs through exposure to 0.10 fraction of inspired O2 (FiO2). Five control (C) lambs were kept in 0.21 FiO2. The ventilatory response (percent increase from baseline) to acute hypoxia was tested with 0.14 FiO2 and 0.10 FiO2. The tonic activity of the peripheral chemoreceptors was assessed by the transient pure oxygen inhalation test (Dejours' test). The occlusion technique was used to measure the baseline neuromuscular drive of breathing. A markedly decreased early ventilatory response to acute hypoxia persisted in the H lambs for at least 5 wk after termination of H compared with the C group. The second phase of the response was significantly lower only at 12 d (the end of H) and was thereafter comparable to that in the C lambs. The ventilatory response to hyperoxia was significantly lower in the H lambs only at the end of hypoxemia at 12 d and rapidly normalized after return to normoxia. H did not significantly affect resting neuromuscular drive. These results show that postnatal maturation of the ventilatory response to changes in arterial partial pressure of O2 can be delayed by prolonged postnatal hypoxemia. The effect on the response to hyperoxia is transient, whereas the response to acute hypoxia is affected for an extended time. This study illustrates the importance of an adequate postnatal arterial partial pressure of O2 for the development of the ventilatory response to acute hypoxia.

Animals↗

PubMed2003

Differential haemoglobin gene expression in the crustacean Daphnia magna exposed to different oxygen partial pressures.

The quantity and quality of the haemoglobin (Hb) of Daphnia magna is related to oxygen partial pressure in the water. Both the dynamics of hypoxia-induced Hb gene transcription, as well as Hb properties in animals incubated long-term at hyperoxia, normoxia and hypoxia, were investigated. Examination of Hb gene (dhb1-dhb3) transcription showed the expression of dhb2 and especially dhb3 to increase markedly approximately one hour after the onset of hypoxia, whereas dhb1 was expressed more or less constitutively. At an incubation close to anoxia, an onset of dhb3 transcription was found already after two minutes. In long-term incubated animals, concentration and oxygen affinity of Hb were lower at higher oxygen partial pressures. With decreasing oxygen availability, the subunit composition of Hb macromolecules changed. The share of the dhb2-encoded subunit, DHbF, increased already during moderate hypoxia. The increase of dhb3 mRNA (encoding DHbC) may be related to a transient increase of DHbC in the first days of hypoxia and/or to an additional coding of dhb3 for DHbD. The rise of DHbD, and particularly DHbA, only at severe hypoxia coincided with the increase of Hb oxygen affinity. The dhb1-encoded subunits DHbB and DHbE showed either a relatively moderate increase or even a decrease in concentration at hypoxia. In small animals with restricted homeostasis capabilities such as Daphnia, adaptation of the protein equipment seems to be a more effective strategy than allosteric modulator control.

Adaptation, Physiological↗

PubMed1992

The acute effects of MK-801 on cerebral blood flow and tissue partial pressures of oxygen and carbon dioxide in conscious and alpha-chloralose anaesthetized rats.

The dynamic effects of the non-competitive N-methyl-D-aspartate receptor antagonist, MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine] , on cerebral blood flow and tissue partial pressures of oxygen and carbon dioxide were investigated in the striatal and occipital regions of conscious and anaesthetized rats by mass spectrometry. MK-801 (0.5 and 5 mg/kg, i.p.) induced a large increase in the blood flow of both cerebral regions of conscious rats, without significant changes in local tissue partial pressures of oxygen and carbon dioxide. The increase in cerebral blood flow was maximal within 30 min after injection. Its amplitude was independent of the dose of MK-801, but cerebral blood flow remained elevated for up to 4 h after 5 mg/kg MK-801, while it progressively decreased towards its basal level in rats given 0.5 mg/kg MK-801. The amplitude and time-course of the vascular changes were similar in the two cerebral regions studied. The difference in the changes in tissue partial pressure of oxygen induced by MK-801 and by a 6% CO2 inhalation suggests that the MK-801-induced rise in cerebral blood flow in conscious rats is, at least partly, due to an increase in oxidative metabolism. In contrast, MK-801 induced either no changes or decreases in cerebral blood flow in alpha-chloralose-anaesthetized rats. The present results should be taken into account not only to determine the mechanisms by which N-methyl-D-aspartate receptor antagonists may exert their neuroprotective effects but also to further elucidate the sites of action of MK-801 in the central nervous system.

Anesthesia, General↗

PubMed1984

Comparison of transcutaneous and alveolar partial pressure of carbon dioxide during carbon dioxide breathing in healthy children.

In 18 healthy children three to 13 years of age, the transcutaneous partial pressure of carbon dioxide (PtcCO2) (Radiometer electrode) and the alveolar partial pressure of carbon dioxide (PACO2) (Beckman analyzer) were measured simultaneously during the breathing of room air and 5 percent carbon dioxide. The PtcCO2 electrode was placed on the anterior thorax and heated to 42 degrees C. The PACO2 was calculated on the 4/5 part of the carbon dioxide expired trace. Minute ventilation (VE) was measured in 11 cases. There was a significant correlation between PtcCO2 (in millimeters of mercury) and PACO2 (in millimeters of mercury) while breathing room air (PtcCO2 = 0.82 PACO2 + 19.7; r = 0.55; p less than 0.02) and while breathing 5 percent carbon dioxide (PtcCO2 = 0.77 PACO2 + 22.5; r = 0.61; p less than 0.01); however, the ratio of PtcCO2 over PACO2 was significantly lower while breathing 5 percent carbon dioxide (p less than 0.01) than while breathing room air. When considering the relationship between the increase in VE (delta VE while breathing 5 percent carbon dioxide and the changes in PACO2 (delta PACO2) or in PtcCO2 (delta PtcCO2), a significant correlation was found only between delta VE and delta PACO2, ie, delta VE = 0.41 delta PACO2 + 0.44 (r = 0.63; p less than 0.01). These results suggest that breathing carbon dioxide modified the factors acting on PtcCO2, possibly by changes in the vasomotor tone of cutaneous blood vessels. These modifications appeared to be variable from subject to subject. Therefore, we conclude that PtcCO2 does not appear to be an accurate quantitative index to assess ventilatory response to carbon dioxide.

Adolescent↗

PubMed1985

Reliability of transcutaneous measurement of oxygen and carbon dioxide partial pressure with a combined Po2-Pco2 electrochemical sensor in the fetus during labor.

A combined single electrochemical sensor designed to measure synchronously and transcutaneously oxygen partial pressure and carbon dioxide partial pressure (RADIOMETER prototype) was applied onto the scalp in 21 fetuses during labor. The values of tcPo2 respectively tcPco2 were compared with the values of fetal blood analysis (FBA) and blood from the umbilical artery (UA): Comparing the tcPco2 with the values of the FBA we found the values to be very consistent (r = 0.95, p less than 0.001). For the comparison of the tcPco2 with the values of the umbilical artery, the correlation coefficient was lower (r = 0.76, p less than 0.05). The transcutaneous measurement of Po2 as compared with the values of the fetal blood analysis was also quite accurate (r = 0.83, p less than 0.001). Looking at the values of the transcutaneous measurement during the expulsion of the fetus and its comparison with the values of the umbilical artery, it was an interesting finding that values of the transcutaneous estimation of Po2 were much lower in some cases and no statistical correlation was found (p greater than 0.05). We conclude that the combined electrochemical sensor for measuring tcPco2 and tcPo2 is a new additional tool for studying the physiology and pathophysiology of the fetus during labor, but as the accuracy of Po2 and Pco2 in the fetal blood is influenced by the progress of labor, the special characteristic of the transcutaneous measurement has to be taken into account when values are interpreted.

Carbon Dioxide↗

PubMed2004

[Effect of oxygen partial pressure on the band-gap of the TiO2 films prepared by DC reactive sputtering].

TiO2 films have been deposited on glass substrates using DC reactive magnetron sputtering at different oxygen partial pressures from 0.10 to 0.65 Pa. The photoluminescence (PL) spectra of the films were recorded. The results of the PL spectra showed that there were three emission peaks at 370, 472 and 514 nm for the films sputtered at 0.35 and 0.65 Pa, and there were two peaks at 370 and 490 nm for the films sputtered at 0.10 and 0.15 Pa. The band-gap for the films was 3.35 eV. For the films sputtered at 0.35 and 0.65 Pa there were two defect energy levels at 2.63 and 2.41 eV, corresponding to 0.72 and 0.94 eV below conduction band for the band-gap, respectively. For the films sputtered at 0.10 and 0.15 Pa, there was an energy band formed between 3.12 and 2.06 eV, corresponding to 0.23 and 1.29 eV below the conduction band. With increasing the oxygen partial pressure, the defect energy band changed to two energy levels, and the energy levels nearly disappeared for the film sputtered at 0.65 Pa of oxygen partial pressure.

English Abstract↗

PubMed2005

Determination of alveolar-capillary O2 partial pressure gradient by using 15NO.

We propose an approach for determining the alveolar-mean capillary oxygen (O(2)) partial pressure gradient to evaluate the efficiency of O(2) equilibration between alveolar space and pulmonary capillary blood. For this purpose, measurements of the pulmonary [(15)N]nitric oxide diffusing capacity are to be interpolated into the recording of O(2) consumption. We expect the O(2) partial pressure gradient amounting to 3.3 mmHg for breathing room air at rest, a third of that commonly given. The simplicity of our method allows its application to children or even artificially ventilated patients. Therefore, it will enable a new insight into pulmonary O(2) equilibration.

Humans↗

PubMed1997

Modulation of paraquat toxicity by beta-carotene at low oxygen partial pressure in chicken embryo fibroblasts.

The efficiency with which beta-carotene protects against oxidative stress in chicken embryo fibroblasts (CEF) at low O2 partial pressures was assessed. Primary cultures of CEF were grown at low O2 partial pressures and oxidatively stressed by exposure to paraquat (PQ). Activities of the antioxidant enzymes superoxide dismutase (EC 1.15.1.1; SOD), catalase (EC 1.11.1.6; CAT) and glutathione peroxidase (EC 1.11.1.9; GSH-Px) were measured as indices of oxidative stress. CEF incubated with 0.25-1.0 mM-PQ for 18 h exhibited increased SOD and CAT activities compared with non-PQ-treated control cells (P < 0.001). No cytotoxicity as indicated by lactate dehydrogenase (EC 1.1.1.27; LDH) release was observed at PQ concentrations below 2.0 mM. Incorporation of added beta-carotene into 0.25 mM-PQ-treated cells prevented the PQ-induced increases in SOD and CAT, and activities were similar to those seen in non-PQ-treated control cells. GSH-Px activity decreased relative to its control value on exposure to 0.25 mM-PQ and beta-carotene prevented this decrease in a dose-dependent manner. The proportion of LDH released from the CEF treated with beta-carotene remained below the control value of 2.5% at all times.

Animals↗

PubMed1998

Single-breath CO diffusing capacity influenced by initial alveolar partial pressure of CO.

The purpose of this study was to assess the influence of incorrect determinations of the initial alveolar partial pressure of carbon monoxide (CO) at the beginning of breath holding (PIACO) on the pulmonary CO diffusing capacity of the lung (DLCO). Single-breath maneuvers were performed on 14 anesthetized and artificially ventilated rabbits, using 0.2% CO in nitrogen as the indicator gas mixture. Inflation and deflation procedures were carried out in an identical manner on each animal, with inflation always starting from residual volume. End-tidal partial pressure of CO was determined by respiratory mass spectrometry and was used to calculate DLCO values with the application of the three-equation (method 1), as well as the conventional (method 2), solution. In each rabbit, method 2 caused DLCO values to be overestimated when compared with method 1, and this overestimation decreased with increasing time intervals of CO uptake. Because we were able to recalculate this deviation using PIACO values that were obtained by taking the diffusive removal of CO during inflation into account, we concluded that errors in estimating PIACO by applying method 2 significantly contribute to the discrepancy between both methods.

Animals↗

PubMed1993

[Continuous monitoring of spontaneous postoperative respiration. 3. The effect of amiphenazole on cutaneous oxygen and carbon dioxide partial pressure following gynecologic surgery under halothane anesthesia].

METHODS: In an attempt to verify non-invasive respiratory monitoring for patients in the early postoperative period, cutaneous O2 and CO2 pressures were monitored in 30 female patients recovering from major gynaecologic surgery under halothane anaesthesia. In a double-blind and randomized fashion, in the recovery room the patients received a single intravenous bolus injection of placebo or 150 mg amiphenazole, a respiratory stimulant. The data were collected and stored in a personal computer, using the TCM3 system with a combination electrode for simultaneous measuring of cutaneous oxygen and carbon dioxide partial pressures (TINA, Radiometer) at 30-s intervals. The overall observation period was 240 min. Means and standard deviations were calculated for individual data and for data pooled at 15- or 60-min intervals. Groups were compared by means of the chi 2 test, Student's t-test, Wilcoxon rank sum test or analysis of variance (level of significance P < or = 0.05). RESULTS: The study groups were comparable with respect to demographic and anaesthesiological data. The partial pressures for both O2 and CO2 were not statistically significant between groups. Electrode heating was slightly higher with amiphenazole (n.s.), indicating a trend for peripheral vasodilation without a true improvement of spontaneous ventilation. pctO2 and pctCO2 levels were decreased or elevated, respectively, in the first observation hours and slowly returned to normal within the 240-min observation period. Episodes of hypercapnia (pct-CO2 > 50 or > 55 mm Hg) were frequent in the first 2 h (10-30% of individual data for pctCO2 > 50, 2-7% for pctCO2 > 55, respectively), indicating the need for close monitoring of spontaneous respiration after general anaesthesia with halothane. DISCUSSION AND CONCLUSION: The present study confirmed that spontaneous respiration in the early postoperative period can be monitored non-invasively by measuring transcutaneous partial pressures of carbon dioxide and, less precisely due to large individual variations, oxygen. It showed that spontaneous respiration deteriorates after gynaecological surgery under halothane anaesthesia and recovers slowly during the next 4 h. The respiratory stimulant amiphenazole (150 mg i.v.) was of no significant value with respect to the improvement of ventilation.

Adult↗

PubMed1997

Nitrogenase Activity Is Affected by Reduced Partial Pressures of N2 and NO3- 1.

Optimal use of legumes in cropping systems requires a thorough understanding of the interaction between inorganic N nutrition and symbiotic N2 fixation. Our objective was to test the hypothesis that increased NO3- uptake by alfalfa (Medicago sativa L.) would compensate for lower N2 fixation caused by low partial pressure of N2. Root systems of hydroponically grown alfalfa at 2 mg L-1 NO3--N were exposed to (a) 80% N2, (b) 7% N2, (c) 2% N2, or (d) 0% N2. Exposure to reduced partial pressures of N2 reduced total nitrogenase activity (TNA, measured as H2 production in 20% O2 and 80% Ar) by 40% within less than 30 min, followed by a recovery period over the next 30 min to initial activity. Five hours after treatments began, the TNA of plants exposed to 7 and 2% N2 was substantially higher than pretreatment activities, whereas the TNA of plants exposed either to 0 or 80% N2 did not differ from pretreatment values. The decline in TNA due to NO3- exposure over 4 d was not affected by reduced partial pressure of N2. During the 1st h the proportion of electrons used for the reduction of N2 fell from 0.52 to 0.23 for plants exposed to 7% N2, and to 0.09 for plants exposed to 2% N2, and remained unchanged for the rest of the experiment. Although the hypothesis that alfalfa compensated with increased NO3- uptake for lower N2 fixation was not validated by our results, we unexpectedly demonstrated that the decline in TNA upon exposure to NO3- was independent of the N2-fixing efficiency (i.e. the amount of N2 reduced by nitrogenase) of the symbiosis.

Journal Article↗

PubMed1994

Proximate nutritional composition of CELSS crops grown at different CO2 partial pressures.

Two CELSS candidate crops, soybean (Glycine max) and potato (Solanum tuberosum), were grown hydroponically in controlled environments maintained at carbon dioxide (CO2) partial pressures ranging from 0.05 to 1.00 kPa (500 to 10,000 ppm at 101 kPa atmospheric pressure). Plants were harvested at maturity (90 days for soybean and 105 days for potato) and all tissues analyzed for proximate nutritional composition (i.e. protein, fat, carbohydrate, crude fiber, and ash content). Soybean seed ash and crude fiber were higher and carbohydrate was lower than values reported for field-grown seed. Potato tubers showed little difference from field-grown tubers. With the exception of increased crude fiber of soybean seed with increased CO2, no trends were apparent with regard to CO2 effects on proximate composition of soybean seed and potato tubers. Crude fiber of soybean stems and leaves increased with increased CO2, as did soybean leaf protein (total nitrogen). Potato leaf and stem (combined) protein levels also increased with increased CO2, while leaf and stem carbohydrates decreased. Values for leaf and stem protein and ash were higher than values generally reported for field-grown plants for both species. Results suggest that CO2 partial pressure should have little influence on proximate composition of potato tubers or soybean seed, but that high ash and protein levels might be expected from leaves and stems of crops grown in controlled environments of a CELSS.

Atmospheric Pressure↗

PubMed2005

Density-functional calculation of CeO2 surfaces and prediction of effects of oxygen partial pressure and temperature on stabilities.

We have used density-functional theory to investigate (111), (110), (210), (211), (100), and (310) surfaces of ceria (CeO2). Compared with previous interatomic-potential-based studies, our calculations reported a slightly different relative stability ordering and significantly lower surface energies for the stoichiometric surfaces. Using a defect model, the surface stabilities were evaluated as functions of oxygen partial pressure and temperature. Our investigations were restricted to ideal surface terminations, without considering defect formation on those surfaces. We found that at 300 K, the stoichiometric (111) has the lowest free energy for a wide range of oxygen partial pressures up to 1 atm, and only at ultrahigh vacuum does the Ce-terminated (111) becomes the most stable one. The transition point for the Ce-terminated (111) surfaces moves to higher oxygen partial pressures when temperature increases. To improve the prediction of electron density of states, we used the local-density approximation plus U(J) correction method to correct the on-site Coulomb correlation and exchange interaction due to the strongly localized Ce-4f electrons. The optimal parameter combination of U = 7 eV and J = 0.7 eV was found to improve the O 2p-Ce 4f gap without much degradation of ground-state bulk properties or the O 2p-Ce 5d gap. The bulk and surface electronic structures were then analyzed based on the improved density of states.

Journal Article↗

PubMed2004

[A software program for quantitative analysis of alveolar oxygen partial pressure (p(A)O(2)) with oxygen-sensitive (3)He-MRI].

PURPOSE: To develop a software tool for quantitative analysis of alveolar oxygen partial pressure (p(A)O(2)) as well as its time course during apnea. MATERIAL AND METHODS: T (1)-relaxation times of hyperpolarized (3)He are reduced by paramagnetic oxygen rendering (3)He-MRI sensitive to oxygen and thus allowing the assessment of the local oxygen partial pressure in the pulmonary airspaces. Oxygen-related relaxation and loss of polarization by RF-excitation can be discriminated by acquiring two image series with varying interscan delay and/or flip angles. Software was developed to calculate the p(A)O(2) and the decay rate in user-defined regions of interest (ROIs) automatically. Moreover, parameter maps can be calculated. In addition to the analysis of 2-dimensional data sets, the software allows the evaluation of 3-dimensional measurements for the first time. Artifacts due to lung motion were reduced by implementing a motion correction algorithm. RESULTS: The software was successfully applied to data sets from healthy volunteers and from patients with various lung diseases. The parameter maps demonstrated a more homogeneous distribution of p(A)O(2) for the volunteers than for the patients. A regional increase in p(A)O(2) was found in a few patients. CONCLUSION: The described software allows the absolute quantification of p(A)O(2) as well as its variation over time. In the future, therefore, the software may gain importance for detecting mismatches between ventilation and perfusion, e. g., in patients with pulmonary embolism or chronic obstructive lung diseases.

Adult↗

PubMed2004

Transcutaneous partial pressure of oxygen after surgical wounds.

Transcutaneous partial pressure of oxygen (TcPO2) predicts wound healing in critical ischemia. However, no studies have controlled for the effect of wounds on TcPO2. In this study, in 24 hip or knee arthroplasty cases without vascular disease, TcPO2 was measured preoperatively at the incision site, contralaterally, and at a reference site on the chest wall. The measurements were repeated at 2 days and 2 months postoperatively and compared. TcPO2, normal preoperatively, decreased at all sites on the second postoperative day (p < 0.001), with a trend toward a greater decrease at the wound (p = 0.09). All wounds healed, and TcPO2 returned to baseline at all sites 2 months postoperatively. In conclusion, acute surgical wounds are associated with a significant and widespread decrease in cutaneous TcPO2 in the setting of normal arterial perfusion. This decrease is likely multifactorial and deserves further investigation.

Adult↗

PubMed1986

[Correlation of invasive and transcutaneous determination of capillary 02 partial pressure in ventilation endoscopies].

Transcutaneous oxygen-partial-pressure-measurement of the capillary system has proved to be a successful and reliable monitoring method, also under extreme conditions of a respirating-endoscopy with pure oxygen. The feasibility of continuous recording on an ECG-recorder with good coincidence with bloody measurements can be appreciated as being very advantageous. In unphysiological high oxygen-pressure-ranges the disadvantage of the withdrawal-caused error of the bloody determination is avoided with the transcutaneous method which delivers real values.

Blood Gas Analysis↗

PubMed1978

Continuous measurement of gas partial pressures in intracerebral tissue.

A mass spectrograph technique has been developed for measurement of physiological gas partial pressures locally in the brain. The sampling cannula is implanted stereotaxically and remains in situ for several weeks. It is a thin cylinder in shape, and is covered with a thin polyethylene membrane across which gas molecules can be sampled continuously. The conductance of this membrane is well adapted to the limited rate of replacement of gas molecules afforded by the cerebral tissue, hence there is no depletion around the cannula; this depletion has until now been the major problem of this technology. The present technique provides a continuous measurement with fast response time, which is directly proportional to the partial pressures of the gases. The variations can be expressed as a percentage of the base-line value.

Animals↗