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PubMed2001

Temporal dynamics of the partial pressure of brain tissue oxygen during functional forepaw stimulation in rats.

The partial pressure of tissue oxygen (pO2) was measured in rat somatosensory cortex during periodic electrical forepaw stimulation of either 1 min or 4 s in duration, and correlated with simultaneous laser Doppler flowmetry. For both stimulus durations, a transient decrease in tissue pO2 preceded blood flow changes, followed by a peak in blood flow and an overshoot in tissue pO2. With protracted stimulation, tissue pO2 remained only slightly above pre-stimulus baseline, while blood flow was maintained at a reduced plateau phase. A sustained post-stimulus undershoot in tissue pO2 was observed only for the 1 min stimulus. These findings suggest a complex dynamic relationship between oxygen utilization and blood flow.

Afferent Pathways↗

PubMed2002

Surface tension and its temperature coefficient of molten tin determined with the sessile drop method at different oxygen partial pressures.

The surface tension of molten tin has been determined by the sessile drop method at temperatures ranging from 523 to 1033 K and in the oxygen partial pressure (P(O(2))) range from 2.85 x 10(-19) to 8.56 x 10(-6) MPa, and its dependence on temperature and oxygen partial pressure has been analyzed. At P(O(2))=2.85 x 10(-19) and 1.06 x 10(-15) MPa, the surface tension decreases linearly with the increase of temperature and its temperature coefficients are -0.151 and -0.094 mN m(-1) K(-1), respectively. However, at high P(O(2)) (3.17 x 10(-10), 8.56 x 10(-6) MPa), the surface tension increases with the temperature near the melting point (505 K) and decreases above 723 K. The surface tension decrease with increasing P(O(2)) is much larger near the melting point than at temperatures above 823 K. The contact angle between the molten tin and the alumina substrate is 158-173 degrees, and the wettability is poor.

Journal Article↗

PubMed1997

Effects of reduced oxygen partial pressure on cognitive performance in confined spaces.

The reduction of oxygen levels is a technique used both for fire fighting and fire protection in confined spaces. The purpose of this study was to find out if and how reduced oxygen levels affect cognitive performance in a small group of persons living in a confined space such as a submarine. In 3 separate experiments lasting for 11 to 14 days, a total of 22 men were exposed to normoxic and different levels of hypoxic normobaric atmospheres (15, 14, and 13 kPa O2). Each participant completed a cognitive test battery twice every 24-hr period in the first 2 experiments, but only once a day in the 3rd experiment. Performance in almost all tests improved with the number of test sessions performed, despite reductions of the oxygen partial pressure. Under the conditions tested, cognitive performance decrements could not be observed if inspiratory oxygen partial pressure was kept above 13 kPa.

Adult↗

PubMed1991

[CO2-induced acral blood flow and the oxygen partial pressure in arterial occlusive disease].

The effect of CO2-containing water on foot skin blood flow (laser-Doppler flux) and transcutaneous oxygen partial pressure (tcpO2) was measured in 16 patients (15 men and 1 woman; mean age 58 [49-71] years) with peripheral arterial occlusive disease (stage II of Fontaine: bilateral occlusions of the superficial femoral arteries). After 30 minutes lying down and 10 minutes sitting up, one lower leg was immersed in fresh water, the other in CO2-containing water (1400 mg CO2/kg H2O), both at 34 degrees C for 20 minutes. On the next day the measurements were repeated changing sides. Skin blood flow of the dorsum of the foot and rhythmic flow oscillations (flux motion) increased threefold in the CO2 water-bath, after a latency period averaging 2 minutes, within 3 minutes from 1.1 to 3.9 relative units (P less than 0.005). Average tcpO2 increased during the bath in CO2 water by 9 mm Hg (P less than 0.005). There was no change in fresh water. The increase in cutaneous blood flow and oxygen partial pressure, which persisted throughout the period in CO2 water, is interpreted as an increase in microcirculation and can explain part of the effectiveness of this largely empirical treatment.

Aged↗

PubMed1994

Growth of soybean and potato at high CO2 partial pressures.

Soybean and potato plants were grown in controlled environments at carbon dioxide (CO2) partial pressures ranging from 0.05 to 1.00 kPa. The highest yields of edible biomass occurred at 0.10 kPa for both species, with higher CO2 levels being supraoptimal, but not injurious to the plants. Stomatal conductance rates of upper canopy leaves were lowest at 0.10 kPa CO2, while conductance rates at 0.50 and 1.00 kPa were significantly greater than 0.10 kPa. Total water use by the plants was greatest at the highest CO2 pressures (i.e. 0.50 and 1.00 kPa); consequently, water use efficiencies (biomass produced/water used) were low at the highest CO2 pressures. Based on previous CO2 studies in the literature, the increased conductance and water use at the highest CO2 pressures were surprising and pose interesting challenges for managing plants in a CELSS, where CO2 pressures may exceed optimal levels.

Atmospheric Pressure↗

PubMed2003

Effect of intra-operative end-tidal carbon dioxide partial pressure on tissue oxygenation.

Postsurgical infection risk is correlated with subcutaneous tissue oxygenation. Mild hypercapnia augments cutaneous perfusion. We tested the hypothesis that peripheral tissue oxygenation increases as a function of arterial PCO2 in surgical patients. Twenty patients were randomly assigned to intra-operative end tidal PCO2 of 3.99 (control) or 5.99 kPa (hypercapnia). All other anaesthetic management was per protocol. Tissue oxygen partial pressure, transcutaneous oxygen tension, cerebral oxygen saturation, and cardiac output were measured. Mean (SD) subcutaneous tissue oxygen tension was 8.39 (1.86) kPa in control and 11.84 (2.53) kPa hypercapnia patients (p = 0.014). Cerebral oxygen saturation was 55 (4)% for control vs. 68 (9)% for hypercapnia (p = 0.004). Neither cardiac index nor transcutaneous tissue oxygen tension differed significantly between the groups. Mild intra-operative hypercapnia increased subcutaneous and cerebral oxygenation. Increases in subcutaneous tissue oxygen partial pressure similar to those observed in patients assigned to hypercapnia are associated with substantial reductions in wound infection risk.

Adult↗

PubMed1990

Changes in alveolar-arterial oxygen partial pressure difference during orthotopic liver transplantation.

Changes in the alveolar-arterial oxygen partial pressure difference (PAO2-PaO2) were measured in 39 patients undergoing orthotopic liver transplantation without veno-arterial or veno-venous bypass. The operation can be divided into an initial dissection phase, an anhepatic phase when the hepatic artery, portal vein and vena cava are clamped, and a post-anhepatic phase after the vascular clamps are released. There was an initial increase in (PAO2-PaO2) during the dissection phase, followed by an immediate decrease when the liver was removed. This decrease continued throughout the anhepatic period, but a further increase in (PAO2-PaO2) occurred after release of all the vascular clamps and during abdominal closure.

Adolescent↗

PubMed1986

[Airway pressure and transcutaneous O2 and CO2 partial pressure as monitoring measurements for high-frequency jet ventilation?].

Two different methods of measuring airway pressures (n = 7), and the usefulness of transcutaneous pO2 and pCO2 measurement (n = 9) in monitoring High Frequency Jet Ventilation (HFJV), were investigated in critically ill patients. Airway pressures obtained by tip manometer from different points within trachea and mainstem bronchi during HFJV (f = 100/min, inspiratory time 40%, FIO2 0,4, minute volume 25.6 +/- 5.2 l) were nearly identical with pressures obtained from the integrated pressure line of HI-LO-JET endotracheal tubes (R = 0.9638). There was no difference between proximal and peripheral airway pressures. When using a PEEP-valve, rather high values of PEEP may occur due to gas trapping. There was sufficient correlation between transcutaneous and arterial pO2 (R = 0.7573) and poor correlation between transcutaneous and arterial pCO2 (R = 0.4987). paO2 values were 51.1% above, paCO2 values 33.4% below transcutaneous values. Transcutaneous measurement of pO2 and pCO2 is only an additional method in monitoring HFJV which can reveal rough trends but cannot replace blood gas analysis.

Adult↗

PubMed1995

Does the threshold of transcutaneous partial pressure of carbon dioxide represent the respiratory compensation point or anaerobic threshold?

On reaching the respiratory compensation point (RCP) during rapidly increasing incremental exercise, the ratio of minute ventilation (VE) to CO2 output (VCO2) rises, which coincides with changes of arterial partial pressure of carbon dioxide (PaCO2). Since PaCO2 changes can be monitored by transcutaneous partial pressure of carbon dioxide (PCO2,tc) RCP may be estimated by PCO2,tc measurement. Few available studies, however, have dealt with comparisons between PCO2,tc threshold (TAT) and lactic, ventilatory or gas exchange threshold (VAT), and the results have been conflicting. This study was designed to examine whether this threshold represents RCP rather than VAT. A group of 11 male athletes performed incremental exercise (25 W.min-1) on a cycle ergometer. The PCO2,tc at (44 degrees C) was continuously measured. Gas exchange was computed breath-by-breath and hyperaemized capillary blood for lactate concentration ([la-]b) and PaCO2 measurements was sampled each 2 min. The TAT was determined at the deflection point of PCO2,tc curve where PCO2,tc began to decrease continuously. The VAT and RCP were evaluated with VCO2 compared with oxygen uptake (VO2) and VE compared with the VCO2 method, respectively. The PCO2,tc correlated with PaCO2 and end-tidal PCO2. At TAT, power output [P, 294 (SD 40) W], VO2 [4.18 (SD 0.57) l.min.1] and [la(-)] [4.40 (SD 0.64) mmol.l-1] were significantly higher than those at VAT[P 242 (SD 26) W, VO2 3.56 (SD 0.53) l.min-1 and [la(-)]b 3.52 (SD 0.75), mmol.l-1 respectively], but close to those at RCP [P 289 (SD 37) W; VO2 3.97 (SD 0.43) l.min-1 and [la(-)]b 4.19 (SD 0.62) mmol.l-1, respectively]. Accordingly, linear correlation and regression analyses showed that P, VO2 and [la(-)]b at TAT were closer to those at RCP than at VAT. In conclusion, the TAT reflected the RCP rather than VAT during rapidly increasing incremental exercise.

Adult↗

PubMed2000

The cultivation of animal cells at controlled dissolved oxygen partial pressure. Reprinted from Biotechnology and Bioengineering Vol. X, Issue 6, Pages 801-814 (1968).

A 3-liter culture vessel has been developed for the growth of animal cells in suspension at controlled pH and dissolved oxygen partial pressure (pO(2)). The culture technique allows metabolically produced CO(2) to be measured; provision can be made to control the dissolved CO(2) partial pressure. In cultures containing a low serum concentration, gas sparging to control pO(2) was found to cause cell damage. This could be prevented by increasing the serum concentration to 10%, or by adding 0.02% of the surface-active polymer Pluronic F68. The growth of mouse LS cells in batch culture without pO(2) control was found to be limited by the availability of oxygen. Maximum viable cell populations were obtained when dissolved pO(2) was controlled at values within the range 40-100 mm Hg.

Animals↗

PubMed1980

Measurements of the partial pressure of oxygen in the carotid body of fetal sheep and newborn lambs.

The partial pressure of oxygen in chemoreceptors tissue of the carotid body was measured in parallel with arterial oxygen tension in eleven sheep fetuses exteriorized from 9 ewes anaesthetized with pentobarbitone, in 6 of these fetuses in the transitional period following occlusion of the umbilical cord and the start of artificial pulmonary ventilation and in 6 naturally born lambs, 10-36 h old. In the fetal carotid body, O2 gradients were very small and, in the majority of tests, the arterial-to-tissue O2 difference was small or negligible. During the transitional period, this difference increased as arterial PO2 rose and in the newborn lamb, this difference was as large as that reported in the adult carotid body. These results indicate that in the fetal carotid body, the levels of blood flow and metabolism are likely to be homogeneous and that the ratio of O2 supply and O2 consumption is high, that in the transitional period and in the newborn, either O2 supply falls or O2 consumption increases or both, and that these changes are both O2-dependent and persist although arterial PO2 in the newborn is reduced to or close to fetal levels. The possible mechanisms are discussed.

Aged↗

PubMed1988

Value of measuring end tidal partial pressure of carbon dioxide as an adjunct to treadmill exercise testing.

The end tidal partial pressure of carbon dioxide (PCO2) was measured during treadmill exercise in 30 normal controls and 113 patients referred for assessment of chest pain. Among the 92 patients without significant ST depression hypocapnia occurred more often in those reporting "typical" than "atypical" chest pain (17 of 22 patients compared with 29 of 70; p less than 0.01). Hypocapnia was uncommon in patients with significant ST depression whether reporting typical or atypical chest pain (one of 10 patients and two of 11, respectively). Hypocapnia at rest (PCO2 less than 4 kPa) occurred in 16 (14%) patients but in only one control. Hypocapnia occurred during or after exercise in only one control and three of the 21 patients with significant ST depression on exercise (group 1). The remaining 92 patients were divided into those with a history suggestive of hyperventilation (group 2; n = 30) and those without (group 3; n = 62). Hypocapnia developed significantly more often in both these groups (21 and 25 patients respectively) than in controls or patients with significant ST depression. An abnormal response of the PCO2 to exercise provided objective data to support a clinical suspicion of chest pain induced by hyperventilation in 24 cases, suggested a cause for equivocal ST depression other than coronary stenosis in five patients, and led to the diagnosis of previously unsuspected respiratory disease in 14 patients. Measurement of end tidal PCO2 gives additional valuable diagnostic information during the conventional treadmill exercise test in patients with both typical and atypical chest pain.

Carbon Dioxide↗

PubMed1981

[Effect of oxygen partial pressure on citric acid synthesis in Saccharomycopsis lipolytica using n-alkanes].

The dependence of growth formation of citric acids (citrate: isocitrate = 1:1) on oxygen parital pressure of an alkane utilising yeast Saccharomycopsis lipolytica was investigated. During growth oxygen corresponds to a Michaelis-Menten-kinetics (Ks = 2.0 . 10(-5) M). The respiration quotient RQ for a dissolved oxygen concentration in the range of 10-100% (air saturation) is 0.46 +/- +/- 0.04. The phase of product formation is characterized by 3 sections. Immediately after N-exhaustion the cell activities are the highest. They decline during the first 30 hours of production. Besides the production of reserve material in this first section the highest production rate for citrate and isocitrate is observed. The rate of citric acid production depends on the oxygen partial pressure and is governed by Michaelis-Menten-kinetics. The specific production rate and the rate of oxygen consumption correspond to KS-values of 4.0 X 10(-5) and 3.3 X 10(-5) M, respectively. The RQ-value declines to a constant value of 0.23 +/- 0.02 and is not influenced by oxygen partial pressures in the range of 10--100% (related to air saturation). During the second section cell activities remain nearly constant for about 100 h. Due to this constancy the following equation could be derived: 14 O2 + C15H32 leads to 2 C6H8O7 + 3 CO2 + 8 H2O. In the third section the cell activities decline again.

Aerobiosis↗

PubMed1987

Human corticotropin-releasing hormone in man: dose-response of minute ventilation and end-tidal partial pressures of carbon dioxide and oxygen.

The respiratory stimulant properties of iv injections of 33, 67, and 100 micrograms synthetic human corticotropin-releasing hormone (hCRH) were studied in 12 normal men in a single blind, placebo-controlled trial. All doses of hCRH induced a respiratory stimulation in every subject, and the stimulation was dose dependent. The onset of respiratory stimulation occurred within 15-30 sec after hCRH infusion was started. Initially, there was an increase in tidal volume (VT), followed by an increase in respiratory rate. The maximum minute ventilation (VE) occurred 60-120 sec after starting the injection. The 33-micrograms hCRH dose induced a 35% increase in VE from 6.3 +/- 0.6 (+/- SD) to 9.7 +/- 1.3 liters/min (P less than 0.001) due to a marked increase in VT from 531 +/- 105 to 688 +/- 142 ml (P less than 0.001) and only a slight increase in the respiratory rate from 12.4 +/- 3.0 to 14.3 +/- 3.1 breaths/min (P less than 0.001); heart rate was not altered at this dose. The 100-micrograms hCRH dose increased the VE by 81% to 11.5 +/- 1.5 liters/min, mainly due to an increase in VT. VE was elevated for 5.8, 7.2, or 8.3 min after the end of injection of the three hCRH doses. Increases in VE markedly lowered the end-tidal partial pressure of carbon dioxide (P(ET)CO2; nearly identical with the arterial PCO2 in normal subjects). hCRH (33 micrograms) lowered P(ET)CO2 from 40.3 +/- 1.2 to 37.2 +/- 1.9 mm Hg (P less than 0.001), and 100 micrograms hCRH lowered P(ET)CO2 to 33.4 +/- 1.2 mm Hg. End-tidal partial pressure of oxygen, i.e. the most sensitive parameter for the duration of action of respiratory stimulation, was elevated for 8.5, 10.2, and 14 min after injection of 33, 67, or 100 micrograms hCRH. Sixty-seven micrograms of hCRH was the lowest effective dose for an increase in the heart rate (from 66.4 to 79.0 beats/min; P less than 0.001), and 100 micrograms hCRH markedly increased the heart rate by 20% to a peak value of 83.5 beats/min. Heart rate increased within 90 sec and returned to the control value after 5-10 min. These data suggest that hCRH is a rapidly acting, dose-dependent, and potent respiratory stimulant. Since this hyperventilatory effect of hCRH occurred in every subject after all doses tested, respiratory stimulation may represent specific biological activity of CRH rather than a side-effect.

Adult↗

PubMed1975

[Transcutaneous measurement of partial pressure of oxygen in paediatric intensive care (author's transl)].

The method of measuring oxygen partial pressure transcutaneously has provided an opportunity for continuous monitoring of patients on long-term resporator treatment. It has been convincingly demonstrated that serial samples obtained by arterial puncture are inadequate for controlling oxygen supply. An ideal correlation between arterial and transcutaneous pO2 was obtained when the control arterial sample was taken via an indwelling arterial catheter and artefacts, e.g. reaction to the needle puncture, had been eliminated. The necessary percentage of oxygen in the inspiratory mixture can be accurately gauged by continously measuring arterial pO2, as can changes brought about by the application of positive end-expiratory pressure in children on long-term ventilation. The transcutaneous measurement makes it possible to improve continuous monitoring of critically ill patients, and to carry out sparingly and safely long-term ventilation in them.

Blood Gas Analysis↗

PubMed1985

Effects of dibutyryl cyclic AMP and gonadotropin-releasing hormone added prior to filter sterilization of the media and variation in oxygen partial pressure on output of human chorionic gonadotropin from term placental explants.

The effect of 2 mM dibutyryl cyclic AMP (dbcAMP) and 10 and 100 micrograms/ml gonadotropin-releasing hormone (GnRH) added prior to filter sterilization and of varying oxygen partial pressure (5, 20, and 95% oxygen) were evaluated using explants from each of 4 placentas on each of 6 days of culture. There were significant differences between placentas on days 1 and 2 of culture (both p less than 0.025), and day 4 (p less than 0.05), but there were no effects of GnRH or varying oxygen partial pressure on output of human chorionic gonadotropin under the conditions evaluated.

Bucladesine↗

PubMed1997

A new method for measurement of anaesthetic partial pressure in blood.

We have developed a simple, reliable method for rapid analysis of the partial pressure of volatile anaesthetic agents, based on a two-stage, head-space analysis. It is designed to solve the problems associated with reduced solubility of modern anaesthetics. After equilibration and analysis of a 2-ml sample of blood at 37 degrees C, 1 ml is transferred to another vial for a second equilibration. This ensures that there is no vapour in the headspace before the second equilibration. Measurements were performed on human blood samples equilibrated with 1% sevoflurane, 2.5% isoflurane or 3% desflurane in a tonometer. The mean error in the sample measurements was -2.3% of the tonometer reading and the 95% confidence interval for an individual measurement was +/- 8.5%. Blood samples may be stored overnight without any significant change in the results.

Anesthetics, Inhalation↗

PubMed1990

Partial pressures of oxygen and carbon dioxide, pH, and concentrations of bicarbonate, lactate, and glucose in pleural fluid from horses.

Samples of pleural fluid from 20 horses with effusive pleural diseases of various causes were evaluated; samples from 19 horses were used for the study. There were differences for pH (P = 0.001) and partial pressure of oxygen (PO2) between arterial blood and nonseptic pleural fluid (P = 0.0491), but there were no differences for pH, PO2, partial pressure of carbon dioxide (PCO2), and concentrations of bicarbonate (HCO3-), lactate, and glucose between venous blood and nonseptic pleural fluid. Paired comparisons of venous blood and nonseptic pleural fluid from the same horse indicated no differences. There were differences (P = 0.0001, each) for pH, PO2, PCO2, and concentrations of HCO3- between arterial blood and septic pleural fluid. Differences also existed for pH (P = 0.0001), PCO2 (P = 0.0003), and concentrations of HCO3- (P = 0.0001), lactate (P = 0.0051), and glucose (P = 0.0001) between venous blood and septic pleural fluid. Difference was not found for values of PO2 between venous blood and septic pleural fluid, although 4 samples of septic pleural fluid contained virtually no oxygen. Paired comparisons of venous blood and septic pleural fluid from the same horse revealed differences (P less than 0.05) for all values, except those for PO2. These alterations suggested functional and physical compartmentalization that separated septic and healthy tissue. Compartmentalization and microenvironmental factors at the site of infection should be considered when developing therapeutic strategies for horses with septic pleural disease.

Animals↗