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At least 163 records · Page 9Linked to original sources
PubMed1999

[Pre-analytic errors in the determination of arterial O(2)-partial pressure under hyperoxic conditions].

OBJECTIVE: A variety of influences reduce the validity of the measured oxygen partial pressure (paO(2)). Most errors occur when obtaining the blood sample and preparing it for analysis. Unfortunately, there is great controversy concerning the relevance and extent of these pre-analytic errors. Apart from this, the exact estimation of influencing factors under hyperoxic conditions has been neglected. Therefore, the objective of this study was to assess pre-analytic measuring errors for paO(2) under the condition of hyperoxia as completely as possible and to work out solutions to eliminate these errors. METHODS: paO(2) analysis was performed on more than 2000 blood samples. Errors analyzed were the technique of sample taking (direct puncture or from an indwelling catheter), aspirated air bubbles (0.05-0.35 ml), time and temperature of sample storage, and the material, size and manufacturer of the analyzing syringe. RESULTS: The paO(2) was on average 41 mmHg lower in samples taken from the indwelling catheter than by direct puncture. An air bubble size of 0.1-0.25 ml caused a decrease of 17-41 mmHg. Storage time of 2 min accounted for an paO(2) reduction of 6-67 mmHg depending on the type of syringe used. Glass syringes turned out to be more accurate than plastic syringes. The best results were obtained not from commercial "blood gas syringes" but from a simple plastic injection syringe. For all pre-analytic errors correction factors were established. CONCLUSION: All pre-analytic errors investigated caused a significant paO(2) decrease. Even an ideal procedure (almost no air bubble, short storage on ice) contributes a significant error. Only the appropriate correction factors as calculated from this study for routine use lead to the correct results. If they are not taken into account the paO(2) values will be falsely low, potentially leading to misinterpretation and misjudgement of a patient's condition.

Humans↗
PubMed1986

Regulation of Ribulose-1,5-Bisphosphate Carboxylase Activity in Response to Changing Partial Pressure of O(2) and Light in Phaseolus vulgaris.

The regulation of ribulose-1,5-bisphosphate (RuBP) carboxylase (rubisco) activity in Phaseolus vulgaris was studied under moderate CO(2) and high light, conditions in which photosynthesis in C(3) plants can be insensitive to changes in O(2) partial pressure. Steady state RuBP concentrations were higher, the calculated rate of RuBP use was lower and the activation state of rubisco was lower in low O(2) relative to values observed in normal O(2). It is suggested that the reduced activity of rubisco observed here is related to feedback effects which occur when the rate of net CO(2) assimilation approaches the maximum capacity for starch and sucrose synthesis (triose phosphate utilization). The activation state of rubisco was independent of O(2) partial pressure when light or CO(2) was limiting for photosynthesis. Reduced activity of rubisco was also observed at limiting light. However, in this species light dependent changes in the concentration of an inhibitor of rubisco controlled the apparent V(max) of rubisco in low light while changes in the CO(2)-Mg(2+) dependent activation of rubisco controlled the apparent V(max) in high light.

Journal Article↗
PubMed2006

Noninvasive oxygen partial pressure measurement of human body fluids in vivo using magnetic resonance imaging.

RATIONALE AND OBJECTIVES: The oxygen partial pressure (pO2) of human body fluids reflects the oxygenation status of surrounding tissues. All existing fluid pO2 measurements are invasive, requiring either microelectrode/optode placement or fluid removal. The purpose of this study is to develop a noninvasive magnetic resonance imaging method to measure the pO2 of human body fluids. MATERIALS AND METHODS: We developed an imaging paradigm that exploits the paramagnetism of molecular oxygen to create quantitative images of fluid oxygenation. A single-shot fast spin echo pulse sequence was modified to minimize artifacts from motion, fluid flow, and partial volume. Longitudinal relaxation rate (R1 = 1/T1) was measured with a time-efficient nonequilibrium saturation recovery method and correlated with pO2 measured in phantoms. RESULTS: pO2 images of human and fetal cerebrospinal fluid, bladder urine, and vitreous humor are presented and quantitative oxygenation levels are compared with prior literature estimates, where available. Significant pO2 increases are shown in cerebrospinal fluid and vitreous following 100% oxygen inhalation. Potential errors due to temperature, fluid flow, and partial volume are discussed. CONCLUSIONS: Noninvasive measurements of human body fluid pO2 in vivo are presented, which yield reasonable values based on prior literature estimates. This rapid imaging-based measurement of fluid oxygenation may provide insight into normal physiology as well as changes due to disease or during treatment.

Adult↗
PubMed1990

Nitrogen partial pressures in man after decompression from simulated scuba dives.

In five subjects arterial and central venous nitrogen partial pressures (PN2) were measured after decompression from a chamber dive following a decompression schedule for scuba diving. The simulated dives consisted of exposure at rest to air at 6 bar for 30 min. corresponding to a depth of 50 m. Afterwards the subjects were decompressed with decompression stops at 2.5, 2.2, 1.9, 1.6 and 1.3 bar with a total decompression time of 73 min. Immediately after decompression and every 40 min. until the 240th min. arterial and central venous blood samples were analyzed for PN2 using a manometric Van Slyke apparatus. Venous PN2 remained elevated until 160 min. after decompression indicating still incomplete nitrogen wash-out at least two hours after decompression had been accomplished. Bubble formation is discussed as a cause for prolonged nitrogen elimination. Our data confirm that nitrogen elimination is prolonged after decompression from simulated dives at rest.

Arteries↗
PubMed2003

Role of determination of partial pressure of ammonia in cirrhotic patients with and without hepatic encephalopathy.

BACKGROUND/AIMS: To compare venous, arterial and partial pressure of ammonia (pNH(3)) in 27 consecutive cirrhotics with hepatic encephalopathy, 15 cirrhotics without hepatic encephalopathy and nine controls; to reevaluate all parameters after the improvement of encephalopathy. METHODS: Patients were studied by clinical examination and psychometric testing. pNH(3) was calculated from arterial ammonia and pH. RESULTS: In patients with encephalopathy, each form of ammonia was higher than in both controls and patients without encephalopathy. The correlation with the severity of hepatic encephalopathy was similar for venous (r=0.72), arterial ammonia (r=0.76) and pNH(3) (r=0.75). The sensitivity and specificity of each variable in correctly classifying the patients as having or not having hepatic encephalopathy was also similar. Each form of ammonia decreased after the resolution or amelioration of symptoms. However, even in the 17 patients with complete resolution of hepatic encephalopathy, all three ammonia determinations resulted unchanged or increased in some patients. CONCLUSIONS: Despite the significant correlation between pNH(3) and hepatic encephalopathy, our study suggests that neither pNH(3) nor arterial ammonia are, from a clinical point of view, more useful than venous ammonia: all three determinations being limited both for the diagnosis of hepatic encephalopathy and for the clinical management of the patients.

Aged↗
PubMed2001

Control of arterial partial pressure of oxygen in patients with respiratory abnormalities using an adaptive observer.

A system for controlling the arterial partial pressure of oxygen in patients on long-term oxygen therapy is proposed. After performing a parameter estimation of the model of pulmonary system, an adaptive observer is applied to perform the control task. The observer considers the model uncertainties as disturbances and rejects their impact on the system. As a result of this, the quality of the control can be drastically improved. The presented simulation and experimental results show the effectiveness of the proposed scheme. The proposed control scheme is applicable without preliminary adjustment of the control parameters.

Blood Gas Analysis↗
PubMed1986

Effect of elevations of coronary artery partial pressure of carbon dioxide (PCO2) on coronary blood flow.

This study was designed to examine the effect of increases in the partial pressure of carbon dioxide (PCO2) in coronary artery blood on coronary blood flow, coronary reactive hyperemia and the coronary response to intracoronary adenosine administration. The left anterior descending coronary artery was cannulated and perfused over a wide range of perfusion pressure (P) and flow (F) with blood equilibrated with 0 to 40% carbon dioxide in 16 open chest dogs. Increases in coronary artery PCO2 from 20 +/- 2 to 93 +/- 8 to 211 +/- 22 mm Hg (mean +/- SEM) increased the coronary flow from 28 +/- 3 to 68 +/- 16 to 87 +/- 22 ml/min, respectively, at a perfusion pressure of 60 mm Hg and from 49 +/- 6 to 139 +/- 30 to 206 +/- 48 ml/min, respectively, at a perfusion pressure of 100 mm Hg. Coronary reactive hyperemia following a 30 second coronary perfusion line occlusion and the response to an intracoronary bolus of adenosine (60 micrograms) were prominent at a low PCO2 but absent at a high PCO2. Beta-adrenergic blockade did not abolish the increase in coronary flow that occurred at increased PCO2. Thus, progressive elevations of regional coronary PCO2 produced substantial increases in coronary blood flow and maximal or near maximal coronary vasodilation.

Adenosine↗
PubMed2001

Direct measurement of oxygen partial pressure in a flying bumblebee.

The gas transport system of a bumblebee was investigated by measuring the oxygen partial pressure P(O(2)) in the wing muscle. In the resting bee, P(O(2)) showed a regular pattern of fluctuation with a typical period of 70-120s. Fluctuations in muscular P(O(2)) were associated with intermittent abdominal pumping. Ventilation by abdominal movements may not be necessary during rest because P(O(2)) is high (8.5-9.2kPa) in the anaesthetised bee. Thermal effects on muscular P(O(2)) were examined by cooling the bee, causing the amplitude of P(O(2)) fluctuations to increase. In most flight experiments, the bee started to fly after elevating muscle P(O(2)) by abdominal pumping; muscle P(O(2)) then decreased at the onset of flight. However, when a flight began without pre-flight ventilation, P(O(2)) increased monotonically. During flight, muscle P(O(2)) reached a mean level (6.36+/-1.83kPa) that was much higher than the lowest value recorded during discontinuous ventilation during rest. The bumblebee effectively uses abdominal movements to assist in convective gas transport not only during flight but also at rest.

Animals↗
PubMed2003

Dual responses of tissue partial pressure of oxygen after functional stimulation in rat somatosensory cortex.

To compare the spatial heterogeneity of brain tissue partial pressure of oxygen (pO(2)) among local brain regions, we focused on functional and anatomical variations in rat somatosensory cortex. Tissue pO(2) was measured by using an oxygen microelectrode with high spatio-temporal resolution, and investigated in three somatosensory areas including hindlimb (HL), forelimb (FL), and trunk region (Tr). Their anatomical structures were determined with histological techniques (Nissl stain). In addition to the measurement of baseline tissue pO(2), we examined temporal shifts in tissue pO(2) distribution elicited by functional stimulation using the brushing stimulation to the hindlimb, forelimb, and trunk regions of the body. We observed that average tissue pO(2) in the Tr (14+/-10 Torr) was significantly lower than those in the HL (25+/-13 Torr) and FL (24+/-13 Torr). Such regional differences in tissue pO(2) were closely related to the cytoarchitectonic variations among these three areas. In addition, the functional stimulation enlarged the regional differences in the pO(2) depending on each somatosensory area; the pO(2) in the HL increased by 3.6+/-2.9% after the stimulation to hindlimb, whereas that in the Tr decreased by -2.9+/-2.5% after the stimulation to trunk region. Such dual responses of tissue pO(2) (i.e. increase or decrease) after the functional stimulation to the corresponding body regions may provide a criterion to clinically predict regions susceptible to tissue hypoxia, because considerable decrease in tissue pO(2) occurred in the Tr showing the lowest baseline pO(2).

Animals↗
PubMed1989

Monitoring of end-tidal carbon dioxide partial pressure during high frequency jet ventilation.

A new method has been developed to measure end-tidal carbon dioxide partial pressure (PECO2) during high frequency jet ventilation (HFJV). A digital flow controller incorporated in a computerized high frequency jet ventilator was used to deliver either a single deep breath or a series of three deep breaths. On user request, HFJV was interrupted and the deep breaths delivered, after which HFJV was resumed. Using a mathematical model, we were able to predict accurately the pressures to which the lungs would be inflated during deep breaths. The effect of varying the deep breath pressure (Pdb) on the ratio of end-tidal PCO2 to arterial (PCO2 (PECO2:PaCO2) was studied in three dogs. In all the dogs, within an optimum Pdb range of 5-10 cm H2O, PECO2 during the first deep breath was found to be similar (+/- 0.2 kPa) to the PaCO2 immediately before the onset of deep breaths. Deep breaths delivered above or below the optimum Pdb range resulted in a decrease in the ratio PECO2:PaCO2. The frequency of jet ventilation (12-200 b.p.m.) before the onset of the deep breaths did not affect PECO2:PaCO2.

Anesthesia, Intravenous↗
PubMed1994

[The effects of ephedrine and phenylephrine on arterial partial pressure of oxygen during one-lung ventilation].

We investigated the effects of ephedrine (EP) and phenylephrine (PH) on partial pressure of oxygen and intra-pulmonary shunt during one-lung ventilation under general anesthesia with enflurane, fentanyl and oxygen. When systolic blood pressure decreased to less than 80% of the resting values, 30 adult patients who were randomly assigned into 2 groups, received either EP 0.15 mg.kg-1 or PH 2 micrograms.kg-1. In group-EP, PaO2 increased significantly from 187 +/- 112 to 205 +/- 114 mmHg (FIO2 = 1.0, P < 0.05), while in group-PH, PaO2 changed from 209 +/- 129 to 248 +/- 84 mmHg without statistical significance. Intra-pulmonary shunts were essentially unchanged in both groups. Neither dysrhythmia, ST-T changes on electrocardiography, congestive heart failure, nor severe hypoxemia were observed in any patient during the study. These results indicate that EP and PH in above doses can be safely administered to treat arterial hypotension during one-lung ventilation.

Adult↗
PubMed1988

Closed-loop control of the partial pressure of arterial oxygen in neonates.

A closed-loop control system has been developed to regulate automatically the partial pressure of arterial oxygen (PaO2) to a pre-set level in neonates with RDS (Respiratory Distress Syndrome). A microcomputer-based system is described which uses the PaO2 value from an indwelling umbilical artery electrode as the input to a robust control algorithm. The derived control signal is used to modify the position of a motor driven oxygen/air blender, thus regulating the percentage of oxygen delivered in the inspired gas mixture. The parameters of the control algorithm were conservatively chosen, and the safety aspects of the system are discussed. A total of 48 h of closed-loop control were recorded on seven pre-term infants with mild-to-moderate RDS being nursed in headboxes. Ten separate closed-loop control intervals were recorded, and overall the results showed a marked improvement over comparable periods of manual control. The percentage of time for which the recorded PaO2 was within +/- 1 kPa of the chosen target value (10 kPa) was 74.9 +/- 10.2% when averaged over the ten closed-loop control periods. The corresponding figure for the comparable manual control intervals was 45.2 +/- 16.0%.

Algorithms↗
PubMed2002

Mechanisms of scale formation and carbon dioxide partial pressure influence. Part II. Application in the study of mineral waters of reference.

In the first part, we have designed a new model of evolution for the calco-carbonic system which includes the hydrated forms of CaCO3: CaCO3 amorphous, CaCO3 x 6H2O (ikaite) and CaCO3 x H2O (monohydrate) (J. Eur. Hydr. 30 (1999) 47). According to this model, it is the precipitation of one or other of these hydrated forms which could be responsible for the breakdown of the metastable state. After this first step, the precipitates evolve to dehydrated solid forms. Through the elaboration of computer programs in which the CaCO3(0) (aq) ion pair formation was considered, this model was compared to experimental data obtained by the critical pH method applied to synthetic solutions. In the present article, the same method was applied for four French mineral waters, at 25 degrees C under study. Three samples formed a precipitation during the sodium hydroxide addition. For these three cases, this precipitation began for the CaCO3 H2O saturation. The added volume of sodium hydroxide was more than what was required for neutralizing free CO2 initially in solution. These results indicate that during a spontaneous scaling phenomenon, the pH rises at the same time by loss of the initial free CO2 and of the one produced by the hydrogen carbonate ions decomposition. Then we calculated, at various temperatures for the three studied scaling waters: CO2 partial pressures and loss of total carbon corresponding to the solubility products of CaCO3 hydrated forms. The results show that the partial pressure monitoring of the carbon dioxide is important in managing the behavior of scaling waters.

Carbon Dioxide↗
PubMed2003

[Effects of the oxygen partial pressure in inspired gaseous mixture on the functional state of the circulatory, respiratory and erythropoietic systems: a mathematical model].

Oxygen partial pressure in inspired gaseous mixture has a profound effect on the function of the circulatory, respiratory and erythropoietic systems. A mathematical model is proposed to optimize the function of these systems when breathing air with various PO2. The model is based on the principle of minimum energy expenditure. Erythrocyte count, arterial oxygen tension, cardiac output, and pulmonary ventilation are determined as a function of inspired PO2. The model results are in good agreement with the data for permanent altitude residents.

Blood Circulation↗
PubMed2004

Performance of seminal and nodal roots of wheat in stagnant solution: K+ and P uptake and effects of increasing O2 partial pressures around the shoot on nodal root elongation.

Roots of intact wheat plants were grown for 7-12 d in stagnant nutrient solution, containing 0.1% agar, to mimic the lack of convection in waterlogged soil. Net K+ and P uptakes by seminal and nodal roots were measured separately using a split root system. For seminal roots in stagnant solution, net uptakes as a percentage of aerated roots were between 0% and 16% for P, while K+ ranged between 15% uptake and 54% loss. For the more waterlogging-tolerant nodal roots, net uptakes in stagnant nutrient solution, as a percentage of aerated roots, were 31-73% for P and 69-115% for K+. Elongation rates of nodal roots in stagnant nutrient were about 35-43% of those for roots in aerated solution. This partial inhibition occurred in these nodal roots despite their 15% porosity (v/v). Elevation of O2 partial pressures around the shoots to 40 kPa and then to 80 kPa substantially accelerated nodal root elongation in stagnant solution, demonstrating that most of the inhibition seen with ambient O2 around the shoots was associated with a restricted O2 supply to these nodal roots. Thus, in wheat nodal roots, with a partial pressure of 20 kPa O2 around the shoots, O2 diffusion from the shoots did not completely relieve the restrictions on elongation resulting from stagnancy in the nutrient solution. These results contrast with those in the literature for rice, in which roots function efficiently in stagnant solutions (0.1% agar). So, when wheat roots are aerenchymatous there are still restrictions to O2 diffusion in the gas space continuum between the atmosphere and the functional tissues of the roots. This poor acclimation must have been due to inefficiency of the aerenchymatous axes, which may include persistence of anoxic steles, and/or restricted O2 diffusion in other parts of the gas space continuum, in either the shoots and shoot-root junction or in the root tip.

Oxygen↗
PubMed2004

Continuous telemetric monitoring of fetal oxygen partial pressure during labor.

INTRODUCTION: Upright or ambulatory birth positions are favorable for fetal oxygenation. Studies of fetal oxygenation with regard to maternal position require free maternal mobility. Therefore, telemetry for a fetal sensor for such investigations is a pre-requisite. Telemetry-if technically feasible-could enable monitoring of fetal oxygen partial pressure using an existing sensor without restricting the mobility of the parturient woman. We have developed a telemetry system for use with a fetal transcutaneous partial oxygen pressure sensor (ttcpO(2)) and have studied effects of maternal position and position changes during normal labor. MATERIALS AND METHODS: The monitoring system consists of three parts: the telemetry unit with the ttcpO(2) sensor to transmit the tcpO(2) and the heating output telemetrically, a modified CTG monitor and a personal computer storing the measurements. All data were plotted on the CTG recording paper and fed into a new purpose-designed software, displaying fetal heart rate, the uterine contraction intensity, ttcpO(2) and the heating output. Three laboring women, randomly and successively adopting "classical birth positions" (supine or side positions), sitting or vertical or walking position, were studied. RESULTS: Fetal heart rate, uterine contractions, ttcpO(2) and heating output are influenced by the birth positions and by changes of the birth position. In the classical supine and side position there seemed to be lower fetal oxygenation. Sitting, standing and especially walking were more favorable. DISCUSSION: Telemetry is useful to study a possible clinical benefit of individual birth positions.

Equipment Design↗
PubMed2004

Tumor-dependent kinetics of partial pressure of oxygen fluctuations during air and oxygen breathing.

The primary purpose of this study was to examine the kinetics of partial pressure of oxygen (pO2) fluctuations in fibrosarcoma (FSA) and 9L tumors under air and O2 breathing conditions. The overall hypothesis was that key factors relating to oxygen tension fluctuations would vary between the two tumor types and as a function of the oxygen content of the breathing gas. To assist in the interpretation of the temporal data, spatial pO2 distributions were measured in 10 FSA and 8 9L tumors transplanted into the subcutis of the hind leg of Nembutal-anesthetized (50 mg/kg) Fischer 344 rats. Recessed-tip oxygen microelectrodes were inserted into the tumor, and linear pO2 measurements were recorded in 50-microm steps along a 3-mm path, and blood pressure was simultaneously measured via femoral arterial access. Additionally, pO2 was measured at a single location for 90 to 120 minutes in FSA (n=11) or 9L tumors (n=12). Rats were switched from air to 100% O2 breathing after 45 minutes. Temporal pO2 records were evaluated for their potential radiobiological significance by assessing the number of times they crossed a 10-mm-Hg threshold. In addition, the data were subjected to Fourier analysis for air and O2 breathing. FSA and 9L tumors had spatial median pO2 measurements of 4 and 1 mm Hg, respectively. 9L had more low pO2 measurements < or =2.5 mm Hg than did FSA, whereas between 2.5 and 10 mm Hg this pattern was reversed. Pimonidazole staining patterns in FSA and 9L tumors supported these results. Temporal pO2 instability was observed in all experiments during air and O2 breathing. Threshold analyses indicated that the 10 mm Hg threshold was crossed 2 to 5 times per hour, independent of tumor type. However, the magnitude of 9L pO2 fluctuations was approximately eight times greater than FSA fluctuations, as assessed with Fourier transform analysis (Wilcoxon, P < 0.005). O2 breathing significantly increased median pO2 in FSA from 3 to 8 mm Hg (P < 0.005) and caused a significant increase in frequency and magnitude of pO2 fluctuations. One hundred percent O2 breathing had no effect on 9L tumor pO2, and it decreased the magnitude of pO2 fluctuations with borderline significance. These results show that these two tumors differ significantly with respect to spatial and temporal oxygenation conditions under air and O2 breathing. Fluctuations of pO2 of the type reported herein are predicted to significantly affect radiotherapy response and could be a source for genetic instability, increased angiogenesis, and metastases.

Air↗