pO2 Measurements Research Articles

Spatially resolved estimation of metabolic oxygen consumption from optical measurements in cortex.

.Significance: The cerebral metabolic rate of oxygen () is an important indicator of brain function and pathology. Knowledge about its magnitude is also required for proper interpretation of the blood oxygenation level-dependent (BOLD) signal measured with functional MRI. Despite the need for estimating , no gold standard exists. Traditionally, the estimation of has been pursued with somewhat indirect approaches combining several different types of measurements with mathematical modeling of the underlying physiological processes. The recent ability to measure the level of oxygen () in cortex with two-photon resolution in in vivo conditions has provided a more direct way for estimating , but has so far only been used to estimate the average close to cortical penetrating arterioles in rats.Aim: The aim of this study was to propose a method to provide spatial maps of based on two-photon measurements.Approach: The method has two key steps. First, the maps are spatially smoothed to reduce the effects of noise in the measurements. Next, the Laplace operator (a double spatial derivative) in two spatial dimensions is applied on the smoothed maps to obtain spatially resolved estimates.Result: The smoothing introduces a bias, and a balance must be found where the effects of the noise are sufficiently reduced without introducing too much bias. In this model-based study, we explored this balance using synthetic model-based data, that is, data where the spatial maps of were preset and thus known. The corresponding maps were found by solving the Poisson equation, which relates and . MATLAB code for using the method is provided.Conclusion: Through this model-based study, we propose a method for estimating with high spatial resolution based on measurements of in cerebral cortex.

Cerebral tissue pO2 response to treadmill exercise in awake mice

We exploited two-photon microscopy and Doppler optical coherence tomography to examine the cerebral blood flow and tissue pO2 response to forced treadmill exercise in awake mice. To our knowledge, this is the first study performing both direct measure of brain tissue pO2 during acute forced exercise and underlying microvascular response at capillary and non-capillary levels. We observed that cerebral perfusion and oxygenation are enhanced during running at 5 m/min compared to rest. At faster running speeds (10 and 15 m/min), decreasing trends in arteriolar and capillary flow speed were observed, which could be due to cerebral autoregulation and constriction of arterioles in response to blood pressure increase. However, tissue pO2 was maintained, likely due to an increase in RBC linear density. Higher cerebral oxygenation at exercise levels 5–15 m/min suggests beneficial effects of exercise in situations where oxygen delivery to the brain is compromised, such as in aging, atherosclerosis and Alzheimer Disease.

The gaseous gastrointestinal tract of a seawater teleost, the English sole (Parophrys vetulus)

There has been considerable recent progress in understanding the respiratory physiology of the gastrointestinal tract (GIT) in teleosts, but the respiratory conditions inside the GIT remain largely unknown, particularly the luminal PCO2 and PO2 levels. The GIT of seawater teleosts is of special interest due to its additional function of water absorption linked to HCO3− secretion, a process that may raise luminal PCO2 levels. Direct measurements of GIT PCO2 and PO2 using micro-optodes in the English sole (Parophrys vetulus; anaesthetized, artificially ventilated, 10–12 °C) revealed extreme luminal gas levels. Luminal PCO2 was 14–17 mmHg in the stomach and intestinal segments of fasted sole, considerably higher than arterial blood levels of 5 mmHg. Moreover, feeding, which raised intestinal HCO3− concentration, also raised luminal PCO2 to 34–50 mmHg. All these values were higher than comparable measurements in freshwater teleosts, and also greater than environmental CO2 levels of concern in aquaculture or global change scenarios. The PCO2 values in subintestinal vein blood draining the GIT of fed fish (28 mmHg) suggested some degree of equilibration with high luminal PCO2, whereas subintestinal vein PO2 levels were relatively low (9 mmHg). All luminal sections of the GIT were virtually anoxic (PO2 ≤ 0.3 mmHg), in both fasted and fed animals, a novel finding in teleosts.

110 - Emerging adults – a challenge for an integrated psychosomatic approach

There has been considerable recent progress in understanding the respiratory physiology of the gastrointestinal tract (GIT) in teleosts, but the respiratory conditions inside the GIT remain largely unknown, particularly the luminal PCO2 and PO2 levels. The GIT of seawater teleosts is of special interest due to its additional function of water absorption linked to HCO3− secretion, a process that may raise luminal PCO2 levels. Direct measurements of GIT PCO2 and PO2 using micro-optodes in the English sole (Parophrys vetulus; anaesthetized, artificially ventilated, 10–12 °C) revealed extreme luminal gas levels. Luminal PCO2 was 14–17 mmHg in the stomach and intestinal segments of fasted sole, considerably higher than arterial blood levels of 5 mmHg. Moreover, feeding, which raised intestinal HCO3− concentration, also raised luminal PCO2 to 34–50 mmHg. All these values were higher than comparable measurements in freshwater teleosts, and also greater than environmental CO2 levels of concern in aquaculture or global change scenarios. The PCO2 values in subintestinal vein blood draining the GIT of fed fish (28 mmHg) suggested some degree of equilibration with high luminal PCO2, whereas subintestinal vein PO2 levels were relatively low (9 mmHg). All luminal sections of the GIT were virtually anoxic (PO2 ≤ 0.3 mmHg), in both fasted and fed animals, a novel finding in teleosts.

Toward noninvasive quantification of adipose tissue oxygenation with MRI.

Molecular oxygen (O2) plays a key role in normal and pathological adipose tissue function, yet technologies to measure its role in adipose tissue function are limited. O2 is paramagnetic and, in principle, directly influences the magnetic resonance (MR) 1H longitudinal relaxation rate constant of lipids, R1; thus, we hypothesize that MR imaging (MRI) can directly measure adipose O2 via a simple measure of R1. R1 was measured in a 4.7T preclinical MRI system at discrete oxygen partial pressure (pO2) levels. These measures were made in vitro in an idealized system and in vivo in subcutaneous and visceral white adipose of rodents. pO2 was determined using an invasive fiber-optic oxygen monitor. From the MRI and fiber optic data we determined the "relaxivity" of O2 in lipid, a critical parameter in converting the MRI-based R1 measurement into pO2. We used breathing gas challenge to estimate the changes in lipid pO2 (ΔpO2). The relaxivity of O2 in lipid was determined to be 1.7·10-3 ± 4·10-4 mmHg-1s-1 at 4.7T and 37 °C, and was consistent between in vitro and in vivo adipose tissue. There was a strong, significant correlation between MRI- and gold standard OxyLite-based measurements of lipid ΔpO2 for in vivo visceral and subcutaneous fat depots in rodents. This study lays the foundation for a direct, noninvasive measure of adipose pO2 using MRI and will allow for noninvasive measurement of O2 flux in adipose tissue. The proposed approach would be of particular importance in the interrogation of the pathogenesis of type 2 diabetes, where it has been suggested that adipose tissue hypoxia is an independent driver of insulin resistance pathway.

Concurrent tissue oxymetry and blood flowmetry to assess the effect of drugs on cerebral oxygen metabolism

An Oxylite/LDF system (Oxford Optronix, UK) driven by a sensor made of optical fibres for the tissue oxygen tension (pO2) and for the Laser Doppler Blood Flow (BF) was implemented. This has allowed pO2 and BF real time measurements in discrete brain areas of anaesthetised rats that were then challenged with exogenous oxygen (O2) and carbon dioxide (CO2). The results gathered were compared with data obtained following treatment with drugs that have excitatory influence upon the brain activity such as amphetamine or with a central nervous system (CNS) depressant such as CI-966. Altogether these experiments support the methodology for in vivo investigation of pharmacological effects on cerebral oxygen metabolism and could provide new understandings on the effects of psychostimulants and anticonvulsants on selected brain regions.

Noninvasive Fluorine-19 Magnetic Resonance Relaxometry Measurement of the Partial Pressure of Oxygen in Acellular Perfluorochemical-loaded Alginate Microcapsules Implanted in the Peritoneal Cavity of Nonhuman Primates.

We have utilized a noninvasive technique for measuring the partial pressure of oxygen (pO2) in alginate microcapsules implanted intraperitoneally in healthy nonhuman primates (NHPs). Average pO2 is important for determining if a transplant site and capsules with certain passive diffusion characteristics can support the islet viability, metabolic activity, and dose necessary to reverse diabetes. Perfluoro-15-crown-5-ether alginate capsules were infused intraperitoneally into 3 healthy NHPs. Peritoneal pO2 levels were measured on days 0 and 7 using fluorine-19 magnetic resonance relaxometry and a fiber-optic probe. Fluorine-19 MRI was used to determine the locations of capsules within the peritoneal space on days 0 and 7. Gross and histologic evaluations of the capsules were used to assess their biocompatibility postmortem. At day 0 immediately after infusion of capsules equilibrated to room air, capsules were concentrated near the infusion site, and the pO2 measurement using magnetic resonance relaxometry was 147 ± 9 mm Hg. On day 7 after capsules were dispersed throughout the peritoneal cavity, the pO2 level was 61 ± 11 mm Hg. Measurements using the fiber-optic oxygen sensor were 132 ± 7.5 mm Hg (day 0) and 89 ± 6.1 mm Hg (day 7). Perfluoro-15-crown-5-ether capsules retrieved on day 7 were intact and free-floating without host cell attachment, although the numbers of peritoneal CD20 B cells, CD4 and CD8 T cells, and CD14 macrophages increased consistent with a mild foreign body reaction. The peritoneal pO2 of normal NHPs is relatively low and we predict would decrease further when encapsulated islets are transplanted intraperitoneally.

More bullets for PISTOL: linear and cyclic siloxane reporter probes for quantitative 1H MR oximetry

Tissue oximetry can assist in diagnosis and prognosis of many diseases and enable personalized therapy. Previously, we reported the ability of hexamethyldisiloxane (HMDSO) for accurate measurements of tissue oxygen tension (pO2) using Proton Imaging of Siloxanes to map Tissue Oxygenation Levels (PISTOL) magnetic resonance imaging. Here we report the feasibility of several commercially available linear and cyclic siloxanes (molecular weight 162–410 g/mol) as PISTOL-based oxygen reporters by characterizing their calibration constants. Further, field and temperature dependence of pO2 calibration curves of HMDSO, octamethyltrisiloxane (OMTSO) and polydimethylsiloxane (PDMSO) were also studied. The spin-lattice relaxation rate R1 of all siloxanes studied here exhibited a linear relationship with oxygenation (R1 = A′ + B′*pO2) at all temperatures and field strengths evaluated here. The sensitivity index η( = B′/A′) decreased with increasing molecular weight with values ranged from 4.7 × 10−3–11.6 × 10−3 torr−1 at 4.7 T. No substantial change in the anoxic relaxation rate and a slight decrease in pO2 sensitivity was observed at higher magnetic fields of 7 T and 9.4 T for HMDSO and OMTSO. Temperature dependence of calibration curves for HMDSO, OMTSO and PDMSO was small and simulated errors in pO2 measurement were 1–2 torr/°C. In summary, we have demonstrated the feasibility of various linear and cyclic siloxanes as pO2-reporters for PISTOL-based oximetry.

Efficacy and Safety of Traditional Chinese Medicine in Idiopathic Pulmonary Fibrosis: A Meta-Analysis.

Objective To evaluate the efficacy and safety of traditional Chinese medicine (TCM) on lung function and quality of life of idiopathic pulmonary fibrosis (IPF) patients by meta-analysis. Methods Randomized controlled trials (RCTs) related to TCM and IPF were searched on PubMed, EMBASE Cochrane Library, ClinicalTrials, China National Knowledge Infrastructure (CNKI), Wanfang Database, Chin VIP Information (VIP), and Chinese Biomedical Database (CBM) until December 2018. Standard mean difference (SMD) and 95% CI were calculated for the measurements related to lung function (FEV1/FVC, FVC%, FEV1%, TLC%, DLCO% or DLCO, and VC%) and other parameters (PO2, 6MWD, and SGRQ) when comparing TCM treatment to the control group. Relative risk (RR) and 95% CI of adverse events (AEs) were calculated to assess the safety of TCM. Results A total of 40 RCTs comparing TCM to western medicine (WM) and involving 3194 IPF patients were eligible for the meta-analysis. The pooled results showed that TCM treatment improved significantly PO2 (SMD = 0.80, 95% CI 0.54 to 1.06, p < 0.001), FEV1% (SMD = 0.57, 95% CI 0.42 to 0.71, p < 0.001), DLCO% (SMD = 0.38, 95% CI 0.28 to 0.48, p < 0.001), 6MWD (SMD = 0.70, 95% CI 0.56 to 0.84, p < 0.001) and other measurements and reduced SGRQ scores (SMD = −0.51, 95% CI −0.70 to −0.22, p < 0.001). Subgroup analysis of different study durations (3 months, ≥ 6 months) and comparison models (TCM vs. WM, TCM + WM vs. WM or TCM vs. placebo) showed similar results. No significant difference of risk of AEs was observed between both groups (RR = 0.66, 95% CI: 0.27–1.60, p=0.352). There was no obvious publication bias, and the pooled results were stable according to sensitivity analysis. Conclusion To the best of our knowledge, the present study had the largest sample size. Our results indicated that TCM treatment may help provide benefit to the lung function, exercise capacity, and quality of life of IPF patients, alone or combined with WM, when compared to WM. More rigorous RCTs were needed in the future.

Wound monitoring of pH and oxygen in patients after radiation therapy

ObjectivesPostradiogenic wound healing disorders are an important clinical problem. While a variety of treatment modalities are available, there is no strategy to objectively judge treatment success. The aim of this study was to evaluate a 2D luminescence imaging system for pH and oxygen in non-healing wounds after radiotherapy.MethodsLuminescence 2D imaging was performed with the VisiSens (Presens, Regensburg, Germany) 2D imaging systems A1 and A2 for oxygen and pH, respectively. Biocompatible planar luminescent sensor foils were applied to non-irradiated and irradiated skin as well as to radiogenic wounds of five patients and the pH and the oxygen saturation was determined.ResultspH measurements showed significant differences between non-irradiated skin (6.46 ± 0.18) and irradiated skin (6.96 ± 0.26). Radiogenic wounds exhibited the highest pH values (7.53 ± 0.26). Oxygen measurements revealed a mean oxygen saturation of non-irradiated skin of 6.19 ± 0.83 mmHg. The highest value of oxygen saturation (28.4 ± 2.4 mmHg) was found on irradiated skin while irradiated wounds had a poor oxygen saturation (9.4 ± 2.2 mmHg) (mean ± s.e.m.).ConclusionWe found that routine measurement of pH and pO2 in patients could be easily integrated into the clinical routine. The results of the measurements show unfavorable pH and oxygen saturation conditions for wound healing in irradiated wounds. Interestingly, irradiated wounds exhibit a more pronounced hypoxia than irradiated skin which is reflected by an altered pH and pO2 compared to unirradiated skin, which has the potential to serve as a prognostic marker in the future. In addition to the objectification of the treatment success of postradiogenic wound healing disorders, the extent of skin toxicity could already be predicted during radiotherapy with this method.

In vivo imaging with a water immersion objective affects brain temperature, blood flow and oxygenation.

Previously, we reported the first oxygen partial pressure (Po2) measurements in the brain of awake mice, by performing two-photon phosphorescence lifetime microscopy at micrometer resolution (Lyons et al., 2016). However, this study disregarded that imaging through a cranial window lowers brain temperature, an effect capable of affecting cerebral blood flow, the properties of the oxygen sensors and thus Po2 measurements. Here, we show that in awake mice chronically implanted with a glass window over a craniotomy or a thinned-skull surface, the postsurgical decrease of brain temperature recovers within a few days. However, upon imaging with a water immersion objective at room temperature, brain temperature decreases by ~2-3°C, causing drops in resting capillary blood flow, capillary Po2, hemoglobin saturation, and tissue Po2. These adverse effects are corrected by heating the immersion objective or avoided by imaging through a dry air objective, thereby revealing the physiological values of brain oxygenation.

Placental oxygen transfer reduces hypoxia-reoxygenation swings in fetal blood in a sheep model of gestational sleep apnea.

Obstructive sleep apnea (OSA), characterized by events of hypoxia-reoxygenation, is highly prevalent in pregnancy, negatively affecting the gestation process and particularly the fetus. Whether the consequences of OSA for the fetus and offspring are mainly caused by systemic alterations in the mother or by a direct effect of intermittent hypoxia in the fetus is unknown. In fact, how apnea-induced hypoxemic swings in OSA are transmitted across the placenta remains to be investigated. The aim of this study was to test the hypothesis, based on a theoretical background on the damping effect of oxygen transfer in the placenta, that oxygen partial pressure (Po2) swings resulting from obstructive apneas mimicking OSA are mitigated in the fetal circulation. To this end, four anesthetized ewes close to term pregnancy were subjected to obstructive apneas consisting of 25-s airway obstructions. Real-time Po2 was measured in the maternal carotid artery and in the umbilical vein with fast-response fiber-optic oxygen sensors. The amplitudes of Po2 swings in the umbilical vein were considerably smaller [3.1 ± 1.0 vs. 21.0 ± 6.1 mmHg (mean ± SE); P < 0.05]. Corresponding estimated swings in fetal and maternal oxyhemoglobin saturation tracked Po2 swings. This study provides novel insights into fetal oxygenation in a model of gestational OSA and highlights the importance of further understanding the impact of sleep-disordered breathing on fetal and offspring development.NEW & NOTEWORTHY This study in an airway obstruction sheep model of gestational sleep apnea provides novel data on how swings in oxygen partial pressure (Po2) translate from maternal to fetal blood. Real-time simultaneous measurement of Po2 in maternal artery and in umbilical vein shows that placenta transfer attenuates the magnitude of oxygenation swings. These data prompt further investigation of the extent to which maternal apneas could induce similar direct oxidative stress in fetal and maternal tissues.

SUN-185 EARLY PREDICTION OF CARDIAC SURGERY ASSOCIATED ACUTE KIDNEY INJURY BY MEASUREMENT OF URINARY OXYGEN TENSION IN THE INTENSIVE CARE UNIT

Continuous measurement of bladder urinary oxygen tension (PO2) may provide a real-time surrogate measure of oxygenation in the renal medulla. Therefore, urinary PO2 may be a useful tool for early prediction of acute kidney injury (AKI) and potentially also the management of renal oxygenation in patients with AKI. We examined the relationship between urinary PO2, measured in the intensive care unit (ICU), and development of AKI in patients who had undergone cardiac surgery requiring cardiopulmonary bypass (CPB). In 74 patients undergoing on-pump cardiac surgery, bladder urinary PO2 was measured continuously in the ICU using a fibre optic probe placed in the patient’s bladder catheter. AKI was diagnosed by modified ‘Kidney Disease: Improving Global Outcomes’ (KDIGO) criteria, excluding the urine flow criterion. Twenty-eight out of 74 patients (37.8%) developed post-operative AKI (18 Stage 1, 7 Stage 2, and 3 Stage 3). The median time to first diagnosis of AKI, using serum creatinine, was 16.9 hours after entry into the ICU (interquartile range (IQR): 13, 32 h). The median duration of monitoring of urinary PO2 was 37.8 hours (IQR: 24.0, 47.3 h). During the first 3 hours after arrival in the ICU, overall mean urinary PO2 (AKI: 19.4 ± 9.3 vs. non-AKI: 25.3 ± 9.7 mmHg, p = 0.01), and the nadir (lowest recorded) urinary PO2 (AKI: 12.1 ± 6.8 vs. non-AKI: 16.0 ± 5.7 mmHg, p = 0.01) were lower in patients who developed AKI than those who did not. Furthermore, within the first 3 hours of entry to the ICU, 17 of the 28 patients (61%) who developed AKI had urinary PO2 less than or equal to 15 mmHg while this threshold was only reached in 16 of the 46 patients (35%) who did not develop AKI . Patients who developed AKI also experienced longer periods with urinary PO2 less than or equal to 15 mmHg (median time of 10.9 min per hour of measurement) than those who did not (median 0.0 min per hour), p = 0.01. If urinary PO2 fell to 10 mmHg or less at any time during the first 3 hours of the patient’s ICU stay, the odds of developing AKI were 5.6 times greater (95% CI 1.9 – 16.6; p = 0.002) than if it remained greater than 10 mmHg. The area under the receiver-operator curve for this parameter was 0.67 (95% CI 0.54 – 0.81; p = 0.01). Similar observations were made when urinary PO2 was considered over the first 6 hours, or the first 12 hours, after ICU admission, as well as for the entire duration of available monitoring of urinary PO2 in the ICU. In patients who have undergone cardiac surgery requiring CPB, increased risk of AKI can be detected within 3 hours after entry into the ICU, by continuous measurement of bladder urinary PO2. Thus, urinary PO2 has the potential to be a real-time index of risk of AKI in these patients.

Electron paramagnetic resonance oximetry as a novel approach to monitor the effectiveness and quality of red blood cell transfusions.

The goal of red blood cell transfusion is to improve tissue oxygenation. Assessment of red blood cell quality and individualised therapeutic needs can be optimised using direct oxygen (O2) measurements to guide treatment. Electron paramagnetic resonance oximetry is capable of accurate, repeatable and minimally invasive measurements of tissue pO2. Here we present preclinical proof-of-concept of the utility of electron paramagnetic resonance oximetry in an experimental setting of acute blood loss, transfusion, and post-transfusion monitoring. Donor rat blood was collected, leucocyte-reduced, and stored at 4 °C in AS-3 for 1, 7 and 14 days. Red blood cell morphology, O2 equilibrium, p50 and Hill numbers from O2 binding and dissociation curves were evaluated in vitro. Recipient rats were bled and maintained at a mean arterial pressure of 30-40 mmHg and hind limb muscle (biceps femoris) pO2 at 25-50% of baseline. Muscle pO2 was monitored continuously over the course of experiments to assess the effectiveness of red blood cell preparations at different stages of blood loss and restoration. Red blood cell morphology, O2 equilibrium and p50 values of intra-erythrocyte haemoglobin were significantly altered by refrigerated storage for both 7 and 14 days. Transfusion of red blood cells stored for 7 or 14 days demonstrated an equivalently impaired ability to restore hind limb muscle pO2, consistent with in vitro observations and transfusion with albumin. Red blood cells refrigerated for 1 day demonstrated normal morphology, in vitro oxygenation and in vivo restoration of tissue pO2. Electron paramagnetic resonance oximetry represents a useful approach to assessing the quality of red blood cells and subsequent transfusion effectiveness.

Automated Evaluation of Microvascular Blood Flow and Oxygenation following Trauma and Hemorrhage in Rats

Studies evaluating blood flow and oxygen partial pressure (PO2) may not directly measure both parameters and may depend on investigator's selection of measuring sites. In addition, relevant systemic parameters may not be simultaneously recorded. Therefore, we implemented a new automated system for blood flow and PO2 acquisition in large tissue areas while collecting systemic information. In 10 animals anesthetized with isoflurane, cardio‐respiratory parameters were continuously recorded, in experiments lasting up to 4 h. Other data were collected at baseline, and after laparotomy and 30 min hemorrhage (40% of total blood volume). A cremaster muscle was spread over a thermostatically‐controlled pedestal fixed to a motorized stage. Sixteen noninvasive PO2 measurements using oxygen‐dependent phosphorescence quenching and fiber‐optics were performed during a computer‐controlled tissue scan. In the same areas used for PO2 measurements, microvascular blood flow was estimated employing laser speckle contrast imaging. Blood was sampled for extensive biochemistry and coagulation profiles. The system was used successfully by different operators. One set of flow and PO2 measurements was completed in less than 90 s. Changes in muscle flow correlated with local PO2 but several systemic parameters did not correlate with blood flow and PO2, emphasizing the importance of performing both local and systemic evaluations. System advantages include integration between local and multiple systemic parameters, unbiased data collection/analysis, easy implementation, improved performance, no need for customized programming, and simplified training compared to intravital microscopy.Support or Funding InformationSupported by US Army Medical Research and Materiel Command.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A faster PISTOL for 1 H MR-based quantitative tissue oximetry.

Quantitative mapping of oxygen tension (pO2 ), noninvasively, could potentially be beneficial in cancer and stroke therapy for monitoring therapy and predicting response to certain therapies. Intracellular pO2 measurements may also prove useful in tracking the health of labeled cells and understanding the dynamics of cell therapy in vivo. Proton Imaging of Siloxanes to map Tissue Oxygenation Levels (PISTOL) is a relatively new oximetry technique that measures the T1 of administered siloxanes such as hexamethyldisiloxane (HMDSO), to map the tissue pO2 at various locations with a temporal resolution of 3.5minutes. We have now developed a siloxane-selective Look-Locker imaging sequence equipped with an echo planar imaging (EPI) readout to accelerate PISTOL acquisitions. The new tissue oximetry sequence, referred to as PISTOL-LL, enables the mapping of HMDSO T1 , and hence tissue pO2 in under one minute. PISTOL-LL was tested and compared with PISTOL in vitro and in vivo. Both sequences were used to record dynamic changes in pO2 of the rat thigh muscle (healthy Fischer rats, n=6), and showed similar results (P>0.05) as the other, with each sequence reporting a significant increase in pO2 (P<0.05) under hyperoxia compared with steady state normoxia. This study demonstrates the ability of the new sequence in rapidly and accurately mapping the pO2 changes and accelerating quantitative 1 H MR tissue oximetry by approximately 4-fold. The faster PISTOL-LL technique could enable dynamic 1 H oximetry with higher temporal resolution for assesing tissue oxygentation and tracking the health of transplanted cells labeled with siloxane-based probes. With minor modifications, this sequence can be useful for 19 F applications as well.

Automated noninvasive evaluation of blood flow and oxygenation in rats integrated with systemic physiological monitoring.

Many studies evaluating blood flow and oxygen partial pressure (PO2) do not directly measure both parameters, are confined to few locations/microvessels, and depend on investigator's selection of measuring sites. Moreover, clinically/physiologically relevant systemic parameters are not simultaneously recorded. We implemented an automated system for prolonged blood flow/PO2 acquisition in large areas while collecting relevant systemic information. In anesthetized animals, cardiorespiratory parameters were continuously recorded. Other data were collected at baseline and hourly after 4 hours of hemorrhagic shock. A cremaster muscle was spread over a pedestal fixed to a motorized stage. One 2-dimensional tissue scan allowed 16 noninvasive PO2 measurements using oxygen-dependent phosphorescence quenching and fiber optics. Blood flow was estimated using laser speckle contrast imaging in the same areas used for PO2 measurements. At each timepoint, blood was sampled for extensive biochemistry/coagulation profile. The system was used successfully by different operators. A set of flow/PO2 measurements was completed in less than 90 seconds. Muscle flow and PO2 correlated with some but not several systemic parameters, emphasizing the importance of performing both local and systemic evaluations. System advantages include integration between local and over 40 systemic parameters, unbiased data collection/analysis, improved performance/sampled area, easy expansion, implementation and maintenance, no customized programming, and simplified training. Combining this system with trauma/prolonged HS models will enhance our ability to investigate tissue stability and select better resuscitation strategies to improve outcomes and survival. Diagnostic test, level V.

Comparison of arterial and venous blood-gas values in anesthetized Dorset cross-bred lambs (Ovis aries) using a point-of-care analyzer

ObjectiveTo determine the degree of agreement between arterial and venous blood gases in anesthetized lambs using a point-of-care analyzer. Study designProspective experimental study. AnimalsA group of 12 female Dorset cross-bred lambs, weighing 37.3 ± 7.4 kg (mean ± standard deviation). MethodsLambs were anesthetized with isoflurane for catheterization of the jugular vein and femoral artery, and blood samples were collected simultaneously for analysis of pH, PCO2, PO2, base excess (BE), bicarbonate (HCO3−), total carbon dioxide (tCO2), oxygen saturation (SO2), ionized calcium (iCa) and potassium (K+) using the Vet Scan i-STAT handheld analyzer. The Bland–Altman method was used to calculate agreement between arterial and venous measurements. ResultsStrong agreement was identified between arterial and venous pH (bias = 0.04; 95% limits of agreement = 0.02–0.06), K+ (bias = –0.1 and 95% limits of agreement = –0.8 to 0.5) and iCa (bias = 0.04; 95% limits of agreement = –0.08 to 0.0003). There was poor agreement for PO2 (bias = 168.0; 95% limits of agreement = 77.4–258.7) and SO2 (bias = 9.1; 95% limits of agreement = 2.8–15.3), as these values were higher in arterial blood than in venous blood. Moderate agreement was present for BE (bias = 1.7; 95% limits of agreement = –2.7 to 6.1), PCO2 (bias = –2.1; 95% limits of agreement = –7.5 to 3.4), HCO3− (bias = 1.1; 95% limits of agreement = –3.1 to 5.3) and tCO2 (bias = 1.0; 95% limits of agreement = –3.3 to 5.3). Conclusions and clinical relevanceVenous blood can be used for the measurement of pH, K+ and iCa in anesthetized Dorset cross-bred lambs. Arterial blood is required for accurate measurement of PO2, SO2, PCO2, HCO3−, tCO2 and BE to assess systemic blood oxygenation and pulmonary function in anesthetized Dorset cross-bred lambs.

Fluorescence Lifetime Spectroscopy of the Cornea using a Multichannel Scaler

An interface based on Multichannel scaler (MCS; SR430; Stanford Research Systems, USA) has been tested for enabling fluorescence lifetime measurements of pO2-sensitive fluorophores with a custom-made confocal scanning microfluorometer (CSMF) for transcorneal pO2 measurements. SR430 served as a transient photon counter. A trigger pulse, coincident with the rising edge of an excitation pulse for fluorescence, was coupled to accumulate emission pulses detected by a photomultiplier tube (PMT; R928 HA, Hamamatsu, Inc). The pulse started the photon counting and segmented the photon count data into consecutive time bins (ranging from 1 up to 32k), the width of which could be varied from 5 ns to 10.486 ms. With no dead time between bins, photon counting with the fluorescence decay is seamless. Silica-bound Ruthenium phenanthroline, dispersed in silicone rubber, was employed as a fluorophore sensitive to pO2. The test interface for CSMF-MCS system showed sensitive pO2 measurements and hence is suitable to measure local pO2 at any depth across the cornea.

Acid-Base Status Disturbances in Patients on Chronic Hemodialysis at High Altitudes.

Background Acid-base disorders have been previously described in patients with chronic hemodialysis, with metabolic acidosis being the most important of them; however, little is known about the potential changes in acid-base status of patients on dialysis living at high altitudes. Methods Cross-sectional study including 93 patients receiving chronic hemodialysis on alternate days and living in Bogotá, Colombia, at an elevation of 2,640 meters (8,661 feet) over sea level (m.o.s.l.). Measurements of pH, PaCO2, HCO3, PO2, and base excess were made on blood samples taken from the arteriovenous fistula (AVF) during the pre- and postdialysis periods in the midweek hemodialysis session. Normal values for the altitude of Bogotá were taken into consideration for the interpretation of the arterial blood gases. Results 43% (n= 40) of patients showed predialysis normal acid-base status. The most common acid-base disorder in predialysis period was metabolic alkalosis with chronic hydrogen ion deficiency in 19,3% (n=18). Only 9,7% (n=9) had predialysis metabolic acidosis. When comparing pre- and postdialysis blood gas analysis, higher postdialysis levels of pH (7,41 versus 7,50, p<0,01), bicarbonate (21,7mmol/L versus 25,4mmol/L, p<0,01), and base excess (-2,8 versus 2,4, p<0,01) were reported, with lower levels of partial pressure of carbon dioxide (34,9 mmHg versus 32,5 mmHg, p<0,01). Conclusion At an elevation of 2,640 m.o.s.l., a large percentage of patients are in normal acid-base status prior to the dialysis session (“predialysis period”). Metabolic alkalosis is more common than metabolic acidosis in the predialysis period when compared to previous studies. Paradoxically, despite postdialysis metabolic alkalosis, PaCO2 levels are lower than those found in the predialysis period.