Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Partial Pressure”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources
PubMed1977

[Effects of halogenated hydrocarbons on polarographic measurement of oxygen partial pressure (author's transl)].

Halothane can be reduced polarographically. The presence of halothane in a probe therefore may lead to an erroneous determination of oxygen partial pressure with a greater or less overestimation of the actual oxygen tension. In this study we report extent to which halothane influences the polarographic determination of oxygen tension in blood samples and in the transcutaneous determination of arterial oxygen tension. A clear dependence on halothane concentration was found concerning the transcutaneous measurement of oxygen tension, while measurement of oxygen tension in blood samples by means of the Combianalysator (Fa. Eschweiler, Kiel) was not affected by halothane. The different effect of halothane on the oxygen measurement is apperantly due to the size of the polarizing voltage. Below values of 500 to 600 mV halothane is practically not reduced, whereas above this range reduction takes place which results in an additional polarizing current superimposing the signal of the reduction of oxygen.

Halothane↗
PubMed2003

Study on changes of partial pressure of brain tissue oxygen and brain temperature in acute phase of severe head injury during mild hypothermia therapy.

OBJECTIVE: To study the changes of partial pressure of brain tissue oxygen (PbtO2) and brain temperature in acute phase of severe head injury during mild hypothermia therapy and the clinical significance. METHODS: One hundred and sixteen patients with severe head injury were selected and divided into a mild hypothermia group (n=58), and a control group (n=58) according to odd and even numbers of hospitalization. While mild hypothermia therapy was performed PbtO2 and brain temperature were monitored for 1-7 days (mean=86 hours), simultaneously, the intracranial pressure, rectum temperature, cerebral perfusion pressure, PaO2 and PaCO2 were also monitored. The patients were followed up for 6 months and the prognosis was evaluated with GOS (Glasgow outcome scale). RESULTS: The mean value of PbtO2 within 24 hour monitoring in the 116 patients was 13.7 mm Hg +/- 4.94 mm Hg, lower than the normal value (16 mm Hg +/- 40 mm Hg ) The time of PbtO2 recovering to the normal value in the mild hypothermia group was shortened by 10 +/- 4.15 hours compared with the control group (P<0.05). The survival rate of the mild hypothermia group was 60.43%, higher than that of the control group (46.55%). After the recovery of the brain temperature, PbtO2 increased with the rise of the brain temperature. CONCLUSIONS: Mild hypothermia can improve the survival rate of severe head injury. The technique of monitoring PbtO2 and the brain temperature is safe and reliable, and has important clinical significance in judging disease condition and instructing clinical therapy.

Adult↗
PubMed2001

Time required for partial pressure of arterial oxygen equilibration during mechanical ventilation after a step change in fractional inspired oxygen concentration.

OBJECTIVE: To determine the time required for the partial pressure of arterial oxygen (PaO2) to reach equilibrium after a 0.20 increment or decrement in fractional inspired oxygen concentration (FIO2) during mechanical ventilation. SETTING: A multi-disciplinary ICU in a university hospital. PATIENTS AND METHODS: Twenty-five adult, non-COPD patients with stable blood gas values (PaO2/FIO2 > or = 180 on the day of the study) on pressure-controlled ventilation (PCV). Following a baseline PaO2 (PaO2b) measurement at FIO2 = 0.35, the FIO2 was increased to 0.55 for 30 min and then decreased to 0.35 without any other change in ventilatory parameters. Sequential blood gas measurements were performed at 3, 5, 7, 9, 11, 15, 20, 25 and 30 min in both periods. The PaO2 values measured at the 30th min after a step change in FIO2 (FIO2 = 0.55, PaO2[55] and FIO2 = 0.35, PaO2[35]) were accepted as representative of the equilibrium values for PaO2. Each patient's rise and fall in PaO2 over time, PaO2(t), were fitted to the following respective exponential equations: PaO2b + (PaO2[55]-PaO2b)(1-e-kt) and PaO2[55] + (PaO2[35]-PaO2[55])(e-kt) where "t" refers to time, PaO2[55] and PaO2[35] are the final PaO2 values obtained at a new FIO2 of 0.55 and 0.35, after a 0.20 increment and decrement in FIO2, respectively. Time constant "k" was determined by a non-linear fitting curve and 90% oxygenation times were defined as the time required to reach 90% of the final equilibrated PaO2 calculated by using the non-linear fitting curves. RESULTS: Time constant values for the rise and fall periods were 1.01 +/- 0.71 min-1, 0.69 +/- 0.42 min-1, respectively, and 90% oxygenation times for rises and falls in PaO2 periods were 4.2 +/- 4.1 min-1 and 5.5 +/- 4.8 min-1, respectively. There was no significant difference between the rise and fall periods for the two parameters (p > 0.05). CONCLUSION: We conclude that in stable patients ventilated with PCV, after a step change in FIO2 of 0.20, 5-10 min will be adequate for obtaining a blood gas sample to measure a PaO2 that will be representative of the equilibrium PaO2 value.

Adult↗
PubMed1998

Relationship between end-tidal and arterial carbon dioxide partial pressure using a cuffed oropharyngeal airway and a tracheal tube.

We have compared the differences between end-tidal PE'CO2 and arterial PaCO2 carbon dioxide partial pressures during general anaesthesia using either a cuffed oropharyngeal airway (COPA) or a tracheal tube (TT) in spontaneously breathing adult patients. After induction of anaesthesia, a COPA was inserted in 20 patients who were allowed to breathe spontaneously. When steady state was reached, PE'CO2 and PaCO2 were recorded. The COPA was removed, the trachea intubated with a TT and spontaneous ventilation allowed to resume. After a stable PE'CO2 was reestablished, PaCO2 was measured again and PE'CO2 recorded. Mean difference between PaCO2 and PE'CO2 with the COPA was 0.72 (SD 0.45) kPa and with the TT 0.64 (0.40) kPa (ns; paired t test). Our results suggest that Pe'CO2 is a clinically acceptable indicator of PaCO2 in adults breathing spontaneously via a COPA.

Adult↗
PubMed1991

Effect of varying alveolar oxygen partial pressure on diffusing capacity for nitric oxide and carbon monoxide, membrane diffusing capacity and lung capillary blood volume.

1. To examine the effect of varying oxygen partial pressure (PAO2) on nitric oxide (DLNO) and carbon monoxide (DLCO) diffusing capacity (transfer factor), 10 subjects performed combined DLCO/DLNO measurements with the inspired mixture made up with three different oxygen concentrations (25%, 18% and 15%) to give PAO2 values of 12-20 kPa. 2. A novel method is described for calculating membrane diffusing capacity (DM) and pulmonary capillary volume (Qc) from DLNO and DLCO. 3. The mean DMCO was 52.89 mmol min-1 kPa-1 and Qc was 0.056 litre. Reducing PAO2 from 20 to 12 kPa resulted in an increase in DLCO = -0.124 (O2%) + 11.67 (P less than 0.001) and a fall in DLNO = 0.538 (O2%) + 32.01 (P less than 0.001) and a fall in DLNO/DLCO = 0.107 (O2%) + 2.52 (P less than 0.001). DM (P = 0.59) and Qc (P = 0.64) also tended to fall with falling PAO2. 4. It appears more likely that the minor reduction in DLNO that we have observed with falling PAO2 is due to diffusion rather than reaction limitation.

Blood Volume↗
PubMed1986

Arterial-alveolar oxygen partial pressure ratio: a theoretical reappraisal.

The relationship between the arterial-alveolar oxygen partial pressure ratio (PaO2/PAO2) and different fractions of inspired oxygen (FIO2) was studied using a bicompartmental computer model. PaO2/PAO2 was found to be less stable than in previous clinical works probably because the venous admixture varied with changes in the FIO2.

Blood Pressure↗
PubMed1978

The effect of chronic reductions in the arterial partial pressure of oxygen on the radiation response of an experimental tumour.

A previous study by the same authors has reported the effect of acute reductions in the arterial partial pressure of oxygen (PaO2) on tumour response to radiation. The results have been extended in the present paper to investigate tumour response to radiation in animals in which the PaO2 is chronically reduced. The purpose of these experiments was to simulate the condition of cancer patients undergoing radiotherapy in the presence of chronically low PaO2 values as might be expected in patients with chronic respiratory disease. Mice bearing transplantable KHT sarcomas were kept in a 12% O2 environment prior to (10--16 days), during and following the radiation treatment of their tumours. During the period of low PaO2 (about 50 mm Hg) exposure, the mice were found to increase their haemoglobin (Hg) levels by approximately 50%. Because of this increase, the response, determined using a growth delay assay of the tumours irradiated at reduced PaO2 was found to be the same as that observed for tumours in mice breathing air throughout the experiment. In mice with reduced PaO2 levels maintained at normal Hb concentrations by periodic bleeding, tumour response was found to be similar to that of mice with acute PaO2 reductions. These results indicate that chronic PaO2 reductions in the absence of Hb compensation may have a detrimental effect on the success of a radiation treatment.

Animals↗
PubMed2003

Response of photosynthesis in second-generation Pinus radiata trees to long-term exposure to elevated carbon dioxide partial pressure.

Second-generation Pinus radiata D. Don trees, propagated from cuttings of 4-year-old trees previously grown at ambient (36 Pa) and elevated (65 Pa) CO2 partial pressure (Ca) were grown under the same conditions in open-top chambers for a further year. As cuttings of the original trees, these second-generation trees were physiologically the same age as the first-generation trees with the only difference between the two being size. This allowed us to test the effects of tree size independently of age or duration of exposure. Total non-structural carbohydrate concentration, area-based nitrogen concentration, leaf mass per unit area and chlorophyll concentration measured in three foliage age cohorts were unaffected by either age or Ca. There were no signs of photosynthetic down-regulation in trees grown at elevated Ca. When measured at the growth Ca, photosynthetic rate in young needles during summer, autumn and spring was 34, 43 and 38% higher, respectively, in trees grown at elevated Ca than in trees grown at ambient Ca. In older needles, the corresponding photosythetic rate increases were 26, 47 and 49%. Water-use efficiency, determined by stable carbon isotope analysis, was 49% higher in foliage in the elevated Ca treatment than in foliage in the ambient Ca treatment. This increase was entirely due to photosynthetic enhancement, because stomatal conductance did not differ between treatments. We conclude that down-regulation of photosynthesis at elevated Ca is related to tree size rather than tree age or duration of exposure, and that enhanced photosynthetic rates can be maintained while sink strength is high enough to use the excess photosynthates.elevated CO2, needle age, photosynthetic down-regulation, photosynthetic enhancement, sink strength, water-use efficiency.

Carbon Dioxide↗
PubMed1991

Stability of the intraoperative arterial to end-tidal carbon dioxide partial pressure difference in children with congenital heart disease.

The purpose of this study was to evaluate the stability of the arterial PCO2 (PaCO2) to end-tidal PCO2 (PETCO2) partial pressure difference (Pa-ETCO2) during surgery using PETCO2 monitoring, in children with congenital heart disease (CHD). Forty children with CHD were studied: ten children with no interchamber communication and normal pulmonary blood flow (PBF) (normal group); ten acyanotic children with increased PBF (acyanotic-shunting group); ten cyanotic children with mixing type lesions and normal or increased PBF (mixing group), and ten cyanotic children with right-to-left intracardiac shunts demonstrating decreased and variable PBF (cyanotic-shunting group). Simultaneous PaCO2 recordings and PETCO2 measurements were obtained for each patient during five intraoperative events: (1) control time, arterial line placement under anaesthesia; (2) time 1, patient preparation; (3) time 2, immediately after sternotomy; (4) time 3, after heparin administration; and (5) time 4, immediately after aortic cannulation. Initially, cyanotic children demonstrated a greater Pa-ETCO2 compared with acyanotic children (P less than 0.05). There was no difference in the Pa-ETCO2 over time in the control, acyanotic-shunting, or mixing groups. The Pa-ETCO2 in the children with cyanotic-shunting lesions at times 2 and 3 was greater (P less than 0.05) than at their control times. We conclude that the Pa-ETCO2 of children with acyanotic-shunting and mixing congenital heart lesions is stable intraoperatively, although patients with mixing congenital heart lesions may demonstrate large individual variations. In children with cyanotic-shunting congenital heart lesions, the Pa-ETCO2 is not stable. The PETCO2 cannot be used during surgery to estimate reliably the PaCO2 in children with cyanotic CHD.

Adolescent↗
PubMed1976

[The measurement of the partial pressure of oxygen and carbon dioxide and pH of the aqueous humor in man. A preliminary study on 32 normal eyes].

Using a micromethod the authors have measured the pH, and the partial pressure of oxygen and carbon dioxide in the aqueous humour. The results are presented in 32 normal eyes. The authors have studied the variation of these levels in the aqueous in comparison with the same levels measured at the same time under the same conditions in the arterial blood.

Aqueous Humor↗
PubMed1992

Evaluation of the measurement of the intraoperative transcutaneous partial pressure of oxygen (PtcO2) as a prognostic indicator in vascular reconstruction.

The intraoperative transcutaneous partial pressure of oxygen (PtcO2) was used to monitor 58 vascular reconstructive surgery procedures in 54 patients. The study comprised three groups: Group A (24 limbs without any ischemic symptoms or signs), Group B (45 limbs with intermittent claudication), and Group C (12 limbs with ischemic rest pain, ulceration, and gangrene). In addition in 31 patients the chest wall was monitored simultaneously as a control. The results showed that the PtcO2 values increased immediately and significantly to varying degrees and at varying speeds after unclamping. The controls had higher values than Group A (P > 0.05), Group B (P < 0.05), and Group C (P < 0.05) patients. Further study showed that there were no significant differences between the maximal values in the limbs with good distal vessel run-off in Groups A, B, and C, and in the controls (P > 0.05). It is thus concluded that effective vascular reconstruction in the limbs is indicated by a rapid and marked increase of both the PtcO2 value and the response value, while with a slow and low increase of the value, early graft failure and poor distal vessel run-off should be suspected. We believe that this monitoring method dynamically reflects the functional state during vascular reconstruction and is clinically valid.

Adult↗
PubMed2005

Heterogeneous oxidation of Fe(II) on ferric oxide at neutral pH and a low partial pressure of O2.

The objective of this study was to identify the rate and mechanism of abiotic oxidation of ferrous iron at the water-ferric oxide interface (heterogeneous oxidation) at neutral pH. Oxidation was conducted at a low partial pressure of O2 to slow the reactions and to represent very low dissolved oxygen (DO) conditions that can occur at oxic/anoxic fronts. Hydrous ferric oxide (HFO) was partially converted to goethite after 24 h of anoxic contact with Fe(II), consistent with previous results. This resulted in a significant decrease in sorption of Fe(II). No conversion to goethite was observed after 25 min of anoxic contact between HFO and Fe(II). O2 was then introduced into the chamber and sparged (transfer half-time of 1.6 min) into the previously anoxic suspension, and the rate of oxidation of Fe(II) and the distribution between sorbed and dissolved Fe(II) were measured with time. The concentration of sorbed Fe(II) remained steady during each experiment, despite removal of all measurable dissolved Fe(II) in some experiments. The rate of oxidation of Fe(II) was proportional to the concentration of DO and both sorbed and dissolved Fe(II) up to a surface density of 0.02 mol Fe(II) per mol Fe(III), i.e., approximately 0.2 Fe(II) per nm2 of ferric oxide surface area. This result differs from previous studies of heterogeneous oxidation, which found that the rate was proportional to sorbed Fe(II) and DO but did not find a dependence on dissolved Fe(II). Most previous experiments were autocatalytic; i.e., the initial concentration of ferric oxide was low or none, and sorbed Fe(II) was not measured. The results were consistentwith an anode/cathode mechanism, with O2 reduced at electron-deficient sites with strongly sorbed Fe(II) and Fe(II) oxidized at electron-rich sites without sorbed Fe(II). The pseudo-first-order rate constants for oxidation of dissolved Fe(II) were about 10 times faster than those previously predicted for heterogeneous oxidation of Fe(II).

Absorption↗
PubMed1989

Halomethane hepatotoxicity: induction of lipid peroxidation and inactivation of cytochrome P-450 in rat liver microsomes under low oxygen partial pressures.

Halomethane-induced lipid peroxidation and inactivation of cytochrome P-450 were studied in liver microsomes from phenobarbital-pretreated rats in the presence of NADPH at steady-state O2 partial pressures (PO2). As indicated by the formation of thiobarbituric acid-reactive material and the stimulation of O2 uptake, significant lipid peroxidation was induced by those halomethanes containing more than two Cl, Br, or I atoms. Lipid peroxidation decisively depended on the PO2 present, showing distinct maxima at PO2 between 1 and 10 mm Hg. Those halomethanes inducing lipid peroxidation also led to inactivation of microsomal cytochrome P-450, as indicated by a loss of cytochrome P-450 detectable as ferrous CO complex and an equimolar loss of microsomal heme. Under anaerobic conditions inactivation of cytochrome P-450 presumably resulted solely from an attack of halomethane radicals on its heme moiety. Under aerobic conditions lipid peroxidation made an additional contribution to the inactivation of cytochrome P-450. These results suggest that the reductive activation to free radicals, catalyzed by cytochrome P-450, and thus the induction of lipid peroxidation at low but physiological PO2 are characteristic not only of CCl4 but also of other polyhalogenated methanes, especially CBrCl3, CBr4, CHI3, CHBr3, and CHBr2Cl.

Animals↗
PubMed1994

Effects of sample storage time, temperature and syringe type on blood gas tensions in samples with high oxygen partial pressures.

BACKGROUND: Although plastic arterial sampling syringes are now commonly used, the effects of sample storage time and temperature on blood gas tensions are poorly described for samples with a high oxygen partial pressure (PaO2) taken with these high density polypropylene syringes. METHODS: Two ml samples of tonometered whole blood (PaO2 86.7 kPa, PaCO2 4.27 kPa) were placed in glass syringes and in three brands of plastic blood gas syringes. The syringes were placed either at room temperature or in iced water and blood gas analysis was performed at baseline and after 5, 10, 20, 40, 60, 90, and 120 minutes. RESULTS: In the first 10 minutes measured PaO2 in plastic syringes at room temperature fell by an average of 1.21 kPa/min; placing the sample on ice reduced the rate of PaO2 decline to 0.19 kPa/min. The rate of fall of PaO2 in glass at room temperature was 0.49 kPa/min. The changes in PaCO2 were less dramatic and at room temperature averaged increases of 0.47 kPa for plastic syringes and 0.71 kPa for glass syringes over the entire two hour period. These changes in gas tension for plastic syringes would lead to an overestimation of pulmonary shunt measured by the 100% oxygen technique of 0.6% for each minute left at room temperature before analysis. CONCLUSIONS: Glass syringes are superior to plastic syringes in preserving samples with a high PaO2, and prompt and adequate cooling of such samples is essential for accurate blood gas analysis.

Blood Gas Analysis↗
PubMed1975

Effects of increased partial pressures of oxygen on the embryonic and post-embryonic development of drosophila melanogaster.

The objective of this investigation was to study the effects of increased oxygen pressures on the development of Drosophila melanogaster. Oxygen is a potent inhibitor of embryonic and post-embryonic development of Drosophila. The lowest partial pressure of O2 (Po2) found to elicit measurable inhibitory effects on development is 0.6 ATA. Continuous exposure of developing Drosophila to 0.6 ATA O2 elicits primarily a larvicidal effect; surviving larvae exhibit delays in initial puparium formation and in mean day of adult eclosion: several resultant adults exhibit the effects of O2-induced teratogenesis in that body and wing abnormalities become manifest which do not breed true on matings and back crosses. Continuous exposure to 0.8 or 1.0 ATA O2 results in developmental arrest in the second larval instar followed by death. This development arrest is reversible depending upon the duration of exposure. As concerns lethality, early larval stages are more sensitive to O2 than late larval stages which, in turn, are more sensitive than early or late pupal stages: the embryo is the more resistant of the development stages. As concerns sensitivity for teratogenesis, the embryo is the most sensitive stage.

Animals↗
PubMed2001

Gastric mucosal systemic partial pressure of carbon dioxide (PCO(2)) gradient in experimental endotoxin shock in swine--comparison of two methods.

OBJECTIVES: Clinically applicable methods for continuous monitoring of visceral perfusion/metabolism do not exist. Gastric mucosal end-tidal partial pressure of carbon dioxide (PCO(2)) gradient has been used, but it has limitations, especially in patients with lung injury and increased dead space ventilation. We studied the agreement between gastric mucosal end-tidal (DPCO(2gas)) and gastric mucosal arterial PCO(2) (D((t-a))PCO(2)) gradients, and especially the effect of dead space ventilation (V(d)/V(t) ratio) on the agreement. We hypothesized that DPCO(2gas) can be used as a semi-continuous indicator of mucosal arterial PCO(2) gradient in sepsis. DESIGN: A randomized, controlled animal experiment. SETTING: National laboratory animal center. INTERVENTIONS: Twelvehour infusion of endotoxin in landrace pigs. MEASUREMENTS AND RESULTS: We measured end-tidal PCO(2) continuously, gastric mucosal PCO(2) every 10 min (gas tonometry) and arterial PCO(2) every 120 min. Carbon dioxide production and the V(d)/V(t) ratio were determined by indirect calorimetry. In the endotoxin group ( n=7) cardiac index increased and systemic vascular resistance decreased. Endotoxemia increased dead space ventilation by 27% ( p=0.001). Both DPCO(2gas) and D((t-a))PCO(2)increased significantly in the endotoxin group ( p<0.0001 and p=0.049, respectively). Control animals remained stable throughout the experiment. When we compared DPCO(2gas) and D((t-a))PCO(2)(Bland-Altman analysis), the bias and precision were 0.9 and 0.9 kPa in the control group and 2.0 and 2.2 kPa in the endotoxin group, respectively. The disagreement between DPCO(2gas) and D((t-a))PCO(2) increased as the V(d)/V(t) ratio increased. CONCLUSIONS: DPCO(2gas) is a clinically applicable method for continuous monitoring of visceral perfusion/metabolism. Septic lung injury and increased dead space ventilation decrease the accuracy of the method, but this may not be clinically important.

Animals↗