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PubMed1987

Noninvasive monitoring of carbon dioxide: a comparison of the partial pressure of transcutaneous and end-tidal carbon dioxide with the partial pressure of arterial carbon dioxide.

This study compares two noninvasive techniques for monitoring the partial pressure of carbon dioxide (PCO2) in 24 anesthetized adult patients. End-tidal PCO2 (PetCO2) and transcutaneous PCO2 (PtcCO2) were simultaneously monitored and compared with arterial PCO2 (PaCO2) determined by intermittent analysis of arterial blood samples. PETCO2 and PtcCO2 values were compared with PaCO2 values corrected to patient body temperature (PaCO2T) and PaCO2 values determined at a temperature of 37 degrees C (PaCO2). Linear regression was performed along with calculations of the correlation coefficient (r), bias, and precision of the four paired variables: PETCO2 versus PaCO2 and PaCO2T (n = 211), and PtcCO2 versus PaCO2 and PaCO2T (n = 233). Bias is defined as the mean difference between paired values, whereas precision is the standard deviation of the difference. The following values were found for r, bias, and +/- precision, respectively. PETCO2 versus PaCO2: 0.67, -7.8 mm Hg, +/- 6.1 mm Hg; PETCO2 versus PaCO2T: 0.73, -5.8 mm Hg, +/- 5.9 mm Hg; PtcCO2 versus PaCO2: 0.87, -1.6 mm Hg, +/- 4.3 mm Hg; PtcCO2 versus PaCO2T: 0.84, +0.7 mm Hg, +/- 4.8 mm Hg. Although each of these PCO2 variables is physiologically different, there is a significant correlation (P less than 0.001) between the noninvasively monitored values and the blood gas values. Temperature correction of the arterial values (PaCO2T) slightly improved the correlation, with respect to PETCO2, but it had the opposite effect for PtcCO2. In this study, the chief distinction between these two noninvasive monitors was that PETCO2 had a large negative bias, whereas PtcCO2 had a small bias. We conclude from these data that PtcCO2 may be used to estimate PaCO2 with an accuracy similar to that of PETCO2 in anesthetized patients.

Adult↗
PubMed1968

Growth of Streptococcus faecalis under high hydrostatic pressure and high partial pressures of inert gases.

Growth of Streptococcus faecalis in a complex medium was inhibited by xenon, nitrous oxide, argon, and nitrogen at gas pressures of 41 atm or less. The order of inhibitory potency was: xenon and nitrous oxide > argon > nitrogen. Helium appeared to be impotent. Oxygen also inhibited streptococcal growth and it acted synergistically with narcotic gases. Growth was slowed somewhat by 41 atm hydrostatic pressure in the absence of narcotic gases, but the gas effects were greater than those due to pressure. In relation to the sensitivity of this bacterium to pressure, we found that the volume of cultures increased during growth in a volumeter or dilatometer, and that this dilatation was due mainly to glycolysis. A volume increase of 20.3 +/- 3.6 ml/mole of lactic acid produced was measured, and this value was close to one of 24 ml/mole lactic acid given for muscle glycolysis, and interestingly, close to the theoretic volume increase of activation calculated from the depression of growth rate by pressure.

Argon↗
PubMed1977

[Experimentally induced alterations in wedge pressure and O2-partial pressure during acute hypoxia].

Suprarenal occlusion of the aorta by means of a balloon catheter results in an increase in wedge pressure, alterations in blood flow in the pulmonary circulation, and an increase in O2 partial pressure in the arterial blood. It is demonstrated that these changes take place after occlusion of the aorta during normoxia or hypoxia (Pao2:43 mmHg) in anaesthetized normotensive or spontaneously hypertensive mongrel dogs.

Acute Disease↗
PubMed2004

Liver tissue partial pressure of oxygen and carbon dioxide during partial hepatectomy.

BACKGROUND: Data on tissue oxygen partial pressure (PtO2) and carbon dioxide partial pressure (PtCO2) in human liver tissue are limited. We set out to measure changes in liver PtO2 and PtCO2 during changes in ventilation and a 10 min period of ischaemia in patients undergoing liver resection using a multiple sensor (Paratrend Diametrics Medical Ltd, High Wycombe, UK). METHODS: Liver tissue oxygenation was measured in anaesthetized patients undergoing liver resection using a sensor inserted under the liver capsule. PtO2 and PtCO2 were recorded with FIO2 values of 0.3 and 1.0, at end-tidal carbon dioxide partial pressures of 3.5 and 4.5 kPa and 10 min after the onset of liver ischaemia (Pringle manoeuvre). RESULTS: Data are expressed as median (interquartile range). Increasing the FIO2 from 0.3 to 1.0 resulted in the PtO2 changing from 4.1 (2.6-5.4) to 4.6 (3.8-5.2) kPa, but this was not significant. During the 10 min period of ischaemia PtCO2 increased significantly (P<0.05) from 6.7 (5.8-7.0) to 11.5 (9.7-15.3) kPa and PtO2 decreased, but not significantly, from 4.3 (3.5-12.0) to 3.3 (0.9-4.1) kPa. CONCLUSION: PtO2 and PtCO2 were measured directly using a Paratrend sensor in human liver tissue. During anaesthesia, changes in ventilation and liver blood flow caused predictable changes in PtCO2.

Anesthesia, General↗
PubMed2002

19F-MRI of perflubron for measurement of oxygen partial pressure in porcine lungs during partial liquid ventilation.

A method for in vivo measurement of oxygen partial pressure (pO2) in porcine lungs during partial liquid ventilation (PLV) with perflubron (PFOB) was developed. A pulse sequence for high-resolution MRI of the distribution of PFOB in the lung after intratracheal administration was developed as well. Moreover, quantitative measurements of longitudinal relaxation time T(1) of (19)F resonances for assessment of regional pO2 are described. Due to the need to acquire data during a single expiratory breathhold, only low SNRs were achieved in vivo. Therefore, simulations were performed to investigate the influence of background noise on T(1) values calculated from data with low SNR. Based on these simulations, a postprocessing strategy was developed to correct for systematic errors by background noise prior to quantitative analysis. Results of a pilot study in pigs under conditions of PLV are presented.

Animals↗
PubMed1969

Resistance of the protozoan Colpoda maupasi to Martian conditions of atmospheric pressure and low partial pressure of oxygen.

Among the most important factors limiting the active life of animal organisms in Martian conditions are low atmospheric pressure and insignificant amounts of oxygen in the atmosphere (no more than 0.15% of the Earth's atmosphere). The experiments with aerobic protozoon C. maupasi have shown that in conditions of hermetically sealed chambers, for instance in 2.5 liter anaerostats, the protozoon can survive for a long time and reproduce in an atmosphere of air or nitrogen containing 1 or 0.0005% oxygen at a pressure from 15 mm Hg and higher. At the atmospheric pressure 10 mm Hg we observed a considerable decrease in the survival percentage and no reproduction. The exposure to 5 mm Hg resulted in a 100 per cent mortality of the protozoon. In a specially-constructed chamber "Photostat", in which current atmosphere pressure were automatically maintained during an experiment of many days, the reaction of the infusoria was somewhat different: they reproduced and existed not only at the pressure of 10-15 mm Hg, but also at 5 mm Hg, in an atmosphere of both air and nitrogen containing from 1 to 0.0005% O2. This indicates not only low-oxygen consumption of unicellular animals but also the capability of cells to extract some traces of this gas from the atmosphere. Low pressure and some traces of oxygen in the Martian atmosphere are not an impediment for the existence of some of the Earth's animals, such as the protozoon C. maupasi for example.

Anaerobiosis↗
PubMedDate not supplied

[Intra-articular oxygen partial pressure measurements under functional conditions].

Oxygen partial pressure is directly related to the vascularisation of different tissues. Different investigations in tissue (muscle, kidney, brain, heart, bone etc.) proved this correlation. The development of a special flexible microcatheter named Licox enables us to do measurements of intraarticular oxygen partial pressure under physiological and pathological conditions for the first time. The aim of this study was to examine the influence of different knee joint stresses on the intraarticular oxygen partial pressure under normal conditions and in osteoarthritis. The results showed that the different exercise patterns influence the intraarticular oxygen partial pressure. Patients with osteoarthritis showed a lower increase of the intraarticular oxygen partial pressure compared to the control group. This phenomenon is directly correlated to degree velocity of the isokinetic exercises. The same findings occur under ergometric conditions. The method permits functional, intraarticular in vivo measurements under different exercise patterns. For the very first time we were able to measure the influence of the joint movement on the intraarticular process of nutrition under physiological and pathological conditions. Different therapy concepts in osteoarthritis can be evaluated directly in vivo for the first time.

Adult↗
PubMed1999

Mastoid buffering properties: I. Gas partial pressures.

Differences in the gas partial pressures between the middle ear (ME) cavity and the blood are an important factor in ME gas economy. Differences in gas partial pressures between various regions of the ME-mastoid air cell system (ME-MACS) could play a role as well. To determine whether gas partial pressure differences do occur between various compartments in the ME, we measured the rate of gas diffusion from one compartment to another in both an artificial model and in the ME-MACS of human temporal bones. The rate of gas diffusion between various areas of the ME and the mastoid tip was found to be rapid, with a half-life on the order of 2 minutes (range 0.8 to 5.3 minutes). We suggest that this high diffusion rate prevents the buildup of significant differences in gas composition in the ME-MACS system, which can therefore be regarded as a homogeneous gas pocket.

Diffusion↗
PubMed1993

Components of the inspiratory-arterial isoflurane partial pressure difference.

We have measured the partial pressure of isoflurane simultaneously in inspired gas (PIiso), end-expired gas (PE'iso), mixed-expired gas (PEiso), arterial (Paiso) and mixed venous blood (Pviso) in six patients (aged 57-79 yr) anaesthetized with nitrous oxide, oxygen and isoflurane before surgery and after PE'iso had been stable for at least 15 min. We related these changes to the various indices of pulmonary maldistribution to determine if they were sufficient to explain reported differences between PE'iso and Paiso. Alveolar deadspace dilution of end-expired gas was calculated for carbon dioxide and this dilution factor used to calculate the "ideal" alveolar Piso (PAiso) from the observed inspired and end-expired concentrations. Shunt fraction was measured for oxygen and then used to calculate the partial pressure of isoflurane in the pulmonary end-capillary blood (Pc'iso) from the partial pressure in arterial and mixed venous blood. Mean (SE) values were: PIiso 0.69 (0.05) kPa; PE'iso 0.52 (0.04) kPa; PAiso 0.50 (0.04) kPa; Pc'iso 0.38 (0.04) kPa; Paiso 0.35 (0.03) kPa and Pviso 0.22 (0.02) kPa; Paiso: PE'iso 0.66 (0.02) kPa. The mean "ideal" alveolar to pulmonary end-capillary Piso difference was 0.12 (0.01) kPa and highly significant (P < 0.001). Paiso was substantially less than PE'iso but, for isoflurane, the difference was reasonably constant (range 0.14-0.22 kPa). The difference was attributable in part to the effects of shunt and deadspace, but also a failure of equilibration of isoflurane between the alveolar gas and pulmonary end-capillary blood. It is likely to be different for other anaesthetics. We conclude that, while PE'iso may adequately reflect Paiso for isoflurane, it cannot be assumed that the relation between end-expiratory gas and arterial partial pressures is the same for all anaesthetics.

Aged↗
PubMed1988

Hydrogen partial pressures in a thermophilic acetate-oxidizing methanogenic coculture.

Hydrogen partial pressures were measured in a thermophilic coculture comprised of a eubacterial rod which oxidized acetate to H(2) and CO(2) and a hydrogenotrophic methanogen, Methanobacterium sp. strain THF. Zinder and Koch (S. H. Zinder and M. Koch, Arch. Microbiol. 138:263-272, 1984) originally predicted, on the basis of calculations of Gibbs free energies of reactions, that the H(2) partial pressure near the midpoint of growth of the coculture should be near 4 Pa (ca. 4 x 10 atm; ca. 0.024 muM dissolved H(2)) for both organisms to be able to conserve energy for growth. H(2) partial pressures in the coculture were measured to be between 20 and 50 Pa (0.12 to 0.30 muM) during acetate utilization, approximately one order of magnitude higher than originally predicted. However, when DeltaG(f) (free energy of formation) values were corrected for 60 degrees C by using the relationship DeltaG(f) = DeltaH(f) - TDeltaS (DeltaH(f) is the enthalpy or heat of formation, DeltaS is the entropy value, and T is the temperature in kelvins), the predicted value was near 15 Pa, in closer agreement with the experimentally determined values. The coculture also oxidized ethanol to acetate, a more thermodynamically favorable reaction than oxidation of acetate to CO(2). During ethanol oxidation, the H(2) partial pressure reached values as high as 200 Pa. Acetate was not used until after the ethanol was consumed and the H(2) partial pressure decreased to 40 to 50 Pa. After acetate utilization, H(2) partial pressures fell to approximately 10 Pa and remained there, indicating a threshold for H(2) utilization by the methanogen. Axenic cultures of the acetate-oxidizing organism were combined with pure cultures of either Methanobacterium sp. strain THF or Methanobacterium thermoautotrophicum DeltaH to form reconstituted acetate-oxidizing cocultures. The H(2) partial pressures measured in both of these reconstituted cocultures were similar to those measured in the original acetate-oxidizing rod coculture. Since M. thermoautotrophicum DeltaH did not use formate as a substrate, formate is not necessarily involved in interspecies electron transfer in this coculture.

Journal Article↗
PubMed1982

A Direct Confirmation of the Standard Method of Estimating Intercellular Partial Pressure of CO(2).

The partial pressure of CO(2) inside leaves of several species was measured directly. Small gas exchange chambers were clamped above and below the same section of an amphistomatous leaf. A flowing gas stream through one chamber allowed normal CO(2) and water vapor exchange. The other chamber was in a closed circuit consisting of the chamber, an infrared gas analyzer, and a peristaltic pump. The CO(2) in the closed system rapidly reached a steady pressure which it is believed was identical to the CO(2) pressure inside the leaf, because there was no flux of CO(2) across the epidermis. This measured partial pressure was in close agreement with that estimated from a consideration of the fluxes of CO(2) and vapor at the other surface.

Journal Article↗
PubMed2001

Canopy position and needle age affect photosynthetic response in field-grown Pinus radiata after five years of exposure to elevated carbon dioxide partial pressure.

Photosynthesis of tree seedlings is generally enhanced during short-term exposure to elevated atmospheric CO2 partial pressure, but longer-term studies often indicate some degree of photosynthetic adjustment. We present physiological and biochemical evidence to explain observed long-term photosynthetic responses to elevated CO2 partial pressure as influenced by needle age and canopy position. We grew Pinus radiata D. Don. trees in open-top chambers for 5 years in sandy soil at ambient (36 Pa) and elevated (65 Pa) CO2 partial pressures. The trees were well watered and exposed to natural light and ambient temperature. In the fourth year of CO2 exposure (fall 1997), when foliage growth had ceased for the year, photosynthetic down-regulation was observed in 1-year-old needles, but not in current-year needles, suggesting a reduction in carbohydrate sink strength as a result of increasing needle age (Turnbull et al. 1998). In 5-year-old trees (spring 1997), when foliage expansion was occurring, photosynthetic down-regulation was not observed, reflecting significantly large sinks for carbohydrates throughout the tree. Net photosynthesis was stimulated by 79% in trees growing in elevated CO2 partial pressure, but there was no significant effect on photosynthetic capacity or Rubisco activity and concentration. Current-year needles were more responsive to elevated CO2 partial pressure than 1-year-old needles, exhibiting larger relative increases in net photosynthesis to elevated CO2 partial pressure (98 versus 64%). Lower canopy and upper canopy leaves exhibited similar relative responses to growth in elevated CO2 partial pressure. However, needles in the upper canopy exhibited higher net photosynthesis, photosynthetic capacity, and Rubisco activity and concentration than needles in the lower canopy. Given that the ratio of mature to juvenile foliage mass in the canopy will increase as trees mature, we suggest that trees may become less responsive to elevated CO2 partial pressure with increasing age. We conclude that tree response to elevated CO2 partial pressure is based primarily on sink strength and not on the duration of exposure.

Carbon Dioxide↗
PubMed1990

[The arterial-end tidal CO2 partial pressure difference during anesthesia].

Arterial CO2 partial pressure (PaCO2) can be continuously and noninvasively estimated by monitoring end-tidal CO2 partial pressure (PetCO2). However, the difference between the two (P(a-et)CO2) may vary considerably between patients. In 26 patients undergoing general anesthesia for various surgical procedures, P(a-et)CO2 was measured. We tested the hypothesis that certain clinical characteristics are associated with higher P(a-et)CO2 values in a given patient. In addition, we tested the hypothesis that P(a-et)CO2 remains constant during anesthesia by comparing the mean of eight P(a-et)CO2 values, which were measured at 15-min intervals, with the initial (P(a-et)CO2 value. Impaired lung function, defined as a lung score above 6, age above 50 years, and overweight (defined as greater than 120% of ideal body weight) were associated with increased P(a-et)CO2 (mean +/- SD: 6.27 +/- 1.85; 5.27 +/- 2.11; and 6.19 +/- 1.95 mmHg respectively) when compared to normal lung function (lung score less than or equal to 6), age below 50 years, and normal weight (less than 120% of ideal body weight, 3.87 +/- 2.31; 3.55 +/- 2.58; and 3.77 +/- 2.25 respectively). Although these differences are statistically significant, the standard deviations are large and do not allow the prediction of P(a-et)CO2 in a given patient. Initial P(a-et)CO2 correlated well with subsequent P(a-et)CO2 (R = 0.91, P less than 0.001). The mean difference of the subsequent P(a-et)CO2 values from the initial values was 0.05 +/- 0.80 mmHg (mean +/- SD) and was not significantly different from zero. In the patient population studied, P(a-et)CO2 thus remained generally constant during anesthesia.

Adult↗
PubMed1983

Expiratory and arterial partial pressure relations under different ventilation-perfusion conditions.

Inert tracer gas exchange across the human respiratory system is simulated in an asymmetric lung model for different oscillatory breathing patterns. The momentary volume-averaged alveolar partial pressure (PA), the expiratory partial pressure (PE), the mixed expiratory partial pressure (PE), the end-tidal partial pressure (PET), and the mean arterial partial pressure (Pa), are calculated as functions of the blood-gas partition coefficient (lambda) and the diffusion coefficient (D) of the tracer gas. The lambda values vary from 0.01 to 330.0 inclusive, and four values of D are used (0.5, 0.22, 0.1, and 0.01). Three ventilation-perfusion conditions corresponding to rest and mild and moderate exercise are simulated. Under simulated exercise conditions, we compute a reversed difference between PET and Pa compared with the rest condition. This reversal is directly reflected in the relation between the physiological dead space fraction (1--PE/Pa) and the Bohr dead space fraction (1--PE/PET). It is argued that the difference (PET--Pa) depends on the lambda of the tracer gas, the buffering capacity of lung tissue, and the stratification caused by diffusion-limited gas transport in the gas phase. Finally some determinants for the reversed difference (PET--Pa) and the significance for conventional gas analysis are discussed.

Humans↗
PubMed2000

Measurement and manipulation of the partial pressure of oxygen in the rat anterior chamber.

PURPOSE: To measure the partial pressure of oxygen in the anterior chamber of the rat eye under a variety of physiological conditions. METHODS: Polarographic oxygen electrode measurements were made in methoxyflurane-anesthetized Wistar or Sprague-Dawley rats. After ketamine-xylazine or pentobarbital induction, animals were artificially ventilated with a variety of gas mixtures; gases were directed over the corneal surface during measurement of the partial pressure of oxygen in the middle of the pupil at the surface of the lens. RESULTS: The partial pressure of oxygen in the anterior chamber of the rat eye was measured as 63 +/- 9 mm Hg (mean +/- S.D. ). Breathing 100% oxygen and delivery of 100% oxygen to the cornea additively increased aqueous humor oxygen partial pressure to levels above 279 +/- 45 mm Hg with the greatest increase coming from inhaled 100% oxygen. Conversely, inhalation and subsequent transcorneal delivery of 10% oxygen reduced levels to 22 +/- 11 mm Hg. CONCLUSIONS: These results suggest that the partial pressure of oxygen in the anterior chamber is sensitive to the environment in contact with the cornea. In the rat eye, the delivery of oxygen to the anterior chamber via transcorneal diffusion may be more significant than for larger animals.

Anesthesia↗
PubMed1999

Arterial to inspired partial pressure ratio of halothane, isoflurane, sevoflurane and desflurane in rats.

The inspired partial pressure of an anaesthetic is often used as an index of arterial partial pressure in small animal experiments. We have investigated the influence of anaesthetic solubility on the ratio of arterial to inspired partial pressure in 24 rats, allocated randomly to receive halothane, isoflurane or desflurane at four different inspired concentrations. The arterial partial pressure of the volatile agent was measured by two-stage headspace analysis using a gas chromatograph calibrated with the same gas used to calibrate the Datex Capnomac that measured the inspired concentration. Mean values of arterial to inspired ratio at the lowest concentrations were 0.60 (95% confidence intervals 0.50, 0.71) for 0.8% halothane, 0.54 (0.38, 0.69) for 0.8% isoflurane, 0.72 (0.59, 0.86) for 1.5% sevoflurane and 0.71 (0.54, 0.87) for 4% desflurane. Analysis of variance showed a significant effect of anaesthetic agent (P = 0.008) on the arterial to inspired ratio. Thus volatile anaesthetic agents do not demonstrate a fixed arterial to inspired ratio in rats.

Anesthetics, Inhalation↗