Determination Of PO2 Research Articles

Impact of blood collection devices and mode of transportation on peripheral venous blood gas parameters

BackgroundPeripheral venous blood (PVB) gas analysis has become an alternative to arterial blood gas (BG) analysis in assessing acid-base balance. This study aimed to compare the effects of blood collection devices and modes of transportation on peripheral venous BG parameters. MethodsPVB-paired specimens were collected from 40 healthy volunteers into blood gas syringes (BGS) and blood collection tubes (BCT), transported by either a pneumatic tube system (PTS) or human courier (HC) to the clinical laboratory, and compared using a two-way ANOVA or Wilcoxon signed-rank test. To determine clinical significance, the PTS and HC-transported BGS and BCT biases were compared to the total allowable error (TEA). ResultsPVB partial pressure of oxygen (pO2), fractional oxyhemoglobin (FO2Hb), fractional deoxyhemoglobin (FHHb), and oxygen saturation (sO2) showed statistically significant differences between BGS and BCT (p < 0.0001). Compared to HC-transported BGS and BCT, statistically significant increases in pO2, FO2Hb, sO2, oxygen content (only in BCT) (all p < 0.0001), and base excess extracellular (only in BCT; p < 0.0014) concentrations and a statistically significant decrease in FHHb concentration (p < 0.0001) were found in BGS and BCT delivered by PTS. The biases between PTS- and HC-transported BGS and BCT exceeded the TEA for many BG parameters. ConclusionsCollecting PVB in BCT is unsuitable for pO2, sO2, FO2Hb, FHHb, and oxygen content determinations.

Determination of equilibrium state and Sn redox ratio in aluminoborosilicate glass melts by potentiometry and voltammetry

Over the last three decades many studies have reported the investigation of the redox behaviour of multivalent elements (M) in glass melts by voltammetry. In these works the redox ratio at any temperature, described as ([Mx+]/[M(x+n)+]) or the concentration %[Mx+], was determined under the assumption that the melt was equilibrated with air (PO2 = 0.21 bar). Some potentiometric studies have reported the determination of PO2 in glass melts, however no significant attempts have been made to determine the actual redox ratio using a measured PO2 combined with a corresponding voltammogram. Herein, potentiometry and square wave voltammetry of alkali-lean alumino-borosilicate E-model glass melts doped with Sn were performed sequentially at the same equilibrium state. The actual redox ratios of the main pair, [Sn2+]/[Sn4+], derived from the peak potential and oxygen activity, were higher than those at PO2 = 0.21 bar. The temperature dependence of the values converted to %[Sn2+] showed that the actual concentration of Sn2+ in the melts was 3–6% higher than expected at PO2 = 0.21 bar. These results are discussed in terms of the fining behaviour of melts.

Ecophysiology, genotoxicity, histopathology, and gene responses of naphthalene injected Colossoma macropomum (Cuvier, 1818) exposed to hypoxia.

The present study aimed to evaluate the biological responses of Colossoma macropomum to naphthalene injection and subsequent hypoxia exposure, emphasizing the expression of the tumor suppressor gene tp53. Tambaquis were intraperitoneally injected with naphthalene (50 mg/kg) and, after 96 hours, the fish were transferred to respirometry chambers and, submitted to progressive hypoxia for the determination of critical PO2. In a subsequent experiment, the fish received an intraperitoneal injection of naphthalene and were kept for 96 hours under normoxia. Successively, fish were challenged with acute hypoxia (PO2<PO2 crit) during 6 hours. We observed that the PO2 crit was not affected by naphthalene injection. Moreover, hematological parameters were modulated only in response to hypoxia. Fish with naphthalene injection plus hypoxia exposure presented altered activity of the GST and CAT enzymes. Exposure to naphthalene also resulted in DNA damages, which was not influenced by hypoxia. Hypoxia accentuated the hepatic lesions caused by naphthalene, as well as it also impaired the transcription of tp53 in naphtalene injected fish, demonstrating the risks of contaminating aquatic environments, especially environments where hypoxic conditions are common and occur on a daily or on seasonal basis, as in the Amazon basin.

Aerobic exercise improves microvascular dysfunction in fructose fed hamsters

Fructose is a major diet component directly related to severe damages to the microcirculation and to diseases such as obesity, diabetes and hypertension to which physical activity is pointed out as an important non-pharmacological treatment since its positive effects precede anthropometric improvements. In this study we have investigated the effects of a light/moderate aerobic exercise training (AET) on microcirculatory dysfunction elicited by carbohydrate overload during a period of 5months. Male hamsters (Mesocricetus auratus) whose drinking water was substituted (F) or not (C) by 10% fructose solution, during 20weeks, associated or not to AET in the last 4weeks (EC and EF subgroups) had their microcirculatory function evaluated on the cheek pouch preparation, glucose and insulin tolerance (GTT and ITT) tested. Arterial blood was collected for pO2, pCO2, HCO3−, pH, total CO2, saturated O2 and lactate determinations. Liver fragments were observed using an electron microscope. Microcirculatory responses to acetylcholine [Ach, an endothelium-dependent vasodilator; 10−8M — *123.3±7.5% (C), 119.5±1.3% (EC), *98.1±3.2% (F) and 133.6±17.2% (EF); 10−6M — *133.0±4.1% (C), 135.6±4.3% (EC), *103.4±4.3% (F) and 134.1±5.9% (EF); 10−4M — *167.2±5.0% (C), 162.8±5.4% (EC), *123.8±6.3% (F) and 140.8±5.0% (EF)] and to sodium nitroprusside [SNP, an endothelium-independent vasodilator; 10−8M — 118.8±6.8% (C), 114.0±5.0% (EC), 100.2±2.9% (F), 104.9±4.4% (EF); 10−6M — 140.6±11.7% (C), 141.7±5.5% (EC), 125.0±4.7% (F), 138.3±2.8% (EF); 10−4M — 150.4±10.9% (C), 147.9±6.5% (EC), 139.2±7.3% (F), 155.9±4.7% (EF)] and macromolecular permeability increase induced by 30min ischemia/reperfusion (I/R) procedure [14.4±3.5 (C), 30.0±1.9 (EC), *112.0±8.8 (F) and *22.4±0.9leaks/cm2 (EF)] have shown that endothelium-dependent vasodilatation was significantly reduced and I/R induced macromolecular permeability augmented in sedentary fructose (F) subgroup and both improved after AET. Electron microscopy analysis of the liver showed significant differences between exercised and sedentary subgroups with greater amount of glycogen in F subgroups compared to other ones. No significant changes on mean arterial pressure, heart rate or blood gase between subgroups could be detected. Our results point out that AET could normalize microcirculatory dysfunction elicited by long term substitution of drinking water by 10% fructose solution.

Energy metabolism and regeneration are impaired by seawater acidification in the infaunal brittlestar Amphiura filiformis.

Seawater acidification due to anthropogenic release of CO2 as well as the potential leakage of pure CO2 from sub-seabed carbon capture storage (CCS) sites may impose a serious threat to marine organisms. Although infaunal organisms can be expected to be particularly impacted by decreases in seawater pH, as a result of naturally acidified conditions in benthic habitats, information regarding physiological and behavioral responses is still scarce. Determination of PO2 and P(CO2) gradients within burrows of the brittlestar Amphiura filiformis during environmental hypercapnia demonstrated that besides hypoxic conditions, increases of environmental P(CO2) are additive to the already high P(CO2) (up to 0.08 kPa) within the burrows. In response to up to 4 weeks exposure to pH 7.3 (0.3 kPa P(CO2)) and pH 7.0 (0.6 kPa P(CO2)), metabolic rates of A. filiformis were significantly reduced in pH 7.0 treatments, accompanied by increased ammonium excretion rates. Gene expression analyses demonstrated significant reductions of acid-base (NBCe and AQP9) and metabolic (G6PDH, LDH) genes. Determination of extracellular acid-base status indicated an uncompensated acidosis in CO2-treated animals, which could explain the depressed metabolic rates. Metabolic depression is associated with a retraction of filter feeding arms into sediment burrows. Regeneration of lost arm tissues following traumatic amputation is associated with significant increases in metabolic rate, and hypercapnic conditions (pH 7.0, 0.6 kPa) dramatically reduce the metabolic scope for regeneration, reflected in an 80% reduction in regeneration rate. Thus, the present work demonstrates that elevated seawater P(CO2) significantly affects the environment and the physiology of infaunal organisms like A. filiformis.

Triplet–Triplet Annihilation‐Based Anti‐Stokes Oxygen Sensing Materials with a Very Broad Dynamic Range

AbstractA novel concept for designing optical oxygen sensing materials is reported. Oxygen‐sensitive anti‐Stokes emission is generated via triplet–triplet annihilation‐based upconversion and serves as an analytical parameter. Porous glass beads are used to incorporate the “sensing chemistry” including a sensitizer and an annihilator dissolved in a high boiling solvent. The beads are dispersed in silicone rubber or Teflon AF to produce solid state optodes. Inexpensive low power light sources (LEDs) are used for the excitation. The upconverted emission shows unmatched sensitivity both for the luminescence decay time and for the luminescence intensity. The latter features unusual quadratic Stern‐Volmer plots. Much lower sensitivity of the residual NIR luminescence of the sensitizer allows determination of pO2 in the broad dynamic range from trace oxygen quantities to ≈40 kPa. Interrogation of the sensors in frequency domain is demonstrated. Influence of the excitation light power on the calibration, temperature effects, dynamic response to altering pO2, and photostability of the sensing materials are also investigated.

Implications Of Acute Exercise And Inspiratory Hypoxia For Systemic NO Bioavailability

Systemic vascular nitric oxide (NO) bioavailability is known to play a key role in regulation of vascular tone at rest in Normoxic (N) and Hypoxic (H) conditions (Maher et al. Circulation 2008. 117 (5) 594-7). However, the effect of altered oxygen delivery as a function of exercise and inspiratory hypoxia and subsequent implications for NO metabolites remains unknown. PURPOSE: The present study examined the effects of physical exercise and H on NO metabolites in the systemic circulation. Specifically, we hypothesized that exercise would result in a net loss of NO metabolites which would be compounded in hypoxia due to a) PO2 mediated re-apportionment and/or b) oxidative inactivation. METHODS: Fourteen healthy males aged 24 (mean) ± 5 (SD) years performed two incremental tests to volitional exhaustion in N (21%O2) and H (∼12%O2). Maximal oxygen consumption (VO2max) was measured off line using the Douglas bag method and arterial haemoglobin oxygen saturation (SaO2) via pulse oximetry. Blood samples were taken from an antecubital vein before and immediately after exercise for determination of PO2 and plasma concentrations of nitrite (NO), nitrate (NO) and S-nitrosothiols (RSNO) via ozone-based chemiluminescence using modified tri-iodide/vanadium reagents. Data were analyzed with a two-way repeated measures ANOVA and post-hoc Bonferroni-corrected paired samples t-tests and relationships between variables by a Pearson Product Moment correlation coefficient. RESULTS: H decreased SaO2 (N: 96 ± 1 vs H: 77± 4%, P < 0.05) and subsequently VO2max (N: 3.92 ± 0.30 vs H: 3.00 ± 0.17 L/min, P < 0.05). Total NO did not change as a result of exercise and hypoxia (N: -0.4 ± 6.3 vs H: -1.2 ± 7.7μmol). The exercise-induced reduction in NO (N; -137 ± 93 norm vs. H: -78 ± 99 nmol) was mirrored by an exercise-induced increase in RSNO (N: + 11 ± 31 vs. H: + 21 ± 16 nmol (P < 0.05). A more marked reduction in NO was observed during N exercise (P = 0.07). CONCLUSION: These findings demonstrate an exercise induced re-apportionment of NO across the metabolite pool (from nitrite to RSNO) that may help conserve vascular O2 delivery which is especially important in H. Alternatively the reduction in nitrite and tendency towards a decrease total NO may reflect oxidative inactivation.

Urinary Oxygen Tension Measurement in Humans Using Magnetic Resonance Imaging

Renal medullary hypoxia is frequently implicated in renal dysfunction, and urinary oxygen tension (PO(2)) in the renal pelvis can be used as a surrogate for the adjacent renal medullary oxygenation. We sought to assess the feasibility of magnetic resonance (MR) quantification of urinary PO(2) in humans. The longitudinal relaxivity (R1) of fluids is linearly related to PO(2), allowing MR quantification of urinary PO(2). We imaged urine phantoms with a range of PO(2) using a real-time saturation recovery T2-prepped single-shot fast spin-echo sequence to calibrate urine R1 values to PO(2). Following institutional review board approval, we imaged the urinary bladders of seven healthy subjects while they were breathing room air and the renal pelvis of nine healthy subjects while they were breathing room air or 100% oxygen via facemask. The renal pelvic urine PO(2) was compared before, during, and after 100% oxygen breathing. Our phantom study confirmed that urine R1 is linearly related to PO(2): PO(2) (mm Hg) = (R1 - 0.2253 s(-1))/(2.61e(-4) s(-1)/mm Hg). The mean bladder urine PO(2) ranged from 23 to 45 mm Hg among the seven subjects. Successful MR measurements of renal pelvic urine PO(2) were obtained in seven of nine healthy subjects. Following 100% O(2) breathing, the renal pelvic urine PO(2) showed a significant mean increase of 29 mm Hg (P < .05). We show that MR quantification of urinary PO(2) is feasible. Noninvasive renal pelvic urine PO(2) determinations could serve as a valuable indirect measure for renal medullary oxygenation, allowing for clinical investigations of the role of renal medullary hypoxia in renal disease.

Continuous Wave EPR Oximetric Imaging at 300 MHz Using Radiofrequency Power Saturation Effects

A novel continuous wave (CW), radiofrequency (RF), electron paramagnetic resonance (EPR) oximetric imaging technique is proposed, based on the influence of oxygen concentration on the RF power saturation of the EPR resonance. A linear relationship is demonstrated between the partial oxygen pressure (pO(2)) and the normalized signal intensity (I(N)), defined as, I(N) = (I(HP) - I(LP))/I(LP), where I(LP) and I(HP) refer to signal intensities at low (P(L)) and high (P(H)) RF power levels, respectively. A formula for the determination of pO(2), derived on the basis of the experimental results, reliably estimated various oxygen concentrations in a five-tube phantom. This new technique was time-efficient and also avoided the missing angle problem associated with conventional spectral-spatial CW EPR oximetric imaging. In vivo power saturation oximetric imaging in a tumor bearing mouse clearly depicted the hypoxic foci within the tumor.

Measurements of Partial Oxygen Pressure (pO2) using the OxyLite System in R3327-AT Tumors under Isoflurane Anesthesia

The presence of oxygen-deficient tumor cells is a critical issue in cancer therapy. To identify tumor hypoxia, tissue partial oxygen pressure (pO2) can be measured directly. The OxyLite system allows determination of pO2 in tumors and permits continuous measurements of pO2 at a fixed point. In this study, this system was used to continuously measure pO2 in R3327-AT tumors in animals anesthetized with isoflurane. In addition, continuous pO2 measurement was performed in the muscle in non-tumor-bearing animals. In animals breathing isoflurane balanced by air, tumor pO2 at fixed positions decreased rapidly within 1-2 min of probe positioning but remained stable thereafter. In animals breathing isoflurane balanced by pure oxygen, tumor pO2 was higher and remained high. We also measured pO2 values at multiple positions in R3327-AT tumors of various sizes, with anesthetized animals breathing either air or pure oxygen. Our data showed that the frequency of pO2 measurements below 2.5 or 5.0 mmHg was significantly higher in animals breathing air than in animals breathing pure oxygen. Measurements in different-sized tumors showed that the mean pO2 value decreased as tumor volume increased, with the largest change occurring between tumor volumes of 100 and 200 mm3. Our data demonstrate that the OxyLite system, when used with isoflurane anesthesia, is a valuable tool in the study of tumor hypoxia.

Clinical Evaluation of the ABL-77 for Point-of-Care Analysis in the Cardiovascular Operating Room

As a small portable instrument, which can be dedicated to the perfusionist, the Radiometer model ABL-77 point-of-care blood gas, electrolyte, and hematocrit analyzer has come to provide an alternative to in-line monitoring of such parameters. This is not to say that it can necessarily replace the utility of in-line monitoring. However, point of care instruments, such as the ABL-77, can provide faster results than a more remote lab. This study was done as part of an ongoing quality assurance program in conjunction with the main lab department to maintain accreditation. The hypothesis being tested is that during cardiopulmonary bypass (CPB) the ABL-77 is in agreement with alternative instruments used outside the cardiovascular operating room. With the appropriate institutional approval, a total of 20 blood samples were randomly gathered among five patients after initiation of CPB. This was done over a five-day period for pH, pCO2, pO2, potassium, sodium, and hematocrit determinations. Analysis results from the ABL-77 were compared to those made by three other bench top models. These included a Radiometer model ABL-720 analyzer, a Dale Dimension model RxL analyzer, and a Beckerman model LH 750 Coulter Counter. A statistically significant difference is demonstrated for all parameters when each of these instruments is compared to the ABL-77. However, the observed mean differences are only judged to be clinically significant in the case of hematocrit. The ABL-77 is found to demonstrate a negative bias with respect to the different methodologies used by the ABL-720 and the Coulter Counter. This bias may be due to the hemodilution of plasma with crystalloid solution during CPB. This causes error in hematocrit results as the methodology of many point of care instruments is based on the electrical conductivity of whole blood. This may be corrected by using a relationship determined from linear regression analysis. This error adjustment has been implemented as part of a concerted blood conservation effort. Otherwise, the ABL-77 has been found to be reliable and consistent for point of care blood analysis.

Glass syringes are better than plastic for preserving arterial blood gas for oxygen partial pressure determination: an explanation based on nanomaterial composition

Blood gas analysis is a basic and useful laboratory test for the critical care of patients (Wiwanitkit 1999; Barthwal 2004). Arterial blood gas analysis is an essential investigation for assessing clinical oxygenation and acid-base status in critically ill patients (Wiwanitkit 1999; Barthwal 2004), providing information about ventilation, oxygenation, and acid-base status, the three closely interrelated physiological parameters that maintain pH homeostasis. The correct interpretation and application of arterial blood gas analysis requires knowledge of basic applied physiology in relation to these parameters (Wiwanitkit 1999; Barthwal 2004). Quality control of blood gas analysis is therefore important. In general, this quality control should follow the basic principles of good laboratory practice, namely, pre-analytical, focusing on proper specimen collection, handling, and transportation; analytical, focusing on internal quality control and external quality assessment; and post-analytical, comprising good validation and interpretation (Wiwanitkit 1999). An important source of aberrations in blood gas analysis results are errors in the pre-analytical phase (Mollard 2000). Several deficiencies in pre-analytical variables in blood gas analysis have been identified, most of which are caused by negligence and which are easily corrected (Ancic and Munoz 1997). Specific requirements for storage and transport of specimens for blood gas analysis have been proposed (Burnett et al 1994). Delay in analysis can decrease oxygen partial pressure (PO2) and increase carbon dioxide partial pressure (PCO2) because of the metabolism of blood cells. Ice preservation is recommended; however, there is no reason to keep arterial blood in ice if the blood gas analysis is done within 30 minutes (Liss and Payne 1993). The effect of syringe material on collected blood in general clinical chemistry has also been reported, including the diffusion of chemicals across the tube (Hilty et al 1969; Scott et al 1971). For blood gas analysis, the classical method requires a glass syringe; however, the new plastic syringes have been developed to address the increasing problems of blood-borne transmitted diseases (Evers et al 1972). Some reports indicate that glass syringes are superior to plastic syringes in preserving samples, especially for PO2 determination (Pretto and Rochford 1994; Deane et al 2004). However, there has been no specific explanation for this observation. Here, an explanation is attempted based on nanomaterial composition. First, the size of the O2 molecule was calculated based on the chemical-bonding principle (Goldberg 1989). The size of one O2 molecule can be calculated by size of one O2 molecule = 2 × (O2− ion size) + (O-O bond length). This equals 0.346 ([2 × 0.280] + 0.066) nm. Then the pore size and pore density of the glass material (polymer of silicon dioxide, molecular weight = 28.09) and plastic (polypropylene, polymer of propylene, molecular weight = 132.16) were estimated. The pore size of glass and plastic material is equal to about 3–50 nm (pore radius = 1.5–25 nm) (Kin et al 1997) and 200–450 nm (pore radius = 100–225 nm) (Kin et al 1997), respectively. The pore densities of glass and plastic materials are equal to about 4 × 106 pores/cm2 (Diem and Lentner 1971; Kin et al 1997) and 2 × 108 pores/cm2 (Diem and Lentner 1971; Kin et al 1997), respectively. Therefore, the overall areas allowing diffusion, calculated by pore density × π × (pore radius)2, are estimated as 3 × 10−7−8 × 10−5 cm2/cm2 of glass and 6 × 10−2−3 × 10−1 cm2/cm2 of plastic, respectively. At controlled temperature and other environmental factors, O2 seems to have a greater chance (4–150 times) to diffuse across plastic than glass, which could be a good explanation why a glass syringe can better preserve oxygen in a blood sample for blood gas analysis.

First electrodes for blood Po2 and Pco2 determination

This essay looks at the historical significance of an APS classic paper that is freely available online: Severinghaus JW and Bradley AF. Electrodes for blood Po2 and Pco2 determination. J Appl Physiol 13: 515—520, 1958 ( http://jap.physiology.org/cgi/reprint/13/3/515 ).

The significance of the blood gas analyzer.

This essay looks at the historical significance of an APS classic paper that is freely available online: Severinghaus JW and Bradley AF. Electrodes for blood Po2 and Pco2 determination. J Appl Physiol 13: 515—520, 1958 ( http://jap.physiology.org/cgi/reprint/13/3/515 ).

Dynamic response of breast tumor oxygenation to hyperoxic respiratory challenge monitored with three oxygen-sensitive parameters.

The simultaneous measurement of three oxygen-sensitive parameters [arterial hemoglobin oxygen saturation (SaO2), tumor vascular-oxygenated hemoglobin concentration ([HbO2]), and tumor oxygen tension (pO2)] in response to hyperoxic respiratory challenge is demonstrated in rat breast tumors. The effects of two hyperoxic gases [oxygen and carbogen (5% CO2 and 95% O2)] were compared, by use of two groups of Fisher rats with subcutaneous 13762NF breast tumors implanted in pedicles on the foreback. Two different gas-inhalation sequences were compared, i.e., air-carbogen-air-oxygen-air and air-oxygen-air-carbogen-air. The results demonstrate that both of the inhaled, hyperoxic gases significantly improved the tumor oxygen status. All three parameters displayed similar dynamic response to hyperoxic gas interventions, but with different response times: the fastest for arterial SaO2, followed by biphasic changes in tumor vascular [HbO2], and then delayed responses for pO2. Both of the gases induced similar changes in vascular oxygenation and regional tissue pO2 in the rat tumors, and changes in [HbO2] and mean pO2 showed a linear correlation with large standard deviations, which presumably results from global versus local measurements. Indeed, the pO2 data revealed hetergeneous regional response to hyperoxic interventions. Although preliminary near-infrared measurements had been demonstrated previously in this model, the addition of the pO2 optical fiber probes provides a link between the noninvasive relative measurements of vascular phenomena based on endogenous reporter molecules, with the quantitative, albeit, invasive pO2 determinations.

OXYGEN PARTIAL PRESSURE PROFILE INSIDE MICROVESSEL

The objective of this project was to determine the profile of oxygen partial pressure (PO2) inside small vessels in a hamster model. Microcirculation of skeletal skin muscle and subcutaneous connective tissue was visualized in a dorsal skin-fold. The system allows noninvasive in vivo measurement of intravascular PO2 at the microscopic level. PO2 determination is based on the O2-dependent quenching of phosphorescence of palladium-porphyrins hound to albumin. This compound was injected intravenously in the dosage of 0.1 ml probe/ 100 g animal. The phosphorescence emission was excited by epiillumination with a strobe Xenon arc (415nm) and measured by a photomultiplier in a well-defined area as small as 5 × 1.5 μm. A selected portion of the phosphorescence decay was fitted by a single exponential, and the Stern-Volmer equation was used to calculate P02. Simultaneous transillumination of the tissue also allows measurement of vessel diameter and red blood cell velocity in the same vessel. This study shows that there is a small PO2 loss around the center for the microvessel in opposition is a substantial PO2 loss from the blood as it passes through the arteriolar network.Figure 1: Caption Not Available.

Determination of macromolecular exchange and PO2 in the microcirculation: a simple system for in vivo fluorescence and phosphorescence videomicroscopy.

We have developed a system with two epi-illumination sources, a DC-regulated lamp for transillumination and mechanical switches for rapid shift of illumination and detection of defined areas (250-750 microm(2)) by fluorescence and phosphorescence videomicroscopy. The system permits investigation of standard microvascular parameters, vascular permeability as well as intra- and extravascular PO2 by phosphorescence quenching of Pd-meso-tetra (4-carboxyphenyl) porphine (PORPH). A Pechan prism was used to position a defined region over the photomultiplier and TV camera. In order to validate the system for in vivo use, in vitro tests were performed with probes at concentrations that can be found in microvascular studies. Extensive in vitro evaluations were performed by filling glass capillaries with solutions of various concentrations of FITC-dextran (diluted in blood and in saline) mixed with different amounts of PORPH. Fluorescence intensity and phosphorescence decay were determined for each mixture. FITC-dextran solutions without PORPH and PORPH solutions without FITC-dextran were used as references. Phosphorescence decay curves were relatively unaffected by the presence of FITC-dextran at all concentrations tested (0.1 microg/ml to 5 mg/ml). Likewise, fluorescence determinations were performed in the presence of PORPH (0.05 to 0.5 mg/ml). The system was successfully used to study macromolecular extravasation and PO2 in the rat mesentery circulation under controlled conditions and during ischemia-reperfusion.

Clinical performance of an in-line point-of-care monitor in neonates.

To evaluate the bias, precision, and blood loss characteristics of an ex vivo in-line point-of-care testing blood gas and electrolyte monitor designed for use in critically ill newborn infants. Study participants included consecutive neonates with an umbilical artery catheter (UAC) in use for clinical laboratory testing. The in-line monitor (VIA LVM Blood Gas and Chemistry Monitoring System, VIA Medical, San Diego, CA) was directly connected to the participant's UAC and the monitor's determinations of pH, PCO(2), PO(2), sodium, potassium, and hematocrit (Hct) were compared with those simultaneously drawn and measured with a standard bench top laboratory instrument (Radiometer 625 ABL; Radiometer America, Inc, Westlake, OH). The bias (the mean difference from the reference method) and precision (1 standard deviation of the mean difference) performance criteria of the in-line monitor were derived using standard laboratory procedures. Sixteen neonates monitored for a total of 37 days had a total of 229 paired blood samples available for comparison by the 2 methods. Bias and precision performance characteristics of the in-line monitor were similar to reports of other point-of-care devices (ie, pH: -.003 +/-.024; PCO(2):.35 +/- 2.84 mm Hg; PO(2):.39 +/- 7.30 mm Hg; sodium:.52 +/- 2.34 mmol/L; potassium:.17 +/-.18 mmol/L; and Hct:.61 +/- 2.80%). The range of values observed for each parameter included much of the range anticipated among critically ill neonates (ie, pH: 7.15-7.65; PCO(2): 25-75 mm Hg; PO(2): 25-275 mm Hg; sodium: 127-150 mmol/L; potassium: 2.6-5.5 mmol/L; and Hct: 32%-60%). Mean blood loss (+/- standard deviation) per sample with the in-line monitor was approximately one-tenth that of the reference method: 24 +/- 7 microL versus 250 microL, respectively. There was no evidence of hemolysis and no patient related safety issues were identified with use of the in-line monitor. Repeated laboratory testing of critically ill neonates using an ex vivo in-line monitor designed for use in neonates provides reliable laboratory results. The blood loss and hemolysis data obtained suggests that this monitoring device offers potential for reducing neonatal blood loss-and possibly transfusion needs-during the first weeks of life. Before this promising technology can be routinely recommended for care of critically ill neonates, greater practical experience in a variety of clinical settings is needed.

Quantification of Regional Intrapulmonary Oxygen Partial Pressure Evolution during Apnea by 3He MRI

We present a new method to determine in vivo the temporal evolution of intrapulmonary oxygen concentrations by functional lung imaging with hyperpolarized 3Helium (3He→). Single-breath, single-bolus visualization of 3He→ administered to the airspaces is used to analyze nuclear spin relaxation caused by the local oxygen partial pressure pO2(t). We model the dynamics of hyperpolarization in the lung by rate equations. Based hereupon, a double acquisition technique is presented to separate depolarization by RF pulses and oxygen induced relaxation. It permits the determination of pO2 with a high accuracy of up to 3% with simultaneous flip angle calibration using no additional input parameters. The time course of pO2 during short periods of breathholding is found to be linear in a pig as well as in a human volunteer. We also measured the wall relaxation time in the lung and deduced a lower limit of 4.3 min.

Effects of tiletamine/zolazepam premedication on propofol anaesthesia in dogs

The cardiovascular and pulmonary effects of tiletamine/ zolazepam, propofol and tiletamine/zolazepam plus propofol were studied in five mongrel dogs. A cannula inserted into a raised carotid artery was used to...