SEARCH · PubMed Health

Results for “Partial Pressure”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 55 records · Page 3Linked to original sources

PubMed2005

Measurement of oxygen partial pressure in the mandibular bone using a polarographic fine needle probe.

In this study, the oxygen partial pressure in the cancellous bone substance of the mandible was measured for the first time with a polarographic fine needle probe. This has so far only been established in soft tissue. The aim was to prove and to test the feasibility in principle of this method of measurement in order to ascertain the normal values for the O2 partial pressure in healthy bone. These values were afterwards compared with the results of measurements in areas of different pathological bone conditions in order to assess the clinical suitability of the method for "mapping" during mandibular resection. Measurements of oxygen partial pressure were made in a total of 42 patients (16 women, 26 men). Of these, 12 patients with clinically normal bones served as a control group. Seventeen patients had osteoradionecrosis following radiation treatment, and 13 patients presented with chronic osteomyelitis of the mandible. All measurements were carried out with a polarographic fine needle probe applied to the cancellous bone substance. The statistical analysis included a comparison of the mean values of the oxygen partial pressures measured. No statistical correlation between oxygen partial pressure and pH and hemoglobin values could be detected. The average oxygen partial pressure in the healthy mandibular bone was 71.4 mmHg. In non-healthy bone, the value fell to an average of 30.6 mmHg (osteoradionecrosis 32.3 mmHg, chronic osteomyelitis of the mandibular bone 28.4 mmHg). Statistically, the differences in the group values ascertained were highly significant (P < 0.005). The data found show that this method can be successfully used to detect poorly perfused bone. The values are reproducible and reflect the clinical situation. In the long term, the method appears to be a suitable diagnostic tool for assessing the oxygen supply in bone in studying various clinical problems related to bone surgery.

Adult↗

PubMed1999

Predicted sevoflurane partial pressure in the brain with an uptake and distribution model comparison with the measured value in internal jugular vein blood.

OBJECTIVE: In order to predict the partial pressure of volatile anesthetics in brain tissue, we developed a pharmacokinetic simulation model suitable for real time application. The accuracy of this model was examined by comparing the predicted values against measured values for blood sampled from the internal jugular vein, which was used as a measure of the partial pressure in the brain. METHODS: Our model consists of six compartments: alveoli, arterial blood, a group of vessel-rich organs (VRG), muscle, fat, and venous blood. A volatile anesthetic, sevoflurane partial pressure in each compartment were calculated using the parameters of volume, blood flow, and solubility for each tissue as reported in previous studies. Simulated sevoflurane partial pressures in VRG were considered to reflect those in the brain. We studied 11 patients undergoing elective abdominal surgery or mastectomy. Sevoflurane was maintained at a concentration of 3% (by vaporizer setting) for 25 min. Sampling points were at 0 min (before sevoflurane administration) and 1, 2, 4, 9, 16, and 25 min after the start of inhalation. We measured the sevoflurane partial pressure in inspiratory gas (PI(S)), in end-expiratory gas (PET(S)), in arterial blood (Pa(S)), and in internal jugular vein blood (Pj(S)). These values were compared against those for the simulated brain (PB(S)sim). RESULTS: The sevoflurane partial pressures increased, in order from least rapid to most rapid, as follows: Pj(S), PB(S)sim, Pa(S), PET(S), and PI(S). The differences between Pj(S) and PB(S)sim were significantly smaller than those between Pj(S) and PET(S) at all sampling points. PB(S)sim did not differ significantly from Pj(S) at any sampling points after 4 min of inhalation, while PET(S) differed significantly from Pj(S) at all sampling points. CONCLUSION: We conclude that our model is clinically useful for predicting sevoflurane partial pressure in the brain, assuming that Pj(S) reflects the sevoflurane partial pressure in the brain.

Anesthetics, Inhalation↗

PubMed1989

Effect of total and partial pressure (oxygen and carbon dioxide) on aerobic microbial processes.

In industrial bioreactors, levels and gradients of total and partial pressures are considerably higher than on the laboratory scale. In the relevant range (in general up to 2 or 3 bar, maximum approx. 10 bar), effects of total pressure on aerobic cultures are negligibly small. CO2 partial pressures of more than approx. 100 mbar may have inhibitory effects on aerobic cultures. Growth of aerobic cultures can be enhanced by O2 partial pressures higher than 210 mbar (corresponding to air at 1 bar), if oxygen transfer is limited. In many cases, however, increased O2 partial pressure (higher than approx. 1 bar) is toxic to aerobic cultures and inhibits microbial growth and product formation. Stepwise and cyclic variations of O2 partial pressure may have positive or negative effects, depending on strain of microorganism, culturing conditions, and range of dissolved oxygen concentration. Knowledge of these effects is required in process development and bioreactor scale-up.

Aerobiosis↗

PubMed1959

Partial pressure of ammonia in alveolar air.

The partial pressure of ammonia in alveolar air was measured and found to be the same (within the limits of experimental error) as the calculated partial pressure of ammonia in arterial plasma. It is likely that ammonia is equilibrated between alveolar air and the blood during its passage through the pulmonary capillaries.

Ammonia↗

PubMed1995

Effect of partial pressure on solubility of isoflurane in blood.

The effect of partial pressure of isoflurane on its solubility in blood of different haematocrit was determined at different isoflurane partial pressures, using a syringe--flask method and gas chromatography with blood from one donor. The solubility of isoflurane decreased with increasing blood haematocrit (39.5%, 51.9% and 61.9%) and isoflurane partial pressure from 1 MAC to 4 MAC. The solubility in 50% and 60% haematocrit blood at 2, 3 and 4 MAC was significantly different from the solubility in normal blood at 1 MAC (P < 0.05). We conclude that the solution of isoflurane in blood (especially in high haematocrit blood) does not obey Henry's law.

Adult↗

PubMed1985

Germination, respiration, and adenylate energy charge of seeds at various oxygen partial pressures.

The effect of O(2) partial pressure on the germination and the respiration of 12 cultivated species was studied. The reciprocal of the time necessary to observe rootlet emergence in 50% of the seeds was used to approach the germination rate. The maximum germination and respiration rates were reached in most seeds at O(2) pressures close to that of air. Decreasing the O(2) pressure produced a gradual decrease of the germination rate. The seeds could be classed in two groups according to their response to low O(2) pressures. Group I includes lettuce, sunflower, radish, turnip, cabbage, flax, and soybean: at O(2) pressures close to 2 kilopascals, the germination in this group was stopped and the adenylate energy charge was lower than 0.6. Group II includes rice, wheat, maize, sorghum, and pea. The germination rate of these seeds was also gradually decreased by lowering the O(2) partial pressure but germination still occured, very slowly, at 0.1 kilopascal; the adenylate energy charge remained higher than 0.6. These differences in the germination rates and adenylate energy charge values could not be explained by differences in the sensitivity of respiration to O(2).

Journal Article↗

PubMed1975

[Nomogram for the determination of arterial oxygen partial pressure of man in relation to high altitude and in dependence from age (author's transl)].

If somebody ascends from sea level to higher altitude within a short time, the change of the atmospheric conditions can be a danger for his life. Therefore, a nomogram was constructed which allows to read off the arterial oxygen partial pressures and the corresponding arterial oxygen saturation in relation to altitude. On the basis of the oxygen partial pressure of the atmosphere determined by steps of 500 m from sea level up to an antitude of 10,000 m, we calculated the decrease of the oxygen partial pressure from the inspired air to the arterial blood. When passing our airways, the inspired oxygen partial pressure is dimished by the adaptation to BTPS conditions and by the increasing CO2 partial pressure when approaching the alveolar gas exchanging zone. Another oxygen partial pressure gradient formed by inhomogeneities of ventilation to perfusion, diffusing capacity to perfusion and shunt perfusion is found at the alveolar-arterial barrier. The value of this alveolar-arterial oxygen partial pressure difference is closely correlated to age. With the values of the single steps, the nomogram was constructed. Seven abscissas show the oxygen partial pressure gradients from the inspired air at a distinct altitude to the arterial blood. In relation to a lot of CO2-depending oxygen dissociation curves, it is possible to read off additionally the corresponding arterial oxygen saturation for a person in rest up to an altitude of 10,000 m.

Adult↗

PubMed1989

[The effects of ephedrine and phenylephrine on arterial partial pressure of oxygen].

The changes in arterial partial pressure of oxygen were studied following intravenous injections of either ephedrine, 0.2mg.kg-1, or phenylephrine 2.5 micrograms.kg-1, to restore arterial hypotension. Eighty one adult patients underwent general anesthesia, being mechanically ventilated, were divided into two groups; both lung ventilation group (68 patients) and one lung ventilation group (13). In both lung ventilation group, PaO2/FIO2 changed from 390 +/- 132 to 400 +/- 137 mmHg, and 428 +/- 124 to 438 +/- 136 following administrations of ephedrine and phenylephrine, respectively. The results were not statistically significant. In the one lung ventilation group, PaO2/FIO2 did not change significantly from 190 +/- 45 to 186 +/- 29 with ephedrine and 267 +/- 138 to 317 +/- 230 with phenylephrine. We observed neither arrhythmia, severe hypoxemia, nor decrease in PaO2/FIO2 by more than 100mmHg. These results indicate that with respect to changes in arterial partial pressure of oxygen, the clinical doses of ephedrine and phenylephrine can be safely administered to patients under general anesthesia to restore arterial hypotension.

Adult↗

PubMed1976

[Measurement of the oxyten partial pressure in the gingiva].

The partial pressure of oxygen (pO2) in the inflamed gingiva was measured in 24 patients before and after the application of Gingivox. The Gingivox treatment led to a significant increase in pO2 from 72.2 mm Hg to 94.6 mmHg. The arterial pO2 values of all patients, measured on the hyperaemic ear-lobe, lay within the range of normal values. The measurements were performed by means of the micro-Astrup equipment of the firm of Radiometer, Copenhagen.

Adolescent↗

PubMed1997

Antioxidant and prooxidant role of beta-carotene in murine normal and tumor thymocytes: effects of oxygen partial pressure.

The effects of the partial pressure of oxygen (pO2) on antioxidant efficiency of beta-carotene in inhibiting radical-initiated lipid peroxidation were studied in murine normal and tumor thymocytes. At 150 mm Hg pO2 (the pressure of oxygen in normal air), beta-carotene acted as an antioxidant, inhibiting radical-induced lipid peroxidation in both normal and tumor thymocytes. At 760 mm Hg p02, beta-carotene lost its antioxidant activity in normal thymocytes and exhibited a dose-dependent prooxidant effect in tumor thymocytes. In these cells, the prooxidant effect of beta-carotene was also accompanied by an increase of endogenous alpha-tocopherol loss. beta-Carotene radical-trapping and autooxidation reactions were faster at 760 mm Hg pO2 than at 150 mm Hg pO2 in both normal and tumor thymocytes and the carotenoid was more rapidly consumed in tumor cells. These data point out a key role of the oxygen tension on the antioxidant effectiveness of beta-carotene. They also show a selective prooxidant effect of beta-carotene under 100% oxygen in tumor cells.

Amidines↗

PubMed1978

Leaf Conductance in Relation to Assimilation in Eucalyptus pauciflora Sieb. ex Spreng: Influence of Irradiance and Partial Pressure of Carbon Dioxide.

Rates of assimilation and transpiration in Eucalyptus pauciflora Sieb. ex Spreng were measured at various ambient partial pressures of CO(2) and various irradiances and were used to estimate leaf conductance and intercellular partial pressure of CO(2). The responses of leaf conductance and rate of assimilation to change in intercellular partial pressure of CO(2) were expressed in terms of feedback. They are small in the sense that their combined effect was to reduce disturbances in intercellular partial pressure of CO(2) by 30% only. The magnitude of the feedback had no influence on the system as affected by irradiance, because the direct responses of conductance and rate of assimilation to changes in irradiance in the range 0.25 to 2 millieinsteins per meter per second were such that intercellular partial pressure was maintained almost constant.

Journal Article↗

PubMed1981

Transcutaneous measurements of carbon dioxide partial pressure in sick neonates.

The authors measured the partial pressure of carbon dioxide transcutaneously (PtcCO2) in 15 sick newborns and compared the PtcCO2 to simultaneously measured partial pressure of arterial carbon dioxide (PaCO2). The PtcCO2 values reflected changes in the PaCO2 values. A linear regression on 106 paired PtcCO2 and PaCO2 values produced a correlation coefficient of 4 = 0.91 with a slope of 1.89 and a y-intercept of --9.4. The authors found the measurement of PtcCO2 to be a clinically useful method of continuously following the trend of PaCO2.

Arteries↗

PubMed2003

Sapwood development in Pinus radiata trees grown for three years at ambient and elevated carbon dioxide partial pressures.

Clonal trees of Pinus radiata D. Don were grown in open-top chambers at a field site in New Zealand for 3 years at ambient (37 Pa) or elevated (65 Pa) carbon dioxide (CO2) partial pressure. Nitrogen (N) was supplied to half of the trees in each CO2 treatment, at 15 g N m-2 in the first year and 60 g N m-2 in the subsequent 2 years (high-N treatment). Trees in the low-N treatment were not supplied with N but received the same amount of other nutrients as trees in the high-N treatment. In the first year, stem basal area increased more in trees growing at elevated CO2 partial pressure and high-N supply than in control trees, suggesting a positive interaction between these resources. However, the relative rate of growth became the same across trees in all treatments after 450 days, resulting in trees growing at elevated CO2 partial pressure and high-N supply having larger basal areas than trees in the other treatments. Sapwood N content per unit dry mass was consistently about 0.09% in all treatments, indicating that N status was not suppressed by elevated CO2 partial pressure. Thus, during the first year of growth, an elevated CO2 partial pressure enhanced carbon (C) and N storage in woody stems, but there was no further stimulus to C and N deposition after the first year. The chemical composition of sapwood was unaffected by elevated CO2 partial pressure, indicating that no additional C was sequestered through lignification. However, independent of the treatments, early wood was 13% richer in lignin than late wood. Elevated CO2 partial pressure decreased the proportion of sapwood occupied by the lumina of tracheids by up to 12%, indicating increased sapwood density in response to CO2 enrichment. This effect was probably a result of thicker tracheid walls rather than narrower lumina.

Carbon Dioxide↗

PubMed2003

[Photosynthesis and free radical yield of Litchi chinensis leaves under increased CO2 partial pressure in atmosphere].

The maximum photosynthetic rate of litchi saplings leaves grown under a CO2 partial pressure of 77 +/- 5 Pa was 23% lower than that of 39.3 Pa, and slight decreases in respiration rate in light and CO2 compensation point excluding of respiration in light were observed. The maximum rates of carboxylation (Vcmax) and photosynthetic electron transport (Jmax) were decreased in saplings grown under 77 +/- 5 Pa CO2 partial pressure. It may suggest that there was a lower energy level of photosystem I(PSI) in the saplings leaves under 77 +/- 5 Pa CO2 partial pressure, and free radical yield decreased by 39% in the saplings under 77 +/- 5 Pa CO2, as comparied with that under atmospheric CO2. The percentage of infection by Peronophythora litchi increased from 1.8% under atmospheric CO2 to 9.5% under enriched CO2. It may mean that the decreasing photosynthetic and respiration metabolism would make it lower the production of O2-., and leaves were infected by P. litchi more easily. The controlling of the popularization of P. litchi for litchi plantation must be paid wide attention, as air CO2 partial pressure will increase continuously.

Carbon Dioxide↗

PubMed1998

Estimation of arterial CO2 partial pressure by measurement of tracheal CO2 during high-frequency jet ventilation in patients with a laryngectomy.

Tracheal and arterial CO2 partial pressures were measured simultaneously in 27 laryngectomized patients both while they were awake and during high-frequency jet ventilation. Tracheal gas was sampled during brief interruptions of high-frequency jet ventilation. Agreement between tracheal and arterial CO2 partial pressures was assessed using the Bland-Altman method. The tracheal-arterial CO2 partial pressures gradient during spontaneous breathing was significantly lower (P < 0.0002) than during high-frequency jet ventilation. During spontaneous ventilation, the bias was -0.77 kPa (95% CI = -0.99 to -0.55 kPa), and the upper and lower limits of agreement were 0.29 kPa (95% CI = -0.11 to -0.7 kPa) and -1.83 kPa (95% CI = -2.24 to -1.43 kPa). During high-frequency jet ventilation, the bias was -1.61 kPa (95% CI = -1.76 to -1.46 kPa), and the limits of agreement were -0.48 kPa (95% CI = -0.75 to -0.21 kPa) and -2.74 kPa (95% CI = -3.01 to -2.47 kPa). Despite the poor agreement between tracheal CO2 partial pressure and arterial CO2 partial pressure, it is sufficient to allow for adjustment of ventilator settings during jet ventilation.

Adult↗

PubMed1997

Influence of isokinetic and ergometric exercises on oxygen partial pressure measurement in the human knee joint.

We conducted the first in vivo investigation on the influence of joint movement on intraarticular oxygen partial pressure. The development of a special flexible microcatheter allowed measurements of intraarticular oxygen partial pressure under both physiological and pathological conditions. The aim of this study was to evaluate the influence of different knee joint stresses on intraarticular oxygen partial pressure under physiological (healthy patients) and pathological (patients with osteoarthritis) conditions. The results show that the different exercise patterns influence the intraarticular oxygen partial pressure. Patients with osteoarthritis showed a lower increase of intraarticular oxygen partial pressure compared with healthy patients. This phenomenon is directly correlated to the degree velocity of the isokinetic exercises. We found the same results under ergometric conditions. This method allows functional, intraarticular in vivo measurements under different exercise patterns. For the first time, we were able to measure the influence of joint movement on the intraarticular process of nutrition under physiological and pathological conditions. Also, to evaluate for the first time in vivo different concepts for osteoarthritis therapy.

Adult↗

PubMed1999

A new measuring device for non-invasive determination of oxygen partial pressure and oxygen conductance of the skin and other tissues.

About fifty percent of the oxygen consumption of the skin is supplied by diffusion through the surface. This portion of the skin oxygen supply becomes of high importance in case of arterial occlusion. The oxygen permeation coefficient (P) of the upper layers and the oxygen pressure field within the skin determine the diffusive oxygen uptake from the outside. To our knowledge, the permeation coefficient (P) until now was only estimated by indirect methods of little practicability (Baumberger et al., 1951; Eberhard et al., 1978). An oxygen partial pressure of the skin is conventionally measured by modified CLARK type electrodes. A disadvantage of this so-called transcutaneous electrode is its oxygen consumption and the fixed coupling of the consumption with the oxygen pressure to be determined. Therefore the measurement always induces a systematic error (the so-called stirring effect) which depends, among other factors, on the oxygen availability of the skin under the electrode. The new device combines a consumption-free oxygen partial pressure detector on the basis of luminescence quenching by oxygen with an independently working specific oxygen consumer realized by an active galvanic chain (silver-lead element). The chain permits setting any oxygen mass flow (mO2) in a certain range by varying the electrode current choosing different resistors within the electrical circuit. According to the diffusion law, the surface oxygen pressure (ePO2) being measured is a linear function of the oxygen flow (mO2) directed to the cathode: ePO2 identical to -(1/P).(mO2/A) + icPO2; A: area under the cathode. The intracutaneous oxygen partial pressure (icPO2) is a virtual quantity defined by the equation given. Only by using an active electrode different oxygen mass flows can be set and so the oxygen conductance of the upper skin layers can be assessed. First experiments on human skin in the gluteal region of an adult delivered an estimated value of the permeation coefficient (P): 2.2.10(-5) ml O2 (STPD)/(atm.s.cm2) at 42 degrees C skin surface temperature; the intracutaneous partial pressure obtained was 5.5 kPa (41 mmHg) (STPD: "standard temperature pressure dry" conditions of the gas). At 42 degrees C skin temperature no burning occurs. The determined O2-conductance is in the same range as estimated formerly (see above). The intracutaneous oxygen partial pressure determined seems to be a realistic value of the tissue at 42 degrees C. By in vitro measurements with technical membranes the new device and procedure was validated giving precise values of the oxygen conductance. Hence the new method may be used for calibration of the oxygen flux optode (Holst et al., 1993). The O2-permeation coefficient (P) could be an important parameter for evaluating dermatological applications (which attempt to increase P) in the treatment of local dermal oxygen deficiency. The intracutaneous oxygen partial pressure found is a reasonable value for a surface temperature of 42 degrees. Because of the independence of the O2-partial pressure determined and the O2-consumption the new device exhibits no stirring effect and it provides more insight into the limitations of conventional transcutaneous oxygen measurement.

Adult↗

PubMed1990

Tissue oxygen partial pressure distribution within the human skeletal muscle during hypercapnia.

In ten subjects CO2-inhalation elicited a significant increase in mean oxygen partial pressure within biceps muscle by more than 35%. Though mean oxygen partial pressure within biceps muscle increased, the distribution of oxygen partial pressure (pO2-histogram) did not change suggesting a physiological distribution of oxygen delivery within biceps muscle during hypercapnia. Buffering the blood pH did not abolish the effects of the CO2-inhalation. Therefore, a decrease of peripheral blood pH could not account for the hypercapnia induced increase of mean oxygen partial pressure within biceps muscle. Our data suggest that oxygen delivery to skeletal muscle was increased during hypercapnia, most probably due to a hypercapnia induced rise of mean capillary blood flow.

Adult↗