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PubMed1998

Use of a handheld device for analysis of blood electrolyte concentrations and blood gas partial pressures in dogs and horses.

OBJECTIVE: To compare, for blood samples from dogs and horses, blood electrolyte concentrations, blood gas partial pressures, and Hct obtained using a handheld analyzer with those obtained using a standard chemistry analyzer and to compare results obtained with the handheld analyzer using warm versus cold test cartridges. DESIGN: Case series with analysis of split samples. SAMPLE POPULATION: Blood samples from 22 dogs and 17 horses. PROCEDURE: Sodium, potassium, ionized calcium, bicarbonate, and total CO2 concentrations, pH, PO2, PCO2, base excess, and Hct were determined by use of a handheld analyzer and test cartridges that had been allowed to warm to ambient temperature or had been recently removed from a refrigerator. Results were compared with those from a standard chemistry analyzer by use of linear regression. RESULTS: For canine samples, values obtained with the handheld analyzer and warm cartridges were highly correlated (r2 > or = 0.83) with values obtained with the standard chemistry analyzer, except for sodium concentration (r2 = 0.6). For equine samples, values obtained with the handheld analyzer and warm cartridges were highly correlated (r2 > or = 0.79) with values obtained with the standard chemistry analyzer, except for Hct (r2 = 0.38). For all samples, results obtained with cold and warm cartridges were moderately correlated (r2 > or = 0.69). CLINICAL IMPLICATIONS: Results obtained with the handheld analyzer were similar to those obtained from the standard chemistry analyzer, with the exception of sodium concentration for canine samples and Hct for equine samples. Results were not substantially affected by use of cold, rather than warm, test cartridges.

Acid-Base Equilibrium↗
PubMed1999

Blood oxygen partial pressure affects plasma prolactin concentration in humans.

Responses of plasma prolactin (PRL) concentration to acute and repeated changes in blood oxygen partial pressure (PO2a) at rest were investigated in two studies (A; B), with special reference to possible effects mediated via serotonin (5-HT) synthesis. In A, nine male subjects inhaled for 105 min gas containing different oxygen fractions for 6 days. Gas concentrations consisted of 14% (A14), 21 % (A21), 40% (A40), 60% (A60) and 80% (A80) O2 mixed with N2 as well as 100% O2 (A100). Venous and capillary blood samples were drawn before and every 15 min during gas inhalation for analysis of plasma PRL and PO2a. In B, two groups of subjects (B I; B II) were exposed to 30 min day(-1) of gas inhalation over 14 consecutive days. Gas concentration consisted for B I of 14% O2/86% N2 and for B II of 100% O2. During pre- and post-examination a baseline blood sample was drawn, followed by a neuroendocrine test of serotonergic function using a partial 5-HT1A receptor agonist (60 mg of buspirone hydrochloride). In A, each increase of inhaled oxygen fraction also resulted in higher blood POb2a. In A14, A21 and A40, plasma PRL concentrations did not change from basal level. Increases in plasma PRL concentration were found in A60 after 30 min as well as in A80 and A100 after 15 min. A higher blood PO2a induced a higher plasma PRL secretion but also an earlier decline from peak plasma PRL value despite continued inhalation of the respective oxygen concentration. During post-examination in B, basal plasma PRL concentrations were increased in B I and decreased in B II. Plasma PRL response to stimulation challenge was not affected by treatments. Thus, chronic adaptations of basal plasma PRL concentrations to decreased/increased blood PO2a were not related to up/down-regulation, respectively, of central serotonergic receptor function.

Adult↗
PubMed1997

Carbon dioxide and oxygen partial pressure measurements in the cerebrospinal fluid in a conventional blood gas analyzer: analysis of bias and precision.

Cerebrospinal fluid (CSF) gas tension measurements have been used as a marker of cerebral oxygenation in animal models and in human studies. Discrepancies in the measurement of PCO2 and PO2 in non-blood solutions by standard blood gas analyzers have been described. The CSF is a physiological non-blood fluid with an ability to carry only dissolved O2 or CO2. The aim of this experiment was to determine the bias and precision of CSF pCO2 and pO2 measurements of a contemporary blood gas analyzer and a continuous gas sensor. CSF from human patients was tonometered to known PCO2 and PO2 using standard calibration gases in a bubble tonometer. Following equilibration, a continuous measurement of the partial pressure of gases in the CSF in the tonometer solution was made using a calibrated Paratrend 7 gas sensor (Biomedical Sensors, Bucks., UK) inserted into the equilibration chamber of the tonometer and continuous CSF pH, PCO2 and PO2 measurements recorded at 1-min intervals. After equilibration, a 3-ml CSF sample was aspirated anaerobically from the tonometer and analysed in duplicate using an ABL 620 (Radiometer, Copenhagen) blood gas analyser. The measured pCO2 and pO2 from the ABL 620 blood gas analyser and the Paratrend 7 sensor were paired with the expected values to calculate bias and precision. Small offsets in PCO2 and large offsets in PO2 measurement were seen with the ABL 620 blood gas analyser. This study brings into question clinical decisions based on CSF PO2 measurements. The implications for calibrating CSF sensors against CSF gas measurements are discussed.

Blood Gas Analysis↗
PubMed1977

Differentiation of the intracytoplasmic membrane of Rhodopseudomonas palustris induced by variations of oxygen partial pressure or light intensity.

The photosynthetic apparatus of Rhodopseudomonas palustris contains, in addition to reaction center bacteriochlorophyll (Bchl) two spectral forms of light harvesting (LH) Bchl, i.e. LH Bchl I, characterized by an infrared absorption maximum at 880 nm (890 nm at 77 degrees K) and LH Bchl II absorbing at 805 and 855 nm (805 and 870 nm at 77 degrees K). LH Bchl I seems to be associated with a single protein species of an apparent mol. wt. of 13 000 whereas LH Bchl II is apparently associated with two proteins of mol. wts. of 9000 and 11 000. Cells in anaerobic cultures adapt to changes of light intensity 1. by variation of the size of the photosynthetic unit, i.e. the molar ratio of LH Bchl II to reaction center Bchl, 2. by variation of the number of photosynthetic units per unit of membrane area, 3. by regulation of the size of the intracytoplasmic membrane system. During adaptation of changes of oxygen partial pressure cells are able to synthesize reaction center Bchl, LH Bchl and intracytoplasmic membranes at different rates. The synthesis of reaction center Bchl and LH Bchl I are, however, coordinated with each other, while the synthesis of LH Bchl II and reaction center Bchl proceed independently.

Adaptation, Biological↗
PubMed1990

The influence of oxygen administration to the mother during labor on the fetal transcutaneously measured carbon-dioxide partial pressure.

The aim of this study was to plot the course of the transcutaneously measured PCO2 (tcPCO2) in the fetus during oxygenation of the mother. In our examination 35 parturients with a suspicious or pathologic CTG were given pure oxygen for 10 minutes at a flow speed of 10 l/min. The fetal tcPCO2 was measured with a TCM 3 measuring device from Radiometer. The measuring temperature was 41 degrees C. The fetal tcPCO2 was 67.2 +/- 3.9 mmHg before the O2 application, during the O2 application it was 67.3 +/- 14.1 mmHg and for the period after the O2 application we found an average measurement of 66.7 +/- 13.9 mmHg. Further we investigated whether, depending on the original levels of the fetal tcPCO2 an O2 application to the mother had a measurable effect on the fetal tcPCO2 levels. The average levels of the tcPCO2 in the fetuses with pathological original levels of greater than or equal to 60 mmHg or with normal levels of less than 60 mmHg did not show any significant differences before, during or after the O2 application. Our own results and reports given in the literature about an increase in the fetal O2 partial pressure during maternal oxygenation lead to the conclusion that in cases with fetal hypoxia, the O2 application to the mother--in addition to other measures for intrauterine reanimation or speedy termination of labor--could be of advantage.

Blood Gas Monitoring, Transcutaneous↗
PubMed2005

Partial pressure of nitrogen in breathing mixtures and risk of altitude decompression sickness.

BACKGROUND: Many aircraft oxygen systems do not deliver 100% O2. Inert gases can be present at various levels. The purpose of this study was to determine the effect of these inert gas levels on decompression sickness (DCS). METHODS: Subjects were exposed for 4 h to 5486 m (18,000 ft) with zero prebreathe, using either mild (Test A) or strenuous exercise (Test B), and breathing 60%N2/40%O2. Test C used a breathing mixture of 40%N2/60%O2 at 6858 m (22,500 ft) with zero prebreathe and mild exercise. Test D investigated a breathing mixture of 2.8%N2/4.2%argon/93%O2 with 4 h exposures to 7620 m (25,000 ft), mild exercise, and 90 min of preoxygenation. The controls were from previous studies using similar conditions and 100% O2. RESULTS: The DCS risk for Tests A and B and the Control for B was 7%; the Control for Test A was 0% (n.s.). Breathing the 40%N2/60%O2 mixture (Test C) resulted in 43% DCS compared with 53% DCS with 100% O2 (n.s.). When the 2.8%N2/4.2%argon/93%O2 mixture was used, the results showed 25% DCS compared with 31% DCS with 100% O2 (n.s.). CONCLUSIONS: The increased nitrogen and argon levels in the breathing gas while at altitudes of 5486 m to 7620 m did not increase DCS risk. These results support the concept of using the partial pressure gradient of inert gases instead of the percentage of N2 or argon in a breathing gas mixture to determine the risk of DCS during altitude exposure.

Aerospace Medicine↗
PubMed1997

Arterial oxygen partial pressures reduce the insulin-dependent induction of the perivenously located glucokinase in rat hepatocyte cultures: mimicry of arterial oxygen pressures by H2O2.

Liver glucokinase (GK) is localized predominantly in the perivenous zone. GK mRNA was induced by insulin maximally under venous O2 partial pressure (pO2) and only half-maximally under arterial pO2. CoCl2 and desferrioxamine mimicked venous pO2 and enhanced the insulin-dependent induction of GK mRNA under arterial pO2. H2O2 mimicked arterial pO2 and reduced insulin-induced GK mRNA under venous pO2 to the lower arterial levels. Thus the zonal O2 gradient in liver seems to have a key role in the heterogenous expression of the GK gene.

Animals↗
PubMed2006

Nutrient availability and atmospheric CO2 partial pressure modulate the effects of nutrient heterogeneity on the size structure of populations in grassland species.

BACKGROUND AND AIMS: Size-asymmetric competition occurs when larger plants have a disproportionate advantage in competition with smaller plants. It has been hypothesized that nutrient heterogeneity may promote it. Experiments testing this hypothesis are inconclusive, and in most cases have evaluated the effects of nutrient heterogeneity separately from other environmental factors. The aim of this study was to test, using populations of Lolium perenne, Plantago lanceolata and Holcus lanatus, two hypotheses: (a) nutrient heterogeneity promotes size-asymmetric competition; and (b) nutrient heterogeneity interacts with both atmospheric CO2 partial pressure (P(CO2)) and nutrient availability to determine the magnitude of this response. METHODS: Microcosms consisting of monocultures of the three species were grown for 90 d in a factorial experiment with the following treatments: P(CO2) (37.5 and 70 Pa) and nutrient availability (NA; 40 and 120 mg of N added as organic material) combined with different spatial distribution of the organic material (NH; homogeneous and heterogeneous). Differences in the size of individual plants within populations (size inequality) were quantified using the coefficient of variation of individual above-ground biomass and the combined biomass of the two largest individuals in each microcosm. Increases in size inequality were associated with size-asymmetric competition. KEY RESULTS: Size inequality increased when the nutrients were heterogeneously supplied in the three species. The effects of NH on this response were more pronounced under high nutrient supply in both Plantago and Holcus (significant NA x NH interactions) and under elevated P(CO2) in Plantago (significant P(CO2) x NA x NH interaction). No significant two- and three-way interactions were found for Lolium. CONCLUSIONS: Our first hypothesis was supported by our results, as nutrient heterogeneity promoted size-asymmetric competition in the three species evaluated. Nutrient supply and P(CO2) modified the magnitude of this effect in Plantago and Holcus, but not in Lolium. Thus, our second hypothesis was partially supported.

Atmospheric Pressure↗
PubMed2006

[Transcutaneous measurement of partial pressure of carbon dioxide and oxygen saturation: validation of the SenTec monitor].

OBJECTIVE: To validate a monitor for transcutaneous measurement of oxygen saturation (SpO2) and partial pressure of carbon dioxide (TcPCO2). PATIENTS AND METHODS: This observational study included 140 Caucasian nonsmokers without jaundice. Patients underwent forced spirometry, measurement of SpO2 and TcPCO2 with the SenTec monitor, and arterial blood gas analysis (readings with 2 devices) during the stabilization phase of the monitor. In the statistical analysis, values from the 2 devices for measuring arterial blood gases were compared by mean differences for PaCO2 and oxygen saturation (SaO2). The arithmetic mean of the 2 blood gas measurements was calculated and relations between them and the SpO2 and TcPCO2 were assessed by the Pearson correlation coefficient (r) and the intraclass correlation coefficient (ICC) as a measure of agreement. Bland-Altman analysis was used to test data dispersion. RESULTS: Ten patients were excluded due to a systematic error in the gas calibrator. The mean (SD) time to stabilization of the monitor before reading was 13.9 (2.4) minutes. The forced expiratory volume in the first second was greater than 80% in 40 patients, between 60% and 79% in 23, between 40% and 59% in 30, and less than 40% in 37. The mean (SD) differences between arterial blood gas measurements were 0.28 (1.0) mm Hg for PaCO2, -0.06% (0.86%) for SaO2, and -0.9 (2.7) mm Hg for PaO2. In the tests for correlation and agreement, r was 0.74 and ICC was 0.73 for SaO2 and SpO2; r was 0.92 and ICC was 0.92 for PaCO2 and TcPCO2. The subgroup analyses did not show any noteworthy differences. The Bland Altman analysis showed no significant dispersion. It was observed that the SenTec monitor underestimated oxygen saturation values by around 1% with respect to SaO2 and overestimated carbon dioxide pressure by 1 mm Hg with respect to PaCO2 values. CONCLUSIONS: The stabilization time recommended for the SenTec monitor before taking a reading is 20 minutes. The overestimates and underestimates by the monitor are not clinically relevant. Finally, the values for SpO2 and TcPCO2 measured by the validated monitor are reliable.

Blood Gas Monitoring, Transcutaneous↗
PubMed1985

Effects of changes in CO2 partial pressure on the sensation of respiratory drive.

The purpose of this study was to determine whether a change in respiratory sensation accompanies an increase in CO2 partial pressure (PCO2) in the absence of any changes in the level and pattern of thoracic displacement and respiratory muscle force. Eleven normal subjects were artificially hyperventilated with a positive-pressure mechanical respirator. In separate trials the tidal volume (VT) was set at 10 and 18 ml/kg and the frequency of ventilation (f) was adjusted to maintain the base-line end-tidal PCO2 at approximately 30 Torr. Thereafter, at a constant controlled VT and f, the PCO2 was progressively increased by raising the inspired CO2 concentration. There were no changes in respiratory motor activity as determined from the peak inspiratory airway pressure (Paw) until the PCO2 reached 40.8 +/- 1.0 and 40.1 +/- 1.0 (SE) Torr in the large and small VT trials, respectively. Initially there was no conscious awareness of the change in respiratory activity. Subjects first signaled that ventilatory needs were not being satisfied only after a further increase in PCO2 to 44.7 +/- 1.3 and 42.3 +/- 1.0 (SE) Torr in the large and small VT trials and after the Paw had fallen to 55-60% of the base-line value. The results suggest that changes in respiratory sensation produced by increasing chemical drive are a consequence of increases in respiratory efferent activity, but a direct effect of changes in PCO2 on respiratory sensation cannot be excluded.

Adult↗
PubMed1991

Metabolism of cholesterol and phospholipids in cultured human vascular smooth muscle cells: differences between artery and vein-derived cells and the effect of oxygen partial pressure.

Human smooth muscle (SM) cells derived from vena saphena magna, aorta abdominalis and arteria mamaria were grown in culture under 40 or 145 mmHg oxygen partial pressure (pO2) and their lipid metabolism studied. Esterification of the cellular [3H]cholesterol was higher by 2.5-fold in artery derived than in vein-derived cells and was slightly higher in cultures exposed to 145 mmHg than to 40 mmHg pO2. Cholesterol efflux in the presence of high density lipoprotein (HDL) in the incubation medium was higher in artery-derived than vein-derived cells. Apolipoprotein (apo) AI also supported cholesterol efflux to a higher extent in artery than in vein-derived cells. Cholesterol efflux in the presence of apo AI was accompanied by a decrease of 50% in cellular [3H]cholesteryl ester in both cell types. SM cultures exposed to [3H]choline incorporated about 90% of the radioactivity to phosphatidylcholine (PC) and 10% to sphingomyelin (SPM). During 5 days exposure to [3H]choline, 10 to 15% and 20 to 30% of the newly synthesized PC and SPM, respectively, were released by vein-derived cells into the incubation medium. The relative amount of SPM of the total radioactive phospholipids released by vein-derived cultures was significantly higher in cultures growing under 40 mmHg than 145 mmHg pO2 reaching a value of up to 33% of the radioactive phospholipids in the incubation medium. HDL was shown to serve as an acceptor for phospholipids released by both vein and artery-derived SM cells, while free apo AI supported phospholipid efflux in artery but not in vein-derived SM cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Arteries↗
PubMed2003

Scientific and technological aspects of oxygen-sensitive electrodes for measurements of oxygen partial pressure in patch-clamp experiments.

Anoxia/hypoxia induces dramatic changes in brain activity leading to the damages in brain structure. Several minutes of decrease in environmental oxygen partial pressure (P(O2)) can irreversibly destroy nerve cells. Therefore, investigations of intracellular mechanisms responsible for hypoxia-induced changes of mammalian nerve system are very important. On-line adjustment and measurements of P(O2) in bath solution during patch-clamp experiments are especially topical. At the recent time, a special interest on the on-line measurements of oxygen contents in bath solution has appeared as a result of application of old approaches previously used for polarographic measurements of oxygen contents in the blood and tissues. Here we describe the simple method of manufacturing oxygen-sensitive microelectrodes, which can be used with standard patch-clamp amplifier. We also describe the main principles of polarographic method and properties of oxygen-sensitive electrodes used in patch-clamp experiments.

Biophysics↗
PubMed1988

Metabolic Acclimation to Anoxia Induced by Low (2-4 kPa Partial Pressure) Oxygen Pretreatment (Hypoxia) in Root Tips of Zea mays.

Young intact plants of maize (Zea mays L. cv INRA 508) were exposed to 2 to 4 kilopascals partial pressure oxygen (hypoxic pretreatment) for 18 hours before excision of the 5 millimeter root apex and treatment with strictly anaerobic conditions (anoxia). Hypoxic acclimation gave rise to larger amounts of ATP, to larger ATP/ADP and adenylate energy charge ratios, and to higher rates of ethanol production when excised root tips were subsequently made anaerobic, compared with root tips transferred directly from aerobic to anaerobic media. Improved energy metabolism following hypoxic pretreatment was associated with increased activity of alcohol dehydrogenase (ADH), and induction of ADH-2 isozymes. Roots of Adh1(-) mutant plants lacked constitutive ADH and only slowly produced ethanol when made anaerobic. Those that were hypoxically pretreated acclimated to anoxia with induction of ADH2 and a higher energy metabolism, and a rate of ethanol production comparable to that of nonmutants. All these responses were insensitive to the presence or absence of NO(3) (-). Additionally, the rate of ethanol production was about 50 times greater than the rate of reduction of NO(3) (-) to NO(2) (-). These results indicate that nitrate reductase does not compete effectively with ADH for NADH, or contribute to energy metabolism during anaerobic respiration in this tissue through nitrate reduction. Unacclimated root tips of wild type and Adhl(-) mutants appeared not to survive more than 8 to 9 hours in strict anoxia; when hypoxically pretreated they tolerated periods under anoxia in excess of 22 hours.

Journal Article↗
PubMedDate not supplied

[Mechanism of action of hyaluronic acid in gonarthrosis of both knee joints in a right/left comparison. Study with dynamometry, oxygen partial pressure, temperature and Lequesne score].

In a controlled prospective randomized study we evaluated the effectiveness of intraarticular injected hyaluronic acid regarding the changes in the parameters dynamometry, synovial oxygen partial pressure, intraarticular temperature and the knee joint function (Lequesne score). We examined 18 patients with osteoarthritis in both knee joints (Kellgren classification II or III according to x-ray) in right/left comparison. The evaluated parameters were measured before and after a 5-week treatment phase with 5 intraarticular injections (one injection per week). With regard to the efficacy results changes in dynamometric measurement for flexion and extension (for all angular velocities) and Lequesne-score indicate a marked improvement after treatment with hyaluronic acid. The differences between treated and untreated knee were significant. In extension the p-value was 0.0008 and in flexion p = 0.0015. The p-value of the Lequesne-index between the verum and control group was p = 0.0002. After treatment values for oxygen pressure were higher than at baseline and for the intraarticular temperature a small decrease at the end of the treatment phase was documented. The intraarticular injection of hyaluronic acid is effective and safe in the treatment of patients with gonarthrosis. The treatment resulted in a functional improvement of the knee joint and had a good pain-lowering effect in patients suffering from gonarthrosis.

Aged↗
PubMed1995

The Resistance of the Diffusion Barrier in Nodules of Myrica gale L. Changes in Response to Temperature but Not to Partial Pressure of O2.

Rates of C2H2 reduction and CO2 evolution by nodules were measured in a flowthrough system using intact plants of Myrica gale L. Both activities increased linearly with increasing partial pressure of O2 (pO2) up to 18 kPa. The linear relationship between CO2 evolution and pO2 at pO2 values between 6 and 18 kPa suggests that the diffusion barrier has a constant resistance. The lack of a variable resistance was further supported by sustained increases and decreases in nodule activities in response to changes in pO2 in the range of 6 to 20 kPa O2. When pO2 was increased above 20 kPa, C2H2 reduction and CO2 evolution continually declined with time. These results confirm that the diffusion barrier in nodules of M. gale is not variable in response to changes in pO2. The effect of temperature was examined at 8 and 20 kPa O2. Rates of C2H2 reduction and CO2 evolution increased with increasing temperature from 10 to 30[deg]C at both pO2 values. These results indicate that the diffusion resistance of the barrier changes as temperature changes, with the resistance decreasing as temperature increases.

Journal Article↗
PubMed1998

Prediction of arterial partial pressure of oxygen with pulse oxygen saturation measurements.

OBJECTIVES: We studied 22 neonates with gestational ages from 26 to 40 weeks to determine how accurately pulse oxygen saturation (SpO2) could predict arterial partial pressure of oxygen (PaO2) and how much time and effort would be required to achieve and maintain a desired SpO2 value. STUDY DESIGN: SpO2 was maintained at 90%, 92%, 94%, 96%, and 98% by adjustment of FiO2. PaO2 was correlated with SpO2 by nonlinear mixed effects regression analysis. RESULTS: PaO2(y) correlated positively with SpO2(x): y = (0.03). e0.08(x). Variation of PaO2 increased from a range of +/- 10 Torr at SpO2 = 90% to +/- 28 Torr at SpO2 = 98%, principally as a result of decreasing hemoglobin-oxygen affinity, with no effect of advancing gestational age, subject temperature, pH, PaCO2. Considerable time (18 +/- 14 SD minutes) and effort (5 +/- 3 SD FiO2 adjustments/min were required to achieve and maintain a desired SpO2. CONCLUSIONS: PaO2 varied broadly with SpO2 in a clinically acceptable range of SpO2 (90% to 98%), and the variability increased at higher SpO2 values. Considerable time and effort were required to achieve and maintain desired SpO2 values.

Gestational Age↗
PubMed1996

The relationship between partial pressure of oxygen and perfusion in two murine tumors after X-ray irradiation: a combined gadopentetate dimeglumine dynamic magnetic resonance imaging and in vivo electron paramagnetic resonance oximetry study.

Changes of partial pressure of oxygen (pO2) and blood perfusion were studied in MTG-B and RIF-1 tumors (n = 5 each) before and after a single 20-Gy dose of X-ray irradiation. Using electron paramagnetic resonance oximetry, we have observed an initial fast decrease of pO2 after irradiation, followed by a slow increase. The time course of these changes was faster in the MTG-B tumors than in the RIF-1 tumors. Gadopentetate dimeglumine (Gd-DTPA) dynamic magnetic resonance imaging studies showed a reduction in uptake of Gd-DTPA at the time of minimum pO2 and a recovery at the time of maximum pO2 in each tumor. Previous work indicates that there is microscopic heterogeneity in tumors, with well-vascularized "capillary regions" being closer to capillaries than poorly vascularized "noncapillary regions." We propose a two-component (slow and fast) model of Gd-DTPA uptake that is designed to quantify the kinetics of these two compartments by analyzing the total tumor uptake kinetics without having to identify specific regions of interest. Total perfusion in the tumors was greatly reduced at the time of minimum oxygenation, and the volume of the slow component increased after irradiation. We conclude that a decrease in blood perfusion is one of the main causes of the decline in pO2 observed after irradiation.

Animals↗
PubMed1996

Continuous monitoring of partial pressure of brain tissue oxygen in patients with severe head injury.

Ischemia is one of the major factors causing secondary brain damage after severe head injury. We have investigated the value of continuous partial pressure of brain tissue oxygen (PbrO2) monitoring as a parameter for cerebral oxygenation in 22 patients with severe head injury (Glasgow Coma Scale score, < or = 8). Jugular bulb oxygenation, intracranial pressure, and cerebral perfusion pressure were simultaneously recorded. O2 and CO2 reactivity tests were performed daily to evaluate oxygen autoregulatory mechanisms. PbrO2 monitoring was started an average of 7.0 hours after trauma with a mean duration of 74.3 hours. No complications were seen, and the calibration of the catheters after measurement showed a zero drift of 1.2 +/- 0.8 mm Hg and a sensitivity drift of 9.7 +/- 5.3%. In 86% of patients, PbrO2 was < 20 mm Hg in the acute phase. Mean PbrO2 significantly increased during the first 24 hours after injury. Two distinct patterns of change of PbrO2 over time were noted. The first pattern was characterized by normal stable levels after 24 hours, and the second was characterized by transiently elevated levels of PbrO2 during the second and third days. PbrO2 values < or = 5 mm Hg within 24 hours after trauma negatively correlated with outcome. O2 reactivity was significantly lower in patients with good outcomes. CO2 reactivity showed no constant pattern of change over time and was not correlated with outcome. Increased hyperventilation was shown to decrease PbrO2 in some patients. Accurate detection of the moment of cerebral death was possible on the basis of the PbrO2 measurements. The correlation between PbrO2 and other parameters, such as intracranial pressure and cerebral perfusion pressure, was weak. We conclude that PbrO2 monitoring is a safe and clinically applicable method in patients with severe head injury. The early occurrence of ischemia after head injury can be monitored on a continuous basis. Deficiency of oxygen autoregulatory mechanisms can be demonstrated, and their occurrence is inversely related to outcome. For practical clinical use, the method seemed to be superior to jugular oximetry.

Adolescent↗