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PubMed1986

Determination of permeabilities for two gases from recording the partial pressure of one gas.

When a flexible diffusion layer separates two closed gas chambers containing different mixtures of several gases, the different permeabilities of the layer for these gases lead to differences in the total gas pressures of the two chambers resulting in bulging of the layer and consequent changes in the chamber volumes. Application of the gas laws to binary gas mixtures provides two equations relating the partial pressure changes of one gas in any of the two chambers to the partial pressure difference between the two chambers across the layer. This permits the calculation of the two unknown factors, permeability (or Krogh's diffusion coefficient) of the layer for the measured gas and the permeability ratio of the two gases. Thus the permeabilities of both gases can be determined from recording the partial pressure of one of the gases only. We filled the gas chambers with different mixtures of oxygen and a second gas (nitrogen or carbon dioxide) at atmospheric pressure, closed the chambers, and measured the diffusion of the gases across thin (12-500 microns) layers of various materials by recording the oxygen partial pressure in both chambers with polarographic oxygen electrodes. Permeabilities of these layers for oxygen and the other gas were determined for plastic layers (MEM213, Silastic, Teflon), as well as water and methemoglobin solutions either in a fluid layer or soaked in Millipore filters. The data agreed well with those obtained from other studies in most cases.

Gases↗

PubMed2002

Stimulation of nitric oxide synthase in cerebral cortex due to elevated partial pressures of oxygen: an oxidative stress response.

The purpose of this investigation was to determine the impact of elevated partial pressures of O(2) on the steady state concentration of nitric oxide ((*)NO) in the cerebral cortex. Rodents with implanted O(2)- and (*)NO-specific microelectrodes were exposed to O(2) at partial pressures from 0.2 to 2.8 atmospheres absolute (ATA) for up to 45 min. Elevations in (*)NO concentration occurred with all partial pressures above that of ambient air. In rats exposed to 2.8 ATA O(2) the increase was 692 +/- 73 nM (S.E., n = 5) over control. Changes were not associated with alterations in concentrations of nitric oxide synthase (NOS) enzymes. Based on studies with knock-out mice lacking genes for neuronal NOS (nNOS) or endothelial NOS (eNOS), nNOS activity contributed over 90% to total (*)NO elevation due to hyperoxia. Immunoprecipitation studies indicated that hyperoxia doubles the amount of nNOS associated with the molecular chaperone, heat shock protein 90 (Hsp90). Both (*)NO elevations and the association between nNOS and Hsp90 were inhibited in rats infused with superoxide dismutase. Elevations of (*)NO were also inhibited by treatment with the relatively specific nNOS inhibitor, 7 nitroindazole, by the ansamycin antibiotics herbimycin and geldanamycin, by the antioxidant N-acetylcysteine, by the calcium channel blocker nimodipine, and by the N-methyl-D-aspartate inhibitor, MK 801. Hyperoxia did not alter eNOS association with Hsp90, nor did it modify nNOS or eNOS associations with calmodulin, the magnitude of eNOS tyrosine phosphorylation, or nNOS phosphorylation via calmodulin kinase. Cerebral cortex blood flow, measured by laser Doppler flow probe, increased during hyperoxia and may be causally related to elevations of steady state (*)NO concentration. We conclude that hyperoxia causes an increase in (*)NO synthesis as part of a response to oxidative stress. Mechanisms for nNOS activation include augmentation in the association with Hsp90 and intracellular entry of calcium.

Animals↗

PubMed2002

Ventilatory sensitivity to changes in inspired and arterial carbon dioxide partial pressures in the chicken.

To determine if intrapulmonary chemoreceptors could be the sole peripheral chemoreceptors responsible for ventilatory responses to inhaled CO2, we studied the relationships of minute ventilation, tidal volume, and respiratory frequency to inspired and arterial partial pressure of CO2 (P(I)CO2 and PaCO2) in decerebrate upright chickens when the birds inspired gases containing four low partial pressures of CO2 (0.02, 5.0, 8.2, and 11.4 torr). Because of variability in the measured variables from time to time in the same birds, as well as between birds, and because of the limited precision in measuring PaCO2, a 4 x 4 Latin square design and four statistical methods of data analyses (modified reduced major axis estimator, maximum likelihood estimator, average slope method, and summary slope method) were used. Tidal volume, minute ventilation, and PaCO2 increased, but respiratory frequency remained unchanged, as gases containing increased partial pressures of CO2 were inhaled. The results indicate that intrapulmonary chemoreceptors are not the sole receptors stimulated by inhaling gas containing even low partial pressures of CO2 and that stimulation of arterial and central chemoreceptors also occurs. Stimulation of these latter chemoreceptors may account for the increase in ventilation. Further, the results demonstrate the importance of maintaining a low level of environmental CO2 in poultry houses to minimize its influence on ventilation.

Animals↗

PubMed2006

Exhaled breath condensate pH standardised for CO2 partial pressure.

Exhaled breath condensate (EBC) pH is considered to reflect the acid-base balance of the airways. Current pH measurements do not take into account the effect of CO2. The aim of the present study was to determine the effect of condensate CO2 partial pressure on pH and to provide a more precise mode of EBC pH determination. Condensate pH and CO2 partial pressure were measured in parallel from 12 healthy volunteers and 12 asthmatics using a blood gas analyser in neat, argon de-aerated and CO2-loaded samples. The regression analysis was used to test the relationship between pH and CO2, and to calculate the pH at a CO2 level of 5.33 kPa (physiological alveolar CO2 partial pressure). Reproducibility of different pH readings was compared using the Bland-Altman test. Condensate CO2 concentration was variable both in neat and argon de-aerated samples. There was a close negative logarithmic relationship between CO2 and pH. Calculation of pH at a CO2 level of 5.33 kPa provided reproducibility approximately six times as good as that of the currently used measurements. Condensate CO2 partial pressure influences pH measurements. Determination of pH at a standard CO2 level provides the most reproducible condensate pH values to date.

Acid-Base Equilibrium↗

PubMed1984

Carbon tetrachloride metabolism in vivo and exhalation of volatile alkanes: dependence upon oxygen partial pressure.

Metabolism of carbon tetrachloride in rats at atmospheric and reduced oxygen pressure has been determined indirectly by its disappearance from the inhaled air; it is inversely related to oxygen concentration and increases with decreasing partial pressure, as expected for reductive dehalogenation; oxygen partial pressure has been reduced to about a third of normobaric conditions. Concurrently exhalation of ethane and pentane as indication of lipid peroxidation has been monitored, showing a drastic increase when the oxygen partial pressure is reduced in the presence of carbon tetrachloride. Time course and duration of these processes indicate that the total metabolism of carbon tetrachloride is limited by the concomitant destruction of cytochrome P-450; also, oxidative destruction of polyunsaturated fatty acids apparently does not proceed beyond the end of metabolic activation of carbon tetrachloride. The molar ratios of the amount of metabolized carbon tetrachloride to the amounts of exhaled hydrocarbons lead to the same conclusion, namely that "lipid peroxidation" in this case does not proceed as an autocatalytic, self-propagating chain reaction.

Animals↗

PubMed1992

Variations in corticomotor and somatosensory evoked potentials: effects of temperature, halothane anesthesia, and arterial partial pressure of CO2.

The effects of temperature, halothane concentration, and arterial partial pressure of CO2 on corticomotor evoked potentials (CMEPs) and somatosensory evoked potentials (SSEPs) were studied. Hypothermia causes an increase in CMEP and SSEP latencies. Corticomotor evoked potential amplitude increases with hypothermia to reach a maximum at or below 28 degrees C. As the temperature decreases from 42 degrees C, SSEP amplitude initially increases to reach a maximum between 36 and 34 degrees C and then decreases with further reductions in temperature. Increased arterial partial pressure of CO2 decreases amplitude and increases latencies of the CMEPs and SSEPs. The concentration of halothane has no effect on CMEP amplitude or latency. However, SSEP amplitude is inversely related to halothane concentration, and SSEP latency is directly related to halothane concentration. These results suggest that physiologic variables must be carefully measured when evoked potentials are utilized in any animal or human study. Moreover, each type of evoked potential has a unique response to alterations of these variables.

Animals↗

PubMed1976

Quadrupole mass filtering for registration of blood gas partial pressures.

With a newly developed quadrupole mass spectrometer several blood gas partial pressures are recorded simultaneously and continuously. In the mass filter the separation of the ions to be detected takes place in a hyperbolic electric field with variable direct and alternating voltages with a constant frequency of 2.4 MHz. For blood gas analysis a fully relaxed experimental animal was artifically ventilated and provided with arterial and venous catheters. Each catheter consisted flexible steel tubing (external diameter 0.6 mm) slotted near the end and covered with a silicone rubber membrane. The distance from the measuring tip to the mass spectrometer was 150 cm. Experiments with blood, in vivo equilibrated with gas mixtures, showed good reproducibility; the mean error of the helium partial pressure, for example, was less than 4%. During respiration using a gas mixture with 40% argon, the time constant t63% was found to be 55 s for the whole experimental arrangement including the experimental animal.

Animals↗

PubMed1989

Effects of Ambient and Acute Partial Pressures of Ozone on Leaf Net CO(2) Assimilation of Field-Grown Vitis vinifera L.

Mature, field-grown Vitis vinifera L. grapevines grown in open-top chambers were exposed to either charcoal-filtered air or ambient ozone partial pressures throughout the growing season. Individual leaves also were exposed to ozone partial pressures of 0.2, 0.4, or 0.6 micropascals per pascal for 5 hours. No visual ozone damage was found on leaves exposed to any of the treatments. Chronic exposure to ambient O(3) partial pressures reduced net CO(2) assimilation rate (A) between 5 and 13% at various times throughout the season when compared to the filtered treatment. Exposure of leaves to 0.2 micropascals per pascal O(3) for 5 hours had no significant effect on A; however, A was reduced 84% for leaves exposed to 0.6 micropascals per pascal O(3) when compared to the controls after 5 hours. Intercellular CO(2) partial pressure (c(i)) was lower for leaves exposed to 0.2 micropascals per pascal O(3) when compared to the controls, while c(i) of the leaves treated with 0.6 micropascals per pascal of 0(3) increased during the fumigation. The long-term effects of ambient O(3) and short-term exposure to acute levels of O(3) reduced grape leaf photosynthesis due to a reduction in both stomatal and mesophyll conductances.

Journal Article↗

PubMed2006

An evaluation of transcutaneous carbon dioxide partial pressure monitoring during apnea testing in brain-dead patients.

BACKGROUND: Diagnosis of brain death usually requires an arterial carbon dioxide partial pressure (Paco2) of 60 mmHg during the apnea test, but the increase in Paco2 is unpredictable. The authors evaluated whether transcutaneous carbon dioxide partial pressure (Ptcco2) monitoring during apnea test can predict that a Paco2 of 60 mmHg has been reached. METHODS: The authors compared Ptcco2 measured with a transcutaneous ear sensor (V-Sign Sensor, Sentec Digital Monitoring System; SENTEC-AG, Therwil, Switzerland) and Paco2 obtained from arterial blood gas measurements in 32 clinically brain-dead patients. RESULTS: In the first 20 patients, the mean Paco2-Ptcco2 gradient was 0.7 +/- 3.6 mmHg at baseline and 8.7 +/- 7.1 mmHg after 20 min of apnea. Using receiver operating characteristic curve analysis (area under the curve: 0.983 +/- 0.013), the best threshold value of Ptcco2 to predict that a Paco2 of 60 mmHg had been reached was 60 mmHg (positive predictive value: 1.00 [0.93-1.00]). In the following 12 patients investigated with use of this Ptcco2 target value of 60 mmHg, the mean duration of the apnea test (11 +/- 4 vs. 20 +/- 0 min; P < 0.001), hypercapnia (74.0 +/- 4.9 vs. 98.3 +/- 20.0 mmHg; P < 0.001), acidosis (pH: 7.18 +/- 0.06 vs. 7.11 +/- 0.08; P < 0.001), and decrease in arterial oxygen partial pressure (-47 +/- 44 vs. -95 +/- 89; P < 0.05) at the end of the test were reduced as compared with the 20-min apnea test group. CONCLUSION: During the apnea test in brain-dead patients, a Ptcco2 of 60 mmHg accurately predicts that a Paco2 of 60 mmHg has been reached. This may allow a reduction in the duration of the apnea test and consecutively limit occurrence of complications.

Adult↗

PubMed1991

The effect of different atmospheric ozone partial pressures on photosynthesis and growth of nine fruit and nut tree species.

Nursery stock of peach (Prunus persica L. Batsch, cv. O'Henry), nectarine (P. persica L. Batsch, cv. Fantasia), plum (P. salicina Lindel., cv. Casselman), apricot (P. armeniaca L., cv. Tilton), almond (P. dulcis Mill., cv. Nonpareil), prune (P. domestica L., cv. Improved French), cherry (P. avium L., cv. Bing), oriental pear (Pyrus pyrifolia Rehd., cv. 20th Century), and apple (Malus pumula Mill., cv. Granny Smith) were planted in open-top chambers on April 1, 1988 at the University of California's Kearney Agricultural Center located in the San Joaquin Valley (30 degrees 40' N 119 degrees 40' W). Trees were exposed to three atmospheric ozone partial pressures (charcoal-filtered air (C), ambient air (A), or ambient air + ozone (T)) from August 1 to November 17, 1988. The mean 12-h (0800 to 2000 h) ozone partial pressures measured in open-top chambers during the experimental period were 0.030, 0.051, and 0.117 microPa Pa(-1) in the C, A and T treatments, respectively. Leaf net CO(2) assimilation rate decreased linearly with increasing 12-h mean ozone partial pressure for the almond, plum, apricot, prune, pear, and apple cultivars. Stomatal conductances of apricot, apple, almond, and plum decreased linearly with increasing ozone partial pressure. Cross-sectional area relative growth rates of almond, plum, apricot, and pear decreased linearly with increasing ozone partial pressure. Net CO(2) assimilation rate, stomatal conductance, and trunk growth of cherry, peach and nectarine were unaffected by the ozone treatments. Reduced leaf gas exchange probably contributed to ozone-induced growth reduction of the susceptible species and cultivars. Several of the commercial fruit tree species and cultivars studied were relatively tolerant to the ozone treatments.

Journal Article↗

PubMed1988

Relationship between the transfer rate and the gap in partial pressure of gas molecules at a heterogeneous interface.

The kinetic energy of a gas molecule dissolved in an aqueous solution in the stationary state is inversely proportional to its solubility according to the distribution law of kinetic energy between the gas and liquid phases. From the difference in solubility, it is deduced that the gas molecule undergoes a change in energy in the passage across a heterogeneous interface, which is countered by a difference in energy level, or a gap in partial pressure, between the two sides. In order words, unless there is the gap in partial pressure, which has hitherto been disregarded in solving the diffusion equation, it is impossible to equalize the efflux of gas molecules with the influx. The relationship between the gap in partial pressure and the transfer rate is theoretically derived from the difference in solubility. The transfer rate is evaluated by multiplying the gap size by the transfer coefficient n, which in turn is expressed by an equation containing the unique value, k, for conductivity across the interface. Comparing the theoretical and experimental transfer coefficients obtained across the gas-liquid interface, the k value at which a gas traverses the liquid side per unit difference in partial pressure is estimated to be 6.58 x 10(-3) cm.s-1.Atm-1. Gas solubility in the RBC membrane is estimated to be ca. 22% of that in water, regardless of gas type, for O2, CO, and CO2. The increase in transfer coefficient across the RBC membrane by convection is explained by an additional change in kinetic energy in extracellular fluid attributable to an external force. The reduction in the transfer coefficient in the presence of increased protein is ascribed to an increase in kinetic energy of the membrane at the RBC boundary. The solubility in the membrane is linearly related to added protein concentration.

Animals↗

PubMed1992

Partial pressures of oxygen and carbon dioxide in bone and their correlation with bone-blood flow: effect of decreased arterial supply and venous congestion on intraosseous oxygen and carbon dioxide in an animal model.

Pathological changes in bone have been related to a preceding impediment of the arterial or venous bone circulation and hypoxia. In this study, we analyzed the feasibility of mass spectrometry in measuring intraosseous oxygen and carbon dioxide. The partial pressures were also measured in intraosseous blood samples, and blood flow in bone was measured with the radioactive microspheres technique. The average partial pressure of oxygen in the lateral femoral condyle was 34 +/- 1.6 mm Hg when measured in intraosseous blood samples and 36.3 +/- 2.3 mm Hg when measured with the on-line mass spectrometer, with significant correlation between the methods. The absolute value of the partial pressure of carbon dioxide measured in situ with mass spectrometry was correlated with the value in the withdrawn blood. There was no significant difference in partial pressures of oxygen and carbon dioxide between the two sides or between repetitive measurements. Arterial occlusion resulted in severe hypoxia, whereas more moderate changes followed venous occlusion.

Animals↗

PubMed1996

Mild temperature hyperthermia combined with carbogen breathing increases tumor partial pressure of oxygen (pO2) and radiosensitivity.

The partial pressure of oxygen (pO2) of FSaII tumors grown in the leg of C3H mice significantly improved when the tumors were heated by immersing the tumor-bearing legs in a water bath at 41.5 degrees C for 60 min. The tumor pO2 also substantially increased when the tumor-bearing mice breathed carbogen (95% O2:5% CO2). Additionally, mild hyperthermia followed by carbogen breathing further increased the tumor pO2 and increased radiation cytotoxicity as assessed by the in vivo/in vitro excision assay for surviving FSaII cells. It was concluded that mild hyperthermia in combination with carbogen breathing is potentially useful to reoxygenate radioresistant hypoxic cells and improve the radiotherapy of human tumors.

Animals↗

PubMed1979

Some characteristics of transcutaneously monitored oxygen partial pressure in normal newborns.

The transcutaneous oxygen partial pressure (PtcO2) was monitored in 50 healthy, normally and spontaneously delivered newborns. Measurements were performed during the first to fourth day of life. The electrode temperature was 44.5 degrees C. The mean PtcO2 level recorded during about 45 min was 9.2 kPa (S.D. 1.4) recorded from the minute-to-minute values. The PtcO2 level normally oscillated to a certain extent and the oscillations were closely related to the breathing pattern of the patient. When the patient fell asleep during measurement, the normal oscillating pattern was replaced by a "silent pattern". During crying, the PtcO2 level showed four main reaction aptterns. A decrease in the PtcO2 level could be observed during breast-feeding. One child, recently fed, vomited a small amount of breast milk after a short period of crying and apparently had a laryngospasm, shown by a sudden drop in the PtcO2 level without any other signs of discomfort. The study shows that PtcO2 (and thus also PaO2) very sensitively reacts to changes in activity. This implies that earlier used methods for determination of PaO2 might give values that are not representative for the steady state as the sampling method per se might influence the recorded PO2 value.

Breast Feeding↗

PubMed2006

Monitoring of cerebral oxygenation with near infrared spectroscopy and tissue oxygen partial pressure during cardiopulmonary resuscitation in pigs.

BACKGROUND AND OBJECTIVE: The present study was designed to compare cerebral oxygenation measured with near infrared spectroscopy and local brain tissue oxygen partial pressure, respectively, in pigs during cardiopulmonary resuscitation. Since tissue overlying the brain may have an impact on near infrared spectroscopy readings, we tested whether optode placement on intact skin or on the skull yielded comparable results. METHODS: Twelve healthy pigs were anaesthetized and subjected to continuous haemodynamic, near infrared spectroscopy and brain tissue oxygen partial pressure monitoring. After 4 min of untreated ventricular fibrillation, cardiopulmonary resuscitation was started and arginine vasopressin was administered repeatedly three times. Near infrared spectroscopy values recorded were both the tissue oxygenation index and the tissue haemoglobin index as well as relative changes of chromophores (haemoglobin and cytochrome oxidase). Four animals served as control and were measured with both near infrared spectroscopy optodes mounted on the intact skin of the forehead, while in the remaining eight animals, one near infrared spectroscopy optode was implanted directly on the skull. RESULTS: Near infrared spectroscopy readings at the skin or at the skull differed consistently throughout the study period. After arginine vasopressin administration, near infrared spectroscopy values at the different locations showed a transient dissociation. In contrast to near infrared spectroscopy measured on intact skin, near infrared spectroscopy readings obtained from skull showed a significant correlation to brain tissue oxygen partial pressure values (r = 0.67, P < 0.001). CONCLUSION: Near infrared spectroscopy readings obtained from skin and skull differed largely after vasopressor administration. Near infrared spectroscopy optode placement therefore may have an important influence on the tissue region investigated.

Animals↗

PubMed1997

Continuous monitoring of the partial pressure of oxygen in cerebral venous blood.

OBJECTIVE: Clinical oxygen monitoring in the injured brain is somewhat difficult. However, ischemia is one of the major factors responsible for secondary tissue damage after head injury or subarachnoid hemorrhage. Therefore, the aim of the present study was to investigate the value of continuously monitoring the partial pressure of oxygen in cerebral venous blood (PcvO2) during changes in intracranial pressure (ICP). METHODS: In eight domestic pigs with Clark type probes placed in the posterior third of the superior sagittal sinus, PcvO2 was continuously registered while ICP was stepwise elevated by an inflatable balloon placed below the tentorium. Arterial blood pressure was continuously monitored, cerebral perfusion pressure (CPP) was calculated, and arterial partial carbon dioxide pressure and partial pressure of oxygen were registered intermittently. RESULTS: The mean intraparenchymal ICP before the start of balloon inflation was 5 +/- 1 mm Hg, the mean CPP was 80 +/- 15 mm Hg, and the mean PcvO2 was 36 +/- 3 mm Hg. At maximum ICP elevation, CPP decreased to 20 +/- 12 mm Hg, PcvO2 decreased to 10 +/- 6 mm Hg, and ICP increased to 90 +/- 10 mm Hg. Strong linear correlations between ICP and PcvO2 and between CPP and PcvO2 were revealed, and mean correlation coefficients of 0.89 for ICP/PcvO2 and 0.73 for CPP/PcvO2 were calculated. CONCLUSION: The present study demonstrates that polarographic PcvO2 monitoring in the superior sagittal sinus is a reliable method for the early detection of reduced CPP during ICP elevation. This technique is capable of registering the global oxygen supply and oxygen consumption of the brain. It seems superior to jugular venous oxymetry and is better suited for clinical use because of a somewhat low artifact susceptibility.

Animals↗

PubMedDate not supplied

Cournand lecture. Expiratory partial pressure curves in the diagnosis of emphysema.

The deformation of expiratory partial pressure curves of respiratory and inert gases (O2, CO2, He, Ar, SF6), as measured by means of mass spectrometry, was analysed in healthy subjects and in patients with asthma, chronic bronchitis and/or pulmonary emphysema. Patients with emphysema could best be distinguished from the other groups when the comparison was based on the shape of expirogram phase II. Phase II was characterized by the volume V25-50 which was expired between 25% and 50% of the inspiratory/end-tidal partial pressure difference. Comparative measurements of V25-50 of O2, CO2, He and SF6 in 10 healthy subjects (mean age: 30.8 yr) and in 10 patients with advanced emphysema (mean age: 60.8 yr) showed a linear increase of V25-50 with increasing inspired volume (VI) being 3-5 times higher in the patients than in normals. V25-50 increased with the sequence He less than SF6 approximately equal to CO2 less than O2 in both groups. The separation between phase II volumes of He and SF6 was more pronounced in the patients with emphysema than in the healthy subjects. Variations of the breathing pattern in eight healthy subjects revealed a linear increase of V25-50 with increasing VI and, to a lower extent, with increasing respiratory frequency, while a decrease of V25-50 with increasing breath-holding time and only very small changes with variations of inspiratory as well as expiratory duration were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1988

The effect of amino acid infusion on partial pressure of oxygen in pelvic urine of the rat.

Renal function decreases with age, but the precise mechanism of the decrease is unknown. Recently, Brenner et al. have proposed the hypothesis that high protein intake may injury renal function in various clinical settings including the aging kidney. Since connective tissue in the renal papilla changes with age, high protein intake may have some deleterious effect on the renal papilla. In this study, the effect of amino acid infusion on partial pressure of oxygen of pelvic urine was examined in the rat. After amino acid infusion, glomerular filtration rate significantly increased and partial pressure of oxygen of pelvic urine decreased, while partial pressure of oxygen of arterial blood remained unchanged. The findings imply that high protein intake may affect the renal papilla both acutely and chronically through renal medullary hypoxia.

Amino Acids↗